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PS1313 High Efficiency, High Power White-LED Driver
FEATURES
On Board Power MOSFET Drives up to 4 strings of parallel LEDs Up to 87% Efficiency 1.4MHz Fixed Switching Frequency Open Load Shutdown Low 100mV Feedback Voltage Soft Start PWM Dimming Control UVLO, Thermal Shutdown Internal Circuit Limit Available in SOT26 Package WLED Backlight Cell Phones Handheld Computers and PDAs Digital Cameras Small LCD Displays LED Module Game Devices
DESCRIPTION
APPLICATIONS
The PS1313 is a step up converter designed for driving up to 4 branches with 4 white LEDs in series in each branch, providing backlight in cell phones, PDAs, and other hand-held devices. The PS1313 uses current mode, fixed frequency architecture to regulate the LED current, which is measured through an external current sense resistor. Its low 100mV feedback voltage reduces power loss and improves efficiency. The OV pin monitors the output voltage and turns off the converter if an overvoltage condition is present due to an open circuit condition. The PS1313 includes under-voltage lockout, current limiting and thermal overload protection preventing damage in the event of an output overload. The PS1313 is available in small 6-pin SOT26 Package.
TYPICAL APPLICATION CIRCUIT
Fig: Typical Application Circuit with 20mA Output
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PS1313
Fig: PS1313 for Innolux 8" Panel LED Back light unit
PIN CONFIGURATION
PIN DESIGNATOR
Name SW GND FB EN OVP IN Pin 1 2 3 4 5 6 Type Switch Ground Feedback Enable input. Over voltage input. Battery input. Function Connect inductor between SW and IN. Ground pin Adjustable feedback input, connect to resistor voltage divider. EN=High: normal operation. (Supports both TTL and CMOS Logic). Measures the output voltage for over voltage protection. Boost regulator input.
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PS1313
BLOCK DIAGRAM
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PS1313
ABSOLUTE MAXIMUM RATINGS
Symbol VSW VEN PD TSTG RJA TJ,MAX TL ESD Parameter DC Voltage at Pin 1 Enable Input Voltage at Pin 2 Continuous Power Dissipation Storage Temperature Range Thermal Resistance, Junction-To-Air Operating Junction Temperature Lead Temperature (Soldering, 5sec) ESD Capability, HBM model Value -0.5 to +28 -0.3 to +6.0 Internally limited -65 to +150 235 -40 to +125 260 2.0 Unit V V W C C /W C C kV
RECOMMENDED OPERATING CONDITIONS
Symbol VIN VEN TJ Parameter DC Supply Voltage at Pin 1 Enable Input Voltage at Pin 2 Operating Junction Temperature Value +2.5 to 6 0 to VIN -40 to +125 Unit V V C
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PS1313
ELECTRICAL CHARACTERISTICS
( Vin = 2.5V, TA = +25C, unless otherwise noted. Typical values are at TA = +25C.) Symbol VIN UVLO Parameter Operating Input Voltage Under Voltage Lock-out UVLO Hysteresis Supply Current (quiescent) Supply Current ISH FOSC DMAX VFB Supply Current (shutdown) Operation Frequency Maximum Duty Cycle Feedback Voltage Feedback Input Bias Current RDS(ON) ILIM VEN IEN MOSFET ON resistance Current Limit Enable Threshold Enable Input Bias Current Thermal Shut-down Over Voltage Threshold OV Hysteresis VFB=270mV 0.63 Vin=3 Turn ON Turn OFF VEN =0, 5V 1.18 1 0.4 6 160 VOV rising 18 2.6 90 Test Condition Min 2.5 Vin going Lo. 2.05 2.15 80 235 Typ Max 5.5 2.25 Units V V mV 240 A
IG
No Switching (Vin=5V, VFB= 270mV) Switching FB=0 VEN =0 1.3
1935 0.15 1.4 94 100 110 1.5 1.5
A A MHz % mV A A V V A C V V
VOV
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PS1313
OPERATION DESCRIPTION
The PS1313 is a high efficiency, fixed frequency, peak current mode boost regulator. It has the architecture to regulate the voltage at the feedback pin, so that a regulated fixed current is achieved to drive white LEDs. The power MOS is turned ON through the control circuitry, at the start of each oscillator cycle and thus the charging phase is initiated. The error amplifier, consisting of a voltage comparator and current sense amplifier, is basically, a PWM comparator. The voltage comparator amplifies the difference between the reference and feed back voltage. When the output of the current sense amplifier, reaches the output of the voltage comparator, the POWER MOS is turned OFF and thus the charging phase is terminated. To prevent sub-harmonic oscillations at duty cycles greater than 50 percent, a stabilizing ramp is added to the current sense signal. In this way the peak current level keeps the output in regulation. The PS1313 has internal soft start mechanism, to limit the inrush current at startup and to limit the amount of overshoot on the output, also. An internal blanking time is provided during start up, to prevent the start of switching before all the circuitry become ready for operation. The current limit is increased by a fourth every 60s giving a total soft start time of 240s.
