ACT8828 datasheet(42/49 Pages) ACTIVE-SEMI

42 / 49 page

ActivePath

TM CHARGER

ACT8828

Rev 3, 24-Sep-09

Active-Semi

Innovative Power

- 42 -

www.active-semi.com

ActivePMU

TM and ActivePathTM are trademarks of Active-Semi.

2CTM is a trademark of Philips Electronics.

ACIN CHGLEV

CHARGE

CURRENT

ICHG (mA)

PRECONDITION

CHARGE CURRENT

ICHG (mA)

90mA or 12%

ISET

(Smallest one)

90mA or 12%ISET

(Smallest one)

450mA or ISET

(Smallest one)

12% × ISET

50% × ISET

12% × ISET

ISET

12% × ISET

FUNCTIONAL DESCRIPTION CONT’D

current-limited nSTAT outputs that can directly drive

LED indicators or provide a logic-level status signal

to the host microprocessor

Dynamic Charge Current Control (DCCC)

The

ACT8828's

ActivePath

charger

features

Dynamic Charge Current Control (DCCC) circuitry,

which continuously monitors the input supply and

prevents input overload conditions by dynamically

adjusting the charge current to keep the input voltage

from dropping below the DCCC voltage threshold.

By default, the DCCC voltage threshold is set to

4.4V, but it may also be programmed by connecting

a resistor from DCCC to GA, where the resistor has

value given by the following equation:

VDCCC = 2 × (IDCCC × RDCCC)

(2)

Where RDCCC is the value of the external resistor,

and IDCCC is the value of the current sourced from

DCCC, typically 100μA.

Charger Current Programming

The ACT8828's ActivePath charger features a

flexible charge current-programming scheme that

combines the convenience of internal charge

current programming with the flexibility of resistor

based charge current programming. Current limits

and charge current programming are managed as a

function of the ACIN and CHGLEV pins, in

combination with RISET, the resistance connected to

the ISET pin.

ACIN and CHGLEV Inputs

ACIN is a logic input that configures the current-limit

of ActivePath's linear regulator as well as that of the

battery charger. ACIN features a precise 1.25V

logic threshold, so that the input voltage detection

threshold may be adjusted with a simple resistive

voltage divider. This input also allows a simple, low-

cost dual-input charger switch to be implemented

with just a few, low-cost components.

When ACIN is driven to a logic high, the ActivePath

operates in “AC-Mode” and the charger charges at

the current programmed by RISET,

ICHG = 1V/RISET × KISET

(3)

where KISET = 640 when CHGLEV is driven to a

logic high, and K = 320 when CHGLEV is driven to

a logic low.

When ACIN is driven to a logic-low, the ActivePath

circuitry operates in “USB-Mode”, which enforces a

maximum charge current setting of 500mA, if

CHGLEV is driven to a logic-high, or 100mA, if

CHGLEV is driven to a logic-low.

The ACT8828's charge current settings are

summarized in the table below:

Table 16:

ACIN and CHGLEV Inputs Table

Note that the actual charging current may be limited

to a current that is lower than the programmed fast

charge current due to the ACT8828’s internal

thermal

regulation

loop.

See

the

Thermal

Regulation

and Protection section for more

information.

Battery Temperature Monitoring

The

ACT8828

continuously

monitors

the

temperature of the battery pack by sensing the

resistance of its thermistor, and suspends charging

if the temperature of the battery pack exceeds the

safety limits.

In a typical application, shown in Figure 7, the TH

pin is connected to the battery pack's thermistor

input. The ACT8828 injects a 100µA current out of the

TH pin into the thermistor, so that the thermistor

resistance is monitored by comparing the voltage at

TH to the internal VTHH and VTHL thresholds of 0.5V

and 2.5V, respectively. When VTH > VTHL or VTH < VTHH

charging and the charge timers are suspended. When

VTH returns to the normal range, charging and the

charge timers resume.

The net resistance from TH to G required to cross

the threshold is given by:

100µA × RNOM × kHOT = 0.5V → RNOM × kHOT = 5kΩ

100µA × RNOM × kCOLD = 2.5V → RNOM × kCOLD = 25kΩ

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