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Rev 0; 3/06
Single-Channel Automotive CCFL Controller
General Description
The DS3881 is a single-channel cold-cathode fluorescent lamp (CCFL) controller for automotive applications that provides up to 300:1 dimming. It is ideal for driving CCFLs used to backlight liquid crystal displays (LCDs) in navigation and infotainment applications and for driving CCFLs used to backlight instrument clusters. The DS3881 is also appropriate for use in marine and aviation applications. The DS3881 features EMI suppression functionality and provides a lamp current overdrive mode for rapid lamp heating in cold weather conditions. The DS3881 supports a single lamp configuration with fully independent lamp control and minimal external components. Multiple DS3881 controllers can be cascaded to support applications requiring more than one lamp. Control of the DS3881, after initial programming setup, can be completely achieved through I2C* software communication. Many DS3881 functions are also pin-controllable if software control is not desired.
Features
o Single-Channel CCFL Controller for Backlighting LCD Panels and Instrument Clusters in Automotive Navigation/Infotainment Applications o Minimal External Components Required o I2C Interface o Per-Channel Lamp-Fault Monitoring for LampOpen, Lamp-Overcurrent, Failure to Strike, and Overvoltage Conditions o Status Register Reports Fault Conditions o Accurate (5%) Independent On-Board Oscillators for Lamp Frequency (40kHz to 100kHz) and DPWM Burst-Dimming Frequency (22.5Hz to 440Hz) o Lamp and DPWM Frequencies can be Synchronized with External Sources to Reduce Visual LCD Artifacts in Video Applications o Spread-Spectrum Lamp Clock Reduces EMI o Lamp Frequency can be Stepped Up or Down to Move EMI Spurs Out of Band o Lamp Current Overdrive Mode with Automatic Turn-Off Quickly Warms Lamp in Cold Temperatures o Analog or Digital Brightness Control o 300:1 Dimming Range Possible Using the Digital Brightness Control Option o Programmable Soft-Start Minimizes Audible Transformer Noise o On-Board Nonvolatile (NV) Memory Allows Device Customization o 8-Byte NV User Memory for Storage of Serial Numbers and Date Codes o Low-Power Standby Mode o 4.75V to 5.25V Single-Supply Operation o Temperature Range: -40C to +105C o 24-Pin TSSOP Package
DS3881
Applications
Automotive LCDs Instrument Clusters Marine and Aviation LCDs
Pin Configuration
TOP VIEW
A0 1 SDA 2 SCL 3 LSYNC 4 LOSC 5 BRIGHT 6 PSYNC 7 POSC 8 A1 9 GND_S 10 SVML 11 SVMH 12 24 FAULT 23 GB1 22 GA1 21 VCC
DS3881
20 PDN 19 LCO 18 GND 17 STEP 16 N.C. 15 OVD1 14 LCM1 13 VCC
Ordering Information
PART DS3881E+ DS3881E+T&R TEMP RANGE -40C to +105C -40C to +105C PIN-PACKAGE 24 TSSOP (173 mils) 24 TSSOP (173 mils)
+Denotes lead-free package. TSSOP *Purchase of I2C components from Maxim Integrated Products, Inc., or one of its sublicensed Associated Companies, conveys a license under the Philips I2C Patent Rights to use these components in an I2C system, provided that the system conforms to the I2C Standard Specification as defined by Philips. Typical Operating Circuit appears at end of data sheet. ______________________________________________ Maxim Integrated Products 1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at 1-888-629-4642, or visit Maxim's website at www.maxim-ic.com.
Single-Channel Automotive CCFL Controller DS3881
ABSOLUTE MAXIMUM RATINGS
Voltage Range on VCC, SDA, and SCL Relative to Ground.....................................-0.5V to +6.0V Voltage Range on Leads Other than VCC, SDA, and SCL ......................-0.5V to (VCC + 0.5V), not to exceed +6.0V Operating Temperature Range .........................-40C to +105C EEPROM Programming Temperature Range .........0C to +70C Storage Temperature Range .............................-55C to +125C Soldering Temperature...................See J-STD-020 Specification
Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
RECOMMENDED OPERATING CONDITIONS
(TA = -40C to +105C)
PARAMETER Supply Voltage Input Logic 1 Input Logic 0 SVML/H Voltage Range BRIGHT Voltage Range LCM Voltage Range OVD Voltage Range Gate-Driver Output Charge Loading SYMBOL VCC VIH VIL VSVM VBRIGHT VLCM VOVD QG (Note 2) (Note 2) (Note 1) CONDITIONS MIN 4.75 2.0 -0.3 -0.3 -0.3 -0.3 -0.3 TYP MAX 5.25 VCC + 0.3 1.0 VCC + 0.3 VCC + 0.3 VCC + 0.3 VCC + 0.3 20 UNITS V V V V V V V nC
ELECTRICAL CHARACTERISTICS
(VCC = +4.75V to +5.25V, TA = -40C to +105C.)
PARAMETER Supply Current Input Leakage (Digital Pins) Power-Down Current Output Leakage (SDA, FAULT) Low-Level Output Voltage (LSYNC, PSYNC) Low-Level Output Voltage (SDA, FAULT) Low-Level Output Voltage (GA1, GB1) High-Level Output Voltage (LSYNC, PSYNC) SYMBOL ICC IL IPDN ILO VOL VOL1 VOL2 VOL3 VOH High impedance IOL = 4mA IOL1 = 3mA IOL2 = 6mA IOL3 = 4mA IOH = -1mA 2.4 -1.0 CONDITIONS GA, GB loaded with 600pF -1.0 MIN TYP 12 +1.0 1 +1.0 0.4 0.4 0.6 0.4 MAX UNITS mA A mA A V V V V
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Single-Channel Automotive CCFL Controller
ELECTRICAL CHARACTERISTICS (continued)
(VCC = +4.75V to +5.25V, TA = -40C to +105C.)
PARAMETER High-Level Output Voltage (GA, GB) UVLO Threshold: VCC Rising UVLO Threshold: VCC Falling UVLO Hysteresis SVML/H Threshold: Rising SVML/H Threshold: Falling LCM and OVD DC Bias Voltage LCM and OVD Input Resistance Lamp Off Threshold Lamp Over Current Lamp Regulation Threshold OVD Threshold Lamp Frequency Source Frequency Range Lamp Frequency Source Frequency Tolerance Lamp Frequency Receiver Frequency Range Lamp Frequency Receiver Duty Cycle DPWM Source (Resistor) Frequency Range DPWM Source (Resistor) Frequency Tolerance DPWM Source (Ext. Clk) Frequency Range DPWM Source (Ext. Clk) Duty Cycle DPWM Receiver Min Pulse Width BRIGHT Voltage: Minimum Brightness BRIGHT Voltage: Maximum Brightness Gate Driver Output Rise/Fall Time GA1 and GB1 Duty Cycle SYMBOL VOH1 VUVLOR VUVLOF VUVLOH VSVMR VSVMF VDCB RDCB VLOT VLOC VLRT VOVDT fLFS:OSC fLFS:TOL fLFR:OSC fLFR:DUTY fDSR:OSC fDSR:TOL fDSE:OSC fDFE:DUTY tDR:MIN VBMIN VBMAX tR / tF CL = 600pF (Note 6) 2.0 100 44 (Note 5) POSC resistor 2% over temperature LOSC resistor 2% over temperature (Note 3) (Note 3) (Notes 3, 4) (Note 3) 0.22 2.2 0.9 0.9 40 -5 40 40 22.5 -5 22.5 40 25 0.5 2.03 1.95 3.7 200 2.08 2.02 1.1 50 0.25 2.5 1.0 1.0 0.28 2.8 1.1 1.1 100 +5 100 60 440.0 +5 440.0 60 2.15 2.07 IOH1 = -1mA CONDITIONS MIN VCC 0.4 4.3 TYP MAX UNITS V V V mV V V V k V V V V kHz % kHz % Hz % Hz % s V V ns %
DS3881
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Single-Channel Automotive CCFL Controller DS3881
I2C AC ELECTRICAL CHARACTERISTICS (See Figure 9)
(VCC = +4.75V to +5.25V, TA = -40C to +105C, timing referenced to VIL(MAX) and VIH(MIN).)
