SMM665B
Preliminary Information
VDD (+2.7V to +5.5V)
or 12VIN ( +8V to +15V)
2.7V
2.5V
2.0V
1.8V
1.5V
RST#
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t1
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Figure 2 – Example Power Supply Sequencing and System Start-up Initialization using the SMM665B. Any
order of supply sequencing can be applied using the SMM665B. Power supply ordering, trimming and Active
DC control allows supply cascade sequencing, automatic level adjustment, margin testing and reset control.
GENERAL DESCRIPTION
The SMM665B is a highly integrated and accurate
power supply controller, monitor and sequencer. It
has the ability to automatically control, monitor and
cascade sequence up to six power supplies. Also, the
SMM665B can monitor the VDD input, the 12V input,
two general-purpose analog inputs and the internal
temperature sensor.
The SMM665B has four
operating modes: Power-on sequencing mode,
monitor mode, supply margining mode using Active
DC Output Control (ADOC
TM
), and Power-off
sequencing mode.
Power-on sequencing can be initiated via the
PWR_ON/OFF pin or I
2
C control. In this mode, the
SMM665B 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 Active DC
Control, 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
SMM665B enters monitor mode. In the monitor mode,
the SMM665B 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
Active DC Output Control feature of the SMM665B
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 11 channels every
Summit Microelectronics, Inc
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 trigger a Power-off or a Force Shutdown
operation.
While the SMM665B 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
SMM665B can margin six 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 SMM665B is in the monitoring mode. It can
be initiated by either bringing the PWR_ON/OFF pin
inactive, through I
2
C control or triggered by a channel
exceeding its programmed thresholds. Once Power-
off is initiated, it will disable the Active DC Control and
sequence the PUP outputs off in either the same or
reverse order as Power-on sequencing and monitor
the supply voltages to ensure cascading of the
supplies as they turn off. The sequence termination
timer can be programmed to immediately disable all
channels if the Power-off sequencing stalls. The RST
output will remain active throughout this mode while
the HEALTHY output remains inactive.
2089 1.1 10/20/04
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SUMMIT [ SUMMIT MICROELECTRONICS, INC. ]