Under Voltage Lockout: When the input supply goes too low (below 2.15V) the PS1313 produces an internal UVLO (under voltage lockout) signal that shuts down the chip. This mechanism protects the chip from producing false logic due to low input supply. Thermal Overload Protection: Thermal-overload protection limits total power dissipation in the PS1313. When the junction temperature exceeds Tj= +160C, the thermal sensor signals the shutdown logic and turning off most of the internal circuitry. The thermal sensor turns internal circuitry on again after the IC's junction temperature drops by 20C. The regulator then starts functioning in the required mode based on the supply voltage. Thermal-Overload protection is designed to protect the PS1313 in the event of a fault condition. For continual operation, do not exceed the absolute maximum junction temperature rating of Tj = +150C. Open Load Protection: Open load protection in PS1313, protects the chip from destruction, due to excessive high voltage. When, in any case, one or more LEDs in the LED string fails, the feedback pin is pulled down to zero. As a result, the chip runs at maximum duty cycle, boosting the output voltage higher and higher. The open load protection mechanism, checks this condition, if OV pin is tied to the top of the LED string. If the output voltage exceeds the OV threshold (18V) and persists there for a certain span of time (15S), the switching stops, allowing the output to discharge. The open load protection mechanism includes a hysteretic comparator. The switching is enabled again, when the output voltage has fallen to a certain level. Because the chip doesn't turn OFF fully, no power recycling is necessary, when this condition takes place. But it's highly recommended, not to use the chip in that mode of operation for longer span of time.
Setting the LED current : The LED current can be set, according to the requirement, by feedback to ground resistor, R1. The current through the LEDs is selected by the following equation: ILED=100mV/R1 Current Limit : The PS1313 includes a current limiter. It monitors the peak current through the inductor and controls gate of the power device. Enable Input : The PS1313 features an active-high Enable input (EN) pin that allows on/off control of the regulator. The PS1313 bias current reduces to less than microampere when it is shutdown. The output remains at a schottky forward voltage lower than the SW pin, if a schottky diode is connected between SW and OV pin, at shut. The Enable input is TTL/CMOS compatible.
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PS1313
Dimming Control: LED is a current driven device. Hence, current through the LED needs to be controlled to have dimming control. Different ways are there to control dimming for PS1313, in the normal mode of operation. In the first way, the feedback voltage is controlled using an external voltage source. As shown in the figure-8, current starts flowing down R1, R2 and R3, as the external voltage increases. The loop will continue to regulate the feedback voltage to 100mV, and as a result, the current through the LEDs has to decrease as the same amount of that being injected from the external source. With the external voltage from 0 to 2V, the resistor values shown for R2 and R3 can control LED current from 0 to 20mA.
Dimming can also be achieved using logic signal to EN pin. As shown in Figure-9, the PWM signal can be applied to the EN pin of PS1313. The LEDs will switch between full load to completely shut down state. The average current through the LEDs will be proportional to the duty cycle of PWM. The PWM signal in figure-9 should be of 1 KHz or less, because of the presence of the soft-start mechanism.
PS1313
PS1313
Figure 9: PWM dimming control using Logic signal
Figure 8: Dimming control using a DC voltage
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PS1313
PACKAGE INFORMATION
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PS1313
DISCLAIMERS
LIFE SUPPORT Power IC's products are NOT designed to be used as components in devices intended to support or sustain human life. The use of Power IC's products in components intended for surgical implants into the body or other applications, in which failure of Power IC's products could create a situation where personal death or injury may occur, is NOT authorized without the express written approval of Power IC's Chief Executive Officer. Power IC will NOT be held liable for any damages or claims resulting from the use of its products in medical applications. MILITARY Power IC's products are NOT designed for use in military applications. The use of Power IC's products in military applications is NOT authorized without the express written approval of Power IC's Chief Executive Officer. Power IC will NOT be held liable for any damages or claims resulting from the use of its products in military applications. RIGHT TO MAKE CHANGES Power IC reserves the right to change this document and/or this product without notice. Customers are advised to consult their Power IC sales representative before ordering.
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