PARAMETER SCL Clock Frequency Bus Free Time Between Stop and Start Conditions Hold Time (Repeated) Start Condition Low Period of SCL High Period of SCL Data Hold Time Data Setup Time Start Setup Time SDA and SCL Rise Time SDA and SCL Fall Time Stop Setup Time SDA and SCL Capacitive Loading EEPROM Write Time SYMBOL fSCL tBUF tHD:STA tLOW tHIGH tHD:DAT tSU:DAT tSU:STA tR tF tSU:STO CB tW (Note 9) (Note 10) 20 (Note 9) (Note 9) (Note 8) (Note 7) CONDITIONS MIN 0 1.3 0.6 1.3 0.6 0 100 0.6 20+ 0.1CB 20+ 0.1CB 0.6 400 30 300 300 0.9 TYP MAX 400 UNITS kHz s s s s s ns s ns ns s pF ms
NONVOLATILE MEMORY CHARACTERISTICS
(VCC = +4.75V to +5.25V)
PARAMETER EEPROM Write Cycles SYMBOL CONDITIONS +85C (Note 11) MIN 30,000 TYP MAX UNITS
Note 1: All voltages are referenced to ground unless otherwise noted. Currents into the IC are positive, out of the IC negative. Note 2: During fault conditions, the AC-coupled feedback values are allowed to be below the absolute max rating of the LCM1 or OVD1 pin for up to 1 second. Note 3: Voltage with respect to VDCB. Note 4: Lamp overdrive and analog dimming (based on reduction of lamp current) are disabled. Note 5: This is the minimum pulse width guaranteed to generate an output burst, which will generate the DS3881's minimum burst duty cycle. This duty cycle may be greater than the duty cycle of the PSYNC input. Once the duty cycle of the PSYNC input is greater than the DS3881's minimum duty cycle, the output's duty cycle will track the PSYNC's duty cycle. Leaving PSYNC low (0% duty cycle) disables the GA1 and GB1 outputs in DPWM receiver mode. Note 6: This is the maximum lamp frequency duty cycle that will be generated at GA1 or GB1 outputs with spread-spectrum modulation disabled. Note 7: I2C interface timing shown is for fast-mode (400kHz) operation. This device is also backward compatible with I2C standardmode timing. Note 8: After this period, the first clock pulse can be generated. Note 9: CB--total capacitance allowed on one bus line in picofarads. Note 10: EEPROM write time applies to all the EEPROM memory. EEPROM write begins after a stop condition occurs. Note 11: Guaranteed by design.
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Single-Channel Automotive CCFL Controller DS3881
Typical Operating Characteristics
(VCC = 5.0V, TA = +25C, unless otherwise noted.)
ACTIVE SUPPLY CURRENT vs. SUPPLY VOLTAGE
DS3881 toc01
ACTIVE SUPPLY CURRENT vs. TEMPERATURE
7.0 VCC = 5.0V SUPPLY CURRENT (mA) 6.5 VCC = 4.75V VCC = 5.25V
DS3881 toc02
INTERNAL FREQUENCY CHANGE vs. TEMPERATURE
0.8 FREQUENCY CHANGE (%) 0.6 0.4 0.2 0 -0.2 -0.4 -0.6 -0.8 -1.0 105 -40.0 32.5 TEMPERATURE (C) 105 LAMP FREQUENCY DPWM FREQUENCY
DS3881 toc03
7.0 DPWM = 100% 6.5 SUPPLY CURRENT (mA) 6.0 5.5 5.0 4.5 4.0 GATE QC = 3.5nC fLF:OSC = 64kHz SVML< 2V DPWM = 10% DPWM = 50%
1.0
6.0
5.5 fLF:OSC = 64kHz 5.0 GATE QC = 3.5nC -40.0 DPWM = 100% 32.5 TEMPERATURE (C)
4.75 4.80 4.85 4.90 4.95 5.00 5.05 5.10 5.15 5.20 5.25 SUPPLY VOLTAGE (V)
TYPICAL OPERATION AT 11V
DS3881 toc04
TYPICAL OPERATION AT 13V
DS3881 toc05
TYPICAL OPERATION AT 16V
DS3881 toc06
10s 5.0V GA 10s 5.0V GB 10s 2.00V LCM 10s 2.00V OVD
10s 5.0V GA 10s 5.0V GB
10s 5.0V GA 10s 5.0V GB
10s 2.00V LCM 10s 2.00V OVD
10s 2.00V LCM 10s 2.00V OVD
TYPICAL STARTUP WITH SVM
DS3881 toc07
BURST DIMMING AT 150Hz AND 10%
DS3881 toc08
BURST DIMMING AT 150Hz AND 50%
DS3881 toc09
2ms 5.0V SVML 2ms 5.0V GB
1ms 5.0V GA 1ms 5.0V GB
1ms 5.0V GA 1ms 5.0V GB 1ms 2.00V LCM 1ms 2.00V OVD
2ms 2.00V LCM 2ms 2.00V OVD
1ms 2.00V LCM 1ms 2.00V OVD
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Single-Channel Automotive CCFL Controller DS3881
Typical Operating Characteristics (continued)
(VCC = 5.0V, TA = +25C, unless otherwise noted.)
LAMP STRIKE WITH OPEN LAMP, AUTO RETRY DISABLED
DS3881 toc11 DS3881 toc12
SOFT-START AT VINV = 16V
DS3881 toc10
LAMP STRIKE--EXPANDED VIEW
50s 5.0V GA 50s 5.0V GB
1ms 5.0V GA 1ms 5.0V GB
0.5s 5.0V GA 0.5s 5.0V GB
50s 2.00V LCM 50s 2.00V OVD
1ms 2.00V LCM 1ms 2.00V OVD
0.5s 2.00V LCM 0.5s 2.00 OVD
LAMP OUT (LAMP OPENED), AUTO-RETRY DISABLED
DS3881 toc13
0.1s 5.0V GA 0.1s 5.0V GB LAMP OPENED 0.1s 2.00V LCM 0.1s 2.00V OVD
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Single-Channel Automotive CCFL Controller
Pin Description
PIN 1, 9 2 3 NAME A0, A1 SDA SCL FUNCTION Address Select Input. Determines I2C slave address. Serial Data Input / Output. I2C bidirectional data pin, which requires a pullup resistor to realize high logic levels. Serial Clock Input. I2C clock input. Lamp Frequency Input/Output. This pin is the input for an externally sourced lamp frequency when the DS3881 is configured as a lamp frequency receiver. If the DS3881 is configured as a lamp frequency source (i.e., the lamp frequency is generated internally), the frequency is output on this pin for use by other lamp frequency receiver DS3881s. Lamp Oscillator Resistor Adjust. A resistor to ground on this lead sets the frequency of the internal lamp oscillator. Analog Brightness Control Input. Used to control the DPWM dimming feature. Ground if unused. DPWM Input/Output. This pin is the input for an externally generated DPWM signal when the DS3881 is configured as a DPWM receiver. If the DS3881 is configured as a DPWM source (i.e., the DPWM signal is generated internally), the DPWM signal is output on this pin for use by other DPWM receiver DS3881s. DPWM Oscillator Resistor Adjust. A resistor to ground on this lead sets the frequency of the DPWM oscillator. This lead can optionally accept a 22.5Hz to 440Hz clock that will become the source timing of the internal DPWM signal. I2C Interface Ground Connection. GND_S must be at the same potential as GND. Low-Supply Voltage Monitor Input. Used to monitor the inverter voltage for undervoltage conditions. High-Supply Voltage Monitor Input. Used to monitor the inverter voltage for overvoltage conditions. Power Supply Connections. Both pins must be connected. Lamp Current Monitor Input. Lamp current is monitored by a resistor placed in series with the low voltage side of the lamp. Overvoltage Detection. Lamp voltage is monitored by a capacitor divider placed on the high voltage side of the transformer. No Connection. Do not connect any signal to this pin. Lamp Frequency Step Input. This active-high digital input moves the lamp oscillator frequency up or down by either 1%, 2%, 3%, or 4% as configured in the EMIC register. This pin is logically ORed with the STEPE bit in the EMIC register. Ground Connection Lamp Current Overdrive Enable Input. A high digital level at this input enables the lamp current overdrive circuit. The amount of overdrive current is configured by the LCOC register. When this input is low, the lamp current is set to its nominal level. This pin is logically ORed with the LCOE bit in the LCOC register. Lamp On/Off Control Input. A low digital level at this input turns the lamp on. A high digital level clears the fault logic, turns the lamp off, and places the device into the power-down mode. This pin is logically ORed with the PDNE bit in the CR2 register.
DS3881
4
LSYNC
5 6 7
LOSC BRIGHT PSYNC
8 10 11 12 13, 21 14 15 16 17 18 19
POSC GND_S SVML SVMH VCC LCM1 OVD1 N.C. STEP GND LCO
20 22, 23 24
PDN
GA1, GB1 MOSFET A and B Gate Drive. Connect directly to logic-level mode n-channel MOSFET. FAULT Active-Low Fault Output. This open-drain pin requires external pullup resistor to realize high-logic levels.
