LT1952-1 Datasheet, PDF (1/24 Pages) Linear Technology – Single Switch Synchronous Forward Controller

FEATURES
n _{Synchronous Rectifier Control for High Efficiency}
n _{Programmable Volt-Second Clamp}
n _{Output Power Levels from 25W to 500W}
n _{Low Current Start-Up}
(LT1952: 460μA; V_IN On/Off = 14.25V/8.75V)
(LT1952-1: 400μA; V_IN On/Off = 7.75V/6.5V)
n _{True PWM Soft-Start}
n _{Low Stress Short-Circuit Protection}
n _{Precision 107mV Current Limit Threshold}
n _{Adjustable Delay for Synchronous Timing}
n _{Accurate Shutdown Threshold with Programmable}
Hysteresis
n _{Programmable Slope Compensation}
n _{Programmable Leading Edge Blanking}
n _{Programmable Frequency (100kHz to 500kHz)}
n _{Synchronizable to an External Clock up to 1.5 • fOSC}
n _{Internal 1.23V Reference}
n _{2.5V External Reference}
n _{Current Mode Control}
n _{Small 16-Pin SSOP Package}
APPLICATIONS
n _{Telecommunications Power Supplies}
n _{Industrial and Distributed Power}
n _{Isolated and Non Isolated DC/DC Converters}
LT1952/LT1952-1
Single Switch Synchronous
Forward Controller
DESCRIPTION
The LT^®1952/LT1952-1 are current mode PWM controllers
optimized to control the forward converter topology, using
one primary MOSFET. The LT1952/LT1952-1 provide
synchronous rectifier control, resulting in extremely
high efficiency. A programmable Volt-Second clamp
provides a safeguard for transformer reset that prevents
saturation. This allows a single MOSFET on the primary
side to reliably run at greater than 50% duty cycle for high
MOSFET, transformer and rectifier utilization. The devices
include soft-start for controlled exit from shutdown and
undervoltage lockout. A precision 107mV current limit
threshold, independent of duty cycle, combines with soft-
start to provide hiccup short-circuit protection. The LT1952
is optimized for micropower bootstrap start-up from high
input voltages. The LT1952-1 allows start-up from lower
input voltages. Programmable slope compensation and
leading edge blanking allow optimization of loop bandwidth
with a wide range of inductors and MOSFETs. Each device
can be programmed over a 100kHz to 500kHz frequency
range and the part can be synchronized to an external
clock. The error amplifier is a true op amp, allowing a wide
range of compensation networks. The LT1952/LT1952-1
are available in a small 16-pin SSOP package.
L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
TYPICAL APPLICATION
36V to 72V Input, 12V at 20A Semi-Regulated Bus Converter
SUPPLY FROM BIAS
WINDING OF T1
V_IN T1
40k
PA0905
16V
10μF
V_REF
V_IN
52.3k
COMP
V_IN
340k
SS_MAXDC
OUT
LT1952/ OC
LT1952-1
I_SENSE
Si7450
0.005Ω
Si7370
s2
100k
SD_V_SEC
LTC3900
13k
FB
SYNC
SOUT
FG CG
T2
SYNC
L1
PA1494.242
V_OUT
12V
20A
47μF
16V
PH4840
s2
X5R
s2
GND
R_OSC
220pF
560Ω
0.1μF 0.1μF
PGND BLANK DELAY
40k 40k 178k
1952 TA01
12V Bus Converter
V_OUT vs V_IN
16
14
12
10
8
36 42 48 54 60 66 72
V_IN (V)
1952 TA01b
19521fd
1