LT4356 Linear Technology Corporation, LT4356 Datasheet - Page 13

• Manufacturer Part Number: LT4356
• Description: Overvoltage Protection Regulator And Inrush Limiter
• Manufacturer: Linear Technology Corporation

APPLICATIONS INFORMATION
Supply Transient Protection
The LT4356-1 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
SMAJ58CA
Figure 7. Overvoltage Regulator with N-Channel MOSFET
Reverse Input Protection
Figure 8. Overvoltage Regulator with P-Channel MOSFET
Reverse Input Protection
SMAJ58CA
12V
V
D2*
IN
12V
0.1μF
V
D2*
IN
C2
0.1μF
*DIODES INC.
*DIODES INC.
C2
10Ω
R6
10mΩ
11
12
R
6
7
SNS
10mΩ
11
12
R
V
SHDN
A
IN
6
7
SNS
SNS
CC
OUT
+
V
SHDN
A
IN
5
SNS
CC
OUT
+
5
1N4148
Si4435
D1
Q2
GND
R6
10k
10
2N3904
1N5245
LT4356DE-1
GND
Q3
15V
10
IRLR2908
LT4356DE-1
D1
R7
10k
TMR
Q2
1
R4
10Ω
C
0.1μF
TMR
TMR
IRLR2908
1
GATE
Q1
R5
1M
C
0.1μF
4
IRLR2908
TMR
R3
10Ω
GATE
Q1
OUT
43561 F08
4
FLT
R3
10Ω
EN
FB
3
OUT
43561 F07
2
8
9
FLT
EN
FB
3
2
8
9
R1
59k
R2
4.99k
V
12V, 3A
CLAMPED AT 16V
OUT
R1
59k
R2
4.99k
V
12V, 3A
CLAMPED
AT 16V
OUT
power trace parasitic inductance should be minimized by
using wide traces. A snubber circuit dampens the ringing
associated with voltage spikes. A 10Ω resistor in series with
a 0.1μF capacitor between V
up to 1μH feed point inductance. A surge suppressor, D2,
in Figure 9, at the input will clamp the voltage spikes.
A 1μF ceramic capacitor, C
clamp the voltage spike if the input voltage rise time is
faster than 10μs. A total bulk capacitance in the range of
22μF is also required close to the V
converter, if not already provided by the 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
SMAJ58A
Figure 9. Overvoltage Regulator with Low Battery Detection
V
UNDERVOLTAGE
IN
D2
383k
100k
R4
R5
0.1μF
100V
C2
CC
12
11
6
7
and GND traces.
R6
10Ω
V
SHDN
IN
A
CC
OUT
+
10mΩ
R
SNS
GND
LT4356DE-1
SNS
10
5
IRLR2908
GATE
L
Q1
TMR
, is needed at the OUT pin to
CC
4
R3
10Ω
1
C
47nF
TMR
and GND is effective with
SNS
OUT
43561 F09
FLT
3
EN
FB
in Figure 9) is recom-
2
9
8
CC
R1
59k
R2
4.99k
FAULT
pin of the DC/DC
LT4356-1
SHDN
CONVERTER
DC-DC
V
CC
GND
13
C
1μF
CERAMIC
43561fd
L