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LX1744
INTEGRATED PRODUCTS
Dual Output Boost - LED Driver / LCD Bias
PRODUCTION DATASHEET
DESCRIPTION The LX1744 is a compact high efficiency step-up boost regulator for driving white or color LEDs in LCD lighting applications while supplying the necessary LCD bias voltage with an additional integrated boost converter. Designed for maximum efficiency and featuring a psuedo-hysteretic PFM topology (that decreases output voltage ripple), the LX1744 minimizes system cost and condenses layout area making it ideal for PDA, smart-phone, and digital camera applications. While the LCD Bias generation is implemented using an internal N-Channel MOSFET, the LED driver utilizes an external N-Channel MOSFET in order to maintain maximum efficiency along with flexible power requirements. The LX1744's control circuitry is optimized for portable systems with a shutdown current of less than 1A. The input voltage range of 1.6V to 6.0V allows for a wide selection of system battery voltages and start-up is guaranteed at a VIN equal to 1.6V with sustained operation as low as 1.1V. The maximum LED drive current is easily programmed using one external current sense resistor in series with the LEDs. In this configuration, LED current provides a feedback signal to the FB pin, maintaining constant current regardless of varying LED forward voltage (VF). Depending on the MOSFET selected, the LX1744 is capable of achieving an LED drive in excess of 1.0W. The LX1744 provides simple dynamic adjustment of the LED drive current (0% to 100% full range dimming) and the LCD Bias output voltage (up to 15% typ) through separate IC interfaces. Each interface has an internal RC filter allowing designers to make these adjustments via a direct PWM input signal or an analog reference signal. Further, any PWM amplitude is easily accommodated using a single external resistor. The LX1744 is available in the 14-Pin TSSOP, and the miniature 16-Pin MLP requiring minimal PCB area.
KEY FEATURES > 90% Maximum Efficiency Low Quiescent Supply Current Externally Programmable Peak Inductor Current Limit for Maximum Efficiency Logic Controlled Shutdown < 1A Shutdown Current Dynamic Output LED Current and LCD Bias Voltage Adjustment via Analog Reference or Direct PWM Input 14-Pin TSSOP or 16-Pin MLPQ Package
APPLICATIONS
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Pagers Smart Phones PDAs Handheld Computers General LCD Bias Applications LED Driver
IMPORTANT: For the most current data, consult MICROSEMI's website: http://www.microsemi.com
PRODUCT HIGHLIGHT
L1
ILED = 20mA to 0mA
C1 4.7F
VBAT = 1.6V to 6.0V - VLCD
47H 1206 Case Size
DRV IN SRC
VLCD1 = VIN to 25V
SW1
OVP LFB
FB1
CS
LX1744
LSHDN SW2 REF FB2 GND SHDN1 ADJ1 ADJ2 BRT
ON OFF
RSET 15
ON OFF
VLCD2 = VIN to 25V
SHDN2
ON OFF
LX1744 Evaluation Board
LX1744 LX1744
PACKAGE ORDER INFO
TA (C) -40 to 85
PW
Plastic TSSOP 14-Pin
LQ
Plastic MLP-Q 16-Pin LX1744CLQ
RoHS Compliant / Pb-free Transition DC: 0442
RoHS Compliant / Pb-free Transition DC: 0430
LX1744CPW
Note: Available in Tape & Reel. Append the letters "TR" to the part number. (i.e. LX1744CLQ-TR)
Copyright (c) 2000 Rev. 1.1b, 2005-03-01
Microsemi
Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 1
LX1744
INTEGRATED PRODUCTS
Dual Output Boost - LED Driver / LCD Bias
PRODUCTION DATASHEET
ABSOLUTE MAXIMUM RATINGS
PACKAGE PIN OUT
SW SHDN FB ADJ REF IN LSHDN 1 2 3 4 5 6 7 14 13 12 11 10 9 8 GND SRC DRV CS OVP LFB BRT
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Supply Input Voltage ...........................................................................-0.3V to 7V Feedback Input Voltage (VFB, VLFB).......................................-0.3V to VIN + 0.3V Shutdown Input Voltage (V SHDN , V LSHDN )) ...........................-0.3V to VIN + 0.3V PWM Input Amplitude (ADJ, BRT).......................................-0.3V to VIN + 0.3V Analog Adjust Input Voltage (VADJ, VBRT) .............................-0.3V to VIN + 0.3V SRC Input Current ................................................................................ 800mARMS Operating Temperature Range .........................................................-40C to 85C Maximum Operating Junction Temperature ................................................ 150C Storage Temperature Range...........................................................-65C to 150C RoHS Peak Package Solder Reflow Temperature (40 second maximum exposure) ..................................................... 260C (+0, -5)
Note: Exceeding these ratings could cause damage to the device. All voltages are with respect to Ground. Currents are positive into, negative out of specified terminal.