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Single-Channel Automotive CCFL Controller DS3881
Functional Diagrams
PDN LCO SDA SCL I2C DEVICE CONFIGURATION AND CONTROL PORT A0/A1 GND_S FAULT CHANNEL FAULT FAULT HANDLING LSYNC CHANNEL ENABLE I2C INTERFACE EEPROM CONTROL REGISTERS 8 BYTE USER MEMORY STATUS REGISTERS System SYSTEM Enable / ENABLE/ POR POR 2.0V
UVLO VREF
VCC [4.75V TO 5.25V] SVML SUPPLY VOLTAGE MONITOR--LOW SVMH SUPPLY VOLTAGE MONITOR--HIGH
2.0V
LAMP FREQUENCY INPUT/OUTPUT STEP LAMP FREQUENCY UP OR DOWN
[40kHz ~ 100kHz] LFSS BIT AT CR1.2 x512 PLL [20.48MHz ~ 51.20MHz] SINGLE CCFL CONTROLLER
LCM1 LAMP CURRENT MONITOR
STEP
OVD1 OVERVOLTAGE DETECTION
LOSC EXTERNAL RESISTOR LAMP FREQUENCY SET
40kHz TO 100kHz OSCILLATOR (5%) DPSS BIT AT CR1.3
DS3881
MUX RGSO BIT AT CR1.4 MUX DPSS BIT AT CR1.3 DPWM SIGNAL
GA1 GB1
DPWM SIGNAL INPUT/OUTPUT ANALOG BRIGHTNESS CONTROL EXTERNAL RESISTOR DPWM FREQUENCY SET/DPWM CLOCK INPUT
PSYNC
MOSFET GATE DRIVERS
BRIGHT POSC MUX POSCS BIT AT CR1.1 RAMP GENERATOR
22.5Hz TO 440Hz OSCILLATOR (5%)
GND 22.5Hz TO 440Hz
Figure 1. Functional Diagram
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Single-Channel Automotive CCFL Controller
Functional Diagrams (continued)
DS3881
LAMP OUT 300mV CHANNEL ENABLE LAMP OVERCURRENT CHANNEL FAULT DIGITAL CCFL CONTROLLER LOCE BIT IN CR1.0 LAMP STRIKE AND REGULATION 64 LAMP CYCLE INTEGRATOR OVERVOLTAGE VLRT (1.0V NOMINAL) OVD1 OVERVOLTAGE DETECTOR 1.0V GA1 GB1 MOSFET GATE DRIVERS 2.5V LCM1 LAMP CURRENT MONITOR
DIMMING PWM SIGNAL 512 x LAMP FREQUENCY [20.48MHz ~ 51.20MHz] LAMP FREQUENCY [40kHz ~ 80kHz]
LAMP MAXIMUM VOLTAGE REGULATION
GATE DRIVERS
Figure 2. Per Channel Logic Diagram
Detailed Description
The DS3881 uses a push-pull drive scheme to convert a DC voltage (8V to 16V) to the high-voltage (300VRMS to 1000VRMS) AC waveform that is required to power the CCFL. The push-pull drive scheme uses a minimal number of external components, which reduces assembly cost and makes the printed circuit board design easy to implement. The push-pull drive scheme also provides an efficient DC-to-AC conversion and produces near-sinusoidal waveforms. Each DS3881 drives two logic-level n-channel MOSFETs that are connected between the ends of a step-up transformer and ground (see the Typical Operating Circuit). The transformer has a center tap on the primary side that is connected to a DC voltage supply. The DS3881 alternately turns on the two MOSFETs to create the high-voltage AC waveform on the secondary side. By varying the duration of the MOSFET turn-on times, the CCFL current is able to be accurately controlled. A resistor in series with the CCFL's ground connection enables current monitoring. The voltage across this resistor is fed to the lamp current monitor (LCM) input and compared to an internal reference voltage to deter-
mine the duty cycle for the MOSFET gates. The CCFL receives current monitoring and control, which maximizes the lamp's brightness and lifetime. Block diagrams of the DS3881 are shown in Figures 1 and 2. More operating details of the DS3881 are discussed on the following pages of this data sheet.
Memory Registers and 2C-Compatible Serial Interface I
The DS3881 uses an I2C-compatible serial interface for communication with the on-board EEPROM and SRAM configuration/status registers as well as user memory. The configuration registers, which are a mixture of shadowed EEPROM and SRAM, allow the user to customize many DS3881 parameters such as the soft-start ramp rate, the lamp and dimming frequency sources, brightness of the lamps, fault-monitoring options, channel enabling/disabling, EMI control, and lamp current overdrive control. The eight bytes of NV user memory can be used to store manufacturing data such as date codes, serial numbers, or product identification numbers. The device is shipped from the factory with the configuration registers programmed to a set of default configuration parameters. To inquire about custom programming, contact the factory.
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Single-Channel Automotive CCFL Controller DS3881
Shadowed EEPROM
The DS3881 incorporates SRAM-shadowed EEPROM memory locations for all memory that needs to be retained during power cycling. At power-up, SEEB (bit 7 of the BLC register) is low, which causes the shadowed locations to act as ordinary EEPROM. Setting SEEB high disables the EEPROM write function and causes the shadowed locations to function as ordinary SRAM cells. This allows an infinite number of write cycles without causing EEPROM damage and also eliminates the EEPROM write time, tW from the write cycle. Because memory changes made when SEEB is set high are not written to EEPROM, these changes are not retained through power cycles, and the power-up EEPROM values are the last values written with SEEB low. The DS3881 can generate its own DPWM signal internally (set DPSS = 0 in CR1), which can then be sourced to other DS3881s if required, or the DPWM signal can be supplied from an external source (set DPSS = 1 in CR1). To generate the DPWM signal internally, the DS3881 requires a clock (referred to as the dimming clock) to set the DPWM frequency. The user can supply the dimming clock by setting POSCS = 1 in CR1 and applying an external 22.5Hz to 440Hz signal at the POSC pin, or the dimming clock can be generated by the DS3881's internal oscillator (set POSCS = 0 in CR1), in which case the frequency is set by an external resistor at the POSC pin. These two dimming clock options are shown in Figure 3. Regardless of whether the dimming clock is generated internally or sourced externally, the POSC0 and POSC1 bits in CR2 must be set to match the desired dimming clock frequency. The internally generated DPWM signal can be provided at the PSYNC I/O pin (set RGSO = 0 in CR1) for sourcing to other DS3881s, if any, in the circuit. This allows all DS3881s in the system to be synchronized to the same DPWM signal. A DS3881 that is generating the DPWM signal for other DS3881s in the system is referred to as the DPWM source. When bringing in an externally generated DPWM signal, either from another DS3881 acting as a DPWM source or from some other user-provided source, it is input into the PSYNC I/O pin of the DS3881, and the receiving DS3881 is referred to a DPWM receiver. In this mode, the BRIGHT and POSC inputs are disabled and should be grounded (see Figure 5). When the DPWM signal is generated internally, its duty cycle (and, thus, the lamp brightness) is controlled either by a user-supplied analog voltage at the BRIGHT input or through the I2C interface by varying the 7-bit PWM code in the BPWM register. When using the BRIGHT pin to control burst dimming, a voltage of less than 0.5V causes the DS3881 to operate with the minimum burst duty cycle, providing the lowest brightness setting, while any voltage greater than 2.0V causes a 100% burst duty cycle (i.e., lamps always being driven), which provides the maximum brightness. For voltages between 0.5V and 2V, the duty cycle varies linearly between the minimum and 100%. Writing a nonzero PWM code to the BPWM register disables the BRIGHT pin and enables I2C burst dimming control. Setting the 7-bit PWM code to 0000001b causes the DS3881 to operate with the minimum burst duty cycle, while a setting of 1111111b causes a 100% burst duty cycle. For settings between these two codes, the duty cycle varies linearly between the minimum and 100%.
Lamp Dimming Control
The DS3881 provides two independent methods of lamp dimming that can be combined to achieve a dimming ratio of 300:1 or greater. The first method is "burst" dimming, which uses a digital pulse-width-modulated (DPWM) signal (22.5Hz to 440Hz) to control the lamp brightness. The second is "analog" dimming, which is accomplished by adjusting the lamp current. Burst dimming provides 128 linearly spaced brightness steps. Analog dimming provides smaller substeps that allow incremental brightness changes between burst dimming steps. This ability is especially useful for lowbrightness dimming changes, where using burst dimming alone would cause visible brightness step changes. Analog dimming also allows the brightness to be reduced below the minimum burst dimming level, which provides for the maximum dimming range. Burst dimming can be controlled using a user-supplied analog voltage on the BRIGHT pin or through the I2C interface. Analog dimming can only be controlled through the I2C interface. Therefore, for applications that require the complete dimming range and resolution capability of the DS3881, I2C dimming control must be used. Burst Dimming Burst dimming increases/decreases the brightness by adjusting (i.e., modulating) the duty cycle of the DPWM signal. During the high period of the DPWM cycle, the lamps are driven at the selected lamp frequency (40kHz to 100kHz) as shown in Figure 6. This part of the cycle is called the "burst" period because of the lamp frequency burst that occurs during this time. During the low period of the DPWM cycle, the controller disables the MOSFET gate drivers so the lamps are not driven. This causes the current to stop flowing in the lamps, but the time is short enough to keep the lamps from de-ionizing.
