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LX1745
INTEGRATED PRODUCTS
Triple Output Boost - LED Driver / LCD Bias
PRODUCTION DATASHEET
DESCRIPTION The LX1745 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 voltages with an additional two integrated boost converters. Designed for maximum efficiency and featuring a psuedo-hysteretic PFM topology (that decreases output voltage ripple), the LX1745 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 for LCD Bias generation, the LED driver utilizes an external N-Channel MOSFET in order to maintain maximum efficiency along with flexible power requirements.. The LX1745's control circuitry is optimized for portable systems with a shutdown current of less than 1A. The input voltage range of 1.6V to 6.0 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 LX1745 is capable of achieving an LED drive in excess of 1.0W. The LX1745 provides simple dynamic adjustment of the LED drive current (0% to 100% full range dimming) and the LCD Bias output voltages (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 LX1745 is available in the lowprofile 20-Pin TSSOP.
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 Two LCD Bias Voltage Adjustments Via Analog Reference Or Direct PWM Input 20-Pin TSSOP 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
LX1745
LSHDN SW2 REF FB2 GND SHDN1 ADJ1 ADJ2 BRT
ON OFF
RSET 15
ON OFF
VLCD2 = VIN to 25V
SHDN2
ON OFF
LX1745 Evaluation Board
LX1745 LX1745
PACKAGE ORDER INFO
TA (C) -40 to 85
PW 20-Pin
Plastic TSSOP
LX1745-CPW
Note: Available in Tape & Reel. Append the letter "T" to the part number. (i.e. LX1745-CPWT)
Copyright 2000 Rev. 1.1a, 2004-02-06
Microsemi
Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 1
LX1745
INTEGRATED PRODUCTS
Triple Output Boost - LED Driver / LCD Bias
PRODUCTION DATASHEET
ABSOLUTE MAXIMUM RATINGS
PACKAGE PIN OUT
Supply Input Voltage ...........................................................................-0.3V to 7V Feedback Input Voltage (VFBx) ...............................................-0.3V to VIN + 0.3V Shutdown Input Voltage (V SHDN x) ..........................................-0.3V to VIN + 0.3V PWM Input Amplitude (ADJx, BRT).....................................-0.3V to VIN + 0.3V Analog Adjust Input Voltage (VADJx, VBRT)............................-0.3V to VIN + 0.3V SRC Input Current ................................................................................ 500mARMS Operating Temperature Range .........................................................-40C to 85C Maximum Operating Junction Temperature ................................................ 150C Storage Temperature Range...........................................................-65C to 150C Lead Temperature (Soldering 10 seconds) .................................................. 300C
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. x denotes respective pin designator 1, 2, or 3
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SW1 ADJ1 SHDN1 IN LSHDN DRV SRC GND SHDN2 SW2
1 2 3 4 5 6 7 8 9 10
20 19 18 17 16 15 14 13 12 11
GND FB1 REF OVP BRT CS LFB ADJ2 FB2 GND
PW PACKAGE
(Top View)
THERMAL DATA
PW
Plastic TSSOP 20-Pin 90C/W
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 2000 Rev. 1.1a, 2004-02-06
Microsemi
Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 2
LX1745
INTEGRATED PRODUCTS
Triple Output Boost - LED Driver / LCD Bias
PRODUCTION DATASHEET
FUNCTIONAL PIN DESCRIPTION Name IN DRV SRC OVP LFB GND BRT REF SWx FBx 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.
