ACT8941A datasheet(35/42 Pages) ACTIVE-SEMI

35 / 42 page

ACT8941A

Rev 0, 12-Mar-13

- 35 -

www.active-semi.com

ActivePMU

TM and ActivePathTM are trademarks of Active-Semi.

I2CTM is a trademark of NXP.

Innovative PowerTM

Active-Semi Proprietary―For Authorized Recipients and Customers

General Description

The ACT8941A features an advanced battery

charger that incorporates the patent-pending

ActivePath architecture for system power selection

This combination of circuits provides a complete,

advanced

battery-management

system

that

automatically selects the best available input

supply, manages charge current to ensure system

power availability, and provides a complete, high-

accuracy (±0.5%), thermally regulated, full-featured

single-cell linear Li+ charger that can withstand

input voltages of up to 12V.

ActivePath

Architecture

The

ActivePath

architecture

performs

three

important functions:

1) System Configuration Optimization

2) Input Protection

3) Battery-Management

System Configuration Optimization

The ActivePath circuitry monitors the state of the

input supply, the battery, and the system, and

automatically reconfigures itself to optimize the

power system. If a valid input supply is present,

ActivePath

powers the system from the input while

charging the battery in parallel. This allows the

battery to charge as quickly as possible, while

supplying the system. If a valid input supply is not

present, ActivePath powers the system from the

battery. Finally, if the input is present and the

system current requirement exceeds the capability

of the input supply, ActivePath allows system power

to be drawn from both the battery and the input

supply.

Input Protection

Input Over-Voltage Protection

The ActivePath circuitry features input over-voltage

protection circuitry. This circuitry disables charging

when the input voltage exceeds the voltage set by

OVPSET[-] as shown in Table 8, but stands off the

input voltage in order to protect the system. Note

that the adjustable OVP threshold is intended to

provide the charge cycle with adjustable immunity

against upward voltage transients on the input, and

is not intended to allow continuous charging with

input voltages above the charger's normal operating

voltage range. Independent of the OVPSET[-]

setting, the charge cycle is not allowed to resume

until the input voltage falls back into the charger's

normal operating voltage range (i.e. below 6.0V).

In an input over-voltage condition this circuit limits

VVSYS to 4.6V, protecting any circuitry connected to

VSYS from the over-voltage condition, which may

exceed this circuitry's voltage capability. This circuit

is capable of withstanding input voltages of up to

12V.

Table 8:

Input Over-Voltage Protection Setting

Input Supply Overload Protection

The ActivePath circuitry monitors and limits the total

current drawn from the input supply to a value set

by the ACIN and CHGLEV inputs, as well as the

resistor connected to ISET. Drive ACIN to a logic-

low for “USB Mode”, which limits the input current to

either 100mA, when CHGLEV is driven to a logic-

low, or 450mA, when CHGLEV is driven to a logic-

high. Drive ACIN to a logic-high for “AC-Mode”,

which limits the input current to 2A, typically.

Input Under Voltage Lockout

If the input voltage applied to CHGIN falls below

3.5V (typ), an input under-voltage condition is

detected and the charger is disabled. Once an input

under-voltage condition is detected, a new charge

cycle will initiate when the input exceeds the under-

voltage threshold by at least 500mV.

Battery Management

The ACT8941A features a full-featured, intelligent

charger for Lithium-based cells, and was designed

specifically to provide a complete charging solution

with minimum system design effort.

The core of the charger is a CC/CV (Constant-

Current/Constant-Voltage),

linear-mode

charge

controller. This controller incorporates current and

voltage sense circuitry, an internal 70mΩ power

MOSFET,

thermal-regulation

circuitry,

full-

featured state machine that implements charge

control and safety features, and circuitry that

eliminates the reverse blocking diode required by

conventional charger designs.

The charge termination voltage is highly accurate

(±0.5%), and features a selection of charge safety

time-out periods that protect the system from

operation with damaged cells. Other features

ActivePath

TM CHARGER

OVPSET[1]

OVPSET[0]

OVP THRESHOLD

6.6V

7.0V

7.5V

8.0V

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