SMS64
Preliminary
APPLICATIONS INFORMATION (CONTINUED)
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 t
SLEW
(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 t
PRTO
.
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.
Summit Microelectronics, Inc
2060 2.22 10/09/03
11
SUMMIT [ SUMMIT MICROELECTRONICS, INC. ]
