LT4256-3CGNTR Linear Technology, LT4256-3CGNTR Datasheet - Page 17

• Manufacturer Part Number: LT4256-3CGNTR
• Manufacturer: Linear Technology

Specifications of LT4256-3CGNTR

• Family Name: LT4256-3
• Package Type: SSOP N
• Operating Supply Voltage (min): 10.8V
• Operating Supply Voltage (max): 80V
• Operating Temperature (min): 0C
• Operating Temperature (max): 70C
• Operating Temperature Classification: Commercial
• Product Depth (mm): 3.99mm
• Product Height (mm): 1.5mm
• Mounting: Surface Mount
• Pin Count: 16
• Lead Free Status / RoHS Status: Not Compliant

APPLICATIO S I FOR ATIO
In order to use this feature as designed, a bidirectional
Zener diode is needed for D1. When the LT4256-3 com-
mands the MOSFET off (and a bidirectional Zener is used),
the output discharges very slowly (t
130µA). Several variations can be implemented to dis-
charge the output faster. The recommeded method is
shown in Figure 17 and uses an external PNP transistor,
diode and resistor to discharge the output quickly.
GND
V
48V
CC
U
GND
V
48V
CC
0.01µF
(SHORT PIN)
C3
U
0.1µF
(SHORT PIN)
C3
R1
64.9k
R2
4.02k
R3
4.02k
Figure 16. High dV/dt MOSFET Turn-On Protection Circuit
W
OFF
C2
33nF
R1
64.9k
R2
4.02k
R3
4.02k
D2
SMAT70A
1
2
4
9
Figure 17. Enhanced Output Pull-Down Circuit
= (C
C2
33nF
D2
SMAT70A
UV
OV
OPEN
TIMER
1
2
4
9
V
LOAD
CC
LT4256-3
UV
OV
OPEN
TIMER
16
0.010Ω
GND
R5
V
U
CC
LT4256-3
8
16
0.033Ω
SENSE
PWRGD
RETRY
• V
GND
R5
GATE
V
15
OUT
8
SENSE
PWRGD
FB
OUT
RETRY
GATE
V
15
OUT
13
12
10
7
5
FB
)/
IRF540
13
12
10
7
5
Q1
UV = 36V
OV = 73V
PWRGD = 40V
R7
100Ω
R6
1k
IRF530
UV = 36V
OV = 73V
PWRGD = 40V
The equation to set the nominal discharge current is:
where R
The maximum current equation is:
C1
10nF
Q1
R6
10Ω
R7
100Ω
I
I
1N4148
DISCHG
MAX
C1
10nF
D1
CMPZ5241BS
11V
D3
D1
CMPZ5241BS
11V
PROG
=
R
D3
1N4148W
R
B
=
7000
18k
PROG
R
5000
must be less than 1k.
PROG
Q2
2N4920
R
PROG
(
350
(
R8
36.5k
R9
4.02k
130
4256 F16
µ
A
R9
4.02k
R8
36.5k
µ
)
4256 F17
A
R4
27k
+
)
R4
51k
C
+
L
V
48V
1.2A
OUT
C
L
V
48V
4A
OUT
LT4256-3
17
42563fa
(11)
(12)