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Single-Channel Automotive CCFL Controller DS3881
RESISTOR-SET DIMMING CLOCK
EXTERNAL DIMMING CLOCK
ANALOG DIMMING CONTROL VOLTAGE 0.5V DPWM SIGNAL 22.5Hz TO 440Hz EXTERNAL RESISTOR SETS DPWM RATE
2.0V BRIGHT
ANALOG DIMMING CONTROL VOLTAGE 0.5V DPWM SIGNAL 22.5Hz TO 440Hz EXTERNAL DPWM CLOCK 22.5Hz TO 440Hz
2.0V BRIGHT
PSYNC POSC
PSYNC POSC
Figure 3. DPWM Source Configuration Options
Analog Dimming Analog dimming changes the brightness by increasing or decreasing the lamp current. The DS3881 accomplishes this by making small shifts to the lamp regulation voltage, VLRT (see Figure 2). Analog dimming is only possible by software communication with the lower five bits (LC4-LC0) in the BLC register. This function is not pin controllable. The default power-on state of the LC bits is 00000b, which corresponds to 100% of the nominal current level. Therefore on power-up, analog dimming does not interfere with burst dimming functionality if it is not desired. Setting the LC bits to 11111b reduces the lamp current to 35% of its nominal level. For LC values between 11111b and 00000b, the lamp current varies linearly between 35% and 100% of nominal. Lamp Frequency Configuration The DS3881 can generate its own lamp frequency clock internally (set LFSS = 0 in CR1), which can then be sourced to other DS3881s if required, or the lamp clock can be supplied from an external source (set LFSS = 1 in CR1). When the lamp clock is internally generated, the frequency (40kHz to 100kHz) is set by an external resistor at the LOSC. In this case, the DS3881 can act as a lamp frequency source because the lamp clock is output at the LSYNC I/O pin for synchronizing any other DS3881s configured as lamp frequency receivers. While DS3881 is sourcing lamp frequency to other DS3881's and spread-spectrum modulation or frequency step features are enabled, the LSYNC output is not affected by either EMI suppression features. The DS3881 acts as a lamp frequency receiver when the lamp clock is supplied externally. In this case, a 40kHz to 100kHz clock must be supplied at the
DPWM RECEIVER
BRIGHT
DPWM SIGNAL 22.5Hz TO 440Hz
PSYNC
POSC
Figure 4. DPWM Receiver Configuration
LSYNC I/O. The external clock can originate from the LSYNC I/O of a DS3881 configured as a lamp frequency source or from some other source.
Configuring Systems with Multiple DS3881s
The source and receiver options for the lamp frequency clock and DPWM signal allow multiple DS3881s to be synchronized in systems requiring more than 1 lamp. The lamp and dimming clocks can either be generated on board the DS3881 using external resistors to set the frequency, or they can be sourced by the host system to synchronize the DS3881 to other system resources. Figure 5 shows various multiple DS3881 configurations that allow both lamp and/or DPWM synchronization for all DS3881s in the system.
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Single-Channel Automotive CCFL Controller DS3881
ANALOG BRIGHTNESS 0.5V RESISTOR-SET DIMMING FREQUENCY RESISTOR-SET LAMP FREQUENCY
2.0V
ANALOG BRIGHTNESS BRIGHT PSYNC LSYNC POSC LOSC BRIGHT PSYNC 0.5V
2.0V
BRIGHT PSYNC LSYNC POSC N.C. LOSC BRIGHT
DS3881
LAMP FREQUENCY SOURCE DPWM SOURCE
LAMP CLOCK (40kHz TO 100kHz) RESISTOR-SET DIMMING FREQUENCY
DS3881
LAMP FREQUENCY RECEIVER DPWM SOURCE
DS3881
PSYNC
DS3881
LSYNC LAMP FREQUENCY RECEIVER N.C. POSC DPWM RECEIVER N.C. LOSC
LSYNC LAMP FREQUENCY RECEIVER N.C. POSC DPWM RECEIVER N.C. LOSC
ANALOG BRIGHTNESS 0.5V
2.0V
BRIGHT PSYNC
ANALOG BRIGHTNESS 0.5V
2.0V
BRIGHT PSYNC LSYNC POSC N.C. LOSC BRIGHT
DS3881
LAMP FREQUENCY SOURCE DPWM SOURCE
DIMMING CLOCK (22.5Hz TO 440Hz) RESISTOR-SET LAMP FREQUENCY
LSYNC POSC LOSC BRIGHT PSYNC
LAMP CLOCK (40kHz TO 100kHz) DIMMING CLOCK (22.5Hz TO 440Hz)
DS3881
LAMP FREQUENCY RECEIVER DPWM SOURCE
DS3881
PSYNC
DS3881
LSYNC LAMP FREQUENCY RECEIVER N.C. POSC DPWM RECEIVER N.C. LOSC
LSYNC LAMP FREQUENCY RECEIVER N.C. POSC DPWM RECEIVER N.C. LOSC
DPWM SIGNAL (22.5Hz TO 440Hz)
BRIGHT PSYNC LSYNC N.C. POSC
DPWM SIGNAL (22.5Hz TO 440Hz)
BRIGHT PSYNC LSYNC N.C. POSC N.C. LOSC BRIGHT
DS3881
LAMP FREQUENCY SOURCE DPWM RECEIVER LAMP CLOCK (40kHz TO 100kHz)
DS3881
LAMP FREQUENCY RECEIVER DPWM RECEIVER
RESISTOR-SET LAMP FREQUENCY
LOSC BRIGHT PSYNC
DS3881
PSYNC
DS3881
LSYNC LAMP FREQUENCY RECEIVER N.C. POSC DPWM RECEIVER N.C. LOSC
LSYNC LAMP FREQUENCY RECEIVER N.C. POSC DPWM RECEIVER N.C. LOSC
Figure 5. Frequency Configuration Options for Designs Using Multiple DS3881s
12
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Single-Channel Automotive CCFL Controller
DPWM Soft-Start
At the beginning of each lamp burst, the DS3881 provides a soft-start that slowly increases the MOSFET gate-driver duty cycle (see Figure 6). This minimizes the possibility of audible transformer noise that could result from current surges in the transformer primary. The soft-start length is fixed at 16 lamp cycles, but the soft-start ramp profile is programmable through the four soft-start profile registers (SSP1/2/3/4) and can be adjusted to match the application. There are seven different driver duty cycles to select from to customize the soft-start ramp (see Tables 5a and 5b). The available duty cycles range from 0% to 19% in ~3% increments. In addition, the MOSFET duty cycle from the last lamp cycle of the previous burst can be used as part of the soft-start ramp by using the most recent value duty cycle code. Each programmed MOSFET gate duty cycle repeats twice to make up the 16 softstart lamp cycles.
DS3881
DPWM SIGNAL 22.5Hz TO 440Hz
LAMP CURRENT
SOFT-START SOFT-START (EXPANDED) LAMP CYCLE GA1/GB1 MOSFET GATE DRIVERS 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
SOFT-START PROFILE REGISTER
SSP1. 0-3
SSP1. 4-7
SSP2. 0-3
SSP2. 4-7
SSP3. 0-3
SSP3. 4-7
SSP4. 0-3
SSP4. 4-7
PROGRAMMABLE SOFT-START PROFILE WITH INCREASING MOSFET PULSE WIDTHS OVER A 16 LAMP CYCLE PERIOD RESULTS IN A LINEAR RAMP IN LAMP CURRENT.
