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19-4370; Rev 0; 11/08
EVALUATION KIT AVAILABLE
High-Efficiency, White LED Step-Up Converter with I2C Interface in 2mm x 2mm WLP
General Description
The MAX8831 integrates a 60mA, 28V PWM DC-DC step-up converter with five low-dropout LED current regulators for display and keypad backlighting in cell phones, PDAs, and other portable devices. The IC provides up to 90% efficiency over the entire input voltage range of 2.7V to 5.5V. The step-up converter operates at a fixed 2MHz switching frequency, enabling the use of very small external components to achieve a compact circuit area. For improved efficiency, the step-up converter automatically transitions to pulse-skipping mode at light loads. Each of the five current regulators accommodates up to 9 series LEDs (depending on LED string forward voltage), and is independently programmed using an I2C interface. Two of the current regulators (LED1, LED2) are intended to support display backlight functions and are programmable up to 25mA using a 128-step logarithmic dimming scheme. The other three regulators (LED3, LED4, LED5) are suitable for keyboard backlight functions or for driving signal indicators, and are programmable up to 5mA using a 32-step logarithmic dimming scheme. The low-current regulators (LED3, LED4, LED5) can be operated from the step-up converter or from a separate low-voltage source. The I2C interface controls all operational aspects of the current regulators, including: on/off state, LED current, ramp-up/ramp-down timers, and blink rate timers (LED3, LED4, LED5). The MAX8831 write/read addresses are factory programmed at 0x9A/0x9B (contact the factory for other address options). The MAX8831 features open/short LED fault detection, output overvoltage protection, thermal shutdown, and open-circuit Schottky diode detection, with the status of each fault monitored continually for readback through the I2C interface. The MAX8831 is available in a tiny 2mm x 2mm, 16-bump WLP package.
Features
28V Step-Up DC-DC Converter Integrated NMOS Power Switch > 90% Efficiency Fixed 2MHz Switching Pulse Skipping for Improved Light-Load Efficiency Tiny External Components I2C Programmable (0x9A Write/0x9B Read), Compatible with 1.8V Logic Two 25mA Regulators for Display Backlighting I2C-Programmable Output Current (50A to 25.25mA) 128-Step Logarithmic Dimming Individually Programmable Ramp (Up/Down) Timers Low Dropout (200mV max) Three 5mA Current Regulators for Keypad Lighting I2C-Programmable Output Current (50A to 5.0mA) 32-Step Logarithmic Dimming Individually Programmable Ramp (Up/Down) Timers Individual Blink Rate and Duty Cycle Timers Low Dropout (150mV max) Open/Short LED and Open-Circuit Diode Detection Thermal-Shutdown and Output Overvoltage Protection Ultra-Low 0.1mA Shutdown Current Tiny 2mm x 2mm, 16-Bump WLP Package
MAX8831
Ordering Information
PART MAX8831EWE+T TEMP RANGE -40C to +85C PIN-PACKAGE 16 WLP 2mm x 2mm
Applications
Cell Phones PDAs Smartphones
+Denotes a lead(Pb)-free/RoHS-compliant package.
T = Tape and reel.
________________________________________________________________ Maxim Integrated Products
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High-Efficiency, White LED Step-Up Converter with I2C Interface in 2mm x 2mm WLP MAX8831
ABSOLUTE MAXIMUM RATINGS
IN to GND ..............................................................-0.3V to +6.0V VDD, COMP to GND.....................................-0.3V to (VIN + 0.3V) SDA, SCL to GND.......................................-0.3V to (VDD + 0.3V) OUT, LX, LED1-LED5 to GND................................-0.3V to +30V ILX (Note 1) .....................................................................1.2ARMS PGND to GND .......................................................-0.3V to +0.3V Operating Temperature Range ...........................-40C to +85C Continuous Power Dissipation (TA = +70C) 16-Bump, 2mm x 2mm WLP (derate 8.2mW/C above +70C ambient) ...................660mW Junction Temperature ......................................................+150C Storage Temperature Range .............................-65C to +150C Bump Temperature (soldering, reflow) ............................+260C
Note 1: LX has an internal clamp diode to PGND. Applications that forward bias this diode should take care not to exceed the power dissipation limits of the device.
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.
ELECTRICAL CHARACTERISTICS
(VIN = 3.6V, VGND = VPGND = 0V, VDD = 1.8V, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 1)
PARAMETER IN Supply Voltage VDD Supply Voltage IN Undervoltage Lockout Threshold IN Quiescent Current IN Shutdown Current VDD Standby Current IN Standby Current OUT Leakage Current LED_ CURRENT REGULATORS LED_ Current Regulator Dropout Voltage (Note 2) ILED1 or ILED2 = 25mA setting ILED3 or ILED4 or ILED5 = 5.0mA setting ILED1 or ILED2 = 25.25mA setting LED_ Current Accuracy ILED3 or ILED4 or ILED5 = 5.0mA setting LED_ Leakage Current LED_ Regulation Voltage N-CHANNEL SWITCH LX Current Limit LX On-Resistance ILX = 200mA 780 VLED_ = 5.5V, VDD = GND TA = +25C TA = -40C to +85C TA = +25C TA = -40C to +85C TA = +25C TA = +85C -2 -5 -2 -5 0.01 0.1 0.35 860 0.3 200 150 +2 +5 +2 +5 1 mV mV % % A V mA No load, 2MHz switching VDD = GND VSDA = VSCL = VDD VSDA = VSCL = VDD VIN = VOUT = 5.5V, VDD = GND TA = +25C TA = +85C TA = +25C TA = +85C TA = +25C TA = +85C TA = +25C TA = +85C CONDITIONS MIN 2.7 1.6 2.4 1.5 0.1 0.1 0.1 0.1 2 2 0.01 0.1 1 5 1 1 TYP MAX 5.5 5.5 2.6 UNITS V V V mA A A A A
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High-Efficiency, White LED Step-Up Converter with I2C Interface in 2mm x 2mm WLP
ELECTRICAL CHARACTERISTICS (continued)
(VIN = 3.6V, VGND = VPGND = 0V, VDD = 1.8V, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 1)
PARAMETER LX Leakage Current OSCILLATOR Operating Frequency Maximum Duty Cycle Minimum On-Time COMP Soft-Start Charge Current COMP Input Resistance to GND I2C INTERFACE SDA, SCL Logic Input High Voltage SDA, SCL Logic Input Low Voltage SDA Output Low Voltage SDA, SCL Logic Input Current FAULT PROTECTION Thermal Shutdown Thermal-Shutdown Hysteresis Output Overvoltage Threshold Output Overvoltage Hysteresis Open LED_ Sense Voltage Shorted LED_ Sense Voltage Open/Short LED Debounce Timer LED_ enabled, measured at LED_ LED_ enabled, measured at LED_, VOUT = 10V VOUT - 2.2V VOUT rising 28 4 100 VOUT - 0.7V 16 120 Temperature rising +160 20 30 C C V V mV V ms VDD = 1.6V to 5.5V VDD = 1.6V to 5.5V ISDA = 3mA VIL = 0V or VIH = 5.5V TA = +25C TA = +85C 0.03 0.01 0.1 0.7 x VDD 0.3 x VDD 0.4 1 V V V A Step-up converter off -20 20 A k VLED1 or VLED2 = 0.2V Skip mode 1.8 87 2 92 30 2.2 100 MHz % ns CONDITIONS VIN = VLX = 5.5V, VDD = GND TA = +25C TA = +85C MIN TYP 0.01 0.1 MAX 1 UNITS A
MAX8831
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High-Efficiency, White LED Step-Up Converter with I2C Interface in 2mm x 2mm WLP MAX8831
I2C INTERFACE TIMING CHARACTERISTICS
(VDD = 1.6V to 5.5V, TA = -40C to +85C, unless otherwise noted.) (Note 1)
PARAMETER I2C Clock Frequency Bus-Free Time Between STOP and START Repeated START Condition Hold Time Repeated START Condition Setup Time STOP Condition Setup Time SCL Clock Low Period SCL Clock High Period SDA Hold Time SDA Setup Time SYMBOL fSCL tBUF tHD_STA tSU_STA tSU_STO tLOW tHIGH tHD_DAT tSU_DAT 1.3 0.6 0.6 0.6 1.3 0.6 0 100 0.1 0.1 0.1 0.2 0.2 0.01 50 CONDITIONS MIN TYP MAX 400 UNITS kHz s s s s s s s ns
Note 1: All devices are 100% production tested at TA = +25C. Limits over the operating temperature range are guaranteed by design. Note 2: LED dropout voltage is defined as the LED_ to GND voltage when current into LED_ drops 10% from the value at VLED_ = 0.5V.