PW PACKAGE
(Top View)
GND
GND 14
16 SW SHDN1 FB 1 2 3 4 5 REF
15
SRC 13 12 11 10 9 DRV CS OVP LFB 8 BRT
THERMAL DATA
ADJ
N.C.
6 IN
7 LSHDN
LQ PW
Plastic MLPQ 16-Pin 31C/W
THERMAL RESISTANCE-JUNCTION TO AMBIENT, JA
LQ PACKAGE
(Bottom View) ("N.C." = No Internal Connection)
Plastic TSSOP 14-Pin 90C/W
RoHS / Pb-free 100% Matte Tin Lead Finish
THERMAL RESISTANCE-JUNCTION TO AMBIENT, JA
Junction Temperature Calculation: TJ = TA + (PD x JA). The JA numbers are guidelines for the thermal performance of the device/pc-board system. All of the above assume no ambient airflow.
PACKAGE DATA PACKAGE DATA
Copyright (c) 2000 Rev. 1.1b, 2005-03-01
Microsemi
Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 2
LX1744
INTEGRATED PRODUCTS
Dual Output Boost - LED Driver / LCD Bias
PRODUCTION DATASHEET
FUNCTIONAL PIN DESCRIPTION
WWW .Microsemi .C OM
Name IN DRV SRC OVP LFB GND
Description Unregulated IC Supply Voltage Input - Input range from +1.6V to 6.0V. Bypass with a 1F or greater capacitor for operation below 2.0V. LED MOSFET Gate Driver - Connects to an external N-Channel MOSFET. LED MOSFET Current Sense Input - Connects to the External N-Channel MOSFET Source. Over Voltage Programming Pin - Connects to a resistor divider between the output load and GND to set the maximum output voltage. OVP has a voltage threshold of 1.2V LED Current Feedback Input - Connects to a current sense resistor between the LED output load and GND to set the LED drive current. Common terminal for ground reference. LED Dimming Signal Input - Provides the internal reference, via an internal filter and gain resistor, allowing for a dynamic output LED current adjustment that corresponds to the PWM input signal duty cycle. Either a PWM signal or analog voltage can be used. The actual BRT pin voltage range is from VIN to GND. Minimize the current sense resistor power dissipation by selecting a range for VBRT = 0.0V to 0.5V. Buffered Reference Output - Connected to the internal bandgap reference voltage of 1.2V. LCD Bias Inductor Switch Connection - Internally connected to the drain of a 28V N-channel MOSFET. SW is high impedance in shutdown. Feedback Input - Connect to a resistive divider network between the output and GND to set the output voltage between VCC (IN) and 25V. The feedback threshold is 1.29V. LCD Bias Adjustment PWM Signal Input - Connect to an RC filter allowing for dynamic output voltage adjustment >15%, corresponding to a varying duty cycle. Either a PWM signal or analog voltage can be used. The ADJ input voltage range is from 0.9V to VIN DC. The ADJx pin should be connected to ground when the internal reference is used. LED Driver Active-Low Shutdown Input - A logic low shuts down the LED driver circuitry and reduces the supply current by 60A (Typ). Pull LSHDN high for normal operation. LCD Bias Active-Low Shutdown Input - A logic low shuts down the LCD Bias circuitry and reduces the supply current by 60A (Typ). Pull SHDNx high for normal operation. Current-Sense Amplifier Input - Connecting a resistor between CS and GND sets the peak inductor current limit.
