Datasheet

AD8280
Rev. C | Page 21 of 24
TESTI
A
IOUTxx/AVOUTxx
TEST OK
A
IOUTxx/AVOUTxx
TEST FAILS
A
IOUTxx/AVOUTxx
ALARMED
TEST OK
NORMAL OPERATION
DURING SELF-TEST MODE
UNALARMED
A
IOUTxx/AVOUTxx
ALARMED
A
IOUTxx/AVOUTxx
LOW AT FALLING EDGE OF TESTI:
PART PASSES SELF-TEST
HIGH AT FALLING EDGE OF TESTI:
PART FAILS SELF-TEST
08911-045
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 t
RE
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 t
RE
max time has elapsed.
• After the t
ST
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 t
ST
max. The status of the self-test on the
AVOUTxx pin is valid until t
STV
min after the trailing edge
of the TESTI pulse.
• The alarm state is valid again t
FE
max after the trailing edge
of the pulse.