AD8450ASTZ datasheet(23/42 Pages) AD

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AD8450

Data Sheet

Rev. B | Page 22 of 41

Battery formation and test systems charge and discharge

batteries using a constant current/constant voltage (CC/CV)

algorithm. In other words, the system first forces a set constant

current in or out of the battery until the battery voltage reaches

a target value. At this point, a set constant voltage is forced

across the battery terminals.

The AD8450 provides two control loops—a constant current

(CC) loop and a constant voltage (CV) loop—that transition

automatically after the battery reaches the user defined target

voltage. These loops are implemented via two precision specialty

amplifiers with external feedback networks that set the transfer

function of the CC and CV loops. Moreover, in the AD8450,

these loops reconfigure themselves to charge or discharge the

battery by toggling the MODE pin.

Battery formation and test systems must also be able to detect

overvoltage and overcurrent conditions in the battery to prevent

damage to the battery and/or the control system.

The AD8450 includes two comparators to detect overcurrent

and overvoltage events. These comparators output a logic low at

the FAULT pin when either comparator is tripped.

Battery formation and test systems used to condition high

current battery cells often employ multiple independent

channels to charge or discharge high currents to or from the

battery. To maximize efficiency, these systems benefit from

circuitry that enables precise current sharing (or balancing)

among the channels—that is, circuitry that actively matches

the output current of each channel. The AD8450 includes a

specialty precision amplifier that detects the maximum output

current among several channels by identifying the channel with

the maximum voltage at its PGIA output. This maximum

voltage can then be compared to all the PGIA output voltages

to actively adjust the output current of each channel.

Figure 49 is a block diagram of the AD8450 that illustrates the

distinct sections of the AD8450, including the PGIA and PGDA

measurement blocks, the loop filter amplifiers, the fault com-

parators, and the current sharing circuitry. Figure 50 is a block

diagram of a battery formation and test system.

BATTERY

LEVEL

SHIFTER

ADP1972

PWM

VCTRL

SENSE

RESISTOR

ISVP

ISVN

BVPx

BVNx

AVCC

OUTPUT

DRIVERS

BATTERY

CURRENT

AVEE

BUFFER

–

1×

VINT

BUFFER

VSET

ISET

VINT

ISMEA

BVMEA

OCPS

OCPR

OVPR VREF

OVERCURRENT

COMPARATOR

OVERVOLTAGE

COMPARATOR

FAULT

OVPS

OUTPUT

FILTER

PGDA

–

PGIA

SYSTEM POWER CONVERSION

SYSTEM LOOP COMPENSATION

1×

SET

BATTERY

CURRENT

VISET

VVSET

SET

BATTERY

VOLTAGE

POWER CONVERTER

(SWITCHED OR LINEAR)

AD8450

CONTROLLER

CONSTANT

VOLTAGE LOOP

FILTER AMPLIFIER

CONSTANT

CURRENT LOOP

FILTER AMPLIFIER

MODE

SWITCHES (3)

C = CHARGE

D = DISCHARGE

NOR

Figure 50. Signal Path of a Li-Ion Battery Formation and Test System Using the AD8450

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