BRT
REF SW FB
ADJ
LSHDN SHDNx
CS
P D PACKAGE DATA
Copyright (c) 2000 Rev. 1.1b, 2005-03-01
Microsemi
Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 3
LX1744
INTEGRATED PRODUCTS
Dual Output Boost - LED Driver / LCD Bias
PRODUCTION DATASHEET
Unless otherwise specified, the following specifications apply over the operating ambient temperature 0C TA otherwise noted and the following test conditions: VIN = 3V, ILED = 20mA, SHDN1 = VIN, SHDN2 = VIN Parameter
LED DRIVER
ELECTRICAL CHARACTERISTICS
70C except where
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Symbol
Test Conditions VBRT = 100mV VBRT = 20mV VLFB = 100mV BRT = VREF
Min 95 5 -100 0.0 0 -100 1.6
LX1744 Typ 100 20
Max 115 35 100 VIN 60 100
Units
LFB Threshold Voltage LFB Input Bias Current BRT Input Voltage Range BRT Input Bias Current LED Driver Shutdown Input Bias Current LED Driver Shutdown High Input Voltage LED Driver Shutdown Low Input Voltage Current Sense Bias Current Efficiency DRV Sink/Source Current DRV On-Resistance Maximum Switch On-Time Minimum Switch Off-Time Switch Peak Current OVP Threshold Voltage
LCD BIAS Output Voltage Range FB Threshold Voltage FB Input Current LCD Bias Shutdown Input Bias Current LCD Bias Shutdown High Input Voltage LCD Bias Shutdown Low Input Voltage Peak Inductor Current Limit Internal NFET On-resistance Switch Pin Leakage Current Efficiency Switch On-Time Switch Off-Time ADJ Input Voltage Range ADJ Input Bias Current ENTIRE REGULATOR Operating Voltage Minimum Start-up Voltage Start-up Voltage Temperature Coefficient Reference Voltage Quiescent Current
VLFB VBRT I SHDN1 V SHDN1 V SHDN1 ICS
mV nA V nA nA V
0.0V LSHDN VIN VIN = 2V VIN = 2V ILOAD = 2mA VIN = 5V, DRV = 3V VCC = 5V VFB = 1V VFB = 1V RCS = 0 RCS = 2k
0.4 4 90 100 12 300 170 210 1.21V 1.196
V A % mA S nS mA
85
tON tOFF IPK VOVP VOUT VFB
200
15 410
1.15 1.172 VFB = 1.4V
1.26 25 1.220 200 100
V V V nA nA V
I SHDN V SHDN V SHDN ILIM RDS(ON) ILEAK tON tOFF VADJ IADJ VIN
SHDN = GND
VIN = 2V VIN = 2V ISW = 10mA, TA = 25C, VIN = 5V VSW = 25V ILOAD = 2mA VFB = 1V VFB = 1V VADJ = 1.5V 1.6 TA = +25C -2 195 1.1 1.6
0.4
V mA A % s Ns V A V V mV/C V A
1 85 150 0.9 0.3 400 1.5 1 6.0 1.6 1.21 120 60 60 0.35 1.236 200 135 135 0.5
ELECTRICALS ELECTRICALS
VREF IQ VFB = 0.3V, VLFB < VBRT - 0.1V VFB = 0.3V, VLFB < VBRT - 0.1V, V LSHDN < 0.4V VFB = 0.3V, VLFB < VBRT - 0.1V, V SHDN < 0.4V V LSHDN < 0.4V, V SHDN < 0.4V
1.187
Copyright (c) 2000 Rev. 1.1b, 2005-03-01
Microsemi
Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 4
LX1744
INTEGRATED PRODUCTS
Dual Output Boost - LED Driver / LCD Bias
PRODUCTION DATASHEET
SIMPLIFIED BLOCK DIAGRAM
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LFB Control Logic Driver DRV SRC BRT 50pF 2.5M Reference Logic 4A CS GND
IN OVP
Shutdown Logic
LSHDN SHDN FB
REF
Control Logic
Driver
SW
ADJ 50pF 2.5M
Reference Logic
4A
Figure - Simplified Block Diagram
BLOCK DIAGRAM BLOCK DIAGRAM
Copyright (c) 2000 Rev. 1.1b, 2005-03-01
Microsemi
Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 5
LX1744
INTEGRATED PRODUCTS
Dual Output Boost - LED Driver / LCD Bias
PRODUCTION DATASHEET
APPLICATION CIRCUITS
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ILED = 20mA to 0mA
L1
VBAT = 1.6V to 6.0V - VLCD
47H 1206 Case Size
C1 4.7F
DRV IN SRC SW OVP LFB CS
VLCD = VIN to 25V
LX1744
FB LSHDN BRT
ON OFF
RSET 15
ON OFF
SHDN
REF ADJ GND
Figure 1 - LED Driver with Full-Range Dimming plus LCD Bias With Contrast Adjustment Via PWM Input
ILED = 20mA to 0mA
L1
VBAT = 1.6V to 6.0V - VLCD
47H 1206 Case Size
C1 4.7F
DRV IN SRC SW OVP LFB CS
VLCD = VIN to 25V
LX1744
FB LSHDN BRT
ON OFF
RSET 15
ON OFF
SHDN
ADJ GND
REF
APPLICATIONS APPLICATIONS
Figure 2 - LED Driver with Full-Range Dimming plus LCD Bias With Contrast Adjustment Via Analog Voltage Input
Note: The component values shown are only examples for a working system. Actual values will vary greatly depending on desired parameters, efficiency, and layout constraints.
