Calculate the MOSFET thermal resistance required

for a short to ground.

Figure 17 to select a duty cycle. The duty cycle

Layout Considerations

To take full tracking advantage of the switch response time

to an output fault condition, it is important to keep all traces

as short as possible and to maximize the high-current

trace dimensions to reduce the effect of undesirable para-

sitic inductance. Place the MAX4271/MAX4272/MAX4273

close to the card’s connector. Use a ground plane to mini-

mize impedance and inductance. Minimize the current-

sense resistor trace length (<10mm), and ensure accurate

current sensing with Kelvin connections (Figure 18).

When the output is short circuited, the voltage drop

across the external MOSFET becomes large. Hence,

the power dissipation across the switch increases, as

does the die temperature. An efficient way to achieve

good power dissipation on a surface-mount package is

to lay out two copper pads directly under the MOSFET

package on both sides of the board. Connect the two

pads to the ground plane through vias, and use

enlarged copper mounting pads on the top side of the

board.

3V to 12V Current-Limiting Hot Swap Controllers

with Autoretry, DualSpeed/BiLevel Fault Protection

______________________________________________________________________________________

23

CTIM

CSPD

GND

1

2

8

7

ON

STAT

SENSE

GATE

IN

SO

TOP VIEW

3

4

6

5

MAX4271

MAX4272

Pin Configurations

16

15

14

13

12

11

10

9

1

2

3

4

5

6

7

8

RTH

OUTC

INC

REF

ON

STAT

CTIM

CSPD

CTON

MAX4273

QSOP/SO

AUXVCC

IN

CEXT

SENSE

GATE

LLMON

GND

Figure 18. Kelvin Connections for the Current-Sense Resistors

SENSE RESISTOR

HIGH-CURRENT PATH

MAX4271

MAX4272

MAX4273