PS1541 High Efficiency Step Up DC/DC Converter FEATURES On Board Power MOSFET Uses Tiny Capacitor And Inductors 12V at 150mA from 5V input Up to 92% Efficiency Operates with Input Voltage as Low as 2.5V and Output Voltage as High as 22V 620KHz Fixed Switching Frequency Low 1.1V Feedback Voltage Soft Start UVLO, Thermal Shutdown Internal Current Limit Available in SOT-26 packages. APPLICATIONS Cell Phones Handheld Computers and PDAs. Camera Phone Flash Small LCD Displays Digital Still and Video Cameras White LED Driver External Modems DESCRIPTION The PS1541 is a current mode step up converter intended for small, low power applications. The PS1541 switches over 600KHz and allows the use of tiny, low cost capacitors and inductors. Internal soft start results in small inrush current and extends battery life. The PS1541 operates from an input voltage as low as 2.5V and can generate 12V at up to 150mA from a 5V supply. The PS1541 includes under-voltage lockout, current limiting and thermal overload protection preventing damage in the event of an output overload. The PS1541 is available in small 6-pin SOT-26 package. TYPICAL APPLICATION CIRCUIT July 2007 www.picsemi.com © 2007 Power IC. All Rights Reserved. 1 PS1541 PIN CONFIGURATION PIN CONFIGURATION Name SW GND FB EN NC IN July 2007 Pin 1 2 3 4 5 6 Type Switch Ground Feedback Enable input. Not connected 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). Boost regulator input. www.picsemi.com © 2007 Power IC. All Rights Reserved. 2 PS1541 BLOCK DIAGRAM July 2007 www.picsemi.com © 2007 Power IC. All Rights Reserved. 3 PS1541 ABSOLUTE MAXIMUM RATINGS Symbol VSW VEN PD TSTG RθJA 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 Value +2.5 to 6 0 to VIN -40 to +125 Unit V V °C RECOMMENDED OPERATING CONDITIONS Symbol VIN VEN TJ July 2007 Parameter DC Supply Voltage at Pin 1 Enable Input Voltage at Pin 2 Operating Junction Temperature www.picsemi.com © 2007 Power IC. All Rights Reserved. 4 PS1541 ELECTRICAL CHARACTERISTICS ( Vin = 2.5V, TA = +25°C, unless otherwise noted. Typical values are at TA = +25°C.) Symbol Parameter Vin Operating Input Voltage Under Voltage Lock-out UVLO Vout-max Test Condition Min Typ 2.5 Vin going Lo. Maximum Output Voltage Supply Current (quiescent) 2.15 2.2 Max Units 5.5 V 2.4 V 25 V No Switching (Vin=5V, VFB= 1.25V) 135 260 μA Supply Current Switching FB=0 510 750 μA VEN =0 1 μA FOSC Supply Current (shutdown) Operation Frequency DMAX Maximum Duty Cycle VFB Feedback Voltage Iq Ish Feedback Input Bias Current RDS(ON) ILIM VEN IEN July 2007 MOSFET ON resistance Current Limit Enable Threshold Enable Input Bias Current Thermal Shut-down 620 KHz % 93 1.05 VFB=1.25V Vin=3 Turn ON Turn OFF VEN =0, 5V 1.1 1.15 7 nA 0.8 Ω 2.3 A V V μA 0.95 www.picsemi.com © 2007 Power IC. All Rights Reserved. V 0.35 1 145 °C 5 PS1541 TYPICAL OPERATING CHARACTERISTICS Efficiency vs Load Current FB Voltage vs Temperature 1.09 100 FB Voltage(V) Eff (%) 90 80 70 60 50 1.085 1.08 1.075 1.07 0 50 100 150 Load (mA) 200 -40 0 20 40 60 80 Temp (°C) Frquency vs Temperature Temperature vs Duty Cycle 750 94.5 700 94 Duty Cycle (%) Frequency (K H z) -20 Vin=5V, Vout=14V 650 600 550 93.5 93 92.5 92 91.5 500 91 -50 0 50 100 150 -40 Temperature (°C) -10 20 50 80 110 140 Temperature (°C) Temperature vs Supply Current Supply Current (uA) 145 140 135 130 125 120 115 -40 -10 20 50 80 110 140 Temperature (°C) July 2007 www.picsemi.com © 2007 Power IC. All Rights Reserved. 6 PS1541 TYPICAL OPERATING CHARACTERISTICS (Continued) July 2007 www.picsemi.com © 2007 Power IC. All Rights Reserved. 7 PS1541 OPERATION DESCRIPTION The PS1541 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. 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 PS1541 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 60µs giving a total soft start time of 240µs. Under Voltage Lockout When the input supply goes too low (below 2.2V) the PS1541 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 PS1541. When the junction temperature exceeds Tj= +145°C, 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 20°C. The regulator then starts functioning in the required mode based on the supply voltage. Thermal-Overload protection is designed to protect the PS1541 in the event of a fault condition. For continual operation, do not exceed the absolute maximum junction temperature rating of Tj = +125°C. Setting the Output Voltage Set the output voltage by selecting the resistive voltage divider ratio. Use 12kΩ for the low side resistor R2 of the voltage divider. Determine the high-side resistor R1 by the equation: R1= R2(VOUT - VFB)/VFB Where VOUT is the output voltage. Current Limit The PS1541 includes a current limiter. It monitors the peak current through the inductor and controls gate of the power device. Enable Input The PS1541 features an active-high Enable input (EN) pin that allows on/off control of the regulator. The PS1541 bias current reduces to less than microampere when it is shutdown. The Enable input is TTL/CMOS compatible. July 2007 www.picsemi.com © 2007 Power IC. All Rights Reserved. 8 PS1541 PACKAGE INFORMATION July 2007 www.picsemi.com © 2007 Power IC. All Rights Reserved. 9 PS1541 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. July 2007 www.picsemi.com © 2007 Power IC. All Rights Reserved. 10