Copyright (c) 2000 Rev. 1.1b, 2005-03-01
Microsemi
Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 6
LX1744
INTEGRATED PRODUCTS
Dual Output Boost - LED Driver / LCD Bias
PRODUCTION DATASHEET
APPLICATION NOTE
FUNCTIONAL DESCRIPTION The LX1744 is a dual output Pulse Frequency Modulated (PFM) boost converter that is optimized for large step-up voltage applications like LCD biasing and LED drive. Operating in a pseudo-hysteretic mode with a fixed switch "off time" of 300ns, converter switching is enabled when the feedback voltage (VFB) falls below the bandgap reference voltage or the ADJ pin voltage managed by the reference logic block (see Block Diagram). When this occurs, the feedback comparator activates the switching logic, pulling the gate of the power MOSFET high. This in turn connects the boost inductor to ground causing current to flow building up the energy stored in the inductor. The output remains "on", until the inductor current ramps up to the peak current level set either by the CS pin programming resistor (RCS) in the case of the LED driver or by an internal reference threshold for the LCD bias output. During this switch cycle, the load is powered from energy stored in the output capacitor. Once the peak inductor current value is achieved, the driver output is turned off, for the fixed offtime period of 300ns, allowing a portion of the energy stored in the inductor to be delivered to the load causing output voltage to rise at the input to the feedback circuit. If the voltage at the feedback pin is less than the internal reference at the end of the off-time period, the output switches the power MOSFET "on" and the inductor charging cycle repeats until the feedback pin voltage is greater than the internal reference. Typical converter switching behavior is shown in Figure 12. LCD BIAS - OUTPUT VOLTAGE PROGRAMMING Selecting the appropriate values for LCD Bias output voltage divider (Figure 3), connected to the feedback pin, programs the output voltage.
VBAT = 1.6V to 6.0V
Using a value between 40k and 75k for R2 works well in most applications. R1 can be determined by the following equation (where VREF = 1.19V nominal):
R1 = R 2 VOUT - VREF VREF
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eq. 1
LCD BIAS - OUTPUT VOLTAGE ADJUSTMENT The LX1744 allows for the dynamic adjustment of the of the voltage output via an adjustment pin (ADJ). Any voltage applied to the adjustment pin works in conjunction with the internal reference logic. The LX1744 will automatically utilize the internal reference when no signal is detected or when the adjustment signal voltage is below approximately 0.6V. This adjustment pin includes an internal 50pF capacitor to ground (Figure 4) that works with an external resistor to create a low-pass filter. This allows a direct PWM (fPWM 100KHz) signal input to be used for the voltage adjustment signal. (Consequently a DC bias signal can also be used).
LX1744
Reference Logic
50pF 2.5M
ADJ
RADJ_1
Figure 4 - LCD Bias Adjustment Input
Different PWM signal levels can be accommodated by selecting a value for RPWM such that the filtered VADJ value is equal to the reference voltage (eq. 2)
2.5M VADJ = VPWM Duty Cycle 2.5M + R PWM _ 1
eq. 2
LX1744
VOUT
R1 SW FB
LX1744
ADJ CADJ
APPLICATIONS APPLICATIONS
RADJ_1
RADJ_2
R2
Figure 5 - LCD Bias Adjustment Input Filter
Figure 3 - LCD Bias Output Voltage
Ideally the resultant ripple on the ADJ pin should be approximately 1% or 40dB down from the nominal reference. When using a PWM with a frequency that is
Copyright (c) 2000 Rev. 1.1b, 2005-03-01
Microsemi
Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 7
LX1744
INTEGRATED PRODUCTS
Dual Output Boost - LED Driver / LCD Bias
PRODUCTION DATASHEET
APPLICATION NOTE
less than 100kHz, an external filter capacitor will be needed (Figure 5). The value of CPWM is easily calculated based on the PWM frequency and RPWM_1 using the following equation.