LAMP CURRENT
Figure 6. Digital PWM Dimming and Soft-Start
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13
Single-Channel Automotive CCFL Controller DS3881
Setting the Lamp and Dimming Clock (DPWM) Frequencies Using External Resistors
Both the lamp and dimming clock frequencies can be set using external resistors. The resistance required for either frequency can be determined using the following formula: ROSC = K fOSC reaching the strike voltage and could potentially cause numerous other problems. Operating with the transformer voltage at too high of a level can be damaging to the inverter components. Proper use of the SVMs can prevent these problems. If desired, the high and/or low SVMs can be disabled by connecting the SVMH pin to GND and the SVML pin to VCC. R + R2 VTRIP = 2.0 1 R1 The VCC monitor is used as a 5V supply undervoltage lockout (UVLO) that prevents operation when the DS3881 does not have adequate voltage for its analog circuitry to operate or to drive the external MOSFETs. The VCC monitor features hysteresis to prevent VCC noise from causing spurious operation when V CC is near the trip point. This monitor cannot be disabled by any means.
where K = 1600k * kHz for lamp frequency calculations. When calculating the resistor value for the dimming clock frequency, K will be one of four values as determined by the desired frequency and the POSCR0 and POSCR1 bit settings as shown in the Control Register 2 (CR2) Table 6 in the Detailed Register Descriptions section. Example: Selecting the resistor values to configure a DS3881 to have a 50kHz lamp frequency and a 160Hz dimming clock frequency: For this configuration, POSCR0 and POSCR1 must be programmed to 1 and 0, respectively, to select 90Hz to 220Hz as the dimming clock frequency range. This sets K for the dimming clock resistor (RPOSC) calculation to 4k * kHz. For the lamp frequency resistor (R LOSC ) calculation, K = 1600k * kHz, which sets the lamp frequency K value regardless of the frequency. The formula above can now be used to calculate the resistor values for RLOSC and RPOSC as follows: RLOSC = 1600k * kHz = 32.0k 50kHz 4k * kHz RPOSC = = 25.0k 0.160kHz
Fault Monitoring
The DS3881 provides extensive fault monitoring. It can detect open-lamp, lamp overcurrent, failure to strike, and overvoltage conditions. The DS3881 can be configured to disable the output if the channel enters a fault state. Once a fault state has been entered, the FAULT output is asserted and the channel remains disabled until it is reset by a user or host control event. See Step 4, Fault Handling for more detail. The DS3881 can also be configured to automatically attempt to clear a detected fault (except lamp overcurrent) by re-striking the lamp. Configuration bits for the fault monitoring options are located in CR1 and CR2. The DS3881 also has real-time status indicator bits located in the SR1 and SR2 register (SRAM) that assert whenever a corresponding fault occurs.
Supply Monitoring
The DS3881 has supply voltage monitors (SVMs) for both the inverter's transformer DC supply (VINV) and its own VCC supply to ensure that both voltage levels are adequate for proper operation. The transformer supply is monitored for overvoltage conditions at the SVMH pin and undervoltage conditions at the SVML pin. External resistor-dividers at each SVM input feed into two comparators (see Figure 7), both having 2V thresholds. Using the equation below to determine the resistor values, the SVMH and SVML trip points (VTRIP) can be customized to shut off the inverter when the transformer's supply voltage rises above or drops below specified values. Operating with the transformer's supply at too low of a level can prevent the inverter from
VINV R2 VTRIP R1 SVML VINV R2
DS3881
SVMH
VTRIP R1
2.0V
2.0V
Figure 7. Setting the SVM Threshold Voltage
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Single-Channel Automotive CCFL Controller
Figure 8 shows a flowchart of how the DS3881 controls and monitors each lamp. The steps are as follows: 1) Supply Check--The lamps do not turn on unless the DS3881 supply voltage is above 4.3V and the voltage at the supply voltage monitors, SVML and SVMH, are respectively above 2.0V and below 2.0V. 2) Strike Lamp--When both the DS3881 and the DC inverter supplies are at acceptable levels, the DS3881 attempts to strike the lamp. The DS3881 slowly ramps up the MOSFET gate duty cycle until the lamp strikes. The controller detects that the lamp has struck by detecting current flow in the lamp, detected by the LCM1 pin. If during the strike ramp, the maximum allowable voltage is reached on the OVD1 pin, the controller stops increasing the MOSFET gate duty cycle to keep from overstressing the system. The DS3881 goes into a fault handling state (step 4) if the lamp has not struck after the timeout period as defined by the LST0 and LST1 control bits in the SSP1 register. If an overvoltage event is detected during the strike attempt, the DS3881 disables the MOSFET gate drivers and go into the fault handling state. 3) Run Lamp--Once the lamp is struck, the DS3881 adjusts the MOSFET gate duty cycle to optimize the lamp current. The gate duty cycle is always constrained to keep the system from exceeding the maximum allowable lamp voltage. The lamp current sampling rate is user-selectable using the LSC0 and LSC1 bits in CR2. If lamp current ever drops below the lamp out reference point for the period as defined by the LST0 and LST1 control bits in the SSP1 register, then the lamp is considered extinguished. In this case, the MOSFET gate drivers are disabled and the device moves to the fault handling stage. 4) Fault Handling--During fault handling, the DS3881 performs an optional (user-selectable) automatic retry to attempt to clear all faults except a lamp overcurrent. The automatic retry makes 14 additional attempts to rectify the fault before declaring the channel in a fault state and permanently disabling the channel. Between each of the 14 attempts, the controller waits 1024 lamp cycles. In the case of a lamp overcurrent, the DS3881 instantaneously declares the channel to be in a fault state and permanently disables the channel. Once a fault state is entered, the channel remains in that state until one of the following occurs: * VCC drops below the UVLO threshold. * The SVML or SVMH thresholds are crossed. * The PDN pin goes high. * The PDNE software bit is written to a logic 1. * The channel is disabled by the CH1D control bit.
DS3881
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15
Single-Channel Automotive CCFL Controller DS3881
DEVICE AND INVERTER SUPPLIES AT PROPER LEVELS? YES RESET FAULT COUNTER AND FAULT OUTPUT YES FAULT WAIT [1024 LAMP CYCLES] NO FAULT COUNTER = 15? YES
FAULT STATE [ACTIVATE FAULT OUTPUT]
SET FAULT_L AND FAULT_RT STATUS BITS NO AUTORETRY ENABLED? [ARD BIT AT CR1.5]
CLEAR FAULT_RT STATUS BIT
INCREMENT FAULT COUNTER / SET FAULT_RT STATUS BIT
STRIKE LAMP [RAMP AND REGULATE TO OVD THRESHOLD]
LAMP STRIKE TIMEOUT [SEE REGISTER SSP1]
SET STO_L STATUS BIT
IF LAMP REGULATION THRESHOLD IS MET
OVERVOLTAGE [64 LAMP CYCLES]
SET OV_L STATUS BIT
LAMP OVERCURRENT [INSTANTANEOUS IF ENABLED BY THE LOCE BIT AT CR1.0]
RUN LAMP [REGULATE LAMP CURRENT BOUNDED BY LAMP VOLTAGE]
LAMP OUT TIMEOUT [SEE REGISTER SSP1]
SET LOUT_L STATUS BIT
MOSFET GATE DRIVERS ENABLED SET LOC_L STATUS BIT
Figure 8. Fault-Handling Flowchart
16
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Single-Channel Automotive CCFL Controller
EMI Suppression Functionality
The DS3881 contains two electromagnetic interference suppression features: spread-spectrum modulation and lamp oscillator frequency stepping. The first is the ability to spread the spectrum of the lamp frequency. By setting either SS0 and/or SS1 in EMIC register, the controller can be configured to dither the lamp frequency by 1.5%, 3%, or 6%. By setting a non-zero value in SS0/1, spread-spectrum modulation is enabled and oscillator frequency stepping is disabled. In spreadspectrum modulation mode the dither modulation rate is also selectable by setting FS0/1/2, and has either a triangular (SSM = 0) or a pseudorandom profile (SSM = 1). Users have the flexibility to choosing the best modulation rate (through FS0/1/2) for the application. The second EMI suppression scheme is the ability to move the lamp frequency up or down by 1%, 2%, 3%, or 4%. In this scheme, the actual radiated EMI is not reduced but it is moved out of a sensitive frequency region. STEPE bit and/or STEP pin is used to enable lamp frequency stepping (SS0/1 must be 0). Once enabled, the FS0/1/2 value controls the lamp oscillator frequency shift. For example, if the lamp frequency creates EMI disturbing an audio radio station, it can be moved up or down slightly to slide the spurious interferer out of band.
Lamp Current Overdrive Functionality
Another feature the DS3881 offers is the ability to overdrive the lamps to allow them to heat up quickly in cold environments. After setting the LCO0/1/2 bits in the LCOC register and enabling the LCOE bit or LCO pin, the DS3881 overdrives the nominal current settings in 12.5% steps from 112.5% up to 200%. The DS3881 accomplishes this by automatically shifting the lamp regulation threshold, VLRT, upward to allow more current to flow in the lamps (Figure 2). This multilevel adjustment makes it possible to slowly decrease the current overdrive (through I2C) after the lamps have warmed up, so the end user does not see any change in brightness when the overdrive is no longer needed. The DS3881 also features an optional timer capable of automatically turning off the current overdrive. This timer is adjustable from approximately 1.5 minutes to 21 minutes (if a 50kHz lamp frequency is used).
