SMH4811A(2000) 데이터 시트보기 (PDF) - Summit Microelectronics

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SMH4811A
(Rev.:2000)

Distributed Power Hot-Swap Controller

Summit Microelectronics 

SMH4811A

PIN DESCRIPTIONS

VDD

VDD is the positive supply connection. An internal shunt

regulator connected between VDD and VSS develops ap-

proximately 12V that supplies the SMH4804. A resistor

must be placed in series with the VDD pin to limit the

regulator current (RD in the application illustrations).

VSS

VSS is connected to the negative side of the supply.

5VREF

5VREF is a precision 5V output reference voltage that may

be use to expand the logic-input functions on the

SMH4804. The reference output is with respect to VSS.

2.5VREF

2.5VREF is a precision 2.5V output reference voltage that

may be used to expand the logic-input functions on the

SMH4804. The reference output is with respect to VSS.

DRAIN SENSE

The DRAIN SENSE input monitors the voltage at the drain

of the external power MOSFET switch with respect to VSS.

When the MOSFET is turned on the DRAIN SENSE input

will be driven low and will be used as one of the enable

conditions for the PG outputs. This will prevent any

premature activation of the PG outputs.

EN/TS

The Enable/Temperature Sense input is the master en-

able input. When EN/TS is low VGATE, and the PG

outputs are off. As the name suggests, the EN/TS input

may be used as a master enable by a host system, or

alternatively for circuit over-temperature protection using

an external thermistor.

PD1#, PD2#

The PD1# and PD2# inputs are Pin Detect or auxiliary

enable inputs that can optionally be employed by the

designer. These are active low inputs and both inputs

must be at VSS before either VGATE or the PG outputs can

be enabled.

In applications where multi-length connector pins are used

the Pin Detect inputs should be tied to the shortest pins.

On the mating connector side the pins opposite should be

tied directly to VSS. Alternatively, either one or both of the

Pin Detect inputs can be tied to card injector handle

switches, ensuring no power sequencing will occur until

the card is properly seated.

OV and UV

The Under-Voltage and Over-Voltage input pins monitor

the supply voltage for the SMH4804 and the downstream

circuits. Both inputs have a default 2.5V threshold on their

respective comparators. If UV is less than 2.5V, or if OV

is greater than 2.5V, VGATE will be disabled.

CBSENSE

The circuit breaker sense input is used to detect over-

current conditions in the load connected to the power

MOSFET. A low value sense resistor (RS) is tied in series

with the Power MOSFET; one end of the resistor is tied to

VSS and the other end is tied to the Power MOSFET and

the CBSENSE input. A voltage drop of greater than 50mV

(or greater than tCBD) across the resistor will trip the circuit

breaker. A programmable “quick-trip” sense point is also

available. If the CBSENSE input transitions above the

threshold the circuit breaker will immediately trip.

CBFAULT#

CBFAULT# is an open-drain, active-low output that indi-

cates the circuit breaker status. When an over current

condition is detected CBFAULT# is driven low.

Programmable internal hysteresis is provided on the Un-

der-Voltage input and is adjusted in increments of 62.5mV.

The adjustment is made in register R7.

VGATE

The VGATE output activates an external power MOSFET

switch. It is a constant current source (100µA typical)

allowing easy programming of the MOSFET turn on slew

rate.

ENPG

The ENPG input controls the PG# output. When ENPG is

pulled low the PG# output is immediately placed in a high

impedance state. If ENPGA is driven high then the PG#

output will immediately be driven low.

PG#

PG# is an open-drain, active-low output with no internal

pull-up. It is enabled after VGATE is enabled and voltage

across the load is within spec. PG# can be used to switch

a load or enable a DC/DC converter.

SUMMIT MICROELECTRONICS, Inc.

2044 4.1 8/1/00

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