SMS66 datasheet(13/26 Pages) SUMMIT

13 / 26 page

SMS66

Preliminary Information

Summit Microelectronics, Inc

2070 1.0 7/16/03

The SMS66 can be programmed to wait until either or

both VDD and 12VIN inputs are within their respective

voltage threshold limits before Power-on sequencing is

allowed to begin. This ensures that the converters

have their full supply voltage before they are enabled.

Once Power-on sequencing begins, the SMS66 will

wait a Power-on delay time (tDPON) for any channel in

the first sequence position (0) and then activate the

PUPX outputs for those channels.

The Power-on

delay times are individually programmable for each

channel. The SMS66 will then wait until all VMX inputs

of the channels assigned to the first sequence position

(0) are above their programmed UV1 thresholds. At

this point, the SMS66 will enter the second sequence

position (1) and begin to timeout the Power-on delay

times for the associated channels.

This process

continues until all of channels in the sequence have

turned on and are above their UV1 threshold. The

status registers indicates that all sequenced power

supply channels have turned on.

The programmable sequence termination timer can be

used to protect against a stalled Power-on sequence.

This timer resets itself at the beginning of each

sequence position.

All channels in the sequence

position must go above their UV1 threshold before the

sequence termination timer times out (tSTT) or the

sequence will terminate and all PUPX outputs will be

switched to their inactive state. The status registers

contain bits that indicate the sequence has been

terminated and in which sequence position the timer

timed out. This timer has four settings of OFF, 100ms,

200ms and 400ms.

While the SMS66 is in the Power-on sequencing mode

the RST output is held active and the HEALTHY

output is held inactive regardless of trigger sources.

The Power-off and Force Shutdown trigger options are

also disabled while in this mode. Furthermore, the

SMS66

will

not

respond

activity

the

PWR_ON/OFF pin or to a Power-off I

2C command

during Power-on sequencing mode.

MONITORING

Once the Power-on sequence is complete and before

a Power-off sequence has been initiated, the SMS66

continues to monitor all VMX inputs, the VDD and

12VIN inputs, and two temperature sensor inputs with

a 10-bit ADC. Each of these inputs is sampled and

converted by the ADC every 2ms. The ADC input has

a range of 0V to four times the voltage on VREF_ADC

for inputs VMA-F and the VDD input. The range is

extended to 12 times VREF_ADC for the 12VIN input

and is reduced to two times VREF_ADC for the AIN1

and AIN2 inputs.

The SMS66 monitors internal

temperature using the 10-bit ADC and the automonitor

function. Two under temperature and two over

temperature thresholds can be set, each with its own

programmable

trigger

options

and

consecutive

conversion before trigger counter. Resolution is 0.25 C

per bit scaled over the range of -128 C to 127.75 C.

The temperature value can also be acquired over the

2C bus as a 10-bit signed two's complement value.

The SMS66 compares each resulting ADC conversion

with two programmable 10-bit under-voltage limits

(UV1, UV2) and two programmable 10-bit over-voltage

limits (OV1, OV2) for the corresponding input.

consecutive conversion counter is used to provide

filtering of the ADC inputs.

Each limit can be

programmed to require 1, 2, 4 or 6 consecutive out-of-

limit conversions before it is said to be in fault. One in-

limit conversion will remove the fault from the

threshold limit. This provides digital filtering of the

monitored inputs.

The ADC inputs VMA-F can use

additional filtering by connecting a capacitor from the

corresponding CAPX pins to ground to form an analog

RC filter (R=25k

Ω). The input is considered to be in a

fault condition if any of its limit thresholds are in fault.

Setting an OV threshold limit to full-scale (3FFHEX), or

setting an UV threshold limit to 000HEX ensures that

the limit can never be in fault. The status registers

provide the real-time status of all monitored inputs.

The voltage threshold limits for inputs VMA-F, VDD and

12VIN can be programmed to trigger the RST and

HEALTHY outputs as well as a Force Shutdown and

Power-off operation when exceeded. The threshold

limits for the internal temperature sensor and the AIN1

and AIN2 inputs can be programmed to trigger the

RST, HEALTHY, and FAULT outputs.

APPLICATIONS INFORMATION (CONTINUED)

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