DS3881
Detailed Register Descriptions
The DS3881's register map is shown in Table 1. Detailed register and bit descriptions follow in the subsequent tables.
Table 1. Register Map
BYTE ADDRESS E0h E1h E2h E3h F0h F1h F2h F3h F4h F5h F6h F7h F8h-FFh BYTE NAME SR1 RSVD BPWM BLC SSP1 SSP2 SSP3 SSP4 CR1 CR2 EMIC LCOC USER FACTORY DEFAULT 00h 00h 00h 1Fh 21h 43h 65h 77h 00h 08h 00h 00h 00h BIT 7 BIT 6 BIT 5 LOC_L1 RSVD PWM5 CH1D BIT 4 LOUT_L1 RSVD PWM4 LC4 BIT 3 OV_L1 RSVD PWM3 LC3 LST0 BIT 2 STO_L1 RSVD PWM2 LC2 BIT 1 FAULT_L1 RSVD PWM1 LC1 BIT 0 FAULT_RT1 RSVD PWM0 LC0
SVMH_RT SVML_RT RSVD RSVD SEEB LST1 RSVD PWM6 RSVD
MDC code for soft-start lamp cycles 3, 4
MDC code for soft-start lamp cycles 1, 2
MDC code for soft-start lamp cycles 7, 8 MDC code for soft-start lamp cycles 11, 12 MDC code for soft-start lamp cycles 15, 16 DPD PDNE FS2 TO3 EE RSVD RSVD FS1 TO2 EE ARD RSVD FS0 TO1 EE RGSO LSR1 STEPE TO0 EE
MDC code for soft-start lamp cycles 5, 6 MDC code for soft-start lamp cycles 9, 10 MDC code for soft-start lamp cycles 13, 14 DPSS LSR0 RSVD LCOE EE LFSS POSCR1 SSM LCO2 EE POSCS POSCR0 SS1 LCO1 EE LOCE UMWP SS0 LCO0 EE
Note 1: E0h-E3h are SRAM locations, and F0h-FFh are SRAM-shadowed EEPROM. Note 2: Altering the DS3881 configuration during active CCFL operation can cause serious adverse effects.
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Single-Channel Automotive CCFL Controller DS3881
Table 2. Status Register 1 (SR1) [SRAM, E0h]
BIT R/W POWER-UP DEFAULT NAME FUNCTION Fault Condition--Real Time. A real-time bit that indicates the current operating status of channel 1. 0 = Normal condition 1 = Fault condition Fault Condition--Latched. A latched bit that is set when the channel enters a fault condition. This bit is cleared when read, regardless of the current state of fault. Lamp Strike Timeout--Latched. A latched bit that is set when the lamp fails to strike. This bit is cleared when read. Overvoltage--Latched. A latched bit that is set when a lamp overvoltage is present for at least 64 lamp cycles. This bit is cleared when read. Lamp Out--Latched. A latched bit that is set when a lamp out is detected. This bit is cleared when read. Lamp Overcurrent--Latched. A latched bit that is set when a lamp overcurrent is detected. This bit is cleared when read. Supply Voltage Monitor Low--Real Time. A real-time bit that reports the comparator output of the SVML pin. Supply Voltage Monitor High--Real Time. A real-time bit that reports the comparator output of the SVMH pin.
0
R
0
FAULT_RT
1 2 3 4 5 6 7
R R R R R R R
0 0 0 0 0 0 0
FAULT_L STO_L OV_L LOUT_L LOC_L SVML_RT SVMH_RT
Note 1: Writing to this register has no effect on it. Note 2: See Figure 8 for more details on how the status bits are set. Note 3: SR1 is cleared when only the following occurs: * VCC drops below the UVLO threshold. * The SVML or SVMH thresholds are crossed. * The PDNE hardware pin goes high. * The PDNE software bit is written to a logic 1. * The channel is disabled by the CH1D control bit.
Table 3. Brightness Lamp Current Register (BLC) [SRAM, E3h]
BIT 0 1 2 3 4 5 6 7 R/W R/W R/W R/W R/W R/W R/W R/W R/W FACTORY DEFAULT 0 0 0 0 0 0 0 0 NAME LC0 LC1 LC2 LC3 LC4 CH1D RSVD SEEB Channel 1 Disable 0 = Channel 1 enabled 1 = Channel 1 disabled Reserved. Should be set to 0. SRAM-Shadowed EEPROM Write Control 0 = Enables writes to EEPROM 1 = Disables writes to EEPROM These five control bits determine the target value for the lamp current. 11111b is 35% of the nominal level and 00000b is 100% of the nominal level. These control bits are used for fine adjustment of the lamp brightness. FUNCTION
18
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Single-Channel Automotive CCFL Controller
Table 4a. Soft-Start Protocol Registers (SSPx) [Shadowed-EEPROM, F0h, F1h, F2h, F3h]
SSP# SSP1 SSP2 SSP3 SSP4 ADDR F0h F1h F2h F3h FACTORY DEFAULT 21h 43h 65h 77h MSB 7 LST1 RSVD RSVD RSVD 6 5 4 3 LST0 RSVD RSVD RSVD 2 1 Lamp Cycles 1 and 2 Lamp Cycles 5 and 6 Lamp Cycles 9 and 10 Lamp Cycles 13 and 14 Lamp Cycles 3 and 4 Lamp Cycles 7 and 8 Lamp Cycles 11 and 12 Lamp Cycles 15 and 16 LSB 0
DS3881
Table 4b. MOSFET Duty Cycle (MDC)Codes for Soft-Start Settings
BIT 0 R/W R/W NAME MDC0 MDC0/1/2/3: These bits determine a MOSFET duty cycle that repeats twice in the 16 lamp cycle soft-start. 1 2 R/W R/W MDC1 MDC CODE MDC2 0h 1h 2h 3 R/W LST0 / RSVD 3h MOSFET DUTY CYCLE Fixed at 0% Fixed at 3% Fixed at 6% Fixed at 9% MDC CODE 4h 5h 6h 7h MOSFET DUTY CYCLE Fixed at 13% Fixed at 16% Fixed at 19% Most Recent Value FUNCTION
4 5 6 7
R/W R/W R/W R/W
MDC0 MDC1 MDC2 LST1 / RSVD LST1 0 0 1 1
LST0/1: These bits select strike and lamp out timeout. LST0 and LST1 control fault behavior for all lamps. LST0 0 1 0 1 STRIKE AND LAMP OUT TIMEOUT (LAMP FREQUENCY CYCLES) 32,768 65,536 98,304 131,072 EXAMPLE TIMEOUT IF LAMP FREQUENCY IS 50kHz 0.66 seconds 1.31 seconds 1.97 seconds 2.62 seconds
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Single-Channel Automotive CCFL Controller DS3881
Table 5. Control Register 1 (CR1) [Shadowed-EEPROM, F4h]
BIT R/W FACTORY DEFAULT 0 NAME FUNCTION Lamp Overcurrent Enable 0 = Lamp overcurrent detection disabled. 1 = Lamp overcurrent detection enabled. POSC Select. See POSCR0 and POSCR1 control bits in Control Register 2 to select the oscillator range. 0 = POSC input is connected with a resistor to ground to set the frequency of the internal PWM oscillator. 1 = POSC input is a 22.5Hz to 440Hz clock. Lamp Frequency Source Select 0 = Lamp frequency generated internally and sourced from the LSYNC output. 1 = Lamp frequency generated externally and supplied to the LSYNC input. DPWM Signal Source Select 0 = DPWM signal generated internally and sourced from the PSYNC output. 1 = DPWM signal generated externally and supplied to the PSYNC input. Ramp Generator Source Option 0 = Source DPWM at the PSYNC output. 1 = Source internal ramp generator at the PSYNC output. Autoretry Disable 0 = Autoretry function enabled. 1 = Autoretry function disabled. Reserved. Should be set to 0. DPWM Disable 0 = DPWM function enabled. 1 = DPWM function disabled.
0
R/W
LOCE
1
R/W
0
POSCS
2
R/W
0
LFSS
3
R/W
0
DPSS
4
R/W
0
RGSO
5 6 7
R/W R/W R/W
0 0 0
ARD RSVD DPD
20
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Single-Channel Automotive CCFL Controller
Table 6. Control Register 2 (CR2) [Shadowed-EEPROM, F5h]
BIT 0 R/W R/W DEFAULT 0 NAME UMWP User Memory Write Protect 0 = Write access blocked. 1 = Write access permitted. FUNCTION
DS3881
1
R/W
0
POSCR0
DPWM Oscillator Range Select. When using an external source for the dimming clock, these bits must be set to match the external oscillator's frequency. When using a resistor to set the dimming frequency, these bits plus the external resistor control the frequency.
