AD8280 datasheet(15/24 Pages) AD

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AD8280

Rev. C | Page 15 of 24

THEORY OF OPERATION

Figure 44 shows a block diagram of the AD8280. The AD8280

is a threshold monitor that can be used to monitor up to six cell

voltages and two temperature voltages. The part can also be used

in a daisy-chain configuration to monitor as many cells as required.

The benefit of the daisy-chain configuration is that isolation is

required to bring the alarm signal away from the high voltage

environment on only the bottom part of the chain, reducing

system cost and minimizing the board space required.

The cell and temperature voltage inputs are connected to the part

using the VIN0 through VIN6 inputs and the VT1 and VT2 inputs,

respectively. Because the six-cell stack voltage can be up to 30 V,

the input voltages are level-shifted and referenced to the lowest

potential (part ground or VBOTx) of the AD8280. These voltages

are then input into window comparators and compared to trip

points set by external resistor dividers.

If the cell or temperature voltage inputs exceed or fall below the

selected trip points, an alarm, in the form of a digital voltage level,

changes state at the voltage output (AVOUTxx) of the part. The

alarm state also exists in the form of a current output (AIOUTxx)

used to communicate to the other devices when multiple parts

are used in a daisy-chain configuration.

The part contains programmable deglitching circuitry to ensure

that transient voltages appearing at the cell inputs are ignored.

The part also contains its own LDO and reference. The LDO

can be used to drive external components such as thermistors

or isolators, whereas the reference can be used with the voltage

dividers to establish the trip points.

The AD8280 has the following unique features and capabilities:

•

Three, four, five, or six cells can be monitored.

•

Negative or positive temperature coefficient thermistors

can be used.

•

Multiple parts can be configured in a daisy chain to monitor

hundreds of cells. Information about the status of the alarms

on the entire daisy chain, as well as input signals that enable

the part and initiate self-test, are all communicated via the

bottom, or master, part in the chain.

•

Alarm outputs for overvoltage, undervoltage, and overtemp-

erature status can be shared, with each output indicating

the same status for any of the occurring alarm conditions,

or the alarm outputs can function as separate entities with

each indicating the status of the specific condition.

•

An extensive self-test feature ensures that the internal

components are functioning correctly. The self-test is

initiated upon request to the TESTI pin.

I/V

CONVERTER

V/I

CONVERTER

VIN6

VIN5

VIN2

VIN1

AIINOV

AIOUTOV

VT1

SEL0

SEL 1

VTOP

VBOT1

C6O

CT2

C1O

C1U

C6U

DE-

GLITCHING

DE-

GLITCHING

DE-

GLITCHING

DE-

GLITCHING

DE-

GLITCHING

DE-

GLITCHING

VIN3

VIN4

AD8280

CT1

VT2

AVOUTOV

ALARM

LOGIC

VIN0

LDO

REF

ENBO

ENBI

TOP

REF

DGT0

DGT1

LDO

TESTO

TESTI

SELF-

TEST

GENERATOR

BOT

LEVEL

SHIFTER

LEVEL

SHIFTER

AIOUTUV

AIOUTOT

AIINUV AIINOT

DGT2

NPTC

ALRMSEL

AVOUTUV

AVOUTOT

VCC

VCCS

GND2

GND1

VBOT1S

VBOT2

VBOT2S

LDOS

VTOPS

LEVEL

SHIFTER

Figure 44. Functional Block Diagram

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