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Technical content
Features
Input Voltage range: 4.5V to 36V Drives up to 4 strings in parallel, up to 240mA per string Time-shift PWM dimming control External PWM dimming control LED short circuit protection LED open string protection MOSFET over-current protection Over-temperature protection Status output
Applications
UMPC and Notebook Computer Backlight Backlight for GPS, Portable DVD LED Backlight for LCD Monitor/ TV Typical Application Fig.1 Typical Circuit for 4 Strings of LED Line Bar
Leadtrend Technology Corporation www.leadtrend.com.tw LD7889A-DS-00 March 2012 Pin Configuration LED4 ISET OVP RT EN CS GATE VREF LED3 GND PWM STATUS COMP VIN LED2 LED1 LED4 ISET OVP RT EN CS GATE VREF LED3 GND PWM STATUS COMP VIN LED2 LED1 LED4 ISET OVP RT EN CS GATE VREF LED3 GND PWM STATUS COMP VIN LED2 LED1
Leadtrend Technology Corporation www.leadtrend.com.tw LD7889A-DS-00 March 2012
Ordering Information
Part number Package Top Mark Shipping LD7889AGS SOP-16 LD7889AGS 2500 /tape & reel LD7889AGHE TSSOP-EP-16 LD7889AGHE 2500 /tape & reel LD7889AGN DIP-16 LD7889AGN 1800 /Tube/ Carton The LD7889A is green packaged. Pin Descriptions PIN SOP-16 PIN TSSOP-16 PIN DIP-16 NAME FUNCTION 1 5 1 LED4 LED string #4 current input. 2 6 3 ISET LED current resistor setting 3 7 2 OVP Over-voltage protection 4 8 4 RT Operating frequency resistor setting 5 9 5 EN Chip enable pin. 6 10 6 CS Power MOSFET current sense pin. 7 11 7 GATE Low side Power MOSFET Driver 8 12 8 VREF 5V Internal linear regulator output pin with an external ceramic capacitor of 1F or greater. 9 13 9 VIN Input Power of the chip. Bypass with at least 1F ceramic capacitor and place it close to VIN pin. 10 14 10 STATUS LED oper ation status output 11 15 11 COMP Soft start and c ontrol loop Compensation. 12 16 12 PWM PWM dimming input. 13 1 13 LED1 LED string #1 current input. 14 2 14 LED2 LED string #2 current input. 15 3 15 GND IC ground 16 4 16 LED3 LED string #3 current input.
Leadtrend Technology Corporation www.leadtrend.com.tw LD7889A-DS-00 March 2012 Block Diagram LogicGDRV Q R S COMP GM Vref LED Voltage Detector LEB +0.5V Oscillator DIM CTRL ILED= 1200/RISET Current Limit LED Short LED Open 7.2V 0.1V OVP OVP 2 SCP 3.2V 2.0V 0.1V LDO Reference Internal V/I reference Internal Power supply GATE STATUS OVP VIN EN VREF ISET GNDPWM LED4 LED3 LED2 LED1 COMP CS RT Protection Logic
Leadtrend Technology Corporation www.leadtrend.com.tw LD7889A-DS-00 March 2012 Absolute Maximum Ratings VIN 40V CS -0.3V ~ 5.5V VLED1 to VLED4 -0.3V ~ 60V STATUS, OVP, PWM, EN -0.3V ~ 5.5V VREF, COMP, RT, GATE, ISET -0.3V ~ 6V GND 0.3V ILEDx pulse forward current (Pulse time2ms) 400mA ILED1 to ILED4 330mA Package Thermal Resistance TSSOP-EP-16, JA 60 C/W SOP-16, JA 110 C/W DIP-16, JA 80 C/W Operating Temperature Range -40 C to 85C Storage Temperature Range -55 C to 125C Junction Temperature 150 C Lead Temperature (Soldering, 10sec) 260 C ESD Level (Human Body Model) 2KV ESD Level (Machine Model) 200V Recommended Operating Conditions Input Supply Voltage 4.5V to 36V ILED1 to ILED4 20mA to 240mA Caution: Stresses beyond the ratings specified in “Absolute Maximum Ratings” may cause permanent damage to the device. This is a stress only rating and operation of the device at these or any other conditions above those indicated in the operational sections of this s pecification is not implied.
