LTC4211
29
4211fc
For more information www.linear.com/LTC4211
APPLICATIONS INFORMATION
1
2
3
4
8
7
6
5
V
CC
SENSE
GATE
FB
RESET
ON
TIMER
GND
LTC4211
4211 F20
D1
1N4148
D2
1N4148
Q1
1/2 Si4936DY
Q2
1/2 Si4936DY
R2
0.015Ω
5%
R3
10Ω
5%
R8
10Ω
Z1*
C4
0.1µF
C1
10nF
16V
R1
10k
5%
R6
1M
5%
R7
10Ω
5%
R4
2.74k
1%
TRIP POINT: 4.06V
R5
1.2k
1%
C3
0.047µF
25V
C2
0.022µF
25V
C
LOAD
C
LOAD
D3**
V
OUT1
3.3V
2A
V
OUT2
5V
2A
5V OUT
3.3V OUT
CURRENT LIMIT: 3.3A
+
+
R9
10Ω
R10
10k
10k
Z2*
C5
0.1µF
R11
10k
LONG
3.3V
GND
RESET
LONG
**D3 IS OPTIONAL AND HELPS DISCHARGE V
OUT1
IF V
OUT2
SHORTS
PCB EDGE
CONNECTOR
(MALE)
LONG
BACKPLANE
CONNECTOR
(FEMALE)
5V
SHORT
SHORT
ON
Z1, Z2: 1SMA10A OR SMAJ10A
* OPTIONAL
+
V
CC
SENSE
LTC4211
8
34
7 6
C
OUT
V
OUT
5V
5A
OUTPUT
GND
INPUT
GND
4211 F21
5
1
2
R2
15k
GATE
GND TIMER
C
TIMER
FB
ON ON
RESET
R
X
10Ω
V
IN
5V
R
SENSE
0.007Ω
Q1
Si4410DY
R1
36k
RESET
Z1*
C
X
0.1µF
Z1 = 1SMA10A OR SMAJ10A
* OPTIONAL
inserting the board into a backplane connector, results in a
fast rising edge applied on the supply line of the LTC4211.
Since there is no bulk capacitance to damp the para-
sitic track inductance, supply voltage transients excite
parasitic resonant circuits formed by the power MOSFET
capacitance and the combined parasitic inductance from
the wiring harness, the backplane and the cir
cuit board
traces.
I
n these applications, there are two methods that should
be applied together for eliminating these supply voltage
transients: using transient voltage suppressor to clip the
transient to a safe level and snubber networks. Snubber
networks are series RC networks whose time constants are
experimentally determined based on the board’s parasitic
resonance circuits. As a starting point, the capacitors in
these networks are chosen to be 10× to 100× the power
MOSFET’s C
OSS
under bias. The series resistor is a value
determined experimentally and ranges from 1Ω to 50Ω,
depending on the parasitic resonance circuit. For applica
-
tions with supply voltages of 12V or higher the ringing
and overshoot during hot-swapping or when the output is
short-circuited can easily exceed the absolute maximum
specification of the LTC4211. To reduce the danger, tran-
sient voltage suppressors and snubber networks are highly
recommended. For applications with lower supply voltages
such as
5V, usually a snubber is adequate to reduce the
supply ringing, although a transient voltage suppressor
may be required for inductive and high current applications.
Note that in all LTC4211 5V applications schematics, tran
-
sient suppressor and snubber networks have been added
for protection. The transient suppressor is optional and a
simple short-circuit test can be per
formed to determine
if it is necessary. These protection networks should be
mounted very close to the LTC4211’s supply input rail
using short lead lengths to minimize lead inductance.
This is shown in Figure 21, and a recommended layout
of the transient protection devices around the LTC4211
is shown in Figure 22.
Figure 20. Switching 5V and 3.3V
Figure 21. Placing Transient Protection Devices
Close to the LTC4211’s Input Rail
