LTC1647 LINER [Linear Technology], LTC1647 Datasheet - Page 29

• Manufacturer Part Number: LTC1647
• Description: Hot Swap Controller
• Manufacturer: LINER [Linear Technology]

APPLICATIONS INFORMATION
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 circuit board
traces.
In 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
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
RESET
3.3V
GND
ON
5V
CONNECTOR
BACKPLANE
(FEMALE)
OSS
under bias. The series resistor is a value
CONNECTOR
PCB EDGE
(MALE)
LONG
LONG
SHORT
SHORT
LONG
R10
10k
Z1*
Z2*
R11
10k
R8
10Ω
R9
10Ω
C4
0.1μF
C5
0.1μF
C1
10nF
16V
Z1, Z2: 1SMA10A OR SMAJ10A
* OPTIONAL
Figure 20. Switching 5V and 3.3V
10k
CURRENT LIMIT: 3.3A
1
2
3
4
RESET
ON
TIMER
GND
LTC4211
3.3V OUT
5V OUT
SENSE
GATE
V
CC
FB
8
7
6
5
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 performed 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.
Z1*
INPUT
0.015Ω
GND
5%
R2
V
5V
IN
**D3 IS OPTIONAL AND HELPS DISCHARGE V
0.1μF
Figure 21. Placing Transient Protection Devices
Close to the LTC4211’s Input Rail
1N4148
C
10Ω
X
R
D2
X
1/2 Si4936DY
Q1
C3
0.047μF
25V
R3
10Ω
5%
R1
10k
5%
GND
V
CC
8
4
0.007Ω
R
1N4148
SENSE
D1
1M
5%
R6
LTC4211
SENSE
TIMER
1/2 Si4936DY
7
3
Z1 = 1SMA10A OR SMAJ10A
* OPTIONAL
C
Q2
TIMER
Si4410DY
R7
10Ω
5%
RESET
GATE
C2
0.022μF
25V
Q1
ON
FB
6
OUT1
5
1
2
D3**
RESET
ON
IF V
R4
2.74k
1%
R5
1.2k
1%
LTC4211
+
+
TRIP POINT: 4.06V
OUT2
C
C
SHORTS
R1
36k
R2
15k
LOAD
LOAD
+
29
4211 F20
V
5V
5A
OUTPUT
GND
C
V
3.3V
2A
V
5V
2A
OUT
OUT
OUT1
OUT2
4211 F21
4211fb