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High-Efficiency, White LED Step-Up Converter with I2C Interface in 2mm x 2mm WLP
Typical Operating Characteristics
(VIN = 3.6V, VDD = 1.8V, CIN = 1F, COUT = 1F, CVDD = 0.1F, CCOMP = 0.22F, L = TOKO 1098AS-100M, ILED1 = ILED2 = 25.25mA, ILED3 = ILED4 = ILED5 = 5mA, unless otherwise noted.)
CONVERTER EFFICIENCY vs. INPUT VOLTAGE (LED1 STRING)
MAX8831 toc01
MAX8831
CONVERTER EFFICIENCY vs. INPUT VOLTAGE (LED1 AND LED2 STRINGS)
MAX8831 toc02
CONVERTER EFFICIENCY vs. INPUT VOLTAGE (LED3 STRING)
MAX8831 toc03
100 95 EFFICIENCY (%) 90 85 80 75 70 2.5 3.0 3.5 4.0 4.5 5.0 4 LEDs: VOUT = 13.35V 5 LEDs: VOUT = 16.63V 6 LEDs: VOUT = 19.83V 7 LEDs: VOUT = 23.07V 8 LEDs: VOUT = 26.23V
100 95 90 EFFICIENCY (%) 85 80 75 70 65 60 4 LEDs: VOUT = 13.37V 5 LEDs: VOUT = 16.61V 6 LEDs: VOUT = 19.78V 7 LEDs: VOUT = 23.02V 8 LEDs: VOUT = 26.17V 2.5 3.0 3.5 4.0 4.5 5.0
85 80 75 EFFICIENCY (%) 70 65 60 55 50 5 LEDs: VOUT = 15.04V 6 LEDs: VOUT = 17.97V 7 LEDs: VOUT = 20.97V 8 LEDs: VOUT = 23.97V 9 LEDs: VOUT = 26.81V 2.5 3.0 3.5 4.0 4.5 5.0
5.5
5.5
5.5
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
CONVERTER EFFICIENCY vs. INPUT VOLTAGE (LED3-TO-LED5 STRINGS)
MAX8831 toc04
CONVERTER EFFICIENCY vs. INPUT VOLTAGE (LED1-LED5 STRINGS)
MAX8831 toc05
CONVERTER EFFICIENCY vs. LED CURRENT (LED1 STRING)
4 LEDs 6 LEDs 8 LEDs
MAX8831 toc06
90 88 86 EFFICIENCY (%) 84 82 80 78 76 74 72 70 2.5 3.0 3.5 4.0 4.5 5.0 5 LEDs: VOUT = 15.21V 6 LEDs: VOUT = 18.11V 7 LEDs: VOUT = 21.02V 8 LEDs: VOUT = 24.01V 9 LEDs: VOUT = 26.93V
100 95 90 EFFICIENCY (%) 85 80 75 70 65 LED1, LED2: 8 LEDs LED3 TO LED5: 8 LEDs VOUT = 26.81V LED1, LED2: 7 LEDs LED3 TO LED5: 8 LEDs VOUT = 23.86V
90 80 EFFICIENCY (%) 70 60 50 40 30
5.5
2.5
3.0
3.5
4.0
4.5
5.0
5.5
0
5
10
15
20
25
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
LED CURRENT (mA)
CONVERTER EFFICIENCY vs. LED CURRENT (LED1 AND LED2 STRINGS)
3 LEDs 5 LEDs 8 LEDs
MAX8831 toc07
LED1, LED2 CURRENT ACCURACY vs. LED CURRENT
MAX8831 toc08
LED3-TO-LED5 CURRENT ACCURACY vs. LED CURRENT
8 LED CURRENT ACCURACY (%) 6 4 2 0 -2 -4 -6 -8 -10 LED1, LED2: 8 LEDs AT 25.25mA LED3 TO LED5: 9 LEDs 0 1 2 3 4 5 ILED3 (ILED5 = ILED4 = 5mA) ILED5 (ILED4 = ILED3 = 5mA) ILED4 (ILED5 = ILED3 = 5mA)
MAX8831 toc09
90 80 EFFICIENCY (%) 70 60 50 40 30 0
10 8 LED CURRENT ACCURACY (%) 6 4 2 0 -2 -4 -6 -8 -10 LED1, LED2: 8 LEDs LED3 TO LED5: 9 LEDs AT 5mA 0 5 10 15 20 ILED2 (ILED1 = 25.25mA) ILED1 (ILED2 = 25.25mA)
10
5
10
15
20
25
25
LED CURRENT (mA)
LED CURRENT (mA)
LED CURRENT (mA)
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High-Efficiency, White LED Step-Up Converter with I2C Interface in 2mm x 2mm WLP MAX8831
Typical Operating Characteristics (continued)
(VIN = 3.6V, VDD = 1.8V, CIN = 1F, COUT = 1F, CVDD = 0.1F, CCOMP = 0.22F, L = TOKO 1098AS-100M, ILED1 = ILED2 = 25.25mA, ILED3 = ILED4 = ILED5 = 5mA, unless otherwise noted.)
LIGHT-LOAD SWITCHING WAVEFORMS
MAX8831 toc10
HEAVY-LOAD SWITCHING WAVEFORMS
MAX8831 toc11
VIN
100mV/div (AC-COUPLED) 20V/div
VIN
200mV/div (AC-COUPLED) 20V/div
VLX 0V VOUT 100mV/div (AC-COUPLED) 4mA/div 0mA ILED1 ILED1 = 2mA 200ns/div
VLX VOUT ILED1
0V 1V/div (AC-COUPLED) 20mA/div 0mA
ILED2 ILED1 = ILED2 = 25.25mA
20mA/div 0mA 200ns/div
SOFT-START RESPONSE
MAX8831 toc12
SHUTDOWN RESPONSE
MAX8831 toc13
20V/div VOUT 0V 200mA/div IIN 0mA 20mA/div ILED1 ILED2 20mA/div 0mA 20ms/div
VOUT IIN
20V/div 0V 200mA/div 0mA
ILED1 ILED2
20mA/div 20mA/div 0mA 40ms/div
MAXIMUM OUTPUT CURRENT vs. INPUT VOLTAGE
MAX8831 toc14
LED1, LED2 CURRENT ACCURACY vs. INPUT VOLTAGE
MAX8831 toc15
LED3-TO-LED5 CURRENT ACCURACY vs. INPUT VOLTAGE
LED1, LED2: 8 LEDs AT 25.25mA LED3 TO LED5: 9 LEDs ILED4 (ILED5 = ILED3 = 5mA) 0.50 0 ILED3 (ILED4 = ILED5 = 5mA)
MAX8831 toc16
140 MAXIMUM OUTPUT CURRENT (mA) 120 100 80 60 40 20 0 2.5 3.0 3.5 4.0 4.5 5.0
1.50 LED CURRENT ACCURACY (%) 1.00 0.50 0
LED1, LED2: 8 LEDs LED3 TO LED5: 9 LEDs AT 5mA
1.50 LED CURRENT ACCURACY (%) 1.00
ILED1 (ILED2 = 25.25mA)
-0.50 -1.00 -1.50 ILED2 (ILED1 = 25.25mA)
-0.50 -1.00 ILED5 (ILED4 = ILED3 = 5mA) -1.50
5.5
2.5
3.0
3.5
4.0
4.5
5.0
5.5
2.5
3.0
3.5
4.0
4.5
5.0
5.5
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
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High-Efficiency, White LED Step-Up Converter with I2C Interface in 2mm x 2mm WLP
Typical Operating Characteristics (continued)
(VIN = 3.6V, VDD = 1.8V, CIN = 1F, COUT = 1F, CVDD = 0.1F, CCOMP = 0.22F, L = TOKO 1098AS-100M, ILED1 = ILED2 = 25.25mA, ILED3 = ILED4 = ILED5 = 5mA, unless otherwise noted.)
