LT1952_15 Datasheet, PDF (1/28 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 and ThinSOT is a trademark 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
40k ^VIN
T1
PA0905
16V
10µF
52.3k
V_REF
V_IN
COMP
V_IN
340k
SS_MAXDC
OUT
LT1952/ OC
LT1952-1
I_SENSE
Si7450
0.005Ω
Si7370
×2
100k
13k
SD_V_SEC
FB
SYNC
SOUT
LTC3900
FG CG
T2
SYNC
GND
R_OSC
220pF
560Ω
L1
PA1494.242
V_OUT
12V
20A
47µF
16V
PH4840
×2
X5R
×2
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
19521fe
1