SMM766
Preliminary Information
SEQUENCE POSITION
3
1
2
4
5
VDD (+2.7V to +5.5V)
or 12VIN ( +8V to +15V)
2.7V
2.5V
2.0V
1.8V
1.5V
1.2V
Figure 2 – Example power supply sequencing and system start-up initialization using the SMM766. Cascade
sequencing ensures that all supplies in the previous sequence position are valid before the next channel is
released. Using the SMM766 any order of supply sequencing can be applied.
GENERAL DESCRIPTION
The SMM766 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 6 power supplies. In
addition, the SMM766 includes Sequence-Link a
feature that allows for the seamless integration of
other Sequence-Link devices to accommodate
sequencing of up to 48 channels. The SMM766 can
monitor the VDD input, the 12V input, two general-
purpose analog inputs, and the internal temperature
sensor. The SMM766 has four operating modes:
power-on sequencing mode, monitor mode, supply
margining mode using Active DC Output Control
(ADOCTM), and power-off sequencing mode.
The part also enables the triggering of outputs by
monitored fault conditions. The 10-bit ADC cycles
through all 11 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 SMM766 is in its monitoring mode, an I2C
command to margin the supply voltages can bring the
part into margining mode. In margining mode the
SMM766 can margin 6 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.
Power-on sequencing is initiated by the rising edge of
the PWR_ON pin. During power-on sequencing the
SMM766 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
SMM766 enters monitor mode. In the monitor mode,
the SMM766 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 SMM766 increases the accuracy
to ±0.2% (using a ±0.1% external voltage reference).
The power-off sequencing mode can only be entered
while the SMM766 is in the monitoring mode. It can
be initiated by either bringing the PWR_ON pin low,
through I2C 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.
termination timer performs
The sequence
forced-shutdown
a
operation if power-off sequencing stalls.
Summit Microelectronics, Inc
2086 2.1 12/13/2005
3
SUMMIT [ SUMMIT MICROELECTRONICS, INC. ]
