Datasheet

TPS65930/TPS65920
www.ti.com SWCS037G–MAY 2008–REVISED APRIL 2011
4.2 Power References
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 power state-machine in slow mode (filtered, less noisy) when required.
Table 4-12 lists the voltage reference characteristics.
Table 4-12. Voltage Reference Characteristics
Parameter Test Conditions Min Typ Max Unit
Output Load Condition
Filtering capacitor Connected from V
REF
to GNDREF 0.3 1 2.7 μF
Electrical Characteristics
V
IN
Input voltage On mode 2.7 3.6 4.5 V
Internal bandgap reference voltage On mode, measured through TESTV terminal 1.272 1.285 1.298 V
Reference voltage (V
REF
terminal) On mode 0.749 0.75 0.77 V
Retention mode reference On mode 0.492 0.5 0.508 V
I
REF
NMOS sink 0.9 1 1.1 μA
Ground current Bandgap 25 μA
I
REF
block 20
Preregulator 15
V
REF
buffer 10
Retention reference buffer 10
Output spot noise 100 Hz 1 μV/√Hz
A-weighted noise (rms) 200 nV (rms)
P-weighted noise (rms) 150 nV (rms)
Integrated noise 20 to 100 kHz 2.2 μV
I
BIAS
trim bit LSB 0.1 μA
Ripple rejection <1 MHz from VBAT 60 dB
Start-up time 1 ms
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 4-13 lists the characteristics of the backup battery charger.
Table 4-13. 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
Copyright © 2008–2011, Texas Instruments Incorporated Power Module 45
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