CPWM = 50 fPWM RPWM _ 1
eq. 3
where
RPWM _ 1 << 2.5M
eq. 4
LED DRIVER - OUTPUT CURRENT PROGRAMMING Maximum LED current is easily programmed by choosing the appropriate value for RLED (Figure 6). It is recommended that a minimum value of 15 be used for this resistor in order to prevent noise coupling issues on the feedback line. Although, alternate values can be calculated using the following equation:
RLED = VBRT(MAX) ILED(MAX)
D1
300mV (VBRT) be used in order to minimize dissipative losses in the LED current sense resistor (RLED). Like the LCD bias adjustment (ADJ) pin, the BRT pin is connected to an internal 50pF capacitor to ground that works with an external resistor to create a low-pass filter, allowing the BRT pin to driven directly by a PWM signal whose frequency is greater than 100kHz. When this pin is driven by a PWM signal whose frequency is less than 100kHz, an external filter capacitor is needed. This capacitor is selected such that the ripple component of the resultant voltage on the BRT pin is less than 10% of the nominal input voltage. For PWM frequencies greater than 100kHz, the external BRT input resistor is calculated using the following equation.
V (DCMAX ) - VBRT(MAX) RBRT _ 1 = 2.5M PWM VBRT(MAX)
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eq. 6
eq. 5
L1
where VBRT is the selected maximum LED current sense feedback threshold. For PWM frequencies less than 100kHz, the external BRT input resistors and filter capacitor (Figure 4) are calculated using the following equations.
V (DCMAX ) - VBRT(MAX) RBRT _ 1 = RBRT _ 2 PWM VBRT(MAX)
VBAT = 1.6V to 6.0V
ROVP_1 DRV SRC OVP LFB ROVP_2 C1 4.7F
eq. 7
LX1744
RCS CS RLED 15
where RBRT_2 is selected and VBRT(MAX) is the selected maximum LED current sense feedback threshold.
RBRT_1
BRT CBRT RBRT_2
CBRT =
5 fPWM
R + RBRT _ 2 BRT _ 1 R BRT _ 1 RBRT _ 2
eq. 8
Figure 6 - LED Current Programming
where VRIPPLE is selected to be 10% of VBRT, and fPWM is the PWM signal frequency. DIODE SELECTION A Schottky diode is recommended for most applications (e.g. Microsemi UPS5817). The low forward voltage drop and fast recovery time associated with this device supports the switching demands associated with this circuit topology. The designer is encouraged to consider the diode's average and peak current ratings with respect to the application's output and peak inductor current requirements. Further, the diode's reverse breakdown voltage characteristic must be capable of withstanding a
LED DRIVER - LED BRIGHTNESS ADJUSTMENT The LX1744 features a full range dimming LED driver. LED current regulation is accomplished by using the applied BRT pin voltage as the LED current reference. This reference voltage, in conjunction with the LED current setting resistor (RLED), sets the LED output current. Dimming can be accomplished in one of two ways: by applying a variable DC voltage, or by varying the duty cycle (DC) of a PWM control signal, directly to the BRT pin. It is recommended that a maximum signal voltage of
APPLICATIONS APPLICATIONS
Copyright (c) 2000 Rev. 1.1b, 2005-03-01
Microsemi
Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 8
LX1744
INTEGRATED PRODUCTS
Dual Output Boost - LED Driver / LCD Bias
PRODUCTION DATASHEET
APPLICATION NOTE
negative voltage transition that is greater than the output voltage. POWER MOSFET SELECTION The LX1744 can source up to 100mA of gate current. A logi-level N-channel MOSFET with a low turn on threshold voltage, low gate charge and low RDS(ON) is required to optimize overall circuit performance. OVER VOLTAGE PROTECTION PROGRAMMING Since the output of the LED Driver is a current mode configuration, it may be desirable to protect the output from an over-voltage condition in the event the load is removed or not present. The LX1744 includes an over voltage monitor that is easily programmed with two external resistors (Figure 6). This feature eliminates the need for a Zener Diode clamp on the output. Programming is accomplished by first selecting ROVP_2 and then calculating ROVP_1 using the following equation.
R OVP _ 1 = ROVP _ 2 VOVP - VREF VREF
can be chosen from the following equation:
R CS IPK - 0.185 30 10 -6
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eq. 11
which is taken from the following graph (Figure 7).
