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

FEATURES
■ _{Synchronous Rectifier Control for High Efficiency}
■ _{Programmable Volt-Second Clamp}
■ _{Output Power Levels from 25W to 500W}
■ _{Low Current Start-Up}
■ _{True PWM Soft-Start}
■ _{Low Stress Short Circuit Protection}
■ _{Precision 100mV Current Limit Threshold}
■ _{Adjustable Delay for Synchronous Timing}
■ _{Accurate Shutdown Threshold with Programmable}
Hysteresis
■ _{Programmable Slope Compensation}
■ _{Programmable Leading Edge Blanking}
■ _{Programmable Frequency (100kHz to 500kHz)}
■ _{Synchronizable to an External Clock up to 1.5 • fOSC}
■ _{Internal 1.23V Reference}
■ _{2.5V External Reference}
■ _{Current Mode Control}
■ _{Small 16-Pin SSOP Package}
U
APPLICATIO S
■ _{Telecommunications Power Supplies}
■ _{Industrial and Distributed Power}
■ _{Isolated and Non-Isolated DC/DC Converters}
LT1952
Single Switch Synchronous
Forward Controller
DESCRIPTIO
The LT^®1952 is a current mode PWM controller optimized
to control the forward converter topology, using one
primary MOSFET. The LT1952 provides 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, trans-
former and rectifier utilization. The LT1952 includes
soft-start for controlled exit from shutdown, overcurrent
conditions and undervoltage lockout. A precision 100mV
current limit threshold, independent of duty cycle, com-
bines with soft-start to provide hiccup short circuit protec-
tion. Micropower start-up allows the LT1952 to be effi-
ciently started from high input voltages. Programmable
slope compensation and leading edge blanking allow
optimization of loop bandwidth with a wide range of
inductors and MOSFETs. The LT1952 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 is available in a small 16-pin SSOP
package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATIO
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
I_SENSE
Si7450
0.005Ω
Si7370
×2
100k
SD_V_SEC
LTC3900
13k
FB
SYNC
SOUT
FG CG
T2
SYNC
GND
R_OSC
220pF
560Ω
L1
PA1494.242
V_OUT
12V
20A
PH4840
×2
47µF
16V
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
1952f
1