LED1 RAMP-UP
MAX8831 toc17
MAX8831
LED1 RAMP-DOWN
MAX8831 toc18
10mA/div
ILED1
10mA/div
ILED1 RAMP-UP TIMES OF 128ms, 1024ms, AND 8192ms 1s/div
0mA RAMP-DOWN TIMES OF 128ms, 1024ms, AND 8192ms 1s/div
0mA
LED3 RAMP-UP
MAX8831 toc19
LED3 RAMP-DOWN
MAX8831 toc20
2mA/div
ILED3
2mA/div
ILED3 RAMP-UP TIMES OF 128ms, 1024ms, AND 8192ms 1s/div
0mA RAMP-DOWN TIMES OF 128ms, 1024ms, AND 8192ms 1s/div
0mA
LED3 BLINK TIMER
MAX8831 toc21
LED3 BLINK TIMER + RAMP TIMER COMBINED
MAX8831 toc22
2mA/div
2mA/div
ILED3 tON = 512ms, tOFF = 1024ms 400ms/div
0mA
ILED3 tON = 512ms, tOFF = 1024ms, RAMP-UP = 128ms, RAMP-DOWN = 128ms 400ms/div
0mA
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High-Efficiency, White LED Step-Up Converter with I2C Interface in 2mm x 2mm WLP MAX8831
Pin Description
PIN A1 A2 A3 NAME LED1 GND LED3 FUNCTION 25mA LED Current Regulator. Connect LED1 to the cathode of the LED1 diode string. LED1 is high impedance in shutdown. Analog Ground. Connect GND directly to PGND at the output capacitor as close as possible to the IC. 5mA LED Current Regulator. Connect LED3 to the cathode of the LED3 diode string. LED3 is high impedance in shutdown. Step-Up Compensation Node. Connect a 0.22F ceramic capacitor from COMP to GND. The applied COMP capacitance stabilizes the converter and sets the soft-start time. COMP discharges to GND through a 20k resistance when in shutdown. See the Compensation Network Selection section for more details. 25mA LED Current Regulator. Connect LED2 to the cathode of the LED2 diode string. LED2 is high impedance in shutdown. 5mA LED Current Regulator. Connect LED5 to the cathode of the LED5 diode string. LED5 is high impedance in shutdown. 5mA LED Current Regulator. Connect LED4 to the cathode of the LED4 diode string. LED4 is high impedance in shutdown. I2C Serial-Clock Input Step-Up Converter Switching Node. Connect an inductor between IN and LX. LX is high impedance in shutdown. Power Ground. Connect PGND directly to GND at the output capacitor as close as possible to the IC. I2C Serial-Data I/O. Data written on rising edge of SCL, data read on falling edge of SCL. I2C Input Buffer Supply. Connect a 0.1F capacitor from VDD to GND as close as possible to the IC. Connect VDD to a 1.6V to 5.5V supply to enable the I2C interface. Drive VDD low to place the IC in shutdown. Power-Supply Input. Bypass IN to GND with a 1F ceramic capacitor placed as close as possible to the IC. LED Overvoltage Protection Input. Connect OUT to the positive terminal of the output capacitor. OUT monitors voltage at the LEDs. If an overvoltage condition is detected, all LED_ current regulators and the step-up converter are shut down. OUT is high impedance during shutdown.
A4
COMP
B1 B2 B3 B4 C1, D1 C2, D2 C3 C4
LED2 LED5 LED4 SCL LX PGND SDA VDD
D3
IN
D4
OUT
Detailed Description
The MAX8831 integrates a 60mA, 28V PWM DC-DC step-up converter with five low-dropout LED current regulators for display and keypad backlighting in cell phones, PDAs, and other portable devices. The IC provides up to 90% efficiency over the entire input voltage range of 2.7V to 5.5V. The step-up converter operates at a fixed 2MHz switching frequency, enabling the use of very small external components to achieve a compact circuit area. For improved efficiency, the step-up con-
verter automatically operates in pulse-skipping mode at light loads. Figure 1 displays the functional diagram of the MAX8831. Each current regulator accommodates up to 9 series LEDs (depending on LED string forward voltage), and is independently programmed using an I2C interface. Two of the current regulators (LED1, LED2) are intended to support display backlight functions and are programmable up to 25.25mA using a 128-step logarithmic dimming scheme.
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High-Efficiency, White LED Step-Up Converter with I2C Interface in 2mm x 2mm WLP MAX8831
IN UVLO AND BIAS OUT OSC OVP LX LX PWM LOGIC PGND COMP PGND LED1
GND
REF SEL MIN
VDD SDA SCL
I2C INTERFACE
LED2
25mA CURRENT REGULATORS LED3 LED4 LED5
MAX8831
5mA CURRENT REGULATORS
Figure 1. MAX8831 Functional Diagram
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High-Efficiency, White LED Step-Up Converter with I2C Interface in 2mm x 2mm WLP MAX8831
The other three regulators (LED3, LED4, LED5) are suitable for keyboard backlight functions or for driving signal indicators, and are programmable up to 5.0mA using a 32-step logarithmic dimming scheme. The lowcurrent regulators (LED3, LED4, LED5) can be operated from the step-up converter or from a separate lowvoltage source. The I2C interface controls all operational aspects of the current regulators, including: on/off state, LED current, ramp-up/ramp-down timers, and blink rate timers (LED3, LED4, LED5). The MAX8831 I 2 C write/read addresses are factory set at 0x9A/0x9B (contact the factory for other address options). The IC features several protective features, including: open/short LED fault detection, output overvoltage protection, thermal shutdown, and open Schottky diode detection. The status of each fault is monitored continually for readback through the I2C interface.
LED1, LED2 CURRENT vs. ILED1, ILED2 CONTROL REGISTER VALUE
25 LED1, LED2 CURRENT (mA) 20
15
10 5
0 0 20 40 60 80 100 120 140 ILED1, ILED2 CONTROL REGISTER VALUE (INTEGER)
Fixed-Frequency Step-Up Controller
The MAX8831's fixed-frequency, current-mode, step-up controller automatically chooses the lowest active LED_ voltage to complete the feedback loop (Figure 1). Specifically, the difference between the lowest LED_ voltage and the 350mV reference is integrated by the error amplifier. The resulting error signal is compared to the external switch current plus slope compensation to terminate the switch on-time. As the load changes, the error amplifier sources or sinks current to COMP to adjust the required peak inductor current. The slopecompensation signal is added to the current-sense signal to improve stability at high duty cycles. At light loads, the MAX8831 automatically skips pulses to improve efficiency and to prevent overcharging the output capacitor. In SKIP mode, the inductor current ramps up for a minimum on-time of 20ns (typ), then discharges the stored energy to the output. The switch remains off until another pulse is needed to step-up the output voltage. When the MAX8831 is programmed by the I2C interface to use an alternate supply voltage for the LED3, LED4, or LED5 string (see the Low-Current Regulators (LED3, LED4, LED5) section), internal logic masks that LED_ input and it is not used to regulate the step-up converter output.
