LT4356IMS-1 Linear Technology, LT4356IMS-1 Datasheet - Page 15

• Manufacturer Part Number: LT4356IMS-1
• Manufacturer: Linear Technology

Specifications of LT4356IMS-1

• Family Name: LT4356-1
• Package Type: MSOP
• Operating Supply Voltage (min): 4V
• Operating Supply Voltage (max): 80V
• Operating Temperature (min): -40C
• Operating Temperature (max): 85C
• Operating Temperature Classification: Industrial
• Product Depth (mm): 3mm
• Product Height (mm): 0.86mm
• Product Length (mm): 3mm
• Mounting: Surface Mount
• Pin Count: 10
• Lead Free Status / Rohs Status: Not Compliant

APPLICATIONS INFORMATION
The LTC4356 does not need extra compensation compo-
nents at the GATE pin for stability during an overvoltage or
overcurrent event. With transient input voltage step faster
than 5V/μs, a gate capacitor, C1, to ground is needed to
prevent self enhancement 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 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. Another use is to implement undervoltage
lockout, as shown in the typical application “Overvoltage
Regulator with Undervoltage Lockout.” In shutdown, the
auxiliary amplifi er turns off in the LT4356-1 but continues
operating in the LT4356-2.
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).
R3
LT4356S
GATE
Q1
Figure 5
IN4148W
4356 F05
D1
R1
C1
OUT
,
INPUT
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 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.
Figure 7. Overvoltage Regulator with N-channel MOSFET
Reverse Input Protection
100k
SMAJ58CA
Figure 6. Auxiliary LDO Output with Optional Current Limit
R6
12V
V
D2*
IN
*DIODES INC.
BAV99
D1*
LT4356S
*4.7Ω
R
LIM
10mΩ
11
12
R
6
7
SNS
V
SHDN
A
IN
SNS
CC
OUT
+
2N2905A OR
5
1N4148
LT4356-1/LT4356-2
D1
BCP53
A
OUT
4356 F06
IN
11
2N3904
+
GND
Q3
12
IRLR2908
10
R7
10k
LT4356S
Q2
R4
10Ω
TMR
R4
249k
R5
249k
1
1M
R5
C
0.1μF
IRLR2908
TMR
GATE
Q1
4
R3
10Ω
10μF
47nF
OUT
4356 F07
FLT
EN
FB
3
2
8
9
2.5V OUTPUT
≈ 150mA MAX
* OPTIONAL FOR
I
V
CC
LIM
CURRENT LIMIT
OUT
R1
59k
R2
4.99k
, SNS, and
V
12V, 3A
CLAMPED
AT 16V
R
OUT
0.7
1.25
LIM
15
R4 R5
4356fa
R5