LT4256-1 LINER [Linear Technology], LT4256-1 Datasheet - Page 12

• Manufacturer Part Number: LT4256-1
• Description: Positive High Voltage Hot Swap Controllers
• Manufacturer: LINER [Linear Technology]

APPLICATIO S I FOR ATIO
LT4256-1/LT4256-2
Power Good Detection
The LT4256-1/LT4256-2 includes a comparator for moni-
toring the output voltage. The output voltage is sensed
through the FB pin via an external resistor string. The
comparator’s output (PWRGD) is an open collector ca-
pable of operating from a pull-up as high as 80V.
PWRGD can be used to directly enable/disable a power
module with an active high enable input. Figure 12 shows
how to use PWRGD to control an active low enable input
power module. Signal inversion is accomplished by tran-
sistor Q2 and R10.
12
OFF SIGNAL
U
FROM MPU
GND
V
IN
U
GND
48V
V
(SHORT PIN)
Figure 11. How to Use a Logic Signal to Control LT4256 Turn-On/-Off
IN
VN2222
Q2
0.1 F
(SHORT PIN)
C3
W
0.01 F
Figure 12. Active Low Enable PWRGD Application
C3
SMAT70A
R1
64.9k
R2
8.06k
D2
SMAT70A
C2
33nF
U
R1
64.9k
R2
8.06k
1
5
D2
UV
TIMER
C2
33nF
V
1
5
CC
LT4256-1/
LT4256-2
8
100m
GND
UV
TIMER
R5
4
V
SENSE
PWRGD
CC
LT4256-1/
LT4256-2
0.010
8
GATE
GND
7
R5
FB
4
SENSE
PWRGD
The thresholds for the FB pin are 4.45V (low to high) and
4V (high to low). To calculate the PWRGD thresholds, use
the following equations:
GATE
6
2
3
7
R
20
V
FB
IRF530
THPWRGD
8
Q1
UV = 36V
PWRGD = 40V
k
6
2
3
R7
100
R9
4.02k
R6
10
C1
10nF
IRF530
UV = 36V
PWRGD = 40V
Q1
V
R7
100
R6
10
D1
CMPZ5241B
11V
THPWRGD
R
C1
10nF
36.5k
8
R8
4
D1
CMPZ5241B
11V
V
4 45
R
.
9 200
4256 F11
R4
27k
V
1
Q2
2N3904
R10
27k
R8
36.5k
R9
4.02k
1
4256 F07
• R9, high to low
k
PWRGD
C
R
R
L
R4
51k
V
V
8
9
OUT
LOGIC
, low to high
C
L
V
48V
4A
OUT
425612f
(7)
(8)
(9)