POSCR1 2 R/W 0 POSCR1 0 0 1 1
POSCR0 0 1 0 1
DIMMING CLOCK (DPWM) FREQUENCY RANGE (Hz) 22.5 to 55.0 45 to 110 90 to 220 180 to 440
k (k * kHz) 1 2 4 8
Lamp Sample Rate Select. Determines the feedback sample rate of the LCM inputs. 3 R/W 1 LSR0 LSR1 0 0 4 R/W 0 LSR1 1 1 5 6 -- -- 0 0 RSVD RSVD LSR0 0 1 0 1 SELECTED LAMP SAMPLE RATE 4 Lamp Frequency Cycles 8 Lamp Frequency Cycles 16 Lamp Frequency Cycles 32 Lamp Frequency Cycles EXAMPLE SAMPLE RATE IF LAMP FREQUENCY IS 50kHz 12,500Hz 6250Hz 3125Hz 1563Hz
Reserved. This bit should be set to zero. Reserved. This bit should be set to zero.
7
R/W
0
PDNE
Power-Down. Logically ORed with the PDN pin. Setting this bit high resets the controller, clears the fault logic, and places the part in power-down mode. 0 = Normal. All circuitry is off, except I2C interface.
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Single-Channel Automotive CCFL Controller DS3881
Table 7. EMI Control Register (EMIC) [Shadowed-EEPROM, F6h]
BIT R/W FACTORY DEFAULT NAME FUNCTION
0
R/W
0
SS0
LAMP OSCILLATOR SPREAD-SPECTRUM MODULATION SELECT SS1 0 0 SS0 0 1 0 1 SELECTED LAMP FREQUENCY SPREAD SPREAD-SPECTRUM DISABLED 1.5% 3.0% 6.0%
1
R/W
0
SS1
1 1
2
R/W
0
SSM
Lamp Oscillator Spread-Spectrum Modulation Select 0 = Triangular modulation. 1 = Pseudorandom modulation.
3
RSVD
Reserved. This bit should be set to zero.
4
R/W
0
STEPE
Lamp Frequency Step Enable. Logically ORed with the step invoked. 0 = Lamp operates at nominal frequency. 1 = Frequency step invoked.
LAMP OSCILLATOR FREQUENCY STEP SELECT 5 R/W 0 FS0 FS2 0 0 6 R/W 0 FS1 0 0 1 1 7 R/W 0 FS2 1 1 FS1 0 0 1 1 0 0 1 1 FS0 0 1 0 1 0 1 0 1 SELECTED LAMP FREQUENCY STEP (SS0 = 0 AND SS1= 0) Step Up 1% Step Up 2% Step Up 3% Step Up 4% Step Down 1% Step Down 2% Step Down 3% Step Down 4% SPREAD-SPECTRUM MODULATION RATE (SS0 AND/OR SS1 = 1) Lamp Frequency x4 Lamp Frequency x2 Lamp Frequency x1 Lamp Frequency x1/2 Lamp Frequency x1/4 Lamp Frequency x1/8 Lamp Frequency x1/16 Lamp Frequency x1/32
22
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Single-Channel Automotive CCFL Controller
Table 8. Lamp Current Overdrive Control Register (LCOC) [Shadowed-EEPROM, F7h]
BIT R/W FACTORY DEFAULT NAME FUNCTION LAMP CURRENT OVERDRIVE SELECT 0 R/W 0 LCO0 LCO2 0 0 0 1 R/W 0 LCO1 0 1 1 2 R/W 0 LCO2 1 1 LCO1 0 0 1 1 0 0 1 1 LCO0 0 1 0 1 0 1 0 1 SELECTED LAMP CURRENT OVERDRIVE Nominal Current + 12.50% Nominal Current + 25.00% Nominal Current + 37.50% Nominal Current + 50.00% Nominal Current + 62.50% Nominal Current + 75.00% Nominal Current + 87.50% Nominal Current + 100.00%
DS3881
3
R/W
0
LCOE
Lamp Current Overdrive Enable. Logically ORed with the LCO pin. 0 = Lamp operated with nominal current setting. 1 = Lamp overdrive invoked.
AUTOMATIC LAMP CURRENT OVERDRIVE TIMEOUT SELECT 4 R/W 0 TO0 TO3 0 0 0 5 R/W 0 TO1 0 0 0 0 0 6 R/W 0 TO2 1 1 1 1 1 7 R/W 0 TO3 1 1 1 TO2 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 TO1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 TO0 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 SELECTED TIMEOUT IN LAMP FREQUENCY CYCLES Disabled 1 x 222 2 x 222 3x2
22
EXAMPLE TIMEOUT IF LAMP FREQUENCY IS 50kHz -- 1.4 min 2.8 min 4.2 min 5.6 min 7.0 min 8.4 min 9.8 min 11.2 min 12.6 min 14.0 min 15.4 min 16.8 min 18.2 min 19.6 min 21.0 min
4 x 222 5 x 222 6x2
22
7 x 222 8 x 222 9 x 222 10 x 222 11 x 222 12 x 2
22
13 x 222 14 x 222 15 x 2
22
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Single-Channel Automotive CCFL Controller DS3881
I2C Definitions
The following terminology is commonly used to describe I2C data transfers: Master Device: The master device controls the slave devices on the bus. The master device generates SCL clock pulses, start, and stop conditions. Slave Devices: Slave devices send and receive data at the master's request. Bus Idle or Not Busy: Time between stop and start conditions when both SDA and SCL are inactive and in their logic-high states. Start Condition: A start condition is generated by the master to initiate a new data transfer with a slave. Transitioning SDA from high to low while SCL remains high generates a start condition. See the timing diagram for applicable timing. Stop Condition: A stop condition is generated by the master to end a data transfer with a slave. Transitioning SDA from low to high while SCL remains high generates a stop condition. See the timing diagram for applicable timing. Repeated Start Condition: The master can use a repeated start condition at the end of one data transfer to indicate that it will immediately initiate a new data transfer following the current one. Repeated starts are commonly used during read operations to identify a specific memory address to begin a data transfer. A repeated start condition is issued identically to a normal start condition. See the timing diagram for applicable timing. Bit Write: Transitions of SDA must occur during the low state of SCL. The data on SDA must remain valid and unchanged during the entire high pulse of SCL plus the setup and hold time requirements (see Figure 9). Data is shifted into the device during the rising edge of the SCL. Bit Read: At the end of a write operation, the master must release the SDA bus line for the proper amount of setup time (see Figure 9) before the next rising edge of SCL during a bit read. The device shifts out each bit of data on SDA at the falling edge of the previous SCL pulse and the data bit is valid at the rising edge of the current SCL pulse. Remember that the master generates all SCL clock pulses including when it is reading bits from the slave. Acknowledgement (ACK and NACK): An acknowledgement (ACK) or not acknowledge (NACK) is always the 9th bit transmitted during a byte transfer. The device receiving data (the master during a read or the slave during a write operation) performs an ACK by transmitting a zero during the 9th bit. A device performs a NACK by transmitting a one during the 9th bit. Timing (Figure 9) for the ACK and NACK is identical to all other bit writes. An ACK is the acknowledgment that the device is properly receiving data. A NACK is used to terminate a read sequence or as an indication that the device is not receiving data. Byte Write: A byte write consists of 8 bits of information transferred from the master to the slave (most significant bit first) plus a 1-bit acknowledgement from the slave to the master. The 8 bits transmitted by the master are done according to the bit-write definition and the acknowledgement is read using the bit-read definition.
