
4.2
Power References
4.3
Power Control
4.3.1
Backup Battery Charger
TPS65950
Integrated Power Management/Audio Codec
www.ti.com
SWCS032 – OCTOBER 2008
If a short circuit is detected on VRUSB1V8 or VRUSB1V5, the power subchip FSM switches off the
relevant LDO.
The bandgap voltage reference is filtered (resistance/capacitance [RC] filter) using an external capacitor
connected across the VREF output and an analog ground (REFGND). The VREF voltage is scaled,
distributed, and buffered in the device. The bandgap is started in fast mode (not filtered), and is set
automatically by the D machine in slow mode (filtered, less noisy) when required.
Table 4-17 lists the characteristics of the voltage references.
Table 4-17. Voltage Reference Characteristics
Parameter
Test Conditions
Min(1)
Typ(2)
Max(3)
Unit
Output Load Condition
Filtering capacitor
Connected from VREF to REFGND
0.3
1
2.7
F
(1)
Min = Minimum value
(2)
Typ = Typical value
(3)
Max = Maximum value
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 the following 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 4-18 lists the characteristics of the backup battery charger.
Table 4-18. Backup Battery Charger Characteristics
Parameter
Test Conditions
Min(1)
Typ(2) Max(3)
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
A
VBACKUP = 2.8 V, BBCHEN = 1, BBISEL = 01
105
150
270
A
VBACKUP = 2.8 V, BBCHEN = 1, BBISEL = 10
350
500
900
A
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
A
VBACKUP = 0 V, BBCHEN = 1, BBISEL = 01
105
150
270
A
VBACKUP = 0 V, BBCHEN = 1, BBISEL = 10
350
500
900
A
VBACKUP = 0 V, BBCHEN = 1, BBISEL = 11
0.7
1
1.8
mA
End backup battery charging voltage:
IVBACKUP = –10 A, BBSEL = 00
2.4
2.5
2.6
V
VBBCHGEND
IVBACKUP = –10 A, BBSEL = 01
2.9
3.0
3.1
V
IVBACKUP = –10 A, BBSEL = 10
3.0
3.1
3.2
V
IVBACKUP = –10 A, BBSEL = 11
3.1
3.2
3.3
V
(1)
Min = Minimum value
(2)
Typ = Typical value
(3)
Max = Maximum value
Power Module
57