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LTC4211

4211fb

APPLICATIONS INFORMATION

VCC

SENSE

GATE

RESET

TIMER

GND

LTC4211

4211 F20

1N4148

1/2 Si4936DY

0.015Ω

10Ω

Z1*

0.1μF

10nF

16V

10k

10Ω

2.74k

TRIP POINT: 4.06V

1.2k

0.047μF

25V

0.022μF

25V

CLOAD

D3**

VOUT1

3.3V

VOUT2

5V OUT

3.3V OUT

CURRENT LIMIT: 3.3A

10Ω

R10

10k

Z2*

0.1μF

R11

10k

LONG

3.3V

GND

RESET

LONG

**D3 IS OPTIONAL AND HELPS DISCHARGE VOUT1 IF VOUT2 SHORTS

PCB EDGE

CONNECTOR

(MALE)

LONG

BACKPLANE

CONNECTOR

(FEMALE)

SHORT

Z1, Z2: 1SMA10A OR SMAJ10A

* OPTIONAL

VCC

SENSE

LTC4211

COUT

VOUT

OUTPUT

GND

INPUT

GND

4211 F21

15k

GATE

GND

TIMER

CTIMER

RESET

10Ω

VIN

RSENSE

0.007Ω

Si4410DY

36k

RESET

Z1*

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 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 COSS 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 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.

Figure 20. Switching 5V and 3.3V

Figure 21. Placing Transient Protection Devices

Close to the LTC4211’s Input Rail

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