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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. 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.
APPLICATIONS
TYPICAL APPLICATION CIRCUIT
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PS1541
PIN CONFIGURATION
PIN CONFIGURATION
Name SW GND FB EN NC IN 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.
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PS1541
BLOCK DIAGRAM
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PS1541
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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PS1541
ELECTRICAL CHARACTERISTICS
( Vin = 2.5V, TA = +25C, unless otherwise noted. Typical values are at TA = +25C.) Symbol Vin UVLO Vout-max Iq Parameter Operating Input Voltage Under Voltage Lock-out Maximum Output Voltage 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 VFB=1.25V 1.05 Test Condition Min 2.5 Vin going Lo. 2.15 2.2 25 No Switching (Vin=5V, VFB= 1.25V) Switching FB=0 VEN =0 620 93 1.1 7 0.8 Vin=3 Turn ON Turn OFF VEN =0, 5V 2.3 0.95 0.35 1 145 1.15 135 260 Typ Max 5.5 2.4 Units V V V A
510
750 1
A A KHz % V nA A V V A C
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PS1541
TYPICAL OPERATING CHARACTERISTICS
Efficiency vs Load Current
FB Voltage vs Temperature
1.09 FB Voltage(V) 1.085 1.08 1.075 1.07
100 90 Eff (%) 80 70 60 50 0 50 Load (mA) 100 150 200 Vin=5V, Vout=14V
-40
-20
0
20 Temp (C)
40
60
80
Frquency vs Temperature
750 Frequency (K H z) 700
Duty Cycle (%) 94.5 94 93.5 93 92.5 92 91.5
Temperature vs Duty Cycle
650 600 550 500 -50 0 50 Temperature (C) 100 150
91 -40 -10 20 50 80 110 140 Temperature (C)
Temperature vs Supply Current
145 Supply Current (uA) 140 135 130 125 120 115 -40 -10 20 50 80 110 140 Temperature (C)
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PS1541
TYPICAL OPERATING CHARACTERISTICS (Continued)
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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 60s giving a total soft start time of 240s.
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= +145C, 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 PS1541 in the event of a fault condition. For continual operation, do not exceed the absolute maximum junction temperature rating of Tj = +125C.
Setting the Output Voltage Set the output voltage by selecting the resistive voltage divider ratio. Use 12k 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.
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PS1541
PACKAGE INFORMATION
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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.
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