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AD7280

Preliminary Technical Data

Rev. PrD | Page 12 of 33

TYPICAL CONNECTION DIAGRAMS

The AD7280 can be used to monitor 6 battery cells connected

in series. A typical configuration for a 6 cell battery monitoring

application is shown in Figure 10.

10µF

0.1µF

Vin0

Vin1

Vin2

Vin3

Vin4

Vin5

VSS

Vin6

µC/µP

4 WIRE SPI

INTERFACE

OPTIONAL

INTERFACE

PINS

CB6

CB5

CB4

CB3

CB2

CB1

VREG

MASTER

AVCC

DVCC

VDRIVE

VDD

SCLK

SDI

SDO

ALERT

CNVST

AD7280

10uF

0.1uF

CREF

VREF

0.1uF

10uF

10k

Ω

Figure 10. AD7280 Configuration Diagram for 6 Battery Cells

Lithium Ion Battery applications require a significant number

of individual cells to provide the required output voltage.

Individual AD7280s can monitor the cell voltages and

temperatures of 6 series connected cells. The Daisy Chain

Interface of the AD7280 allows each individual AD7280 to

communicate with another AD7280 immediately above or

below it. The daisy chain interface allows the AD7280s to be

electrically connected to the battery management chip, as

shown in Figure 11 without the need for individual isolation

between each AD7280.

Daisy Chain Connection Diagram

As shown in Figure 11 external diodes have been included on

the VDD supply to each AD7280 and on each Daisy Chain signal

between adjacent AD7280’s. These diodes, in combination with

the 10kΩ series resistors on the analog inputs, are

recommended to prevent damage to the AD7280 in the event of

an open circuit in the battery stack.

It is also recommended that a zener diode be placed across the

supplies of each AD7280 as shown in Figure 11. This will

prevent an over voltage across the supplies of each AD7280

during the initial connection of the daisychain of AD7280s to

the battery stack. A voltage rating of 33V is suggested for this

zener diode but lower values may also be used to suit the

application.

When using a chain of AD7280s it is also recommended that a

100kOhm series resistor be placed on the PD input. This is

recommended to limit current into the PD pin in the event that

the uP/DSP or isolators are connected before the supplies of the

master AD7280.

Please refer to the Daisy Chain Interface Section for a more

detailed description of the Daisy Chain Interface.

In an application which includes a safety mechanism, designed

to open circuit the Battery Stack, additional isolation will be

required between the AD7280 above the break point and the

battery management chip.

EMC Considerations

In addition to the standard decoupling capacitors, C2n and C3n,

as shown in Figure 11, it is also recommended that an option for

additional capacitors, C1n and C4n, be included in the circuit to

increase immunity to Electomagnetic Interference. These

capacitors, placed on either side of the VDD protection diode,

would be used to decouple the VDD supply of each AD7280 with

respect to system ground., that is the ground of the master

AD7280 in the daisychain.

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