Leadtrend Technology Corporation www.leadtrend.com.tw LD7889A-DS-00 March 2012
Electrical Characteristics
(VIN=24V, TA=25C, unless otherwise noted.) PARAMETER CONDITIONS MIN. TYP . MAX. UNITS Input Power Input Voltage range 4.5 36 V VIN Operating Current EN=PWM=5V 10 mA VIN Shutdown Current EN=PWM=0V 2 10 A VIN Stand-By Current EN=5V, PWM=0V 600 800 A Under Voltage Lockout Lockout Threshold VREF LOCKOUT 3.6 4.1 4.2 V Resume Threshold VREF RESUME 4.2 4.4 4.6 V Reference Voltage Reference Voltage V REF, VIN>6V 5.25 5.5 5.75 V VREF Output Current Capability I VREF 30 mA Drive Logic GATE Sink Resistance V IN>6V 1 3.5 5 GATE Source Resistance V IN>6V 1 5 9 Minimum MOSFET ON Time 150 ns LED Current Regulation Regulation LED Current per Channel ISET=12K ,KISET=1200 Chip to chip average current 92 100 108 mA Voltage at ISET pin 1.225 1.25 1.275 V LEDs Current Matching LED current=100mA Calculating: %100I2 II Average MINMAX േ2 % LED regulation voltage I LED=100mA/per channel 300 350 mV LED regulation voltage I LED=240mA/per channel 550 650 mV Boost Controller Adjustable Switching frequency 100 1000 kHz Default Switching frequency R RT =260k 180 200 220 kHz Leading edge blanking time 150 ns Voltage at RT pin 1.176 1.2 1.224 V Boost Maximum duty cycle Fsw=500kHz 90 93 96 %
Leadtrend Technology Corporation www.leadtrend.com.tw LD7889A-DS-00 March 2012 PARAMETER CONDITIONS MIN. TYP . MAX. UNITS EN and PWM Dimming Enable 1.8 V EN and PWM Logic Disable 0.8 V EN Pull Down Resistance 1M Turn-on time, PWM rising to ILED from shutdown (Tp1) (Note1) 4000 ns LED rise time (TR) (Note1) 600 ns LED fall time(TF) (Note1) 600 ns LED “ON” Period (tON) (Note1) 1 cycle LED “OFF” Period (tOFF) (Note1) 1 cycle PWM dimming frequency 100 25k Hz Protection LED Open String Protection Threshold OVP 1.9 2.0 2.1 V Shutdown Under Abnormal condition OVP 3.0 3.2 3.4 V LED Short Circuit Protection Threshold LED1~LED4 7.2 V Boost- Short circuit startup During start-up, 0.1 V Boost- Short circuit startup Hysteresis 50 mV Thermal Shutdown threshold 140 C Thermal Shutdown hysteresis 30 C MOSFET Over-Current Protection N-FET Over-Current Protection CS 0.47 0.5 0.53 V STATUS Output Sink Resistance 20 100 Note1:
Leadtrend Technology Corporation www.leadtrend.com.tw LD7889A-DS-00 March 2012 Typical Performance Characteristics 22 LEDs in series, 4 strings parallel, 120mA/string, C OUT=4.7F, unless otherwise noted. Fig. 2 V IN=16V , “FDIM=120Hz, Duty=5%” LED 2 LED 3 ILED 4 LED 1 Fig. 3 V IN=16V, “FDIM =120Hz, Duty=5%” LED 2 LED 3 ILED 4 LED 1 Fig. 4 V IN=16V , “LED Short Protection ,Dim Duty=100%” VOUT RISET ILED4 VST ATUS Fig. 5 VIN=16V , “LED Short Protection, fDIM=200Hz, Duty=10% VOUT RISET ILED4 VSTATUS Fig. 6 VIN=16V, “LED Open Protection ,Dim Duty=100%” VOUT VSTATUS IOUT VOVP Fig. 7 VIN=16V, “LED Open Protection , fDIM =200Hz,Duty=10% VOUT RISET ILED4 VSTATUS
Leadtrend Technology Corporation www.leadtrend.com.tw LD7889A-DS-00 March 2012 Fig. 8 VIN=16V, VLE D=70V , 320mA/string, “fDIM =120Hz,Duty=10%” IL Current VOUT Fig. 9 VIN=16V, VLED=70V , 320mA/string, “fDI M =120H z, Duty=10%” IL Current VOUT Fig. 10 VIN=16 V, VLED=50V, 160mA/string, “fDIM =120Hz,Duty=20%” IL Current VOUT Fig. 1 1 V IN=16V,VLED=50V, 160mA/string, “fDIM =120Hz, Duty=20%” IL Current VOUT
Application Information
The LD7889A is a high-efficiency driver, ideally for LED backlight application. It in corporates with two major functions, a DC-DC boost controller with peak current-mode control and a 4-channel LED driver with constant current of sink capability from 20mA to 240mA per channel. LD7889A features adaptive vo ltage control that adjusts the converter output voltage according to the total forward voltage of LED strings. It det ects the drop of LED voltage across the constant current-s ink drivers and enhances power dissipation in the device. The other features include LED short and open protection, cycle by cycle current limit, and thermal shutdown Current-Mode DC-DC Controller. The peak current-mode controller allows boost converter to generate the required output voltage for LED strings. The switching frequency is programmable in the range between 100 kHz and 1 MHz through a resistor connected from RT pin to ground. Once the device is turned on, the external MOSFET will drive the inductor current to ramp up linearly until the MOSFET reaches the peak current level set by CS pin.