Figure 2. LED1, LED2 String Current vs. ILED1, ILED2 Control Register Value
tions. Each high-current regulator is independently enabled and is programmable from 50A to 25.25mA in 128 logarithmic steps (Table 1, Figure 2) using the I2C interface. Additionally, the I2C interface programs the ramp-up and ramp-down timers for each regulator to one of eight different timing settings. See the MAX8831 I2C Registers section for details on I2C control of the high-current regulators.
Low-Current Regulators (LED3, LED4, LED5)
The MAX8831 also contains three low-dropout (150mV max), 5.0mA linear current regulators (LED3, LED4, LED5) that can each drive up to 9 series LEDs for keypad backlighting or signal indicator functions. Each current regulator is independently enabled, and is programmable from 50A to 5.0mA in 32 logarithmic steps (Table 2, Figure 3) using the I2C interface. Individual ramp-up and ramp-down timers are programmable for LED3, LED4, and LED5, with eight possible timing settings. The individual blink ON and blink OFF timers for each low-current regulator are also programmable, or these features can be disabled. See the MAX8831 I2C Registers section for details. The LED3, LED4, and LED5 low-current regulators can be powered from an alternate external source. By programming the BOOST_CNTL register, internal logic masks that LED_ input and it is not used to regulate the step-up converter output.
High-Current Regulators (LED1, LED2)
The MAX8831 contains two low-dropout (200mV max), 25.25mA linear current regulators (LED1, LED2) that can each drive up to 9 series LEDs (depending on LED string forward voltage) for display backlighting func-
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High-Efficiency, White LED Step-Up Converter with I2C Interface in 2mm x 2mm WLP MAX8831
Table 1. LED1, LED2 Programmable Current Levels and Register Values
ILED_CNTRL REGISTER VALUE 0x00 0x01 0x02 0x03 0x04 0x05 0x06 0x07 0x08 0x09 0x0A 0x0B 0x0C 0x0D 0x0E 0x0F 0x10 0x11 0x12 0x13 0x14 0x15 0x16 0x17 0x18 0x19 0x1A 0x1B 0x1C 0x1D 0x1E 0x1F 0x20 0x21 0x22 0x23 0x24 0x25 ILED_ (mA) 0.05 0.1 0.2 0.25 0.35 0.45 0.55 0.65 0.75 0.85 1 1.1 1.2 1.35 1.45 1.6 1.75 1.85 2 2.15 2.3 2.45 2.6 2.75 2.9 3.05 3.2 3.35 3.5 3.65 3.85 4 4.15 4.35 4.55 4.7 4.9 5.05 ILED_CNTRL REGISTER VALUE 0x2B 0x2C 0x2D 0x2E 0x2F 0x30 0x31 0x32 0x33 0x34 0x35 0x36 0x37 0x38 0x39 0x3A 0x3B 0x3C 0x3D 0x3E 0x3F 0x40 0x41 0x42 0x43 0x44 0x45 0x46 0x47 0x48 0x49 0x4A 0x4B 0x4C 0x4D 0x4E 0x4F 0x50 ILED_ (mA) 6.15 6.35 6.5 6.7 6.9 7.1 7.3 7.45 7.65 7.85 8.05 8.25 8.45 8.65 8.85 9.05 9.25 9.45 9.65 9.9 10.1 10.3 10.5 10.7 10.9 11.15 11.35 11.55 11.8 12 12.2 12.45 12.65 12.85 13.1 13.3 13.55 13.75 ILED_CNTRL REGISTER VALUE 0x56 0x57 0x58 0x59 0x5A 0x5B 0x5C 0x5D 0x5E 0x5F 0x60 0x61 0x62 0x63 0x64 0x65 0x66 0x67 0x68 0x69 0x6A 0x6B 0x6C 0x6D 0x6E 0x6F 0x70 0x71 0x72 0x73 0x74 0x75 0x76 0x77 0x78 0x79 0x7A 0x7B ILED_ (mA) 15.15 15.35 15.6 15.8 16.05 16.3 16.5 16.75 17 17.25 17.45 17.7 17.95 18.2 18.45 18.65 18.9 19.15 19.4 19.65 19.9 20.15 20.4 20.65 20.9 21.15 21.4 21.65 21.9 22.15 22.4 22.65 22.9 23.15 23.4 23.7 23.95 24.2
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High-Efficiency, White LED Step-Up Converter with I2C Interface in 2mm x 2mm WLP MAX8831
Table 1. LED1, LED2 Programmable Current Levels and Register Values (continued)
ILED_CNTRL REGISTER VALUE 0x26 0x27 0x28 0x29 0x2A ILED_ (mA) 5.25 5.45 5.6 5.8 5.95 ILED_CNTRL REGISTER VALUE 0x51 0x52 0x53 0x54 0x55 ILED_ (mA) 14 14.2 14.45 14.65 14.9 ILED_CNTRL REGISTER VALUE 0x7C 0x7D 0x7E 0x7F -- ILED_ (mA) 24.45 24.7 25 25.25 --
Soft-Start
From shutdown, once any LED_ is enabled through the I2C interface, the IC prepares for soft-start. CCOMP is quickly pulled to 1V by an internal pullup clamp. Since the LED_ feedback node voltage is less than the regulation threshold (0.35V typ), 40A current is sourced from the error amplifier (Figure 1) and further charges CCOMP. Once VCOMP reaches 1.25V, the step-up converter starts switching at a reduced duty cycle. As VCOMP rises, the step-up converter duty cycle increases. When VLED_ reaches 0.35V (typ), the error amplifier stops sourcing current to CCOMP, soft-start ends, and the control loop achieves regulation as VLED_ settles. The VCOMP where the IC exits soft-start depends on the load. A 2.5V upper limit to VCOMP is imposed to aid in transient recovery and to allow maximum output for low input voltages. CCOMP is discharged to GND through a 20k internal resistor whenever the step-up converter is turned off, allowing the device to reinitiate soft-start when it is enabled. See the Typical Operating Characteristics for an example of soft-start operation.
LED3, LED4, LED5 CURRENT vs. ILED3, ILED4, ILED5 CONTROL REGISTER VALUE
5 LED3, LED4, LED5 CURRENT (mA)
4
3
2
1
0 0 4 8 12 16 20 24 28 ILED3, ILED4, ILED5 CONTROL REGISTER VALUE (INTEGER)
Figure 3. LED3, LED4, LED5 String Current vs. ILED3, ILED4, ILED5 Control Register Value
Open/Shorted LED Detection
The MAX8831 includes two fault-detection comparators on each LED_ input to detect an open or shorted LED condition. One comparator monitors LED_ voltage and indicates an open LED_ fault when VLED_ falls below 100mV. The other comparator detects when LED_ voltage rises above VOUT - 0.7V, indicating a shorted LED fault. The fault detection comparators are enabled only when the corresponding LED_ current regulator is enabled. Once a fault is detected, the two comparators provide a single bit output (1 = fault, 0 = no fault) to the STAT1 register (bits 0-4), corresponding to the appropriate LED regulator. A debounce time of 16ms (typ) is applied from when a fault condition is detected. At the end of the 16ms debounce time, the status is latched in to the status register and the respective current regulator is disabled. If an open LED condition occurs on a current regulator that is included in the adaptive output voltage
Off, Shutdown, and Standby
The MAX8831 is considered OFF when VIN is below the V UVLO threshold and V DD is below 1.6V. With V IN above the VUVLO threshold, and with VDD low, the IC enters the shutdown state and disables its internal reference. During shutdown, the MAX8831 holds all registers in reset, the step-up converter and all LED current drivers are off, and supply current is reduced to 0.1A (typ). LX and LED1-LED5 are high impedance when the step-up converter is off. While the n-channel MOSFET is turned off, the step-up regulator's output is connected to IN through the external inductor and Schottky diode. With a valid supply voltage applied to VDD (greater than 1.6V) and with VIN above VUVLO, the IC enters a standby condition, whereby it is ready to accept I2C commands. The step-up converter turns on when any current regulator is enabled with an I2C command.