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ADJx
LSHDN SHDNx
CS
PACKAGE DATA PACKAGE DATA
Copyright 2000 Rev. 1.1a, 2004-02-06
Microsemi
Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 3
LX1745
INTEGRATED PRODUCTS
Triple 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, LSHDN = VIN, 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 = 100mv 0.0V SHDN1 VIN RCS = 0k RCS = 2k VIN = 5V, VDRV = 3V VCC = 5V VFB = 1V VFB = 1V
Min 85 5 -100 0 -100
LX1745 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 Current Sense Bias Current Switch Peak Current DRV Sink/Source Current DRV On-Resistance Maximum Switch On-Time Minimum Switch Off-Time OVP Threshold Voltage Reference Voltage
LCD BIAS
VLFB ILFB VBRT IBRT I SHDN1 ICS IPK RDRV(ON) tON tOFF VOVP VREF VOUT VFB IFB I SHDNx ILIM RDS(ON) ILEAK tON tOFF VADJx IADJx VIN V SHDNx V SHDNx
mV nA V nA nA A mA
85
4 170 210 100 12 300 1.21 1.21 1.190
200 1.15 1.186 1.166
15 410 1.26 1.234 25 1.214 200 100
mA S nS V V V nA nA mA A s ns V A V V mV/C V V
Output Voltage Range FBx Threshold Voltage FBx Input Current LCD Bias Shutdown Input Bias Current Peak Inductor Current Internal NFET On-resistance Switch Pin Leakage Current Switch On-Time Switch Off-Time ADJx Input Voltage Range ADJx Input Bias Current
ENTIRE REGULATOR Operating Voltage Minimum Start-up Voltage Start-up Voltage Temperature Coefficient Shutdown High Input Voltage Shutdown Low Input Voltage
VFB = 1.4V
SHDNx = GND
TA = +25C ISW = 10mA, TA = +25C, VIN = 5V VSW = 25V VFB = 1V VFB = 1V 330 1.1
150 0.9 0.3
1.0 400 1.5 1.0 6.0 1.6
Recommended Operating Range
1.6 -2
TA = +25C VIN = 2V VIN = 2V VFBx = 1.4V, VLFB > VBRT - 0.1V VFBx = 1.4V, VLFB > VBRT - 0.1V, V LSHDN < 0.4V VFBx = 1.4V, VLFB > VBRT - 0.1V, V SHDN1 < 0.4V VFBx = 1.4V, VLFB > VBRT - 0.1V, V SHDN2 < 0.4V V SHDN1 < 0.4V, V SHDN2 < 0.4V, V LSHDN < 0.4V 1.6 200 0.35 140 80 0.35
0.4 320 1 220 120 1
E ELECTRICALS
Quiescent Current
IQ
A
Copyright 2000 Rev. 1.1a, 2004-02-06
Microsemi
Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 4
LX1745
INTEGRATED PRODUCTS
Triple 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 Current Limit GND 4A CS Shutdown Logic LSHDN SHDNx FBx Control Logic SWx
IN OVP
REF
Driver
ADJx 50pF 2.5M
Reference Logic
Current Limit
Voltage Reference Control Logic Reference Logic 50pF 2.5M Driver
FBx
SWx
ADJx
Current Limit
B D BLOCK DIAGRAM
Figure 1 - Simplified Block Diagram
Copyright 2000 Rev. 1.1a, 2004-02-06
Microsemi
Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 5
LX1745
INTEGRATED PRODUCTS
Triple Output Boost - LED Driver / LCD Bias
PRODUCTION DATASHEET
APPLICATION CIRCUITS
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ILED = 20mA to 0mA
L1 D1
VBAT = 1.6V to 6.0V
D3
47H 1206 Case Size L2 L3
R5
- VLCD
D4
C1 4.7F
DRV IN SRC R6 SW1
D2
OVP LFB
VLCD1 = VIN to 25V
(Feedforward Capacitor)
FB1 R1
CS RCS
LX1745
LSHDN D3 SW2 REF FB2 R3 GND SHDN2 SHDN1 ADJ1 ADJ2
ON OFF
RLED 15 (typ)
R2
BRT
ON OFF
VLCD2 = VIN to 25V
R4
ON OFF
Figure 2 - LED Driver with Full-Range Dimming plus LCD Bias With Contrast Adjustment Via PWM Input
A APPLICATIONS
Copyright 2000 Rev. 1.1a, 2004-02-06
Microsemi
Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 6
LX1745
INTEGRATED PRODUCTS
Triple Output Boost - LED Driver / LCD Bias
PRODUCTION DATASHEET
APPLICATION NOTE
FUNCTIONAL DESCRIPTION The LX1745 is a triple 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 outputs. 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 14. 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 = R2 VOUT - VREF VREF
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eq. 1
LCD BIAS - OUTPUT VOLTAGE ADJUSTMENT The LX1745 allows for the dynamic adjustment of each of the voltage outputs via an adjustment pin (ADJx). Any voltage applied to the adjustment pin(s) works in conjunction with the internal reference logic. The LX1745 will automatically utilize the internal reference when no signal is detected or when the adjustment signal voltage is below approximately 0.6V. Each of these pins 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).