Leadtrend Technology Corporation www.leadtrend.com.tw LD7889A-DS-00 March 2012 The peak inductor current is sensed by measuring the voltage across the current-sense resistor R CS, which is connected from the source of external MOSFET to ground. LD7889A features leading edge blanking time to suppress the switching noise from the external MOSFET. A PWM comparator compares the current-sense voltage and the slop compensation signal with the output of the GM error amplifier. The device will turn off the external MOSFET when the voltage over CS exceeds the error amplifier’s output voltage. This process repeats in every switching cycle to achieve peak current-mode control. Programming the LED Current The LED current is programm able by placing a resistor between the ISET pin and ground. The ISET pin resistor is recommended to select in the range from 5k to 60k. Set the desired LED current according to the following equation: )k(R 1200)mA(I ISET LED LED Current (mA) Fig. 11 LED Current vs. RISET RISET (K) 120 160 200 240 0 20 40 60 80 100 120 Switching Frequency Selection LD7889A can operate in fixed frequency mode. The constant operation frequency is set by an external resistor connected between RT pin and ground. The resistor sets the charging current for internal oscillator. )k(RT 52000)kHz(FSW Frequency (KHz) Fig. 12 Frequency vs. RT RT (K) 200 400 600 800 1000 0 200 400 600 800 1000 PWM dimming PWM dimming control is achieved by applying an external PWM signal of 100Hz to 25kHz to the PWM pin. Power Sequence and Timing Chart That is, the supply voltage must be applied to VIN pin before the dimming signal (to DIM pin) by at least 1ms and then the shutdown signal ( to EN pin). Please follow the proper power sequence in below timing chart.
Leadtrend Technology Corporation www.leadtrend.com.tw LD7889A-DS-00 March 2012 MOSFET Over-Current Protection The LD7889A provides cycle-by-cycle current limit to protect the MOSFET. During the MOSFET turning on, LD7889A detects the CS pin voltage and if V CS rises above approximately 0.5V, the GATE will shut off. For suppress switch transients could add the RC filter to close the LD7889A CS pin. The typical suggestion value is R=1kΩ, C=100pF. Loop compensation The LD7889A has an internal trans conductance error amplifier for LED current regulation for COMP output to compensate the control loop. In case of open LED event that all LED strings are open, the COMP node will compensate the control loop still. The external inductor, output capacitor, the compensation resistor and the capacitor determine the loop stability. The inductor and output capacitor are chosen based on the performance, size and cost. The compensation resistor and capacitor at COMP are selected to optimize control loop stability. For typical LED applications, a 0.22 F compensation capacitor in series with 3k resistor at COMP is adequate. LED Short Circuit Protection The voltage of LED1 ~ LED4 pins exceeds a typical threshold of approximately 7.2V during normal operation, the corresponding string be turned off and latched. LED Open String Protection When LED1-4 pins voltage falls below about 0.1V and VOT will boost up until the voltage at pin OVP reaches a typical threshold of approximately 2. 0V threshold. That will set the LED output over voltage (V LED_OVP2) as following equation: 2OVP_LED R RR0.2)V(V Thermal protection Thermal protection limits total power dissipation in this device. When the juncti on temperature reaches 140 C approximately, the thermal s ensor signals the shutdown logic turning off this device. The thermal sensor will turn this device on again after the IC’s junction temperature cools by 30C. PCB Layout Guideline It’s recommended to separate the high frequency switching current from the low-level control signals in