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High-Efficiency, White LED Step-Up Converter with I2C Interface in 2mm x 2mm WLP
Table 2. LED3, LED4, and LED5 Programmable Current Levels and Register Values
ILED_CNTRL REGISTER VALUE 0x00 0x01 0x02 0x03 0x04 0x05 0x06 0x07 0x08 0x09 0x0A 0x0B 0x0C 0x0D 0x0E 0x0F ILED_(mA) 0.05 0.1 0.15 0.20 0.25 0.30 0.35 0.45 0.55 0.65 0.80 0.95 1.10 1.25 1.40 1.60 ILED_CNTRL REGISTER VALUE 0x10 0x11 0x12 0x13 0x14 0x15 0x16 0x17 0x18 0x19 0x1A 0x1B 0x1C 0x1D 0x1E 0x1F ILED_(mA) 1.75 1.90 2.10 2.25 2.40 2.60 2.80 3.00 3.25 3.50 3.70 3.90 4.15 4.40 4.70 5.00
Open Schottky Diode Detection
The MAX8831 detects an open external Schottky diode by sensing VOUT before turning on the step-up converter. If VOUT is above 0.8V (typ), the MAX8831 allows the step-up converter to turn on. If VOUT is less than 0.8V (typ), indicating that the external Schottky diode is open, the MAX8831 is put into standby state, the ON/OFF control register bits for the LEDs are set low, and the step-up converter stops switching. Bit 2 (OSDD) of the STAT2 register is updated to a 1 to indicate that an open Schottky diode event has occurred.
MAX8831
Thermal-Shutdown Protection
When the junction temperature exceeds +160C (typ), the ON/OFF control register bits for all LEDs are reset to low and the MAX8831 enters standby mode and the step-up converter stops switching. Bit 1 (TSD) of the STAT2 register is updated to a 1 to indicate that thermal shutdown has occurred.
System States and Fault Handling
The MAX8831 implements two fault registers (STAT1, STAT2) to provide users with fault indication through the I2C interface. The STAT1 register indicates a fault condition for each LED_ string, whether a shorted or open LED_ fault has occurred. In the event of an LED_ fault, the corresponding bit in the STAT1 register is latched and the ON/OFF control bit for that current regulator is cleared. An I2C read of the STAT1 register causes all STAT1 bits to be cleared and the corresponding string to be reenabled. If the fault is persistent, then the corresponding bit in the STAT1 register is set again. All open/short fault monitors are subject to a 16ms blanking period to ensure that the MAX8831 does not respond to a false fault occurrence. The second status register, STAT2, reports the following global system faults: output overvoltage-protection detection (OVP), thermal-shutdown detection (TSD), and open Schottky diode detection (OSDD). If a TSD, OVP, or OSDD fault occurs, the IC enters standby mode, the step-up converter stops switching, and all the current regulators are shut down by clearing their ON/OFF control bits. Once standby occurs, the MAX8831 does not transition back to the ON state until the STAT2 register is read, clearing the fault indication, and an I2C command enabling one or more current regulators is received. See Figure 4 for a state diagram of the MAX8831.
regulation, the output voltage starts to rise. Depending on the converter output voltage and load condition, the output voltage can reach the OVP threshold before the 16ms debounce timer expires. In this case, the converter disables all current regulators, forces the IC into standby mode, and the status register indicates only an OVP fault. If the BOOST_CNTL register is programmed to power LED3, LED4, or LED5 from an alternate source, only open LED detection is enabled for LED3, LED4, or LED5.
Output Overvoltage Protection
The MAX8831 protects the LEDs from excessive voltage by initiating overvoltage protection (OVP) when VOUT rises above 28V (min). When OVP occurs, the MAX8831 turns off the LED current regulators by resetting all ON/OFF control register bits to 0, causing the IC to enter standby status and turn off the step-up converter. Bit 0 (OVP) of the STAT2 register is updated to a 1 to indicate that an OVP event has occurred. The stepup converter automatically restarts after an OVP event when VOUT decreases below 25V (typ).
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High-Efficiency, White LED Step-Up Converter with I2C Interface in 2mm x 2mm WLP MAX8831
SHUTDOWN VDD INVALID. INTERNAL REFERENCE, BIAS, AND OSCILLATOR ARE OFF; I2C REGISTER IS IN RESET.
VDD INVALID FROM ANY CONDITION
VDD VALID
STANDBY I2C READY. INTERNAL REFERENCE, BIAS, AND OSCILLATOR ARE OFF. ALL CURRENT REGULATORS DISABLED
I2C LED_ ENABLE COMMAND RECEIVED
ALL CURRENT REGULATORS DISABLED USING I2C
ENABLE BIT CLEARED FOR FAULTED LED_ STRING AND STAT1 REGISTER IS UPDATED WITH FAULT CONDITION.
LED SHORT OR OPEN FAULT
ONE OR MORE CURRENT REGULATORS ENABLED
ON BOOST CONVERTER AND LEDs ARE ON, INTERNAL REFERENCE, BIAS, AND OSCILLATOR ARE ON.
VIN < VUVLO
UVLO CHECK I2C READY. INTERNAL REFERENCE, BIAS AND OSCILLATOR ARE OFF.
VIN > VUVLO
ENABLE BIT CLEARED FOR ALL LED_, AND STAT2 REGISTER IS UPDATED WITH FAULT CONDITION.
TSD OR OVP FAULT
SCHOTTKY DIODE DETECTED
SCHOTTKY DIODE NOT DETECTED
OPEN SCHOTTKY DIODE DETECTION INTERNAL REFERENCE, BIAS, AND OSCILLATOR ARE ON.
Figure 4. State Diagram of Global Faults
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High-Efficiency, White LED Step-Up Converter with I2C Interface in 2mm x 2mm WLP MAX8831
SDA tSU,DAT tSU,STA tLOW SCL tHIGH REPEATED START CONDITION STOP CONDITION STOP CONDITION tHD,DAT tHD,STA tSU,STO tBUF
tHD,STA START CONDITION
Figure 5. I2C Interface Timing Diagram
SDA
SCL output. Each transmission consists of a START condition (Figure 6) sent by a master, followed by the MAX8831 7-bit slave address plus a R/W bit, a register address byte, 1 or more data bytes, and finally a STOP condition (Figures 5 and 6).
START and STOP Conditions
SCL S START CONDITION P STOP CONDITION
Figure 6. I2C START and STOP Conditions
Both SCL and SDA remain high when the interface is not busy. The master signals the beginning of a transmission with a START (S) condition by transitioning SDA from high to low while SCL is high. When the master has finished communicating with the slave, it issues a STOP (P) condition by transitioning the SDA from low to high while SCL is high. The bus is then free for another transmission (Figure 6).