Peak Inductor Current (mA)
1000 800 600 400 200 0 0 5 10 15 20
RCS (k ) Figure 7 - Peak Current Programming Resistor
eq. 9
where VOVP is the desired maximum voltage on the output. This voltage should be selected to accommodate the maximum forward voltage of all the LEDs, over temperature, plus the maximum feedback voltage. Conversely, it may also be selected according to the maximum VDS voltage of the output MOSFET. INDUCTOR CURRENT LIMIT PROGRAMMING Setting of the peak inductor current limit is an important aspect of the PFM constant off-time architecture; it determines the maximum output power capability and has a marked effect on efficiency. It is recommended that the peak inductor current be set to approximately two times the expected maximum DC input current. This setting will minimize the inductor size, the input ripple current, and the output ripple voltage. Care should be taken to use inductors that will not saturate at the peak inductor current level. The desired peak inductor current can be estimated by the following equation:
IPK = 2 POUT VIN
This graph characterizes the relationship between peak inductor current, the inductance value, and the RCS programming resistor. INDUCTOR SELECTION An inductor value of 47H has been show to yield very good results. Choosing a lower value emphasizes peak current overshoot, effectively raises the switching frequency, and increases the dissipative losses due to increased currents. OUTPUT CAPACITOR SELECTION Output voltage ripple is a function of the several parameters: inductor value, output capacitance value, peak switch current, load current, input voltage, and the output voltage. All of these factors can be summarized by the following equation:
APPLICATIONS APPLICATIONS
L I I eq. 1 IPK IOUT VRIPPLE PK OUT C V - ( V + V ) + V + V - V OUT SW L OUT F IN IN
12
eq. 10
where POUT is the total output power, is the expected conversion efficiency, and VIN is the input voltage. From the calculated desired IPK an RCS resistance value
where VL is the voltage drop across the inductor, VF is the forward voltage of the output catch diode, and VSW is the voltage drop across the power switch. VL+VSW can be approximated at 0.4V and VF can be approximated at 0.4V.
Copyright (c) 2000 Rev. 1.1b, 2005-03-01
Microsemi
Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 9
LX1744
INTEGRATED PRODUCTS
Dual Output Boost - LED Driver / LCD Bias
PRODUCTION DATASHEET
APPLICATION NOTE
NEGATIVE LCD BIAS GENERATION For applications that require it, a negative bias can be easily generated using an inductorless charge pump consisting of only four additional discrete components (Figure 8).
D3
achieved by placing a feed-forward capacitor across the feedback resistor connected to the LCD Bias output (Figure 2). A recommended value of 1nF should be used. PCB LAYOUT Minimizing trace lengths from the IC to the inductor, diode, input and output capacitors, and feedback connection (i.e. pin 3) are typical considerations. Moreover, the designer should maximize the DC input and output trace widths to accommodate peak current levels associated with this circuit.
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VBAT = 1.6V to 6.0V
- VOUT
D4
LX1744
VOUT
R1 SW FB
R2
Figure 8 - Negative Bias Generation
This negative output is a mirror of the positive output voltage. However, it is unregulated. If a regulated negative bias is desired then this is also possible with some additional components. A low current shunt regulator (LX6431 or LX432) and a bipolor pass element can form a simple negative voltage LDO (Figure 9).
D3
VBAT = 1.6V to 6.0V
VNEG_LCD
R4 LX6431, LX432 R5 R3 D4
LX1744
SWx FBx R1
VOUT
R2
Figure 9 - Regulated Negative Bias
R3 is sized to meet the minimum shunt current required for regulation while R4 and R5 are calculated. If R5 is selected to be 100k then R4 is calculated using the following equation:
R VNEG _ LCD = VREF 1 + 4 R 5
APPLICATIONS APPLICATIONS
eq. 13
where VREF is a -2.5V in the case of the LX6431. FEED-FORWARD CAPACITANCE Improved efficiency and ripple performance can be
Copyright (c) 2000 Rev. 1.1b, 2005-03-01
Microsemi
Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
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LX1744
INTEGRATED PRODUCTS
Dual Output Boost - LED Driver / LCD Bias
PRODUCTION DATASHEET
EVALUATION BOARD
Table 1: Input and Output Pin Assignments
Name Input/Output Range Description
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VIN GNDx ADJ SHDN SHDN VLCD -VLCD VOUT LFB BRT DRV REF
0 to 6V 0V 0 to VIN-100mV 0 to VIN 25V -25V 25V 0 to VIN 0 to 350mV 0 to VIN 1.19V Typ.
