SMH4811A Ver la hoja de datos (PDF) - Summit Microelectronics

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SMH4811A

Distributed Power Hot-Swap Controller

Summit Microelectronics 

SMH4811A

Preliminary

Under-/Over-Voltage Filtering

The SMH4811A may also be configured so that an out of

tolerance condition on UV/OV will not shut off the output

immediately. Instead, a filter delay may be inserted so that

only sustained under-voltage or over-voltage conditions

will shut off the output. When the UV/OV filter option is

enabled an out of tolerance condition on UV or OV for

longer than the filter delay time, tUOFLTR, activates the

FAULT# output, and the VGATE and PG outputs will be

latched in the off state. To initiate another power-up

sequence the FAULT# output must first be reset. Refer to

the appropriate section on resetting the FAULT# output.

The Under-/Over-Voltage Filtering feature is disabled in

the default configuration of the device.

Under-Voltage Hysteresis

The Under-Voltage comparator input may be configured

with a programmable level of hysteresis. The compare

level may be set in steps (up to 15) of 62.5mV below 2.5V.

The default under-voltage hysteresis level is set to

62.5mV.

Soft Start Slew Rate Control

Once all of the preconditions for powering up the DC/DC

controller have been met, the SMH4811A provides a

means to soft start the external power FET. It is important

to limit in-rush current to prevent damage to the add-in

card or disruptions to the host power supply. For example,

VDD

UV

OV

PD1# +

PD2#

VGATE

DRAIN

SENSE

CBSENSE

11 ≤ VDD ≤ 13

2.5VREF

tPDD

5V

50mVREF

<tPUVF

VDD – VGT

VDD

2.5VREF

<tCBD

PG#

ENPG

SUMMIT MICROELECTRONICS, Inc.

Figure 2. Complete Power On Timing Sequence

2044 6.1 2/8/01

2044 Fig02 5.0

7

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