I2C Interface
The and interface. The LED1-LED5 current settings, ramp and blink-rate timers, and other configuration parameters are set using the I2C serial interface. See the register definitions for more details. The interface uses a serial-data line (SDA) and a serialclock line (SCL) to achieve bidirectional communication between master(s) and slave(s). A master (typically a microcontroller) initiates all data transfers to and from the MAX8831, and generates the SCL clock that synchronizes the data transfer (Figure 5). The MAX8831 SDA line operates as both an input and an open-drain output. A pullup resistor, typically 4.7k, is required on SDA. The MAX8831 SCL line operates only as an input. A pullup resistor, typically 4.7k, is required on SCL if there are multiple masters on the 2-wire interface, or if the master in a single-master system has an open-drain MAX8831 operates as an I2C slave that receives sends data through an I 2 C-compatible, 2-wire
Bit Transfer
One data bit is clocked onto SDA on the falling edge of SCL and is read on the rising edge of SCL. The data on the SDA line must remain stable while SCL transitions (Figure 7).
Acknowledge
The acknowledge bit is a clocked 9th bit that the recipient uses to handshake receipt of each byte of data (Figure 8). Thus, each byte transferred effectively requires 9 bits. The master generates the 9th clock pulse, and the recipient pulls down SDA during the acknowledge clock pulse, such that the SDA line is stable low during the high period of the clock pulse. When the master is transmitting to the MAX8831, the MAX8831 generates the acknowledge bit because it is the recipient. When the MAX8831 is transmitting to the master, the master generates the acknowledge bit because it is the recipient.
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High-Efficiency, White LED Step-Up Converter with I2C Interface in 2mm x 2mm WLP MAX8831
SDA BY TRANSMITTER D7 D6 D0 NOT ACKNOWLEDGE SDA BY RECEIVER
SDA
SCL SCL 1 DATA LINE STABLE, CHANGE OF DATA DATA IS VALID IS ALLOWED S START CONDITION 2
ACKNOWLEDGE 8 9
CLOCK PULSE FOR ACKNOWLEDGMENT
Figure 7. I2C Bit Transfer
Figure 8. I2C Acknowledge
SDA
1
0
0
1
1
0
1
R/W
ACK
MSB SCL
LSB
Figure 9. MAX8831 Default Slave Address
S S AS P
7-BIT SLAVE ADDRESS START BIT ACKNOWLEDGE SLAVE STOP BIT
0
AS
COMMAND BYTE
AS
DATA BYTE
AS
P
Figure 10. I2C Single-Byte Write
MAX8831 Slave Address
The MAX8831 has a 7-bit-long slave address (Figure 9). The eighth bit following the 7-bit slave address is the R/W bit. It is low for a write command, high for a read command. The slave addresses available for the MAX8831 are 1001101X (with a write/read address of 0x9A/0x9B). Contact the factory for other I2C address options.
Message Format for Writing
A write to the MAX8831 comprises the transmission of the MAX8831's slave address with the R/W bit set to zero (0x9A), followed by at least 1 byte of information. The first byte of information is the command byte (Figure 10), which determines which register of the MAX8831 is to be written by the next byte, if received. If a STOP condition is detected after the command byte is received, the MAX8831 takes no further action beyond storing the command byte. Any bytes received after the command byte are data bytes. The first data
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High-Efficiency, White LED Step-Up Converter with I2C Interface in 2mm x 2mm WLP MAX8831
S 7-BIT SLAVE ADDRESS 0 AS COMMAND BYTE AS FIRST DATA BYTE AS
LAST DATA BYTE
AS
P
S AS P
START BIT ACKNOWLEDGE SLAVE STOP BIT
Figure 11. I2C Multiple-Byte Write
S
7-BIT SLAVE ADDRESS
0
AS
COMMAND BYTE
A
S
7-BIT SLAVE ADDRESS
1
AS
DATA BYTE
AM
P
S AS AM P
START BIT ACKNOWLEDGE SLAVE ACKNOWLEDGE MASTER STOP BIT
Figure 12. I2C Single-Byte Read
S
7-BIT SLAVE ADDRESS
0
AS
COMMAND BYTE
AS
S
7-BIT SLAVE ADDRESS
1
AS
FIRST DATA BYTE S AS AM P START BIT ACKNOWLEDGE SLAVE ACKNOWLEDGE MASTER STOP BIT
AM
LAST DATA BYTE
AM
P
Figure 13. I2C Multiple-Byte Read
byte goes into the internal register of the MAX8831 selected by the command byte. If multiple data bytes are transmitted before a STOP condition is detected, these bytes are stored in subsequent MAX8831 internal registers because the command byte address autoincrements (Figure 11).
bytes from the MAX8831, by first writing the read command (0x9B) to the MAX8831 (Figures 12 and 13). When performing read-after-write verification, reset the command byte's address since the stored byte address is autoincremented after the write.
MAX8831 I2C Registers
The MAX8831 contains 19 registers that are accessible through the I2C interface (Table 3). See the register descriptions for more details. The register contents are reset to the default RESET values (shown in Table 3) if VDD goes low.
Message Format for Reading
The MAX8831 is read using the MAX8831's internally stored command byte as an address pointer, the same way the stored command byte is used as an address pointer for a write. The pointer autoincrements after each data byte is read, using the same rules as for a write. Thus, a read is initiated by first configuring the MAX8831's command byte by writing the command byte corresponding to the beginning register address to be read. The master can now read n consecutive
ON/OFF Control Register The ON/OFF control register (ON/OFF_CNTL) enables and disables the LED1-LED5 current regulators (Table 4). Write a 1 to the LED#_EN bit to enable that
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High-Efficiency, White LED Step-Up Converter with I2C Interface in 2mm x 2mm WLP MAX8831
LED_ current regulator. Write a 0 to the LED#_EN bit to disable that LED_ current regulator. Overvoltage, open Schottky diode, and thermal-shutdown faults automatically clear all LED#_EN bits to turn off all LED current regulators.
LED_ Ramp Control Registers The LED_ ramp control registers (LED1_RAMP_CNTL to LED5_RAMP_CNTL) contains the timing information for each LED current regulator's ramp-up and rampdown rate. The registers at locations 0x03 to 0x07 program the ramp rates of the LED1 to LED5 current regulators, respectively. The ramp-up and ramp-down rates are programmable with eight different timing selections. See Table 5. LED_ Current Control Registers The LED_ current control registers (ILED1_CNTL to ILED5_CNTL) program the individual LED1 to LED5 current regulators (see Tables 1 and 2 for programmable values). Registers located at 0x0B and 0x0C program the current of the LED1 and LED2 current regulators (Table 6). Registers located at 0x0D, 0x0E, and 0x0F program the current of the LED3, LED4, and LED5 current regulators, respectively (Table 7). LED3, LED4, and LED5 Blink Control Registers The blink control registers (LED3_BLINK_CNTL to LED5_BLINK_CNTL) contain the blink control timing data for the LED3, LED4, and LED5 current regulators. The registers allow enabling of the blink function and control the on- and off-time of the blink sequence. The registers located at 0x17, 0x18, and 0x19 control the blink timing of the LED3, LED4, and LED5 current regulators, respectively. See Table 8. The LED1 and LED2 current regulators do not have blink functionality. Boost Control Register The boost control register (BOOST_CNTL) determines if the LED3, LED4, or LED5 current regulators are included in the step-up converter regulation loop. If programmed to be powered from the step-up converter, LED_ is included in the feedback loop. Otherwise, if LED_ is programmed to be powered from an alternate source, LED_ is not included in the feedback loop. LED3, LED4, and LED5 are high impedance in shutdown. If the BOOST_CNTL bits are programmed to power LED3, LED4, or LED5 from an alternate source, open LED detection is enabled only for that current regulator. See Table 9. The LED1 and LED2 inputs are always in the feedback loop and are not programmable with the boost control register.
