ACT2802 datasheet(13/21 Pages) ACTIVE-SEMI

13 / 21 page

ACT2802

Rev 0, 21-Jan-14

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- 13 -

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Table 4: Battery Impedance

Boost Output Plug-in Auto Detection

Figure 13 provides a solution for auto plug-in

detection.

Input Over Voltage Surge

In the case of pure ceramic input capacitor is

chosen, if the input cable is long, stray inductance

may cause over voltage spikes as twice as the

steady-state voltage when input source is plugged

in. Below input circuit is recommended to avoid

input voltage surge. R1 resistor is added in series

with capacitor C1 to damp the potential LC

resonance as shown in Figure 14.

External Input Over Voltage Protection

Considering the maximum voltage rating at VIN pin,

the external OVP circuit as shown in Figure 15 is

recommended if input voltage may go higher than

7V. With the enhanced OVP circuit, input voltage

can be up to 18V.

Flashlight Circuit

Figure 16 shows a circuit with flashlight driver and

control.

LEDs on in Boost Mode

LEDs can be always on during boost mode, the

schematic is shown in Figure17.

Inductor and Capacitor Selection

ACT2802 supports SMD components. 2.2uH

inductor is recommended. Input side, 4.7uF ceramic

capacitor

series

with

2.7Ω

resistor

are

recommended, on battery side, 22uF ceramic

capacitors is recommended while on output side,

22uFx2 ceramic capacitors are recommended.

Battery Temperature Monitoring

The

ACT2802

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, the TH pin is connected to

the battery pack's thermistor input as shown in

Figure 18. The ACT2802 injects a 60µA 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 VTHL and VTHH thresholds of 0.3V

and 1.5V, respectively. When VTH > VTHH or VTH < VTHL

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 GND required to cross

RIMC(KΩ)

100

200

Battery

Impedance

R(mΩ)

Rcs=25mΩ

100

200

Rcs=50mΩ

100

200

400

Figure 13.

Boost output auto detection circuit

Figure 14. Input over voltage surge protection circuit

Figure 15.

Input over voltage protection

Figure 16. Flashlight circuit

Figure 17. LEDs on in boost mode circuit

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