STBC21 datasheet(17/54 Pages) STMICROELECTRONICS

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STBC21

Detailed description

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The charge starts if VCC exceeds 2.8 V, the battery is connected and its temperature is in

the safety range (see

Section 5.5).

In addition, the charge cycle starts if the available supply voltage exceeds by VCC-ASD the

BAT pin voltage level.

The start of charge in case of a discharged battery is already described in a previous

paragraph. Meanwhile, if a fully charged battery is connected, the charge starts in constant

voltage mode with TIMER-2 associated.

5.4

Fast-charge programming

When the battery voltage reaches the pre-charge voltage threshold, the STBC21 starts the

fast-charge phase. In this phase, the device charges the battery with a constant current,

programmable by an external resistor that sets the charge current. The formula used to

select the RPRG is as follows:

Equation 1

where VSET = 1.0 V and KPRG = 1000. During this phase, the battery voltage increases until

it reaches the programmed floating voltage or the safety timer expires and the alarm is

activated.

5.5

Charge auto-limitation

The STBC21 includes an auto-limitation algorithm to avoid explosion risks in the Li+ battery.

This algorithm makes sure that the battery is never charged at its maximum floating voltage

if the temperature is above 45 °C or below 10 °C.

Three more ranges are defined outside the safety range TL-TH (10 °C ~ 45 °C) as reported

Figure 6.

Table 7.

Start of charge

Item

Delay

Enabling condition

Battery connection detection

400 ms

VTEMP < 2.425 V

VCC voltage detection

10 ms

VCC > 2.8 V

Battery temperature detection

100 ms

0.75 V < VTEMP < 2.128 V

)

(

CHG

PRG

SET

PRG

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