Applications Information

Component Selection

External MOSFETs

Select the external N-channel MOSFETs according to

the application’s current requirement. Limit switch power

enough to have a minimum voltage drop at full load.

undervoltage fault at full load. Determine the MOSFET’s

power rating requirement to accommodate a short-cir-

cuit condition on the board during startup (see the

External MOSFET Thermal Considerations section).

Table 3 lists MOSFET and sense resistor manufacturers.

Sense Resistors

The overcurrent sense voltage threshold on the +3.3V

output is 46mV and 31mV on the +5V output. Choose a

sense resistor using the following equation:

Choose the sense resistors’ power rating to accommo-

date the overload current:

Additional External Gate Capacitance

Connecting an external capacitance from the gates of

the external MOSFETs to GND slows the turn on of the

+5V and +3.3V supplies.

Dual PCI 2.2 Hot-Swap Controllers

16

______________________________________________________________________________________

ENABLE_+12VIN

STARTUP_+12VIN

OC_3.3VAUXO_

UV_3.3VAUXO_

RESET

RESET

RESET

DQ

V

Q

POSITIVE EDGE

TRIGGERED D FLIP-FLOP,

RESET IS ACTIVE LOW

OC_3.3VO_

OC_5VO_

OC_+12VO_

OC_-12VO_

UV_3.3VO_

UV_5VO_

UV_+12VO_

POSITIVE EDGE TRIGGERED D FLIP-FLOP,

RESET IS ACTIVE LOW

HIGH = MAIN SUPPLIES

ARE TURNED OFF

MAIN OFF

AUX OFF

HIGH = AUX SUPPLY

TURNED ON

ENABLE_3.3VAUXIN

STARTUP_3.3VAUXIN

V = INTERNAL SUPPLY LOGIC

GENERATED BY THE 12VIN OR THE

3.3VAUXIN, WHICHEVER IS HIGHER

RESET

DQ

V

Q

SEE TABLE 2 FOR EXPLANATION OF SIGNALS.

Figure 4. Main and Auxiliary Supply Shutdown Control Logic for MAX5916