LT1950_15 Datasheet, PDF (1/20 Pages) Linear Technology – Single Switch PWM Controller with Auxiliary Boost Converter

FEATURES
■ _{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}
■ _{±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 • fOSC}
■ _{Current Mode Control}
■ _{Small 16-Pin SSUOP Package}
APPLICATIO S
■ _{Telecom Power Supplies}
■ _{Automotive Power Supplies}
■ _{Portable Electronic Equipment}
■ _{Isolated and Nonisolated DC/DC Converters}
LT1950
Single Switch PWM
Controller with Auxiliary
Boost Converter
DESCRIPTIO
The LT^®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’s
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.
TYPICAL APPLICATIO
36V to 72V DC to 26V/5A (Single Switch) Forward Converter
2.5V
0.1µF
249k
4.99k
SLOPE
V_IN
V_REF
V_IN2
BOOST V_SEC
R_OSC
SHDN
LT1950
BLANK GATE
SYNC
GND
I_SENSE
PGND
FB
COMP
10V_BIAS
V_IN
MBRB20200 47µH
470k
1µF _18k
PA0581
Si7450
47µF
0.015Ω
4.7k
0.022µF ^100k
1950 TA01a
V_OUT
26V
5A
Efficiency vs Load Current
95
V_IN = 36V
90
V_IN = 48V
V_IN = 72V
85
80
75
70
0.5
1.5 2.5 3.5 4.5 5.5
LOAD CURRENT (A)
1950 TA01b 1950fa
1