AD8280 datasheet(20/24 Pages) AD

20 / 24 page

AD8280

Rev. C | Page 20 of 24

ENABLING AND DISABLING THE AD8280

The AD8280 can be disabled or put into a standby mode by

bringing the ENBI pin to logic low, lowering the quiescent

current of the AD8280 from a maximum of 2.0 mA to 1.0 μA

and dropping the LDO and reference output to 0 V. Bringing

the ENBI pin to a logic high takes the part out of standby mode

and enables it.

When the AD8280 is used in a daisy-chain configuration, the

enable/disable signal is a voltage logic level that is sent to the

part designated as the bottom part (the bottom part monitors

the lowest voltage cells). The bottom part transfers the enable/

disable signal up the daisy chain via a current out of the ENBO

pin and into the ENBI pin of the next higher part in the daisy

chain. All the parts in the daisy chain are enabled by sending a

logic high to the ENBI pin of the bottom, or master, part. All

the parts in the daisy chain are disabled by sending a logic low

to the ENBI pin of the bottom part.

ALARM OUTPUT

The alarm status of the AD8280 appears as a voltage logic level

at the AVOUTOV, AVOUTUV, and AVOUTOT pins. When the

AD8280 is in a daisy-chain configuration, the alarm status is

passed from the AIOUTxx pins of one part to the AIINxx pins

of the next lower potential part in the daisy chain. Figure 51

shows the output state when the part is in an unalarmed (logic

low) or alarmed (logic high) state.

If the AD8280 is configured for the shared alarm mode, the status

of all three voltage output pins (AVOUTxx) is the same. In shared

alarm mode, the unused pins can be left floating, they can be tied

to ground through a high resistance to limit the current draw,

or they can be tied together.

SELF-TEST

The AD8280 has the unique capability of extensively testing

its internal components to ensure that they are functioning

correctly. This feature is very important to the designer who is

concerned with meeting the difficult safety integrity level guide-

lines of IEC 61508 or ISO 26262.

The part produces internal fault conditions and compares the

results to what is expected. The status of the alarm signals is

interrupted during the self-test, and the pass/fail status of the

self-test is communicated via the alarm status signal pins

(AVOUTxx and AIOUTxx).

Because the AD8280 uses an internal reference to perform its

self-test, the self-test detects open circuits and short circuits at

the threshold pins, as well.

See Figure 51 for a timing diagram and Figure 52 for timing

definitions related to the self-test feature.

To initiate a self-test, the TESTI pin is prompted with a rising

edge from a 5 V logic level pulse (test pulse). The pulse applied

at TESTI must stay high for a minimum time (tST min). Follow-

ing the rising edge of the pulse to initiate the self-test, the alarm

status for any AVOUTxx or AIOUTxx pin goes into a logic high

status while the part performs its internal self-test. After sufficient

time to perform the test has elapsed and assuming that the part

passes self-test, the alarm status reverts to the unalarmed state,

a logic low. If the part fails self-test, the alarm remains in a logic

high state when the falling edge of the test pulse applied at

TESTI occurs.

The minimum tST is dependent on the status of the DGTx pins.

If all three DGTx pins are tied to a logic low, the self-test ignores

the deglitch function of the part and completes the self-test in a

shorter time (50 ms max). When at least one DGTx pin is set to

logic high, the AD8280 defaults to the minimum deglitch time of

100 ms during the self-test. Because the self-test includes multiple

layers and passes, this minimum time is specified as 700 ms.

Therefore, if a faster self-test is required, the user should set the

internal deglitch time to 0.0 sec and use an external deglitch

circuit if deglitch is required.

Self-Test in Daisy-Chain Configuration

The self-test can also be used when multiple AD8280 parts

are configured in a daisy chain. The test pulse is applied to the

TESTI pin of the bottom part as a voltage and then travels up

the chain as a current. The self-test for each part is started as

soon as the part sees the rising edge of the test pulse, virtually

simultaneously. When the highest part in the chain passes its

self-test, it sends that information to the next lower part in the

daisy chain. Even if that part has already completed its self-test,

it cannot pass its own result on to the next part in the daisy

chain until it receives the pass signal from the part above it.

This process continues with each part lower down the chain.

Therefore, when a pass signal appears at the bottom part in the

daisy chain, it indicates that every part in the daisy chain passed

the self-test. If any part in the chain fails the self-test, the part

below the failing part never receives a pass signal, and, subse-

quently, the bottom part never receives a pass signal either.

Therefore, regardless of whether the bottom part passes self-test,

the AVOUTxx signals at the bottom part never change state from

the logic high that occurred when the self-test was initiated, and

the user will know that there is a failed part in the chain.

AD8280 Datasheet(PDF) 20 Page - Analog Devices

AD8280 Datasheet(HTML) 20 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Datasheet Download

Link URL