SMM764 datasheet(18/33 Pages) SUMMIT

18 / 33 page

SMM764

Preliminary Information

Summit Microelectronics, Inc

2098 1.1 6/29/2005

APPLICATIONS INFORMATION (CONTINUED)

LINKED OPERATION

The SMM764 can be linked to multiple Sequence-

Link

 devices to create a seamless multi-channel

power manager. With linked operation 8 Sequence-

Link devices in a system can sequence up to 46

supplies

within

sequence

positions.

The

sequencing in this mode can be interlaced, sequencing

a supply from device A, then from device B, then again

from device A, etc. This extended sequencing is made

possible by the inclusion of a SEQ_LINK pin.

For this mode of operation, the control pins, including

SEQ_LINK, PWR_ON, and FS# on each device must

be tied together. In addition, the VDD and 12V supply

must also be connected on all linked devices. As a

consequence when multiple devices are linked

together, all devices must be powered by the same

supply.

RESTART

There are two possible conditions in which a restart

sequence may be initiated. The first instance occurs

when either the FS# pin is asserted or the PWR_ON

pin is pulled low thus initiating a command-triggered

restart. The second condition occurs when a user

programmable

fault

triggers

force-shutdown

operation or a power-off sequence thus resulting in a

fault-triggered restart.

In either case, the SMM764 will wait until all voltages

have fallen below their user programmable OFF

thresholds, after all channels are off, the PWR_ON pin

will continue to be held low for a period of time

dependent on the nature of the fault.

When a power-off or force-shutdown condition results

from

command-triggered

power-off

force-

shutdown, the SMM764 will automatically begin the

restart procedure. When restart begins an internal

timer will begin to timeout for a command-triggered

Restart Delay (tCTRD) of 12.5 ms. After this time has

expired the PWR_ON pin is released, allowing the

power-on sequence to begin.

When a power-off or force-shutdown condition results

from a fault-triggered power-off or force-shutdown, the

SMM764 may or may not begin the restart procedure

(see PROGRAMMABLE RETRIES), if restart begins

the internal timer will begin to timeout a fault-triggered

Restart Delay (tFTRD) of 2.4 s before the PWR_ON pin

is released allowing the power-on Sequence to begin.

If the SMM764 is programmed to wait for VDD, 12VIN,

or Internal Temp to be valid (above UV1 and below

OV1) before power-on sequencing may commence,

then this condition will be checked after the restart

timer has expired and the PWR_ON pin has been

released.

The conditions that may lead to a Fault-Triggered

restart include any channel exceeding its user

programmable thresholds (OV or UV), set to trigger

either a force-shutdown or a power-off sequence. In

addition, in the event that the sequence termination

timer times out before a channel reaches its UV1 or

OFF threshold, during sequencing, a Fault-Triggered

restart occur.

2C POWER OFF CONTROL

Power-on sequencing is only permitted while the

PWR_ON pin is active. Once the PWR_ON pin is

active and the SMM764 has entered monitoring mode,

an I

2C command may be issued to commence the

power-off sequence. This condition will continue until

an I

2C “power on” command is issued.

PROGRAMMABLE RETRIES

In the event of a persistent system fault, the SMM764

may be programmed to limit the number of Fault-

Triggered restarts it will allow. This programmable

setting ensures that the SMM764 will not enter a

hiccup-mode

operation,

while

still

reducing

susceptibility to transient fault conditions.

In the event of a Fault-Triggered restart the fault will

be registered and internally compared to the maximum

number of allowable faults. If this number is exceeded

then the fault condition will be latched and the

PWR_ON and FS# pins will be pulled low while the

RST# output is asserted. This fault condition will

remain latched until power is cycled on the SMM764,

at which point the PWR_ON and FS# pins will be

released, the number of faults will be reset zero, and

the restart sequence will begin. The allowable

programmable setting include one, three, and

unlimited retries.

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