SMM764

Preliminary Information

Summit Microelectronics, Inc

2098 1.1 6/29/2005

3

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

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

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

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.

1

2.5V

1.8V

1.5V

VDD (+2.7V to +5.5V)

or 12VIN ( +8V to +15V)

2

3

4

SEQUENCE POSITION

1.2V

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