ACT5830 datasheet(38/41 Pages) ACTIVE-SEMI

38 / 41 page

SINGLE-CELL Li+ BATTERY CHARGER (CHGR)

ACT5830

Rev 2, 20-Jan-11

Innovative Power

- 38 -

www.active-semi.com

ActivePMU

TM is a trademark of Active-Semi.

2CTM is a trademark of NXP.

FUNCTIONAL DESCRIPTIONS

General Description

The ACT5830's internal battery charger is an

intelligent,

stand-alone

CC/CV

(constant-

current/constant-voltage), linear-mode single-cell

charger for Lithium-based cell-chemistries. This

device incorporates current and voltage sense

circuitry, an internal power MOSFET, thermal-

regulation circuitry, a complete state-machine to

implement charge safety features, and circuitry that

eliminates the reverse-blocking diode required by

conventional charger designs. The ACT5830

battery charger operates independently of the

regulators, and is automatically enabled whenever

a valid input supply is available.

The ACT5830's battery charger features software-

programmable

fast-charge

current,

charge

termination voltage, charge safety timeout period.

The ACT5830's battery charger can accept input

supplies in the 4.3V to 6V range, making it

compatible with lower-voltage inputs such as 5-6V

wall-cubes and USB ports. The battery charger,

along with LDO1, LDO2, and LDO3, is enabled and

initiates a charging cycle whenever an input supply

is present.

Enabling/Disabling the Charger

The ACT5830 is enabled when the voltage applied

to CHG_IN is greater than the voltage at BAT and is

greater than 4.0V, and nENCHG is asserted low.

The charger is disabled whenever nENCHG is high,

independent of the voltages at battery and CHG_IN.

The charger may also be disabled via the I2C

interface.

For more information about enabling and disabling

the charger, see the System Startup & Shutdown

section.

Operation Without a battery

The ACT5830's charger is designed to operate with

or without a battery connected. When a battery is

connected, a normal charging cycle is performed as

described below. If no battery is present, however,

the charger will regulate the voltage at BAT to the

voltage programmed by CHGR/VSET[_] to power

the system.

CC/CV Regulation Loop

At the core of the ACT5830's battery charger is a

CC/CV regulation loop, which regulates either

current or voltage as necessary to ensure fast and

safe charging of the battery.

In a normal charge cycle, this loop regulates the

current to the value set in the CHGR/ISET register.

Charging continues at this current until the battery

cell voltage reaches the programmed termination

voltage, as defined in the CHGR/VSET register. At

this point the CV loop takes over, and charge

current is allowed to decrease as necessary to

maintain charging at the termination voltage.

Programming the Charge Current (ISET[_])

In order to accommodate both USB and AC-

powered inputs with a minimum of external

components,

the

ACT5830

features

I2C-

programmable fast-charge current that requires no

external

current-setting

components.

The

CHGR/ISET register sets ISET to any value greater

than [0000] to program the maximum charge

current to values in the 300mA to 1A via software.

See for a detailed list of programmable charge

currents.

Note that the actual charging current may be lower

than the programmed fast-charge current, due to

the ACT5830's thermal regulation loop. See the

Thermal Regulation

section for more information.

Measuring the Charge Current

In order to ease monitoring of the charge current,

the ACT5830 generates a voltage at VICHG that is

proportional to the charge current. The gain is

typically 2.47mV/mA, and this voltage can be easily

read by a system ADC. VICHG is high-impedance

in shutdown.

Thermal Regulation

The ACT5830 features an internal thermal feedback

loop that reduces the charging current as necessary

to ensure that the die temperature does not rise

beyond the thermal regulation threshold of 115°C.

This

feature

protects

the

ACT5830

against

accessing JUNCTION temperature, and allows the

ACT5830 to be used in aggressive thermal designs

without risk of damage. Note that attention to good

thermal design is still required to achieve the fastest

possible charge time.

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