Main power supply for outputs. Common ground reference. Apply a DC voltage or a PWM voltage to this pin to adjust the LCD1 output voltage. PWM inputs should be greater than 120Hz. Pulled up to VIN on board (10K), Ground to inhibit the LED driver output (VOUT). Pulled up to VIN on board (10K), Ground to inhibit the VLCD1. Output voltage test point. Programmed for 18V output, adjustable up to 25V. Output voltage mirror of VLCD1 LED drive voltage probe point. LED current sense feedback. Apply a DC voltage or a PWM voltage to this pin to adjust the LED current. PWM inputs should be greater than 120Hz with a DC portion less than 350mV. LED Driver MOSFET Gate Driver Output Buffered IC reference output.
Note: All pins are referenced to ground.
APPLICATIONS APPLICATIONS
Copyright (c) 2000 Rev. 1.1b, 2005-03-01
Microsemi
Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
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LX1744
INTEGRATED PRODUCTS
Dual Output Boost - LED Driver / LCD Bias
PRODUCTION DATASHEET
EVALUATION BOARD
Table 3: Jumper Position Assignments
Jumper Position Function
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J1 J2 J3 J4
N/A N/A N/A N/A
Close to adjust LED current with on-board potentiometer. Close to adjust VLCD with on-board potentiometer. Remove the factory installed jumper and insert a 4~6cm wire loop (optional) to observe the inductor current waveform using a current probe. Remove jumper to test open-circuit over-voltage protection implemented with R1 and R2
Note: All pins are referenced to ground.
Table 4: Factory Installed Component List
Ref Part Description
C1 C2, C7 C3, C4 C5, C6 C8, C9 C10, C12 C11 CR1, CR2, CR3, CR4 LED1, LED2, LED3, LED4 L1, L2 Q1 R1, R3 R2, R6 R4 R5 R7, R8
CAPACITOR, 4.7F, 1210, 6.3V CAPACITOR, 4.7F, 1210, 35V CAPACITOR, 1000pF, 0805, 35V CAPACITOR, (SPARE), See Note 1 CAPACITOR, 1F, 0805, 35V CAPACITOR, 0.1F, 0805, 6.3V CAPACITOR, 2.2F, 0805, 16V Microsemi UPS5819, SCHOTTKY, 1A, 40V, POWERMITE Microsemi UPWLEDxx, LED, Optomite INDUCTOR, 47H, 480mA, SMT FDV303N MOSFET, 30V, SOT-23
RESISTOR, 1M, 1/16W, 0805 RESISTOR, 75K, 1/16W, 0805 RESISTOR, 1K, 1/16W, 0805 RESISTOR, 15, 1/16W, 0805 RESISTOR, 100K, POT, 1/16W, 0805
RESISTOR, 100K, 1/16W, 0805 R9, R10 R11, R12, R13 RESISTOR, 10K, 1/16W, 0805
U1
Notes 1.
Microsemi LX1744CPW BOOST CONTROLLER
APPLICATIONS APPLICATIONS
Use these locations to insert additional input and/or output capacitance.
Copyright (c) 2000 Rev. 1.1b, 2005-03-01
Microsemi
Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 12
LX1744
INTEGRATED PRODUCTS
Dual Output Boost - LED Driver / LCD Bias
PRODUCTION DATASHEET
EVALUATION BOARD
WWW .Microsemi .C OM
1
DRV test points VOUT
Vin
1
2
1
47.0uH
10K
6 1 3 2 4
IN SW FB /SHDN ADJ
-VLCD
1
CR3 C8 C9 UPS5819 1uF CR4 1uF CR2
DRV SRC OVP LFB CS /LSHDN BRT REF
GND GND NC
12 13 10 9 11 7 8 5
FDV303N
+
2
+
C6 spare
+
C1 4.7uF 6.3V
L2
47.0uH R11 U1 LX1744TSSOP
Q1
1
test points
L1
J3
CR1 UPS5819 J3
1
R1 C3 1000pF 1M R4 1K
LED1
C2 4.7uF 35V
+
C5 spare
J2
VLCD
1
14 15 16
LED2 LED3
2
C4 1M 1000pF
+
J1
1
R3 UPS5819
C10 .1uF
1
2
R2 72K
C7 4.7uF 35V
R6 72K R9 100K
R8
R7
VIN
LED4
1
/SHDN ADJ GND
1 1 1
LFB
R5 R12
10K
15
1 1
GND2 /LSHDN BRT
+
C11 2.2uF 16V C12 .1uF
R10 100K
1
Figure 10 - LX1744EVAL Evaluation Board Schematic
APPLICATIONS APPLICATIONS
Copyright (c) 2000 Rev. 1.1b, 2005-03-01
Microsemi
Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 13
LX1744
INTEGRATED PRODUCTS
Dual Output Boost - LED Driver / LCD Bias
PRODUCTION DATASHEET
VOUT VERSUS VADJ
30 6
GATE DRIVE
WWW .Microsemi .C OM
Output Voltage (V)
25 20 15 10 5 0 0 0.5 1 1.5 2
DRV Voltage (V)
5 4 3 2 1 0 0 20 40 60 80 100 120 140 160
Adjustment Signal Voltage (VADJx) Figure 10 - Output Voltage Vs. Adjustment Signal Threshold
Note: The LX1744 uses the internal voltage reference until the VADJ signal exceeds 0.5V (typ).