SDA
tBUF tLOW tR tF
tHD:STA
tSP
SCL tHD:STA STOP START tHD:DAT NOTE: TIMING IS REFERENCE TO VIL(MAX) AND VIH(MIN). tHIGH tSU:DAT REPEATED START tSU:STA tSU:STO
Figure 9. I2C Timing Diagram 24 ____________________________________________________________________
Single-Channel Automotive CCFL Controller
Byte Read: A byte read is an 8-bit information transfer from the slave to the master plus a 1-bit ACK or NACK from the master to the slave. The 8 bits of information that are transferred (most significant bit first) from the slave to the master are read by the master using the bit read definition above, and the master transmits an ACK using the bit write definition to receive additional data bytes. The master must NACK the last byte read to terminate communication so the slave will return control of SDA to the master. Slave Address Byte: Each slave on the I 2 C bus responds to a slave addressing byte sent immediately following a start condition. The slave address byte (Figure 10) contains the slave address in the most significant seven bits and the R/W bit in the least significant bit. The DS3881's slave address is 10100A1A00 (binary), where A0 and A1 are the values of the address pins (A0 and A1). The address pin allows the device to respond to one of four possible slave addresses. By writing the correct slave address with R/W = 0, the master indicates it will write data to the slave. If R/W = 1, the master will read data from the slave. If an incorrect slave address is written, the DS3881 will assume the master is communicating with another I2C device and ignore the communications until the next start condition is sent. Memory Address: During an I2C write operation, the master must transmit a memory address to identify the memory location where the slave is to store the data. The memory address is always the second byte transmitted during a write operation following the slave address byte. I2C Communication Writing a Data Byte to a Slave: The master must generate a start condition, write the slave address byte (R/W = 0), write the memory address, write the byte of data, and generate a stop condition. Remember the master must read the slave's acknowledgement during all byte write operations. See Figure 11 for more detail. Acknowledge Polling: Any time EEPROM is written, the DS3881 requires the EEPROM write time (tW) after the stop condition to write the contents to EEPROM. During the EEPROM write time, the DS3881 will not acknowledge its slave address because it is busy. It is possible to take advantage of that phenomenon by repeatedly addressing the DS3881, which allows the next byte of data to be written as soon as the DS3881 is ready to receive the data. The alternative to acknowledge polling is to wait for a maximum period of tW to elapse before attempting to write again to the DS3881. EEPROM Write Cycles: The number of times the DS3881's EEPROM can be written before it fails is specified in the Nonvolatile Memory Characteristics table. This specification is shown at the worst-case write temperature. The DS3881 is typically capable of handling many additional write cycles when the writes are performed at room temperature. Reading a Data Byte from a Slave: To read a single byte from the slave the master generates a start condition, writes the slave address byte with R/W = 0, writes the memory address, generates a repeated start condition, writes the slave address with R/W = 1, reads the data byte with a NACK to indicate the end of the transfer, and generates a stop condition. See Figure 11 for more detail.
DS3881
7-BIT SLAVE ADDRESS
1
0
1
0
0 A1 A0
R/W
MOST SIGNIFICANT BIT
A1, A0 PIN VALUE
DETERMINES READ OR WRITE
Figure 10. DS3881's Slave Address Byte
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25
Single-Channel Automotive CCFL Controller DS3881
COMMUNICATIONS KEY S START A ACK NOT ACK X X X X X WHITE BOXES INDICATE THE MASTER IS CONTROLLING SDA SHADED BOXES INDICATE THE SLAVE IS CONTROLLING SDA X X X 8-BITS ADDRESS OR DATA
NOTES 1) ALL BYTES ARE SENT MOST SIGNIFICANT BIT FIRST.
P
STOP REPEATED START
N
2) THE FIRST BYTE SENT AFTER A START CONDITION IS ALWAYS THE SLAVE ADDRESS FOLLOWED BY THE READ/WRITE BIT.
SR
WRITE A SINGLE BYTE S 10 1 0 0 A1 A0 0 A MEMORY ADDRESS A DATA A P
READ A SINGLE BYTE S 10 1 0 0 A1 A0 0 A MEMORY ADDRESS A SR 10 1 0 0 A1 A0 1 A DATA N P
Figure 11. I2C Communications Examples
Applications Information
Addressing Multiple DS3881s On a Common I2C Bus
Each DS3881 responds to one of four possible slave addresses based on the state of the address input pins (A0 and A1). For information about device addressing, see the I2C Communications section.
Setting the RMS Lamp Current
Resistor R7 and R8 in the Typical Operating Circuit set the lamp current. R7 and R8 = 140 corresponds to a 5mARMS lamp current as long as the current waveform is approximately sinusoidal. The formula to determine the resistor value for a given sinusoidal lamp current is: R7 = 1 ILAMP(RMS) x 2
Additionally, its primary/secondary resistance and inductance characteristics must be considered because they contribute significantly to determining the efficiency and transient response of the system. Table 9 shows a transformer specification that has been used for a 12V inverter supply, 438mm x 2.2mm lamp design. The n-channel MOSFET must have a threshold voltage that is low enough to work with logic-level signals, a low on-resistance to maximize efficiency and limit the nchannel MOSFET's power dissipation, and a breakdown voltage high enough to handle the transient. The breakdown voltage should be a minimum of 3x the inverter voltage supply. Additionally, the total gate charge must be less than QG, which is specified in the Recommended DC Operating Conditions table. These specifications are easily met by many of the dual n-channel MOSFETs now available in 8-pin SO packages. Table 10 lists suggested values for the external resistors and capacitors used in the Typical Operating Circuit.
Component Selection External component selection has a large impact on the overall system performance and cost. The two most important external components are the transformers and n-channel MOSFETs. The transformer should be able to operate in the 40kHz to 80kHz frequency range of the DS3881, and the turns ratio should be selected so the MOSFET drivers run at 28% to 35% duty cycle during steady state operation. The transformer must be able to withstand the high open-circuit voltage that is used to strike the lamp.
Power-Supply Decoupling
To achieve best results, it is highly recommended that a decoupling capacitor is used on the IC power-supply pin. Typical values of decoupling capacitors are 0.01F or 0.1F. Use a high-quality, ceramic, surface-mount capacitor, and mount it as close as possible to the VCC and GND pins of the IC to minimize lead inductance.
26
____________________________________________________________________
Single-Channel Automotive CCFL Controller
Table 9. Transformer Specifications (as Used in the Typical Operating Circuit)
PARAMETER Turns Ratio (Secondary/Primary) Frequency Output Power Output Current Primary DCR Secondary DCR Primary Leakage Secondary Leakage Primary Inductance Secondary Inductance Secondary Output Voltage 100ms minimum Continuous 2000 1000 Center tap to one end 5 200 500 12 185 70 500 CONDITIONS (Notes 1, 2, 3) 40 MIN TYP 40 80 6 8 kHz W mA m H mH H mH VRMS MAX UNITS
DS3881
Note 1: Primary should be Bifilar wound with center tap connection. Note 2: Turns ratio is defined as secondary winding divided by the sum of both primary windings. Note 3: 40:1 is the nominal turns ratio for driving a 438mm x 2.2mm lamp with a 12V supply. Refer to Application Note 3375 for more information.
Table 10. Resistor and Capacitor Selection Guide
DESIGNATOR R5, R6 R3, R4 R9 R10 R1 R2 R11 R7 C8 C2 C3 C1 C7 QTY 1 1 1 1 1 1 1 1/Chan 1/Chan 1/Chan 1/Chan 1/Chan 2/DS3881 VALUE 10k 12.5k to 105k 20k to 40k 18k to 45k 4.7k 4.7k 4.7k 140 100nF 10pF 27nF 33F 0.1F TOLERANCE (%) AT +25C 1 1 1 1 5 5 5 1 10 5 5 20 10 TEMPERATURE COEFFICIENT -- -- 153ppm/C 153ppm/C Any grade Any grade Any grade -- X7R 1000ppm/C X7R Any grade X7R -- See the Setting the SVM Threshold Voltage section. 2% or less total tolerance. See the Lamp Frequency Configuration section to determine value. 2% or less total tolerance. See the Lamp Frequency Configuration section to determine value. -- -- -- See the Setting the RMS Lamp Current section. Capacitor value will also affect LCM bias voltage during power-up. A larger capacitor may cause a longer time for VDCB to reach its normal operating level. 2kV to 4kV breakdown voltage required. Capacitor value will also affect LCM bias voltage during power-up. A larger capacitor may cause a longer time for VDCB to reach its normal operating level. -- Place close to VCC and GND on DS3881. NOTES
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27
Single-Channel Automotive CCFL Controller DS3881
Typical Operating Circuit
DEVICE SUPPLY VOLTAGE (5V 5%) INVERTER SUPPLY VOLTAGE (VINV) (8V TO 16V)
VCC R1
VCC
R2 C7 SDA VCC SVMH SVML R5 R6 R3 R4
C1
I2C CONFIGURATION AND CONTROL PORT VCC R11
SCL A0 A1 GND_S
FAULT
DS3881
GA1
CCFL LAMP C2 C3 R7
GB1 LAMP CURRENT OVERDRIVE ENABLE HARDWARE CONTROL LAMP ON/OFF LAMP BRIGHTNESS STEP LAMP FREQUENCY DPWM SIGNAL INPUT/OUTPUT LAMP FREQUENCY INPUT/OUTPUT LCO PDN BRIGHT STEP GND PSYNC LSYNC LOSC POSC R9 R10 OVD1 LCM1 C8 DUAL POWER MOSFET TRANSFORMER OVERVOLTAGE DETECTION LAMP CURRENT MONITOR
Chip Information
TRANSISTOR COUNT: 38,000 SUBSTRATE CONNECTED TO GROUND
Package Information
For the latest package outline information, go to www.maxim-ic.com/DallasPackInfo.
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
28 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 2006 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products, Inc.
is a registered trademark of Dallas Semiconductor Corporation.
Heaney

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