LED_ Status Registers The LED_ status registers (STAT1, STAT2) indicate the fault conditions of the MAX8831 IC and LEDs and are read-only registers. The STAT1 register indicates a fault condition for each LED_ string, whether a shorted or open LED_ fault is causing the fault condition. The second status register, STAT2, reports the following global system faults: output overvoltage-condition detection (OVP), thermal-shutdown condition detection (TSD), and open Schottky diode detection (OSDD). See Tables 10 and 11. See the Open/Shorted LED Detection, Output Overvoltage Protection, Open Schottky Diode Detection, Thermal-Shutdown Protection, and System States and Fault Handling sections for more details. Chip ID The CHIP ID registers (CHIP_ID1 and CHIP_ID2) contains MAX8831 die type and mask revision data. These registers are read-only registers. See Tables 12 and 13.
Applications Information
Inductor Selection
The MAX8831 is optimized for a 10H inductor, although larger or smaller inductors can be used. Using a smaller inductor results in discontinuous current-mode operation over a larger range of output power, whereas use of a larger inductor results in continuous conduction for most of the operating range. To prevent core saturation, ensure that the inductor's saturation current rating exceeds the peak inductor current for the application. For larger inductor values and continuous conduction operation, calculate the worst-case peak inductor current with the following formula: IPEAK = VOUT x IOUT(MAX) 0.9 x VIN(MIN) + VIN(MIN) x 0.5s 2 xL
Otherwise, for small values of L in discontinuous conduction operation, IPEAK is 860mA (typ). Table 14 provides a list of recommended inductors.
Capacitor Selection
Ceramic X5R or X7R dielectric capacitors are recommended for best operation. When selecting ceramic capacitors in the smallest available case size for a given value, ensure that the capacitance does not degrade significantly with DC bias. Generally, ceramic capacitors with high values and very small case size have poor DC bias characteristics.
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High-Efficiency, White LED Step-Up Converter with I2C Interface in 2mm x 2mm WLP
The typical value for the input capacitor is 1F, and the typical value for the output capacitor is 1F. Higher value capacitors can reduce input and output ripple, but at the expense of size and higher cost. not returning to minimum current before turning off during the blink OFF time. The blink ON and blink OFF timers (tON_BLINK and tOFF_BLINK) are programmed according to the following equations as guidance: t ON _ BLINK tLED _ RU 32 32 (LED _ CODE + 1) (LED _ CODE + 1)
MAX8831
Diode Selection
The high switching frequency of the MAX8831 demands a high-speed rectification diode for optimum efficiency. A Schottky diode is recommended due to its fast recovery time and low forward voltage drop. Ensure that the diode's average and peak current rating exceeds the average output current and peak inductor current. In addition, the diode's reverse breakdown voltage must exceed VOUT.
t OFF _ BLINK
tLED _ RD
Compensation Network Selection
The step-up converter is compensated for stability through an external compensation network from COMP to GND. The compensation capacitor is typically 0.22F for most applications. Note that higher CCOMP values increase soft-start duration, as well as the time delay between enabling the step-up converter to initiating soft-start.
Where tLED_RU is the LED_ ramp-up time, tLED_RD is the LED_ ramp-down time, and LED_CODE is the decimal equivalent of the ILED_CNTL register value of Table 2.
Using the LED3, LED4, and LED5 BOOST_CNTRL Bit
The default setting of the BOOST_CNTL bits (low) include the LED3, LED4, and LED5 current regulators in the step-up converter minimum voltage select feedback circuit. This is intended for multi-LED strings powered from the step-up converter. For single LED indicator lights, set the respective BOOST_CNTL bit high, connect the LED anode to the battery or other voltage source, and connect the LED cathode to the respective LED_ input. Ensure the voltage source is high enough to satisfy VF of the LED plus 150mV (current regulator dropout voltage). If BOOST_CNTL bits are set to high for LED3, LED4, and LED5 and LED1 and LED2 are not enabled, the step-up converter does not turn on when LED3, LED4, or LED5 is enabled.
Combining BLINK Timer and RAMP Functions
When using the ramp functionality of LED3, LED4, and LED5 in combination with the blink timer, it is recommended to keep the ramp-up timer shorter than the blink ON timer and the ramp-down timer shorter than the blink OFF timer. See Figure 14. Failing to comply with this restriction results in LED_ current not reaching maximum value during blink ON time, and LED_ current
tON_BLINK BLINK TIMERS
tOFF_BLINK
tON_BLINK
ILED = ILED_CNTL REGISTER SETTING
ILED_ = OFF
t=
tLED_RU 32
t=
tLED_RU 32
Figure 14. Combined Timing Characteristics of RAMP and BLINK Timers
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High-Efficiency, White LED Step-Up Converter with I2C Interface in 2mm x 2mm WLP MAX8831
Table 3. MAX8831 Register Map
REGISTER ON/OFF_CNTL LED1_RAMP_CNTL LED2_RAMP_CNTL LED3_RAMP_CNTL LED4_RAMP_CNTL LED5_RAMP_CNTL ILED1_CNTL ILED2_CNTL ILED3_CNTL ILED4_CNTL ILED5_CNTL LED3_BLINK_CNTL LED4_BLINK_CNTL LED5_BLINK_CNTL BOOST_CNTL STAT1 STAT2 CHIP_ID1 CHIP_ID2 COMMAND/ ADDRESS BYTE (HEX) 0x00 0x03 0x04 0x05 0x06 0x07 0x0B 0x0C 0x0D 0x0E 0x0F 0x17 0x18 0x19 0x1D 0x2D 0x2E 0x39 0x3A TYPE (READ/WRITE) R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W R/W R R R R REGISTER RESET VALUES 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 N/A N/A 0x07 0x0B FUNCTION LED current regulator ON/OFF control LED1 ramp control LED2 ramp control LED3 ramp control LED4 ramp control LED5 ramp control LED1 current sink control LED2 current sink control LED3 current sink control LED4 current sink control LED5 current sink control LED3 blink rate control LED4 blink rate control LED5 blink rate control Adaptive step-up converter control Status register1 Status register2 Die type information Mask revision information
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High-Efficiency, White LED Step-Up Converter with I2C Interface in 2mm x 2mm WLP MAX8831
Table 4. ON/OFF_CNTL Register (Address 0x00)
BIT B7 (MSB) B6 B5 B4 B3 NAME -- -- -- LED5_EN LED4_EN DESCRIPTION Reserved for future use Reserved for future use Reserved for future use 0 = Disable LED5 current regulator 1 = Enable LED5 current regulator 0 = Disable LED4 current regulator 1 = Enable LED4 current regulator B0 (LSB) LED1_EN 0 = Disable LED1 current regulator 1 = Enable LED1 current regulator BIT B2 B1 NAME LED3_EN LED2_EN DESCRIPTION 0 = Disable LED3 current regulator 1 = Enable LED3 current regulator 0 = Disable LED2 current regulator 1 = Enable LED2 current regulator
Table 5. LED#_RAMP_CNTL Registers (Addresses: 0x03, 0x04, 0x05, 0x06, 0x07)
BIT B7 (MSB) B6 B5 B4 LED#_RAMP_DOWN [2:0] B3 NAME -- -- Reserved for future use Reserved for future use Programs LED# current ramp-down rate using bits [5:3] as follows: 000 64ms 001 128ms 010 256ms 010 512ms 100 1024ms 101 2048ms 110 4096ms 111 8192ms Sets LED# current ramp-up rate using bits [2:0] as follows: 000 64ms 001 128ms 010 256ms 010 512ms 100 1024ms 101 2048ms 110 4096ms 111 8192ms DESCRIPTION
B2 B1
LED#_RAMP_UP [2:0] B0 (LSB)
#Indicates the selected LED current regulator (1, 2, 3, 4, or 5).
