SMM764
Preliminary Information
SEQUENCE POSITION
VDD (+2.7V to +5.5V)
or 12VIN ( +8V to +15V)
2.5V
1.8V
1.5V
1.2V
1
2
3
4
Figure 2 – Example power supply sequencing and system start-up initialization using the SMM764. Cascade
sequencing ensures that all supplies in the previous sequence position are valid before the next channel is
released. Using the SMM764 any order of supply sequencing can be applied.
GENERAL DESCRIPTION
The SMM764 is a highly integrated and accurate
power supply controller, monitor, and sequencer. Each
device has the ability to automatically control, monitor
and cascade sequence up to 4 power supplies. In
addition, the SMM764 includes Sequence-Link a
feature that allows for the seamless integration of
other Sequence-Link devices to accommodate
sequencing of up to 46 channels. The SMM764 can
monitor the VDD input, the 12V input, two general-
purpose analog inputs, and the internal temperature
sensor. The SMM764 has four operating modes:
power-on sequencing modes, monitor mode, supply
margining mode using Active DC Output Control
(ADOC
TM
), and power-off sequencing mode.
Power-on sequencing is initiated by the rising edge of
the PWR_ON pin. During power-on sequencing the
SMM764 will sequence the power supply channels on,
in any order, by activating the PUP outputs and
monitoring the respective converter voltages to ensure
cascading of the supplies. Cascade sequencing is the
ability to hold off the next sequenced supply until the
first supply reaches a programmed threshold. A
programmable sequence termination timer can be set
to disable all channels if the power-on sequence stalls.
Once all supplies have sequenced on and the voltages
are above the UV settings, the ADOC, if enabled, will
bring the supply voltages to their nominal settings.
During this mode, the HEALTHY output will remain
inactive and the RST# output will remain active.
Once the power-on sequencing mode is complete, the
SMM764 enters monitor mode. In the monitor mode,
the SMM764 starts the ADOC control of the supplies
and adjusts the output voltage to the programmed
setting under all load conditions, especially useful for
supplies without sense lines. Typical converters have
±2%
accuracy ratings for their output voltage; the
ADOC feature of the SMM764 increases the accuracy
to
±0.2%
(using a ±0.1% external voltage
reference). The part also enables the triggering of
outputs by monitored fault conditions. The 10-bit ADC
cycles through all 9 channels every 2ms and checks
the conversions against the programmed threshold
limits. The results can be used to trigger RST#,
HEALTHY and FAULT# outputs as well as to initiate a
Fault-Triggered
power-off
or
force-shutdown
operation.
While the SMM764 is in its monitoring mode, an I
2
C
command to margin the supply voltages can bring the
part into margining mode. In margining mode the
SMM764 can margin 4 supply voltages in any
combination of nominal, high and low voltage settings
using the ADOC feature, all to within ±0.2% using a
±0.1% external reference. The margin high and low
voltage settings can range from 0.3V to VDD around
the converters’ nominal output voltage setting
depending on the specified margin range of the DC-
DC converter. During this mode the HEALTHY output
is always active and the RST# output is always
inactive regardless of the voltage threshold limit
settings and triggers. Furthermore, the triggers for
power-off and force-shutdown are temporarily
disabled.
The power-off sequencing mode can only be entered
while the SMM764 is in the monitoring mode. It can
be initiated by either bringing the PWR_ON pin low,
through I
2
C control, or triggered by a channel
exceeding its programmed thresholds. Once power-
off is initiated, it will disable the ADOC function and
sequence the PUP outputs off in the reverse order as
power-on sequencing. To ensure cascading of the
supplies during power-off sequencing all supplies will
be monitored as they turn off.
The sequence
termination timer can be programmed to immediately
disable all channels if the power-off sequencing stalls
via a force-shutdown operation.
Summit Microelectronics, Inc
2098 1.1 6/29/2005
3
SUMMIT [ SUMMIT MICROELECTRONICS, INC. ]
