AD8280WASTZ Analog Devices Inc, AD8280WASTZ Datasheet - Page 20

• Manufacturer Part Number: AD8280WASTZ
• Description: Lithium Ion Battery Safety Monitor
• Manufacturer: Analog Devices Inc

Specifications of AD8280WASTZ

• Function: Battery Monitor
• Battery Type: Lithium-Ion (Li-Ion)
• Voltage - Supply: 6 V ~ 30 V
• Operating Temperature: -40°C ~ 105°C
• Mounting Type: Surface Mount
• Package / Case: 48-LQFP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

AD8280
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.
Rev. A | Page 20 of 24
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 (t
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 t
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.
ST
is dependent on the status of the DGTx pins.
ST
min). Follow-