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High-Efficiency, White LED Step-Up Converter with I2C Interface in 2mm x 2mm WLP MAX8831
Table 6. ILED#_CNTL Registers for LED1, LED2 (Addresses: 0x0B, 0x0C)
BIT B7 (MSB) B6 B5 B4 B3 B2 B1 B0 (LSB) ILED# [6:0] Programs LED# current as indicated in Table 1 NAME -- DESCRIPTION Reserved for future use
Table 7. ILED#_CNTL Registers for LED3, LED4, LED5 (0x0D, 0x0E, 0x0F)
BIT B7 (MSB) B6 B5 B4 B3 B2 B1 B0 (LSB) ILED# [4:0] Programs LED# current as indicated in Table 2 NAME -- -- -- DESCRIPTION Reserved for future use Reserved for future use Reserved for future use
#Indicates selected LED current regulator (1 or 2).
#Indicates selected LED current regulator (3, 4, or 5).
Table 8. LED#_BLINK_CNTL Registers (Addresses: 0x17, 0x18, 0x19)
BIT B7 (MSB) B6 B5 B4 LED#_TOFF_BLINK[1:0] B3 B2 -- NAME -- LED#_BLINK_EN -- Reserved for future use 0 1 LED# blink function disabled LED# blink function enabled DESCRIPTION
Reserved for future use Programs LED# blink OFF timer using bits [4:3] as follows: 00 LED# blink OFF timer set to 1024ms 01 LED# blink OFF timer set to 2048ms 10 LED# blink OFF timer set to 4096ms 11 LED# blink OFF timer set to 8192ms Reserved for future use Programs LED# blink ON timer using bits [1:0] as follows: 00 LED# blink ON timer set to 256ms 01 LED# blink ON timer set to 512ms 10 LED# blink ON timer set to 1024ms 11 LED# blink ON timer set to 2048ms
B1
LED#_TON_BLINK[1:0]
B0 (LSB)
#Indicates selected LED current regulator (3, 4, or 5).
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High-Efficiency, White LED Step-Up Converter with I2C Interface in 2mm x 2mm WLP MAX8831
Table 9. BOOST_CNTL Register (Address: 0x1D)
BIT B7 (MSB) B6 B5 NAME -- -- -- DESCRIPTION Reserved for future use Reserved for future use Reserved for future use
Table 10. STAT1 Register (Address 0x2D)
BIT B7 (MSB) B6 B5 NAME -- -- -- DESCRIPTION Reserved for future use Reserved for future use Reserved for future use 0 = No open or short is detected for LED5 1 = Open or short is detected for LED5 0 = No open or short is detected for LED4 1 = Open or short is detected for LED4 0 = No open or short is detected for LED3 1 = Open or short is detected for LED3 0 = No open or short is detected for LED2 1 = Open or short is detected for LED2 0 = No open or short is detected for LED1 1 = Open or short is detected for LED1
B4
0 = LED5 is powered from high-voltage STEP-UP converter. 1= LED5 is powered from LED5_BOOST_CNTL an alternate power source. VLED5 is not used as an input for the feedback loop. 0 = LED4 is powered from high-voltage STEP-UP converter. 1 = LED4 is powered from LED4_BOOST_CNTL an alternate power source. VLED4 is not used as an input for the feedback loop. 0 = LED3 is powered from high-voltage STEP-UP converter. 1 = LED3 is powered from LED3_BOOST_CNTL an alternate power source.VLED3 is not used as input for the feedback loop. Reserved for future use Reserved for future use
B4
LED5_FAULT
B3
LED4_FAULT
B2
LED3_FAULT
B3
B1
LED2_FAULT
B0 (LSB)
LED1_FAULT
B2
B1 B0 (LSB)
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High-Efficiency, White LED Step-Up Converter with I2C Interface in 2mm x 2mm WLP MAX8831
Table 11. STAT2 Register (Address 0x2E)
BIT B7 (MSB) B6 B5 B4 B3 B2 OSDD NAME DESCRIPTION Reserved for future use Reserved for future use Reserved for future use Reserved for future use Reserved for future use Open Schottky diode detection 0 = Schottky diode is present 1 = Schottky diode is missing Thermal-shutdown detection 0 = No thermal shutdown occurred 1 = MAX8831 has entered thermal shutdown since the last read operation of this register Output overvoltage detection 0 = No overvoltage protection has occurred 1 = MAX8831 has entered over voltage protection since last read operation of this register
Table 12. CHIP_ID1 Register (Address: 0x39)
BIT B7 (MSB) B6 B5 B4 B3 B2 B1 B0 (LSB) NAME DESCRIPTION
DIE_TYPE[7:4]
BCD character 0
DIE_TYPE[3:0]
BCD character 7
Table 13. CHIP_ID2 Register (Address 0x3A)
BIT B7 (MSB) B6 B5 B4 B3 B2 B1 B0 (LSB) NAME DESCRIPTION
B1
TSD
DASH [7:4]
BCD character 0
B0 (LSB)
OVP
MASK_REV [3:0]
BCD character B
PCB Layout
Due to fast switching waveforms and high current paths, careful PCB layout is required. Minimize trace lengths between the IC and the inductor, the diode, the input capacitor, and the output capacitor. Minimize trace lengths between the input and output capacitors and the MAX8831 GND terminal, and place input and output capacitor grounds as close together as possible. Use separate power ground and analog ground copper areas, and connect them together at the output capacitor ground. Keep traces short, direct, and wide. Keep noisy traces, such as the LX node trace, away from sensitive analog circuitry. For improved thermal performance, maximize the copper area of the LX and PGND traces. Refer to the MAX8831 EV Kit for an example layout.
Table 14. Recommended Inductors for the MAX8831 Circuit
PART TOKO 1098AS-100M TOKO 1069AS-220M FDK MIP3226D100M Coilcraft EPL2014472ML Coilcraft DO2010472ML L (H) 10 22 10 4.7 4.7 DCR (m) 290 570 160 231 800 ISAT (A) 0.75 0.47 0.9 650 650 SIZE (mm) 2.8 x 3.0 x 1.2 3 x 3 x 1.8 3.2 x 2.6 x 1.0 2.0 x 2.0 x 1.45 2.0 x 2.0 x 1.0
24
______________________________________________________________________________________
High-Efficiency, White LED Step-Up Converter with I2C Interface in 2mm x 2mm WLP MAX8831
VIN 2.7V TO 5.5V L1 10H D1 D2-D9 D10-D17 D18-D26 D27-D35 D36-D44
C1 1F
LX
OUT
LX
C2 1F
MAX8831
IN PGND PGND SCL SDA VDD 1.6V TO 5.5V VDD C3 0.1F LED1 LED2 LED3 COMP C4 0.22F GND LED4 LED5
Figure 15. MAX8831 Applications Circuit
______________________________________________________________________________________
25
High-Efficiency, White LED Step-Up Converter with I2C Interface in 2mm x 2mm WLP MAX8831
Typical Operating Circuit
VOUT UP TO 28V UP TO 25.25mA/LED UP TO 5.0mA/LED
VIN 2.7V TO 5.5V
10H
1F
LX
OUT
LX 1F
MAX8831
IN PGND PGND SCL SDA VDD 1.6V TO 5.5V 0.1F VDD LED1 LED2 LED3 COMP 0.22F LED5 GND LED4
Chip Information
PROCESS: BiCMOS
26
______________________________________________________________________________________
High-Efficiency, White LED Step-Up Converter with I2C Interface in 2mm x 2mm WLP
Pin Configuration
TOP VIEW (BUMPS ON BOTTOM) 1 + 2 3 4
Package Information
For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. PACKAGE TYPE 16 WLP PACKAGE CODE W162B2+1 DOCUMENT NO. 21-0200
MAX8831
MAX8831
A A1 LED1 B B1 LED2 C C1 LX D D1 LX A2 GND B2 LED5 C2 PGND D2 PGND WLP A3 LED3 B3 LED4 C3 SDA D3 IN A4 COMP B4 SCL C4 VDD D4 OUT
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.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 27
(c) 2008 Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc.
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