PICSEMI PS1541

PS1541
High Efficiency
Step Up DC/DC Converter
FEATURES
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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
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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
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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.
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2
PS1541
BLOCK DIAGRAM
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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
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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
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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
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PS1541
TYPICAL OPERATING CHARACTERISTICS (Continued)
July 2007
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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 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
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PS1541
PACKAGE INFORMATION
July 2007
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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.
July 2007
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