Datasheet

LTC4252-1/LTC4252-2
LTC4252A-1/LTC4252A-2
33
425212fe
For more information www.linear.com/LTC4252-1
applicaTions inForMaTion
The internal fault latches of the LTC4252 are disabled as
the TIMER pin is always held low by the SS voltage when
Q2 and Q3 are in analog current limit.
If both power supplies from channel A and B are exactly
equal, then equal load current will flow through Q2 and
Q3 to the load module via the Hot Swap section.
If the channel A supply is greater than the channel B by
more than 100mV, the sense voltage will rise above the
fast comparator trip threshold of 200mV, the GATE will
be pulled low and Q2 is turned off. The GATE ramps up
and regulates Q2 when the channel A supply is equal to
the channel B supply. Likewise, if the channel B supply is
greater than channel A by more than 100mV, it trips the
fast comparator and GATE is pulled low and Q3 is turned
off. The GATE ramps up and regulates Q3 when the channel
B supply is equal to the channel A supply.
Resistors R4, R7 and external FETs Q4 and Q7 limit the
current flow into Q5 and Q8 during their respective sup-
ply source short. When the channel A supply is shorted
to the –48V RTN (or GND), large current flows into Q4
momentarily and creates a voltage drop across R4, which
in turn reduces the gate-to-source voltage of Q4, limiting
the current flow. The sense voltage is lifted up and causes
the fast comparator of LTC4252 to trip and pull the GATE
low instantly. The channel A supply short will not cause
Q3 of channel B diode-OR circuit to turn off.
Similarly, when the channel B supply is shorted to the
–48V RTN (or GND), large current flows into Q7 momen-
tarily and creates a voltage drop across R7, which in turn
reduces the gate-to-source voltage of Q7, thus limiting
the current flow. The increase in sense voltage will trip
the fast comparator of LTC4252 and pull the GATE low
instantly. The channel B supply short will not cause Q2
of channel A diode-OR circuit to turn off. The load short
at the output of Q1 is protected by the Hot Swap section.
Using an EMI Filter Module
Many applications place an EMI filter module in the power
path to prevent switching noise of the module from being
injected back onto the power supply. A typical application
using the Lucent FLTR100V10 filter module is shown in
Figure 23. When using a filter, an optoisolator is required
to prevent common mode transients from destroying the
PWRGD and ON/OFF pins.
425212 F23
UV
OV
V
EE
V
IN
SENSESS
TIMER GATE
PWRGD
DRAIN
LTC4252A-1
R1
392k
1%
R2
30.1k
1%
C
T
0.68µF
C
SS
68nF
C
C
10nF
–48V
R
S
0.02Ω
Q1
IRF530S
1N4003
V
IN
+
C2
0.1µF
100V
V
IN
–
V
OUT
+
V
OUT
–
R
C
10Ω
R3
5.1k
R
IN
3× 1.8k
1/4W
1
9
8
10
3
2
7
6
4
5
C1
10nF
C
IN
1µF
–48RTN
(SHORT PIN)
–48RTN
(LONG PIN)
R
D
1M
*MOC207
*
+
C3
0.1µF
100V
C4
100µF
100V
C6
100µF
16V
C5
0.1µF
100V
LUCENT
FLTR100V10
CASE
V
IN
+
ON/OFF
V
IN
–
V
OUT
+
1
2
4 5
6
7
8
9
5V
3
SENSE
+
SENSE
–
TRIM
V
OUT
–
LUCENT
JW050A1-E
CASE
+
D
IN
†
DDZ13B
**
**DIODES, INC
†
RECOMMENDED FOR HARSH ENVIRONMENTS
Figure 23. Typical Application Using a Filter Module