Datasheet

TPS65950
SWCS032E–OCTOBER 2008–REVISED JANUARY 2011 www.ti.com
4.3 Power Control
4.3.1 Backup Battery Charger
If the backup battery is rechargeable, it can be recharged from the main battery. A programmable voltage
regulator powered by the main battery allows recharging of the backup battery. The backup battery charge
must be enabled using a control bit register. Recharging starts when two conditions are met:
• Main battery voltage > backup battery voltage
• Main battery > 3.2 V
The comparators of the backup battery system (BBS) give the two thresholds of the backup battery charge
startup. The programmed voltage for the charger gives the end-of-charge threshold. The programmed
current for the charger gives the charge current.
Overcharging is prevented by measurement of the backup battery voltage through the GP ADC.
Table 4-19 lists the characteristics of the backup battery charger.
Table 4-19. Backup Battery Charger Characteristics
Parameter Test Conditions Min Typ Max Unit
VBACKUP-to-MADC input attenuation VBACKUP from 1.8 to 3.3 V 0.33 V/V
Backup battery charging current VBACKUP = 2.8 V, BBCHEN = 1, BBISEL = 00 10 25 45 μA
VBACKUP = 2.8 V, BBCHEN = 1, BBISEL = 01 105 150 270 μA
VBACKUP = 2.8 V, BBCHEN = 1, BBISEL = 10 350 500 900 μA
VBACKUP = 2.8 V, BBCHEN = 1, BBISEL = 11 0.7 1 1.8 mA
VBACKUP = 0 V, BBCHEN = 1, BBISEL = 00 17.5 25 45 μA
VBACKUP = 0 V, BBCHEN = 1, BBISEL = 01 105 150 270 μA
VBACKUP = 0 V, BBCHEN = 1, BBISEL = 10 350 500 900 μA
VBACKUP = 0 V, BBCHEN = 1, BBISEL = 11 0.7 1 1.8 mA
End backup battery charging voltage: I
VBACKUP
= –10 μA, BBSEL = 00 2.4 2.5 2.6 V
VBBCHGEND
I
VBACKUP
= –10 μA, BBSEL = 01 2.9 3.0 3.1 V
I
VBACKUP
= –10 μA, BBSEL = 10 3.0 3.1 3.2 V
I
VBACKUP
= –10 μA, BBSEL = 11 3.1 3.2 3.3 V
4.3.2 Battery Monitoring and Threshold Detection
4.3.2.1 Power On/Power Off and Backup Conditions
Table 4-20 lists the threshold levels of the battery.
Table 4-20. Battery Threshold Levels
Parameter Test Conditions Min Typ Max Unit
Main battery charged threshold Measured on VBAT terminal 3.1 3.2 3.3 V
VMBCH
Main battery low threshold VMBLO VBACKUP = 3.2 V, measured on VBAT terminal (monitored 2.55 2.7 2.85 V
on terminal ONNOFF)
Main battery high threshold VMBHI Measured on terminal VBAT, VBACKUP = 0 V 2.5 2.65 2.95 V
Measured on terminal VBAT, VBACKUP = 3.2 V 2.5 2.85 2.95
Batteries not present threshold VBNPR Measured on terminal VBACKUP with VBAT < 2.1 V 1.6 1.8 2.0 V
Measured on terminal VBAT with VBACKUP = 0 V 1.95 2.1 2.25
(monitored on terminal VRRTC)
56 Power Module Copyright © 2008–2011, Texas Instruments Incorporated
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