SMM465 datasheet(16/30 Pages) SUMMIT

16 / 30 page

SMM465

Preliminary Information

Summit Microelectronics, Inc

2085 1.1 05/27/04

Note: Configuration writes or reads of registers 00HEX

to 0FHEX should not be performed while the SMM465 is

margining.

POWER-OFF CASCADE SEQUENCING

The SMM465 can be programmed to perform Power-

off sequencing in either the same order or reverse

order of Power-on cascade sequencing.

Power-off cascade sequencing 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.

enable

software

control

the

Power-off

sequencing feature, the SMM465 offers an I

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 SMM465 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 SMM465 will then wait until all

VMX inputs of the channels assigned to that sequence

position are below the programmed OFF thresholds.

At this point, the SMM465 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 SMM465 is in the Power-off sequencing

mode the RST output is held active and the HEALTHY

output is held inactive regardless of trigger sources

(Figure 8). The Force Shutdown trigger option is also

disabled while in this mode.

Furthermore, the

SMM465 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 SMM465 is in ongoing

operations-monitor

mode,

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)

SMM465 Datasheet(PDF) 16 Page - Summit Microelectronics, Inc.

SMM465 Datasheet(HTML) 16 Page - Summit Microelectronics, Inc.

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Datasheet Download

Link URL