LT1952
1
1952f
APPLICATIO S
U
TYPICAL APPLICATIO
U
DESCRIPTIO
U
FEATURES
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.
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Telecommunications Power Supplies
■
Industrial and Distributed Power
■
Isolated and Non-Isolated DC/DC Converters
, LTC and LT are registered trademarks of Linear Technology Corporation.
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Synchronous Rectifier Control for High Efficiency
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Programmable Volt-Second Clamp
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Output Power Levels from 25W to 500W
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Low Current Start-Up
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True PWM Soft-Start
■
Low Stress Short Circuit Protection
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Precision 100mV Current Limit Threshold
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Adjustable Delay for Synchronous Timing
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Accurate Shutdown Threshold with Programmable
Hysteresis
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Programmable Slope Compensation
■
Programmable Leading Edge Blanking
■
Programmable Frequency (100kHz to 500kHz)
■
Synchronizable to an External Clock up to 1.5 • f
OSC
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Internal 1.23V Reference
■
2.5V External Reference
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Current Mode Control
■
Small 16-Pin SSOP Package
Single Switch Synchronous
Forward Controller
36V to 72V Input, 12V at 20A Semi-Regulated Bus Converter
V
IN
V
IN
T1
PA0905
SUPPLY FROM BIAS
WINDING OF T1
Si7370
×2
PH4840
×2
L1
PA1494.242
47µF
16V
X5R
×2
V
OUT
12V
20A
220pF
560Ω
T2
1952 TA01
V
REF
COMP
SS_MAXDC
SD_V
SEC
FB
SYNC
GND
V
IN
OUT
OC
I
SENSE
SOUT
LT1952
BLANK DELAY
R
OSC
0.1µF
40k
16V
340k
13k
52.3k
40k 40k
PGND
178k
100k
Si7450
0.005Ω
SYNC
FG
CG
LTC3900
10µF
0.1µF
12V Bus Converter
V
OUT
vs V
IN
V
IN
(V)
36
8
V
OUT
(V)
10
16
48
60
66
1952 TA01b
14
12
42
54
72