LX1745
Reference Logic
50pF
ADJx
RADJx_1
2.5M
Figure 4 - LCD Bias Adjustment Input
Different PWM signal levels can be accommodated by selecting a value for RPWM such that the filtered VADJX value is equal to the reference voltage (eq. 2)
2.5M VADJx = VPWM Duty Cycle 2.5M + R PWM _ 1
eq. 2
LX1745
VOUT
R1 SWx FBx
LX1745
ADJx CADJx
RADJx_1
APPLICATIONS APPLICATIONS
RADJx_2
R2
Figure 5 - LCD Bias Adjustment Input Filter
Figure 3 - LCD Bias Output Voltage
Ideally the resultant ripple on the ADJx pin should be approximately 1% or 40dB down from the nominal reference. When using a PWM with a frequency that is
Copyright 2000 Rev. 1.1a, 2004-02-06
Microsemi
Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 7
LX1745
INTEGRATED PRODUCTS
Triple 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 = VBRTx(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 (ADJx) pins, 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
LX1745
RCS CS RBRT_1 BRT CBRT RBRT_2 RLED 15
where RBRT_2 is selected and VBRT(MAX) is the selected maximum LED current sense feedback threshold.
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 LX1745 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 2000 Rev. 1.1a, 2004-02-06
Microsemi
Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 8
LX1745
INTEGRATED PRODUCTS
Triple Output Boost - LED Driver / LCD Bias
PRODUCTION DATASHEET
APPLICATION NOTE
negative voltage transition that is greater than the output voltage. POWER MOSFET SELECTION The LX1745 can source up to 100mA of gate current. An logic 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 LX1745 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.
ROVP _ 1 = ROVP _ 2 VOVP - VREF VREF
can be chosen from the following equation:
RCS 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 )
eq. 9
Figure 7 - Peak Current Programming Resistor
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
eq. L I I 1 IPK IOUT VRIPPLE PK OUT + COUT VIN - ( VSW + VL ) VOUT + VF - VIN
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 2000 Rev. 1.1a, 2004-02-06
Microsemi
Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 9
LX1745
INTEGRATED PRODUCTS
Triple 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 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.
SHDN 0 0 1 1 1 0 1 0 SHDN2 0 1 0 1 1 1 0 0 SHDN1 1 1 1 1 0 0 0 0 LCD1 1 1 1 1 0 0 0 0 LCD2 0 1 0 1 0 0 0 0 LED 0 0 1 1 0 0 0 0
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VBAT = 1.6V to 6.0V
- VOUT
D4
LX1745
VOUT
R1 SWx FBx
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
Table 1 - Enable Logic
VBAT = 1.6V to 6.0V
VNEG_LCD
R4 LX6431, LX432 R5 R3 D4
LX1745
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 2000 Rev. 1.1a, 2004-02-06
Microsemi
Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 10
LX1745
INTEGRATED PRODUCTS
Triple Output Boost - LED Driver / LCD Bias
PRODUCTION DATASHEET
EVALUATION BOARD
Table 2: Input and Output Pin Assignments
Name VIN GND ADJ1 0 to VIN-100mV ADJ2 SHDN SHDN1 SHDN2 VLCD1 -VLCD VLCD2 VOUT FDBK BRT REF 25V -25V 25V 25V 0 to VIN 0 to 350mV 1.19V Typ. 0 to VIN Input/Output Range 0 to 6V 0V 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. Apply a DC voltage or a PWM voltage to this pin to adjust the LCD2 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. Pulled up to VIN on board (10K), Ground to inhibit the VLCD2. Output voltage test point. Programmed for 18V output, adjustable up to 25V. Output voltage mirror of VLCD1 Output voltage test point. Programmed for 22V output, adjustable up to 25V. 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. Buffered IC reference output. Description Main power supply for outputs.
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Note: All pins are referenced to ground.
APPLICATIONS APPLICATIONS
Copyright 2000 Rev. 1.1a, 2004-02-06
Microsemi
Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
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LX1745
INTEGRATED PRODUCTS
Triple Output Boost - LED Driver / LCD Bias
PRODUCTION DATASHEET
EVALUATION BOARD
Table 3: Jumper Position Assignments
Jumper JU1 JU2 JU3 JU4 Position N/A N/A N/A N/A Function 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
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Note: All pins are referenced to ground.
Table 4: Factory Installed Component List
Ref C1 C2, C5, C6 C3, C7, C8 C4, C11 CAPACITOR, 4.7F, 1210, 6.3V CAPACITOR, 4.7F, 1210, 35V CAPACITOR, 1000pF, 0805, 35V CAPACITOR, (SPARE), See Note 1 Part Description
C9, C10, C12, CAPACITOR, 1F, 0805, 35V C13 CR1, CR2, Microsemi UPS5819, SCHOTTKY, 1A, 40V, POWERMITE CR3, CR4, CR5 LED1, LED2, LED3, LED4 L1, L2, L3 Q1 R1, R5 R2, R6, R8 R3 R4 R7 R9, R10, R11 R12, R13 U1
Notes 1. Use these locations to insert additional input and/or output capacitance.