DRV Current (mA) Figure 11 - Gate Drive Voltage Vs. Drive Current
VIN = 5V, TA = 25C
WAVEFORM
90% 85% 80% 75% 70% 65% 60% 55% 50% 0
EFFICIENCY
Efficiency
5
10
15
20
25
Output Current (mA) Figure 13 - LED Driver (Upper) and LCD Bias Efficiency Figure 12 - Typical Switching Waveform
CH1 - SWx Voltage, CH2 - Output Voltage, CH3 - Inductor Current
VIN = 5V, Four LEDs, L = 47H, RCS = 4k VIN = 3.6V, VOUT = 5.5V, L = 47H
VIN = 3.6V, VOUT = 18V, IOUT = 9mA
CHARTS CHARTS
Copyright (c) 2000 Rev. 1.1b, 2005-03-01
Microsemi
Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 14
LX1744
INTEGRATED PRODUCTS
Dual Output Boost - LED Driver / LCD Bias
PRODUCTION DATASHEET
PACKAGE DIMENSIONS
WWW .Microsemi .C OM
PW
14-Pin Thin Small Shrink Outline Package (TSSOP)
MILLIMETERS MIN MAX 0.85 0.95 0.17 0.27 0.09 0.20 4.90 5.10 4.30 4.50 0.65 BSC 0.05 0.15 1.10 0.45 0.75 0 8 6.4 BSC 0.10 INCHES MIN MAX 0.033 0.037 0.007 0.011 0.004 0.008 0.193 0.201 0.169 0.177 0.026 BSC 0.002 0.006 0.043 0.0177 0.030 0 8 0.252 BSC 0.004
E 1 23 F D
P
AH
SEATING PLANE
B
G
L
C
M
DIM A B C D E F G H L M P *LC
LQ
16-Pin Micro Leadframe Package - Quad Package (MLPQ)
MILLIMETERS MIN MAX 0.80 1.00 0 0.05 0.18 0.30 0.23 0.38 4.00 BSC 4.00 BSC 0.65 BSC 2.55 2.80 2.55 2.80 0.20 0.30 0.50 INCHES MIN MAX 0.031 0.039 0 0.002 0.007 0.012 0.009 0.015 0.157 BSC 0.157 BSC 0.026 BSC 0.100 0.110 0.100 0.110 0.008 0.012 0.020
D
b
E
D2
E2 e A1 A3 A
K L
DIM A A1 A3 b D E e D2 E2 K L
MECHANICALS MECHANICALS
Note:
Dimensions do not include mold flash or protrusions; these shall not exceed 0.155mm(.006") on any side. Lead dimension shall not include solder coverage.
Copyright (c) 2000 Rev. 1.1b, 2005-03-01
Microsemi
Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 15
LX1744
INTEGRATED PRODUCTS
Dual Output Boost - LED Driver / LCD Bias
PRODUCTION DATASHEET
NOTES
WWW .Microsemi .C OM
NOTES NOTES
PRODUCTION DATA - Information contained in this document is proprietary to Microsemi and is current as of publication date. This document may not be modified in any way without the express written consent of Microsemi. Product processing does not necessarily include testing of all parameters. Microsemi reserves the right to change the configuration and performance of the product and to discontinue product at any time.
Copyright (c) 2000 Rev. 1.1b, 2005-03-01
Microsemi
Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 16

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