LT1950
Single Switch PWM
Controller with Auxiliary
Boost Converter
DESCRIPTIO
The LT
廬
1950 is a wide input range, forward, boost, flyback
and SEPIC controller that drives an N-channel power
MOSFET with few external components required.
A resistor programmable duty cycle clamp can be used to
generate a volt-second clamp for forward converter appli-
cations. An internal boost switcher is available for creating
a separate supply for the output gate driver, allowing 10V
gate drive from input voltages as low as 3V. The LT1950鈥檚
operating frequency can be set with an external resistor
over a 100kHz to 500kHz range and a SYNC pin allows the
part to be synchronized to an external clock. Additional
programmability exists for leading edge blanking and
slope compensation.
A fast current sense comparator achieves 60ns current
sense delay and the error amplifier is a true voltage mode
error amplifier, allowing a wide range of compensation
networks. An accurate shutdown pin with programmable
hysteresis is available for undervoltage lockout and shut-
down. The LT1950 is available in a small 16-Pin SSOP
package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
FEATURES
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Wide Input Range: 3V to 25V
Programmable Volt-Second Clamp
Output Power Levels from 25W to 500W
Auxiliary Boost Converter Provides 10V Gate Drive
from V
IN
as Low as 3V
Programmable Operating Frequency (100kHz to
500kHz) with One External Resistor
Programmable Slope Compensation
Programmable Leading Edge Blanking
鹵2%
Internal 1.23V Reference
Accurate Shutdown Pin Threshold with
Programmable Hysteresis
60ns Current Sense Delay
2.5V Auxiliary Reference Output
Synchronizable to an External Clock up to 1.5 鈥?f
OSC
Current Mode Control
Small 16-Pin SSOP Package
APPLICATIO S
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Telecom Power Supplies
Automotive Power Supplies
Portable Electronic Equipment
Isolated and Nonisolated DC/DC Converters
TYPICAL APPLICATIO
36V to 72V DC to 26V/5A (Single Switch) Forward Converter
10V
BIAS
SLOPE
2.5V
0.1碌F
249k
V
REF
BOOST
R
OSC
V
IN
V
IN2
V
SEC
SHDN
1碌F
18k
Si7450
470k
47碌F
V
IN
MBRB20200
47碌H
V
OUT
26V
5A
EFFICIENCY (%)
LT1950
BLANK
SYNC
GND
FB
GATE
I
SENSE
PGND
COMP
4.7k
0.015鈩?/div>
4.99k
0.022碌F
100k
1950 TA01a
U
95
90
85
80
75
U
U
Efficiency vs Load Current
V
IN
= 36V
V
IN
= 48V
V
IN
= 72V
70
0.5
1.5
3.5
4.5
2.5
LOAD CURRENT (A)
5.5
1950 TA01b
sn1950 1950fs
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