LT4356CS-3 View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LT4356CS-3' PDF : 24 Pages View PDF
LT4356-3
APPLICATIONS INFORMATION
The LT4356-3 does not need extra compensation compo-
nents at the GATE pin for stability during an overvoltage
or overcurrent event. However, with fast, high voltage
transient steps at the input, a gate capacitor, C1, to ground
is needed to prevent turn-on of the N-channel MOSFET.
The extra gate capacitance slows down the turn off time
during fault conditions and may allow excessive current
during an output short event. An extra resistor, R1, in series
with the gate capacitor can improve the turn off time. A
diode, D1, should be placed across R1 with the cathode
connected to C1 as shown in Figure 5.
Q1
D1
IN4148W
R3
R1
C1
GATE
LT4356-3
43563 F05
Figure 5
Auxiliary Amplifier
An uncommitted amplifier is included in the LT4356-3 to
provide flexibility in the system design. With the negative
input connected internally to the 1.25V reference, the
amplifier can be connected as a level detect comparator
with external hysteresis. The open collector output pin,
AOUT, is capable of driving an opto or LED. It can also
interface with the system via a pull-up resistor to a supply
voltage up to 80V.
The amplifier can also be configured as a low dropout
linear regulator controller. With an external PNP transistor,
such as 2N2905A, it can supply up to 100mA of current
with only a few hundred mV of dropout voltage. Current
limit can be easily included by adding two diodes and one
resistor (Figure 6). The amplifier is turned off when the
LT4356-3 is shut down.
14
INPUT
RLIM 2N2905A OR
*4.7Ω
BCP53
R6
100k
D1*
BAV99
11
LT4356DE-3
AOUT
IN+ 12
R4
249k
R5
249k
2.5V OUTPUT
≈ 150mA MAX
10µF
47nF
* OPTIONAL FOR
CURRENT LIMIT
VOUT
=
1.25
R4 + R5
R5
ILIM ≈
0.7
RLIM
43563 F06
Figure 6. Auxiliary LDO Output with Optional Current Limit
Reverse Input Protection
A blocking diode is commonly employed when reverse
input potential is possible, such as in automotive applica-
tions. This diode causes extra power loss, generates heat,
and reduces the available supply voltage range. During
cold crank, the extra voltage drop across the diode is
particularly undesirable.
The LT4356-3 is designed to withstand reverse voltage
without damage to itself or the load. The VCC, SNS, and
SHDN pins can withstand up to 60V of DC voltage below
the GND potential. Back-to-back MOSFETs must be used
to eliminate the current path through their body diodes
(Figure 7). Figure 8 shows the approach with a P-Channel
MOSFET in place of Q2.
VIN
12V
D2*
SMAJ58CA
RSNS
10mΩ
Q2
Q1
IRLR2908 IRLR2908
Q3
2N3904
R4 R5
10Ω 1M
R3
10Ω
D1
R7
1N4148 10k
5
SNS
6 VCC
4
GATE
3
OUT
FB 2
VOUT
12V, 3A
CLAMPED
AT 16V
R1
59k
R2
4.99k
7 SHDN
11 AOUT
12 IN+
*DIODES INC.
LT4356DE-3
GND
10
TMR
1
CTMR
0.1µF
FLT 8
EN 9
43563 F07
Figure 7. Overvoltage Regulator with N-channel MOSFET
Reverse Input Protection
43563fb
Share Link: 
