AD8451

Data Sheet

APPLICATIONS INFORMATION

This section describes how to use the AD8451 in the context of

a battery formation and test system. This section includes a

design example of a small scale model of an actual system.

FUNCTIONAL DESCRIPTION

The AD8451 is a precision analog front end and controller for

battery formation and test systems. These systems use precision

controllers and power stages to put batteries through charge and

discharge cycles. Figure 49 shows the signal path of a simplified

switching battery formation and test system using the AD8451

controller and the ADP1972 PWM controller. For more

information on the ADP1972, see the ADP1972 data sheet.

The AD8451 is suitable for systems that form and test NiCad,

NiMH, and Li-Ion batteries and is designed to operate in

conjunction with both linear and switching power stages.

The AD8451 includes the following blocks (see Figure 42 and

the Theory of Operation section for more information).

•

A fixed gain IA that senses low-side or high-side battery

current.

•

A fixed gain DA that measures the terminal voltage of the

battery.

•

Two loop filter error amplifiers that receive the battery target

current and voltage and establish the dynamics of the CC and

CV feedback loops.

•

A minimum output selector circuit that combines the

outputs of the loop filter error amplifiers to perform

automatic CC to CV switching.

•

An output clamp amplifier that drives the VCTRL pin. The

voltage range of this amplifier is limited by the voltage at

the VCLP and VCLN pins such that it cannot overrange

the subsequent stage. The output clamp amplifier can drive

switching and linear power converters. Note that an

increasing voltage at the VCTRL pin must translate to a

larger output current in the power converter.

•

A 2.5 V reference whose output node is the VREF pin.

A logic input pin (MODE) that changes the configuration of the

controller from charge to discharge mode. A logic high at the

MODE pin configures charge mode; a logic low configures

discharge mode.

BATTERY

LEVEL

SHIFTER

VCTRL

SENSE

RESISTOR

ISVP

ISVN

BVP

BVN

MODE

SWITCHES

(3)

AVCC

OUTPUT

DRIVERS

BATTERY

CURRENT

AVEE

CV

BUFFER

CONSTANT

CURRENT LOOP

FILTER AMPLIFIER

–

+

–

+

1×

VINT

BUFFER

VSET

ISET

C

D C

D C

D

VINT

ISMEA

BVMEA

OUTPUT

FILTER

DA

–

+

–

+

IA

AD8451

CONTROLLER

1×

SET

BATTERY

VOLTAGE

SET

BATTERY

CURRENT

DC-TO-DC POWER CONVERTER

EXTERNAL

PASSIVE

COMPENSATION

NETWORK

C = CHARGE

D = DISCHARGE

CONSTANT

VOLTAGE LOOP

FILTER AMPLIFIER

ADP1972

PWM

Figure 49. Complete Signal Path of a Battery Test or Formation System Suitable for Li-Ion Batteries

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