Leadtrend Technology Corporation www.leadtrend.com.tw LD7889A-DS-00 March 2012 layout. The high switching current (MOSFET, inductor, gate driver and LED return ends) may disturb the other low-level signals in the feedback loop and protection circuitry. As a result, it may cause the control function to behave abnormally. To avoid these issues, a few guidelines are recommended for the PCB layout, as below. 1. VREF bypass capacitor co nnected with signal ground must be placed as close as possible to the IC. The traces between capacitor and VREF pin should be kept as short as possible to avoid noise interference. 2. VIN bypass capacitor connected with signal ground must be placed as close as possible to the IC. The traces between capacitor and VIN pin should be kept as short as possible to avoid noise interference. 3. Use broader traces for VIN, VOUT and power ground. Components such as the power MOSFET and decoupling capacitors connected to VIN, VOUT and power ground, have high input/output current. To minimize power loss in these traces, the resistance of traces should be kept as low as possible. 4. Use broader traces between power MOSFET drain, inductor and diode. There is high current in these traces. To minimize power loss in these traces, the resistance of traces should be kept as low as possible. 5. Keep the gate drive tr aces short and board between the IC driver output, GATE pin, and the power MOSFET. The driving traces have a high current spike during inverter operation. To minimize power MOSFET switching loss or oscillation voltage in the gate driver signal, the drive traces should be as board and short as possible to minimize resistance and parasitic inductance.
Leadtrend Technology Corporation www.leadtrend.com.tw LD7889A-DS-00 March 2012
Package Information
Dimension in Millimeter Dimension in Inch Symbol Min Max Min Max A 9.800 10.010 0.386 0.394 B 3.800 4.000 0.150 0.157 C 1.346 1.753 0.053 0.069 D 0.330 0.510 0.013 0.020 F 1.27 TYP. 0.05 TYP. H 0.178 0.254 0.007 0.010 I 0.100 0.254 0.004 0.010 J 5.790 6.200 0.228 0.244 M 0.380 1.270 0.015 0.050 θ 0° 8° 0° 8°
Leadtrend Technology Corporation www.leadtrend.com.tw LD7889A-DS-00 March 2012 TSSOP-EP-16 Dimension in Millimeter Dimension in Inch Symbol Min Max Min Max A 4.900 5.100 0.193 0.201 B 4.300 4.500 0.169 0.177 C 0.850 1.200 0.033 0.047 D 0.190 0.300 0.007 0.012 E 2.000 3.000 0.079 0.118 F 0.65 TYP. 0.026 TYP. G 2.000 3.000 0.079 0.118 H 0.127 TYP. 0.005 TYP. I 0.005 0.150 0.000 0.006 J 6.200 6.600 0.244 0.260 M 0.450 0.750 0.018 0.030 θ 0° 8° 0° 8°
Leadtrend Technology Corporation www.leadtrend.com.tw LD7889A-DS-00 March 2012 DIP-16 (300mil) Dimension in Millimeter Dimension in Inch Symbol Min Max Min Max A 18.880 19.320 0.743 0.761 B 6.096 7.112 0.240 0.280 D 0.356 0.584 0.014 0.023 E 1.140 1.780 0.045 0.070 F 2.337 2.743 0.092 0.108 I 2.921 3.556 0.115 0.140 J 7.366 8.260 0.290 0.325 Important Notice Leadtrend Technology Corp. reserves the right to make changes or corrections to its products at any time without notice. Custom ers should verify the datasheets are current and complete before placing order.
Leadtrend Technology Corporation www.leadtrend.com.tw LD7889A-DS-00 March 2012 IR Profile for SMD Devices 100 150 200 250 300 Temp. (ºc) Time (sec.) Ramp up 3ºC/second max. 217ºC 60 ~ 150 seconds Peak Temp. 260 -5/+0ºC, 30 seconds (max.) Preheat 60 ~ 120 seconds 260 217 Ramp down 6ºC/second max. Item Average Ramp-up Rate Pre-heat (150 ~ 200°C) Time Maintained Above 217°C Peak Temp. Ramp-down Rate Required 3°C(max) /sec 60~120 sec 60~150 seconds 260 +0/-5°C 30 seconds 6°C (max) /sec
Leadtrend Technology Corporation www.leadtrend.com.tw LD7889A-DS-00 March 2012
Revision History
Rev. Date Change Notice 00 3/29/2012 Original Specification