SMS64 datasheet(11/24 Pages) SUMMIT

11 / 24 page

SMS64

Preliminary

Summit Microelectronics, Inc

2060 2.22 10/09/03

POWER SEQUENCING

The SMS64 is a programmable controller for power

supply sequencing.

Up to six channels can be

sequenced in any order with several delay options.

In order for a power supply to be sequenced it must

be enabled by a PUP output and monitored by the

corresponding VM input. This channel must also be

programmed to participate in the sequence and be

assigned to a sequence position. If a channel is not

programmed to participate in the sequence it should

be assigned to the null sequence position (position 7)

and the channel will act strictly as a voltage monitor.

A sequence position is given to each channel as an

order to the sequence.

The sequence position

assignments must begin at position 0 and must not

skip positions. Also, multiple channels can be

programmed into the same sequence position to

enable more than one supply at a time. Note: If two

or more channels with high voltage PUP outputs share

the same sequence position their power-on delays

must be either equal or differ by at least tSLEW (time it

takes for the PUP output to slew from 0V to the level

of VGG_CAP).

Each channel selected for sequencing is given a

power-on and power-off delay. The power-on delay is

a delay from the VM input of one channel going out of

fault to the PUP output of another channel going

active. The power-off delay is the delay from the VM

input of one channel turning off to the PUP output of

another channel that is turning off. The power-on and

power-off delay options are 25ms, 50ms, 100ms and

200ms.

If the fast times option is selected in the

configuration register, these delays are divided by 16

(1.5625ms, 3.125ms, 6.25ms and 12.5ms).

Before

the

SMS64

begins

the

power-on

sequencing the voltage monitors are monitoring the

VCC inputs. The power-on sequencing will not begin

until all of the VCC inputs that are selected as

precursors to power-on sequencing are out of their

fault conditions, the ‘precondition qualifiers’.

Power-on sequencing can be initiated by toggling

the PWR_ON/OFF pin from low to high or by writing to

the power-on bit of the command register.

For

automatic start-up the PWR_ON/OFF can be floated

as the device receives power. Either of these will

initiate the power-on sequence as soon as the

precursor conditions are met. During the power-on

sequence power-off commands as well as activity on

the PWR_ON/OFF pin is ignored.

The power-on sequencing begins with the power-

on delay time of the channel(s) in sequence position 0.

Once this delay has timed out the PUP will go active.

At this point the supply connected to the VM input will

begin to turn on.

When this supply reaches its

programmed threshold (under-voltage) and the PUP

output has reached the level of VGG_CAP (high

voltage PUP outputs only) the sequence position

counter will change to position 1 and the power-on

delay timer for the channel(s) in sequence position 1

will begin. This will repeat until all channels that were

programmed for sequencing have turned on and are

not in fault conditions. Once sequencing is complete

RST_B# will clear after tPRTO.

Power-off sequencing can be initiated by a high to

low transition on the PWR_ON/OFF pin, by writing to

the power-off bit of the command register, or triggered

off of a selected fault condition. The SMS64 can be

configured to sequence the supplies off in the same

order or reverse order of the power-on sequence.

During the power-off sequence power-on commands

as well as activity on the PWR_ON/OFF pin is ignored.

The power-off sequencing begins with the power-

off delay time of the channel(s) in the last sequence

position of the power-on sequence (reverse order).

Once this delay has timed out the PUP will turn off. At

this point the supply connected to the VM input will

begin to turn off. When this supply falls below 0.8V

the sequence position counter will change to the next

position and the power-off delay timer for the

channel(s) in current sequence position will begin.

This will repeat until all channels that were

programmed for sequencing have turned off. At this

point the voltage monitors will switch from the VM

inputs to the VCC inputs to monitor for the precursor

conditions to power-on sequencing. Note: With the

OFF sensors disabled (configuration option) the

SMS64 will immediately increment to the next

sequence position instead of waiting until the VM

inputs reach 0.8V.

FORCED SHUTDOWN

The forced shutdown function is always enabled.

This function is used to immediately turn off all PUP

outputs when there is not enough time to perform a

power-off sequence.

Forced shutdown can be

initiated by pulling the FS# pin low, by writing to the

forced shutdown bit of the command register, or

triggered off of a selected fault condition.

APPLICATIONS INFORMATION (CONTINUED)

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