LT4356-3 Linear Technology Corporation, LT4356-3 Datasheet - Page 16

• Manufacturer Part Number: LT4356-3
• Description: Surge Stopper With Fault Latchoff
• Manufacturer: Linear Technology Corporation

APPLICATIONS INFORMATION
LT4356-3
Shutdown
The LT4356-3 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
current at the pin should be limited to no more than 1μA
if no pull up device is used to help turn it on.
Supply Transient Protection
The LT4356-3 is 100% tested and guaranteed to be safe
from damage with supply voltages up to 80V. Neverthe-
less, voltage transients above 100V may cause permanent
damage. During a short-circuit condition, the large change
in current fl owing through power supply traces and associ-
ated wiring can cause inductive voltage transients which
could exceed 100V. To minimize the voltage transients, the
power trace parasitic inductance should be minimized by
using wide traces. A small surge suppressor, D2, in Figure
9, at the input will clamp the voltage spikes.
16
SMAJ58CA
Figure 8. Overvoltage Regulator with P-Channel MOSFET
Reverse Input Protection
12V
V
D2*
IN
*DIODES INC.
10mΩ
11
12
R
6
7
SNS
V
SHDN
A
IN
SNS
CC
OUT
+
5
Si4435
Q2
GND
R6
10k
10
1N5245
LT4356DE-3
15V
D1
TMR
1
C
0.1μF
TMR
IRLR2908
GATE
Q1
4
R3
10Ω
CC
OUT
43563 F08
FLT
EN
FB
3
or below GND by
2
8
9
R1
59k
R2
4.99k
V
12V, 3A
CLAMPED AT 16V
OUT
A total bulk capacitance of at least 22μF low ESR is required
close to the source pin of MOSFET Q1. In addition, the
bulk capacitance should be at least 10 times larger than
the total ceramic bypassing capacitor on the input of the
DC/DC converter.
Layout Considerations
To achieve accurate current sensing, Kelvin connection
to the current sense resistor (R
mended. The minimum trace width for 1oz copper foil is
0.02" per amp to ensure the trace stays at a reasonable
temperature. 0.03" per amp or wider is recommended.
Note that 1oz copper exhibits a sheet resistance of about
530μΩ/square. Small resistances can cause large errors in
high current applications. Noise immunity will be improved
signifi cantly by locating resistive dividers close to the pins
with short V
Design Example
As a design example, take an application with the follow-
ing specifi cations: V
to 80V, V
detection at 6V, and 1ms of overvoltage early warning
(Figure 9).
Figure 9. Overvoltage Regulator with Low-Battery Detection
UNDERVOLTAGE
383k
100k
R4
R5
OUT
V
IN
SMAJ58A
CC
≤ 16V, current limit (I
D2
and GND traces.
12
11
6
7
V
SHDN
IN
A
CC
OUT
+
CC
10mΩ
R
SNS
GND
LT4356DE-3
= 8V to 14V DC with transient up
SNS
10
5
IRLR2908
GATE
Q1
TMR
4
R3
10Ω
1
C
47nF
SNS
TMR
OUT
43563 F09
FLT
3
EN
FB
LIM
in Figure 9) is recom-
2
9
8
) at 5A, low battery
R1
59k
R2
4.99k
FAULT
*SANYO 25CE22GA
SHDN
CONVERTER
C
22μF
L
*
DC-DC
V
CC
GND
43563f