LTC4211 LINER [Linear Technology], LTC4211 Datasheet - Page 28

• Manufacturer Part Number: LTC4211
• Description: Hot Swap Controller with Multifunction Current Control
• Manufacturer: LINER [Linear Technology]

LTC4211
APPLICATIO S I FOR ATIO
voltage side of the MOSFET switch. An abrupt connection,
produced by inserting the board into a backplane connec-
tor, resulting in a fast rising edge applied on the supply line
of the LTC4211.
Since there is no bulk capacitance to damp the parasitic
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 para-
sitic 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 1 to 50 ,
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,
transient voltage suppressors and snubber networks are
highly recommended. For applications with lower supply
28
RESET
3.3V
GND
ON
5V
CONNECTOR
BACKPLANE
(FEMALE)
OSS
under bias. The series resistor is a value
CONNECTOR
PCB EDGE
U
(MALE)
LONG
LONG
SHORT
SHORT
LONG
U
R10
10k
Z1*
Z2*
W
R11
10k
R8
10
R9
10
C4
0.1 F
C5
0.1 F
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
U
RESET
ON
TIMER
GND
LTC4211
3.3V OUT
5V OUT
SENSE
GATE
V
CC
FB
8
7
6
5
0.015
voltage such as 5V, usually a snubber is adequate to
reduce the supply ringing. Although, the need of a tran-
sient voltage suppressor arises for inductive and high
current application. Note that in all LTC4211 5V applica-
tions schematics, transient suppressor and snubber net-
works have been added for protection. The transient
suppressor is optional and a simple short-circuit test can
be performed to determine the need of it. 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 schematically in Figure 21, and
a recommended layout of the transient protection devices
around the LTC4211 is shown in Figure 22.
5%
R2
**D3 IS OPTIONAL AND HELPS DISCHARGE V
INPUT
Z1*
GND
V
5V
IN
1N4148
Figure 21. Placing Transient Protection Devices
Close to the LTC4211’s Input Rail
D2
0.1 F
1/2 Si4936DY
10
C
X
R
Q1
X
C3
0.047 F
25V
R3
10
5%
R1
10k
5%
1N4148
GND
V
CC
D1
1M
5%
R6
8
4
R
0.007
SENSE
1/2 Si4936DY
SENSE
LTC4211
TIMER
Q2
7
3
R7
10
5%
C
Z1 = 1SMA10A OR SMAJ10A
* OPTIONAL
C2
0.022 F
25V
TIMER
Si4410DY
RESET
GATE
OUT1
Q1
ON
FB
D3**
6
IF V
R4
2.74k
1%
R5
1.2k
1%
5
1
2
+
+
TRIP POINT: 4.06V
OUT2
RESET
ON
C
C
SHORTS
LOAD
LOAD
R1
36k
R2
15k
4211 F20
+
V
3.3V
2A
V
5V
2A
OUT1
OUT2
V
5V
5A
OUTPUT
GND
C
OUT
OUT
4211 F21
4211f