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ACT3780

ActivePath™ Battery Charger

Active-Semi, Inc 

ACT3780

Rev 8, 09-Jul-13

The ACT3780's charge current settings are

summarized in the table below:

Table 1:

ACIN and CHGLEV Inputs Table

ACIN

High

High

Low

Low

CHGLEV

High

Low

High

Low

Fast Charge Current

ISET (mA) = 495 / (RISET (kΩ) - 0.036)

0.5 × ISET

Min (450mA, ISET )

Min (90mA, ISET )

Note that the actual charging current may be limited

to a current that is lower than the programmed fast-

charge current due to the ACT3780’s internal

thermal regulation loop. See the Thermal

Regulation and Protection section for more

information.

Dynamic Charge Current Control (DCCC)

The ACT3780's ActivePath Charger features

Dynamic Charge Current Control (DCCC) circuitry,

which continuously monitors the input supply to

prevent input overload conditions. DCCC reduces the

charge current when the SYS voltage decreases to

VDCCC and stops charging when SYS drops below

VDCCC by 1.5% (typical).

The DCCC voltage threshold is programmed by

connecting a resistor from DCCC to GA according

to the following equation:

( ) VDCCC = 2 × IDCCC × RDCCC

(2)

Where RDCCC is the value of the external resistor,

and IDCCC (100µA typical) is the value of the current

sourced from DCCC.

Given the tolerances of the RDCCC and IDCCC ,the

DCCC voltage threshold should be programmed to

be no less than 3.3V to prevent triggering the

UVLO, and to be no larger than 4.4V to prevent

engaging DCCC prematurely. A 19.1k (1%), or

18.7k (1%) resistor for RDCCC is recommended.

Battery Temperature Monitoring

The ACT3780 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 1, the TH

pin is connected to the battery pack's thermistor

input. The ACT3780 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

where RNOM is the nominal thermistor resistance at

room temperature, and kHOT and kCOLD are the ratios

of the thermistor's resistance at the desired hot and

cold thresholds, respectively.

Figure 1:

Simple Configuration

Design Procedure

When designing with thermistors it is important to

keep in mind that their nonlinear behavior typically

allows one to directly control no more than one

threshold at a time. As a result, the design

procedure can change depending on which

threshold is most critical for a given application.

Most application requirements can be solved using

one of three cases,

1) Simple solution

2) Fix VTHH, accept the resulting VTHL

3) Fix VTHL, accept the resulting VTHH

The ACT3780 was designed to achieve an

operating temperature range that is suitable for

most applications with very little design effort. The

simple solution is often found to provide reasonable

results and should always be used first, then the

design procedure may proceed to one of the other

solutions if necessary.

Innovative PowerTM

-9-

Active-Semi Proprietary―For Authorized Recipients and Customers

ActivePathTM is a trademark of Active-Semi.

www.active-semi.com

Copyright © 2013 Active-Semi, Inc.

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