SMS66
Preliminary Information
APPLICATIONS INFORMATION (CONTINUED)
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.
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 I2C 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
Power-off sequencing is the same as power-on
sequencing and can be initiated by the PWR_ON/OFF
pin, via I2C control or triggered by a fault condition on
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.
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 I2C 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.
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 I2C Force Shutdown
command allows the Force Shutdown operation to be
initiated via software control. This I2C Force Shutdown
command sets a volatile register bit that triggers a
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.
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.
Summit Microelectronics, Inc
2070 1.0 7/16/03
14
SUMMIT [ SUMMIT MICROELECTRONICS, INC. ]
