SMH4814SCR03 datasheet(2/44 Pages) SUMMIT

部件名	SMH4814SCR03

功能描述	Dual Feed Active-ORing Programmable Hot Swap Controller

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制造商	SUMMIT [Summit Microelectronics, Inc.]

网页	http://www.summitmicro.com

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SMH4814

Preliminary Information

Summit Microelectronics, Inc

2080 2.0 07/21/05

2

GENERAL DESCRIPTION

The SMH4814 integrated power controller operates

within a wide supply range, typically –32 to –72 volts,

and generates the signals necessary to drive isolated-

output DC/DC converters.

The device accepts two independent –48V feeds via

input pins FEEDA and FEEDB.

The VGATEA pin

controls the flow of power from FEEDA to the load.

The VGATEB pin controls the flow of power from

FEEDB to the load.

The SMH4814 continuously monitors the voltage on

FEEDA and FEEDB. The supply arbitration block in

Figure 2 selects which pin drives power to the device

based on the voltage level on each pin and the

acceptable voltage range. Once the FEEDA or FEEDB

is

selected

the

SMH4814

asserts

the

corresponding VGATE pin. The assertion of this pin

turns on the external low-RDSON FETs to supply power

to the load.

Start-up Procedure

The general start-up procedure is as follows:

1. A physical connection must be made with the

chassis to discharge any electrostatic voltage

potentials when a typical add-in board is inserted

into the powered backplane.

2. The board then contacts the long pins on the

backplane that provide power and ground.

3. As soon as power is applied the device starts up,

but it does not immediately apply power to the

output load.

4. Under-voltage and over-voltage circuits inside the

controller verify that the input voltage is within a

user-specified range.

5. The SMH4814 senses the PD1 and PD0 pin

detection signals to indicate the card is seated

properly.

These requirements must be met for a Pin Detect

Delay period of tPDD. Once this time has elapsed the

hot-swap controller enables VGATE_HS to turn on the

external power MOSFET switch.

The VGATE_HS output is current limited to IVGATE,

allowing the slew rate to be easily modified using

external passive components. During the controlled

turn-on period the VDS of the MOSFET is monitored by

the DRAIN SENSE input. When DRAIN SENSE drops

below 2.5V, and VGATE_HS rises above V12 – VGT,

the SMH4814 asserts the PUPA through PUPD power

good outputs to enable the DC/DC controllers.

Steady-state operation is maintained as long as all

conditions are normal. Any of the following events

may cause the device to disable the DC/DC controllers

by shutting down the power MOSFETs:

An under-voltage or over-voltage condition on the

host power supply.

A failure of the power MOSFET sensed via the

DRAIN SENSE pin.

The PD1/PD0 pin detect signals becoming invalid.

The master enable (EN/TS) falls below 2.5V.

Any of the FB inputs driven low by events on the

secondary side of the DC/DC controllers.

The occurrence of an overcurrent.

The SMH4814 may be configured so that after any of

these events occurs the VGATE output shuts off, and

either latches into an off state or recycles power after

a cooling down period, tCYC.

Powering V12

The SMH4814 contains an internal shunt regulator on

the V12 pin that prevents the voltage from exceeding

12V. It is necessary to use a dropping resistor (RD)

between the host power supply and the V12 pin in

order to limit current into the device and prevent

possible damage. The dropping resistor allows the

device to operate across a wide range of system

supply voltages, typically –32 V to –72V, and also

helps protect the device against common-mode power

surges. Refer to the Applications Section for help on

calculating the RD resistance value.

类似零件编号 - SMH4814SCR03

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