AD8452 datasheet(22/35 Pages) AD

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Data Sheet

AD8452

Rev. 0 | Page 21 of 34

ISET

CC LOOP

AMPLIFIER

CV LOOP

AMPLIFIER

IVE1

ISVN

BVP

BVN

ISMEA

BVMEA

VVSET

VSET

VISET

MODE

VINT

ISVP

MIN

OUTPUT

SELECT

VVE1

VSET

BUFFER

VSETB

–

66×

0.4×

IBAT

SHUNT

BAT

½ BRIDGE AND LPF

IAC

½ BRIDGE DRIVER

PWM

HVAC/12V DC

INVERTER/CONVERTER

VCTRL/

COMP

1×

Figure 37. Functional Block Diagram of the CC and CV Loops in Charge Mode (MODE Pin High)

The VISET voltage source and VVSET voltage source set the

target constant current and the target constant voltage,

respectively. When the CC and CV feedback loops are in a

steady state, the charging current is set at

IBAT =

ISET

where:

IBAT is the steady state charging current.

GIA is the in-amp gain.

RS is the value of the shunt resistor.

The target voltage is set at

VBAT =

VSET

where:

VBAT is the steady state battery voltage.

GDA is the difference amplifier gain.

Because the offset voltage of the loop amplifiers is in series with

the target voltage sources, VISET and VVSET, the high precision of

these amplifiers minimizes this source of error.

Charging Lithium-Ion (Li-Ion) Cells

Charging Li-Ion cells is a demonstrably more difficult process

than charging most other batteries employing recyclable

technologies. The voltage margin of error between optimum

storage capacity and damage caused by overcharge is around

1%. Thus, Li-Ion cells are more critical to over/undercharging

than any other type battery style, rechargeable or not.

Li-Ion batteries also exhibit the highest energy density per unit

of weight and volume than any other style. Such high levels of

energy density make them the first choice for portable applications,

large and small, from cell phones to high capacity energy storage

banks. Realizing their greatest potential requires careful attention

to their charge characterization signature.

Concepts of Constant Current (CC) and Constant

Voltage (CV)

Batteries can be charged in constant current or constant voltage

modes. Figure 38 shows a typical CC/CV multiphase charge

profile for a Li-Ion battery. In the first stage of the charging

process, the battery is charged with a CC of 1 A. When the battery

voltage reaches a target voltage of 4.2 V, the charging process

transitions such that the battery is charged with a CV of 4.2 V.

1.25

0.25

0.50

0.75

1.00

TIME (Hours)

CURRENT (A)

VOLTAGE (V)

1A CC

CHARGE

BEGINS

TRANSITION

FROM 1A CC

TO 4.2V CV

VOLTAGE

RISES TO

VSET

VOLTAGE

RISES TO VSET

CHARGE

TERMINATES

Figure 38. Representative Li-Ion Battery Charge Profile Showing

Seamless CC to CV Transition

The following sequence of events describes how the AD8452

implements a typical CC/CV charging profile required for a

Li-Ion battery. The scenario assumes a newly manufactured,

unformed, never before charged battery, and the charge and

discharge voltage and current levels along with appropriate time

intervals have already been established empirically.

Energy levels (CC, CV, and time intervals are just a small percent of

the battery final ratings). For this example, assume a 3.2 V 10 Ah

battery is charging at IBAT = 2 A and VBAT = 4.2 V. The process

begins with ISET = 66 mV and VSET = 1.68 V, configured for

charge mode. Following the target VSET and ISET, the system is

enabled by applying a logic high to the EN pin.

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