Microsemi UPWLEDxx, LED, Optomite INDUCTOR, 47H, 480mA, SMT FDV303N MOSFET, 30V, SOT-23
RESISTOR, 1M, 1/16W, 0805 RESISTOR, 75K, 1/16W, 0805 RESISTOR, 15, 1/16W, 0805 RESISTOR, 4.02K, 1/16W, 0805 RESISTOR, 1.25M, 1/16W, 0805 RESISTOR, 10K, 1/16W, 0805 RESISTOR, 100K, 1/16W, 0805
Microsemi LX1745CPW BOOST CONTROLLER
APPLICATIONS APPLICATIONS
Copyright 2000 Rev. 1.1a, 2004-02-06
Microsemi
Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 12
LX1745
INTEGRATED PRODUCTS
Triple Output Boost - LED Driver / LCD Bias
PRODUCTION DATASHEET
EVALUATION BOARD
WWW .Microsemi .C OM
1
-VLCD REF
1
C12 1uF L1
+C4 +
R13 100K
1
JU1
1 2
CR1 UPS5819 C9 1uF CR5 UPS5819 C10 1uF CR4 UPS5819
20 19 18 17 16 15 14 13 12 11
R4 4.02K
VOUT
Vin GND
1 1
2
spare
C1 4.7uF 6.3V
47.0uH
JU4
1
R1 C3 1M 1000pF
+
R9 R10 10K 10K ADJ1 SHDN1 SHDN SHDN2 VLCD2
1 1 1
R11 10K
Q1 FDV303N L2 JU2
2 1
C2 4.7uF 35V
+
C11 Spare
1
GND
LED 4
U1
1 2 3 4 5 6 7 8 9 10
L3
2
JU3
1
SW1 LCDGND1 ADJ1 FB1 REF SHDN1 VIN OVP BRT SHDN DRV CS SRC LFB LEDGND ADJ2 SHDN2 FB2 SW2 LCDGND2
R2 72K
LED 3 LED 2 LED 1
1
1
LX1745
1
FDBK
22V
+
CR3 C7
1000pF
R3 15 R12 100K C13 1uF
1
C6 4.7uF 35V
UPS5819 R7 1.25M R8 72K CR2 UPS5819
+
ADJ2 BRT
1
18V C5 4.7uF 35V C8
1000pF
R5 1M
1
VLCD1
R6 72K
Figure 10 - LX1745EVAL Evaluation Board Schematic
APPLICATIONS APPLICATIONS
Figure 11 - LX1745EVAL Evaluation Board
Copyright 2000 Rev. 1.1a, 2004-02-06
Microsemi
Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 13
LX1745
INTEGRATED PRODUCTS
Triple 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)
DRV Current (mA)
Figure 12 - Output Voltage Vs. Adjustment Signal Threshold
Note: The LX1745 uses the internal voltage reference until the VADJ signal exceeds 0.5V (typ).
Figure 13 - 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 15 - LED Driver (Upper) and LCD Bias Efficiency Figure 14 - 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 2000 Rev. 1.1a, 2004-02-06
Microsemi
Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 14
LX1745
INTEGRATED PRODUCTS
Triple Output Boost - LED Driver / LCD Bias
PRODUCTION DATASHEET
PACKAGE DIMENSIONS
WWW .Microsemi .C OM
PW
20-Pin Thin Small Shrink Outline Package (TSSOP)
321 E P
F D AH
SEATING PLANE
B
Dim A B C D E F G H L M P *LC
G
L
INCHES MIN MAX 0.032 0.041 0.007 0.012 0.0035 0.0071 0.252 0.260 0.169 0.176 0.025 BSC 0.002 0.005 - 0.0433 0.020 0.028 0 8 0.246 0.256 - 0.004
C
M
MILLIMETERS MIN MAX 0.80 1.05 0.19 0.30 0.09 0.180 6.40 6.60 4.30 4.48 0.65 BSC 0.05 0.15 - 1.10 0.50 0.70 0 8 6.25 6.50 - 0.10
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 2000 Rev. 1.1a, 2004-02-06
Microsemi
Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 15
LX1745
INTEGRATED PRODUCTS
Triple Output Boost - LED Driver / LCD Bias
PRODUCTION DATASHEET
NOTES
WWW .Microsemi .C OM
NOTES NOTES
Copyright 2000 Rev. 1.1a, 2004-02-06
Microsemi
Integrated Products Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 16

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