SMS66 datasheet(14/26 Pages) SUMMIT

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SMS66

Preliminary Information

Summit Microelectronics, Inc

2070 1.0 7/16/03

The HEALTHY and FAULT outputs of the SMS66 are

active as long as the triggering limit remains in a fault

condition. The RST output also remains active as long

as the triggering limit remains in a fault condition;

however, once the trigger source goes away the RST

will remain active for a reset timeout period (tPRTO).

POWER-OFF SEQUENCING

The SMS66 can be programmed to perform Power-off

sequencing in either the same order or reverse order

of Power-on sequencing.

Power-off sequencing is the same as power-on

sequencing and can be initiated by the PWR_ON/OFF

pin, via I

2C control or triggered by a fault condition on

any of the monitored inputs.

Toggling the

PWR_ON/OFF pin to its inactive state will initiate the

Power-off sequence. To enable software control of

the Power-off sequencing feature, the SMS66 offers

an I

2C command to initiate Power-off sequencing

regardless of the state of the

PWR_ON/OFF pin.

Furthermore, Power-off sequencing can be initiated by

a fault condition on a monitored input.

Once Power-off sequencing begins, the SMS66 will

wait a Power-off delay time (tDPOFF) for any channel in

the last sequence position (reverse order) and then

deactivate the PUP outputs for those channels. The

Power-off delay times are individually programmable

for each channel. The SMS66 will then wait until all

VMX inputs of the channels assigned to that sequence

position are below their programmed OFF thresholds.

At this point, the SMS66 will decrement to the next

sequence position and begin to timeout the Power-off

delay times for the associated channels. This process

continues until all of channels in the sequence have

turned off and are below their OFF thresholds. The

status register reveals that all sequenced channels

have turned off.

The Power-off sequencing mode

ends when all sequenced supplies are below their

OFF thresholds.

The programmable sequence termination timer can be

used to protect against a stalled Power-off sequence.

This timer resets itself at the beginning of each

sequence position.

All channels in the sequence

position must go below their OFF threshold before the

sequence termination timer times out (tSTT) or the

sequence will terminate and all PUP outputs will be

switched to their inactive state. This timer has four

settings of OFF, 100ms, 200ms and 400ms.

The

sequence termination timer can be disabled separately

for Power-off sequencing.

While the SMS66 is in the Power-off sequencing mode

the RST output is held active and the HEALTHY

output is held inactive regardless of trigger sources.

The Force Shutdown trigger option is also disabled

while in this mode. Furthermore, the SMS66 will not

respond to activity on the PWR_ON/OFF pin or to a

Power-on I

2C command during Power-off sequencing

mode.

FORCE SHUTDOWN

The Force Shutdown operation brings all PUPX

outputs to their inactive state. This operation is used

for an emergency shutdown when there is not enough

time to sequence the supplies off.

The Force

Shutdown operation shuts off all sequenced channels

and waits for the supply voltages to drop below their

respective OFF thresholds.

A Force Shutdown operation can be initiated by any

one of four events. The first two methods for initiating

a Force Shutdown are always enabled. Simply taking

the FS pin to its active state will initiate a Force

Shutdown operation and maintain it until the pin is

brought to its inactive state. An I

2C Force Shutdown

command allows the Force Shutdown operation to be

initiated via software control. This I

2C Force Shutdown

command sets a volatile register bit that triggers a

Force Shutdown.

This bit is cleared after all

sequenced channels have dropped below their OFF

voltage threshold.

During Power-on and Power-off

sequencing, the sequence termination timer can

initiate a Force Shutdown operation.

As described in the previous sections, the sequence

termination timer triggers a Force Shutdown operation

if it times out before the power supply voltages

surpass their voltage thresholds.

This Force

Shutdown will remain active until all sequenced power

supply channels have dropped below their OFF

voltage threshold.

While the SMS66 is in monitor

mode, a programmed fault condition on any power

supply channel or on the 12VIN or VDD inputs can

trigger a Force Shutdown.

A Force Shutdown

resulting from this will remain active until all

sequenced power supply channels have dropped

below their OFF voltage threshold.

APPLICATIONS INFORMATION (CONTINUED)

SMS66 Datasheet(PDF) 14 Page - Summit Microelectronics, Inc.

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