AD8280 datasheet(18/24 Pages) AD

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AD8280

Rev. C | Page 18 of 24

TOP AND BOTTOM PART DESIGNATION

When configured in a daisy chain, the AD8280 operates differ-

ently, depending on where it is in the chain: top part (highest

potential), middle part, or bottom part (lowest potential). The

TOP and BOT pins are used to designate the location of each

part in the daisy chain. Table 6 is the logic table for identifying

the location of the part in the daisy chain or, when not used in

a daisy chain, identifying it as a single (standalone) part.

The logic high and logic low for the TOP and BOT pins are

different from those of the other logic pins of the AD8280.

The TOP and BOT pins are referenced to VTOP (logic high)

and VBOTx (logic low), respectively.

Table 6. Designation of the AD8280 in Daisy-Chain and

Standalone Configurations

Desired Condition

TOP1

BOT1

Middle part (middle potential part)

Bottom part (lowest potential part)

Top part (highest potential part)

Single part (highest and lowest potential part)

1 For the TOP and BOT pins only, Logic 1 is VTOP and Logic 0 is VBOTx.

Bottom Part in Daisy-Chain Configuration

The bottom part in a daisy-chain configuration is the master

part and accepts voltage inputs into the ENBI and TESTI pins.

The AIINOV, AIINUV, and AIINOT pins of the bottom part

are connected to the AIOUTOV, AIOUTUV, and AIOUTOT

pins, respectively, of the next higher potential part in the daisy

chain. The AIOUTOV, AIOUTUV, and AIOUTOT pins of the

bottom part can be left floating, or they can be tied to part

ground (VBOTx).

Middle Part in Daisy-Chain Configuration

When the AD8280 is designated as a middle part, the AIINOV,

AIINUV, AIINOT, ENBO, and TESTO pins are connected to

the AIOUTOV, AIOUTUV, AIOUTOT, ENBI, and TESTI pins,

respectively, of the AD8280 above it.

Top Part in Daisy-Chain Configuration

When the AD8280 is designated as a top part, the AIINOV,

AIINUV, AIINOT, ENBO, and TESTO pins can be left floating,

or they can be tied to VTOP.

Standalone Part

When the AD8280 is designated as a single part (used as a stand-

alone part), the AIOUTOV, AIOUTUV, and AIOUTOT pins

can be left floating, or they can be tied to part ground (VBOTx).

The AIINOV, AIINUV, AIINOT, ENBO, and TESTO pins can

be left floating or tied to VTOP. The AD8280 accepts voltage

inputs into the ENBI and TESTI pins.

Alarm Signals in Daisy-Chain Configuration

Regardless of the part designation, the alarm signals are

available as voltage outputs on any part in the chain on the

AVOUTOV, AVOUTUV, and AVOUTOT pins. These signals

indicate the status of the part where the voltage alarms are

monitored, as well as the status of the parts above it in the daisy

chain. Make sure to use isolators to bring those signals outside

the high voltage battery environment.

TYPICAL DAISY-CHAIN CONNECTIONS

Figure 50 shows the typical connections for configuring the part

in a daisy chain.

SHARED OR SEPARATE ALARMS

The AD8280 can be configured for three separate alarms or for

one shared alarm. Tying the ALRMSEL pin to a 5 V logic high

forces the part into separate alarm mode. In this mode, each

alarm trips only for its designated monitoring function. That is,

the OV alarm trips only if an overvoltage condition exists at any

of the cell inputs, the UV alarm trips only if an undervoltage

condition exists at any of the cell inputs, and the OT alarm trips

only if an overtemperature condition exists at either of the

temperature inputs.

In shared alarm mode, any of the three conditions—overvoltage,

undervoltage, or overtemperature—trips the alarm on all three

signal chains. In shared mode, it is necessary to monitor only

one alarm because all three contain the same signal.

DEGLITCHING OPTIONS

The deglitching circuitry is available so that the part is immune

to transients occurring at the cell inputs. If a transient voltage of

a high or low enough level to trip an alarm occurs at the input

to the part, the alarm state does not occur if the transient

voltage is present for less than the selected deglitch time.

The DGT0, DGT1, and DGT2 pins are used to establish the

deglitch time. Table 7 shows the options available and the

corresponding logic levels to use when setting the deglitch

time with the DGT0, DGT1, and DGT2 pins.

Table 7. Fault Detection Time Pin Programming

Deglitch Time

DGT0

DGT1

DGT2

0.0 sec

0.1 sec

0.8 sec

1.6 sec

3.2 sec

6.4 sec

12.8 sec

Do not tie all three deglitching pins (DGT0, DGT1, and DGT2)

to logic high (111); this setting is used only during the testing of

the part at the factory.

Setting the deglitch time to 0.0 sec (000) allows the use of an

external deglitching circuit, if desired. Additionally, when the

deglitch time is set to 0.0 sec, the time required to ensure that

the part has completed its self-test is significantly reduced (see

the Self-Test section). The DGTx pins should be tied to a fixed

logic level and not toggled or changed during operation of the

AD8280.

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