ACT5880 datasheet(82/87 Pages) ACTIVE-SEMI

82 / 87 page

ACT5880

Rev 2, 03-Sep-13

- 82 -

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RB, are used to condition the string to have the

desired ratios at the wanted hot threshold

temperature and cold threshold temperature.

Figure 18:

The Battery Thermal Condition Circuit.

The normal temperature range cells typically work

in -20°C to 40°C while the extended range is -20°C

to 60°C. Giving the a NTC thermistor with 25°C

characteristic resistance of R25, the resistance ratio

at hot threshold temperature is rH and at cold

threshold temperature is rC, the proportion factor A

and B for having the 2 precise ratios 0.748 and

0.349 are found as:

A=0.411·(rC−rH)

B=0.220·rC−1.22·rH

It is necessary to verify how much power is desired

to bias the selected NTC thermister, to assure no

excessive self heating generated.

The resistance ratio r is the ratio of the resistance at

a temperature to the resistance at 25°C. This ratio

is found from the NTC specification in a table or a

curve plot.

Reverse Block

The ACT5880 has a reverse block circuit in the

charge path. Whenever the VCHGIN is less than

VVBAT, as low as to 0V, the reverse block circuit

prevents the reverse leakage from VBAT to CHGIN

and the state machine jumps into Sleep State. This

reverse block circuit does not work in LDO mode

operation.

Input Over Voltage

The CHGIN allows applying continuous 12V and

momentary 14V on it. When the voltage applied on

CHGIN is greater than the over voltage threshold,

the state machine jumps into Sleep State and

charging stops.

As in the real application circuitry often has other

connection to the CHGIN, such as the VBUS of

USB circuit, the pull-up of charge state LED, the

pull-up for BATID input, the pull-up for ACIN input

and the pull-up for TH input. It may not be allowed

to apply higher voltage on the CHGIN considering

those other connections.

Typical Application Consideration

The charger circuit is well compensated, can be

used to charge various capacities cells without

modifying the input and output decoupling caps,

which is 6.8μF~22μF for the input and 4.7μ~10μF

for the output.

Autonomic and Slave Charge

The charge state machine in the ACT5880 is a

complete autonomy. It senses the condition

parameters, manages charge profile and indicates

charge status without any foreign involvement.

The charger wakes up the host system, and calls

for host system involvement if it is configured so.

With this mechanism, the ACT5880 could work as a

slave charger with host system involvement on

demand.

Li+ Poly Cell and Li+ Cell Charge

The scheme and the default setting are optimized

for single cell Li+ poly charging. Li+ poly cells with

4.2V charge termination voltage, which are the

most common battery types in phone designs.

In case of using 18650 cylindrical cell, which is

typically with 4.1V charge termination voltage (the

termination voltage is anode material dependent, is

specified for a battery model), applying 4.2V on it

does not cause instant damage. It is possible to

start with 4.2V battery regulation voltage and then

program it to 4.1V later, but this is not rational for

safe charging. Contact factory for ordering parts

with 4.1V default.

NiMH cells charge

Though the charge scheme is not optimized for

charging NiMH cells, its current limit and voltage

limit, auto-restart features make the ACT5880

charger a practically applicable charger in fix

wireless terminal applications for 3 NiMH cells

charging with its 4.2V to 4.4V battery regulation

voltages. In this kind of applications, the cells are

floating charged at 1.4V to 1.47V per cell, which is

in the good range for floating and uses the most

part of the battery capability. Figure 19 shows the

typical curves for NiMH battery.

RB =B·R25

NTC

=r·R25

=A·R25

0.748

0.349

CHGIN

ACT5880

(Ground )

Battery

Assembly

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