LT4356CDE-1-PBF LINER [Linear Technology], LT4356CDE-1-PBF Datasheet - Page 12

• Manufacturer Part Number: LT4356CDE-1-PBF
• Description: Overvoltage Protection Regulator and Inrush Limiter
• Manufacturer: LINER [Linear Technology]

APPLICATIONS INFORMATION
LT4356-1
count for circuit tolerances this fi gure should be doubled
to 13.2W
Limiting Inrush Current and GATE Pin Compensation
The LT4356-1 limits the inrush current to any load capaci-
tance by controlling the GATE pin voltage slew rate. An
external capacitor can be connected from GATE to ground
to slow down the inrush current further at the expense of
slower turn-off time.
The LTC4356-1 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.
Auxiliary Amplifi er
An uncommitted amplifi er is included in the LT4356-1 to
provide fl exibility in the system design. With the negative
input connected internally to the 1.25V reference, the am-
plifi er can be connected as a level detect comparator with
external hysteresis. The open collector output pin, A
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.
12
2
s.
R3
LT4356-1
GATE
Q1
Figure 5
IN4148W
43561 F05
D1
R1
C1
OUT
,
The amplifi er can also be confi gured 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).
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 LT4356-1 is designed to withstand reverse voltage
without damage to itself or the load. The V
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.
Shutdown
The LT4356-1 can be shut down to a low current mode
when the voltage at the SHDN pin goes below the shutdown
threshold of 0.6V. The quiescent current drops to 7μA.
The SHDN pin can be pulled up to V
up to 60V without damaging the pin. Leaving the pin open
allows an internal current source to pull it up and turn on
the part while clamping the pin to 2.5V. The leakage cur-
rent at the pin should be limited to no more than 1μA if
no pull up device is used to help turn it on.
Figure 6. Auxiliary LDO Output with Optional Current Limit
INPUT
100k
R6
BAV99
D1*
LT4356DE-1
*4.7Ω
2N2905A OR
BCP53
A
OUT
11
43561 F06
CC
* OPTIONAL FOR
CURRENT LIMIT
OUTPUT
or below GND by
CC
, SNS, and
43561fd