STBC21 Datasheet, PDF (17/54 Pages) STMicroelectronics – LI+ battery charger with thermal regulation

STBC21
Detailed description
Table 7. Start of charge
Item
Battery connection detection
V_CC voltage detection
Battery temperature detection
Delay
400 ms
10 ms
100 ms
Enabling condition
V_TEMP < 2.425 V
V_CC > 2.8 V
0.75 V < V_TEMP < 2.128 V
The charge starts if V_CC 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 V_CC-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
R_PRG
=
V_SET
× ( ^KPRG
I_CHG
)
where V_SET = 1.0 V and K_PRG = 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 T_L-T_H (10 °C ~ 45 °C) as reported
in Figure 6.
Doc ID 023256 Rev 1
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