AD8280 datasheet(21/24 Pages) AD

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AD8280

Rev. C | Page 21 of 24

TESTI

AIOUTxx/AVOUTxx

TEST OK

AIOUTxx/AVOUTxx

TEST FAILS

AIOUTxx/AVOUTxx

ALARMED

TEST OK

NORMAL OPERATION

DURING SELF-TEST MODE

UNALARMED

AIOUTxx/AVOUTxx

ALARMED

AIOUTxx/AVOUTxx

LOW AT FALLING EDGE OF TESTI:

PART PASSES SELF-TEST

HIGH AT FALLING EDGE OF TESTI:

PART FAILS SELF-TEST

Figure 51. Timing Diagram for Alarms at AIOUTxx and AVOUTxx

Self-Test and Alarm Conditions

If an alarm occurs just prior to or just after the self-test pulse is

initiated, the alarm causes the self-test to fail. The time span for

this condition depends on the deglitch time.

•

Deglitch time = 0.0 sec. The part fails self-test if an alarm

occurs in the time period from 20 ms before the leading

edge of the self-test pulse to 20 ms after the leading edge

of the self-test pulse.

•

Deglitch time > 0.0 sec. The part fails self-test if an alarm

occurs in the time period from 120 ms before the leading

edge of the self-test pulse to 120 ms after the leading edge

of the self-test pulse.

Therefore, in the unusual circumstance that the part fails self-

test and there is an alarm condition state after the self-test, it

is recommended that the user retest the part to ensure that

an alarm did not occur just prior to or just after initiating the

self-test.

The self-test works when the part is in the shared alarm mode

or in the separate alarm mode. When the part is in the separate

alarm mode, the self-test status on an output pertains only to

that portion of the internal circuit relevant to the condition being

monitored: overvoltage, undervoltage, or overtemperature.

Self-Test Timing and Monitoring Strategy

When monitoring the signals for self-test on the AD8280, note

the following items:

•

After initiating a self-test of the AD8280 with a rising edge

on the TESTI pin, the alarm appearing at the AVOUTxx

pin remains valid up to tRE max.

•

When the rising edge of the TESTI pulse occurs, the user

should monitor the AVOUTxx pin to make sure that it is

in the high state after the tRE max time has elapsed.

•

After the tST max time has elapsed, the user can verify that

the AVOUTxx pin has changed to the low state, indicating

that the part or parts passed the self-test. The user must

also ensure that the minimum length of the TESTI pulse

is greater than tST max. The status of the self-test on the

AVOUTxx pin is valid until tSTV min after the trailing edge

of the TESTI pulse.

•

The alarm state is valid again tFE max after the trailing edge

of the pulse.

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