SMM665C datasheet(15/36 Pages) SUMMIT

15 / 36 page

SMM665C

Summit Microelectronics, Inc

2125 3.1 7/22/2008

APPLICATIONS INFORMATION (CONTINUED)

While the SMM665C is in the Power-on sequencing

mode the RST output is held active and the HEALTHY

output is held inactive regardless of trigger sources

(Figure 8). The Power-off and Force Shutdown trigger

options are also disabled while in this mode.

Furthermore, the SMM665C will not respond to activity

on the PWR_ON/OFF pin or to a Power-off I

command during Power-on sequencing mode.

ONGOING OPERATIONS-MONITORING MODE

During ongoing operations mode, the part can (1)

monitor (2) actively control via ADOC, and (3) use

force shutdown if necessary.

Once the Power-on sequence is complete and before

a Power-off sequence has been initiated, the

SMM665C 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 SMM665C monitors internal temperature using

the 10-bit ADC and the auto-monitor function. Two

under

temperature

and

two

over

temperature

thresholds

can

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 be acquired over the I

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

The SMM665C 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.

A 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.

The HEALTHY and FAULT outputs of the SMM665C

are active as long as the triggering limit remains in a

fault condition. The RST output also remains active as

long as the triggering limit remains in a fault condition;

however, once the trigger source goes away the RST

will remain active for a reset timeout period (tPRTO).

AUTO-MONITOR MODE

The auto-monitor mode, responsible for monitoring all

voltage thresholds and triggering the programmable

options, is paused during an I

2C transaction. This is

done to allow the I

2C interface to access the internal

data bus that is used in the auto-monitor function

Specifically, the auto-monitor is paused approximately

100ns after the falling edge of SCL during

transmission of the R/W bit of a valid slave address.

For normal I

2C transactions, the auto-monitor function

is resumed following an I

2C STOP issued at the end of

the transaction or upon the NACK of an invalid slave

address. For I2C ADC conversion transactions, which

employ acknowledge polling, the auto-monitor function

is resumed after the conversion has completed

(approximately 300us after the second ACK of the

transaction) and following a I

2C STOP issued at the

end of the transaction or upon the NACK of an invalid

slave address.

During every suspension of the auto-monitor, a 25ms

timer is activated. The clock stage will determine the

exact timeout period, typically between 25msec and

50msec. Should the I

2C transaction fail, this timer will

expire and restart the auto-monitor.

See “Auto-Monitor Function” section for timing details

and conditions under which the auto-monitor timer will

be asserted.

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