TSC2000_08 Datasheet, PDF (30/35 Pages) Texas Instruments – PDA ANALOG INTERFACE CIRCUIT

OPERATION—BATTERY MEASUREMENT
An added feature of the TSC2000 is the ability to monitor the
battery voltage on the other side of a voltage regulator (DC/
DC converter), as shown in Figure 21. The V_BAT1 input is
divided down by 4 so that an input range of 0.5V to 6.0V can
be measured. Because of the division by 4, this input range
would be represented as 0.125V to 1.5V to the A/D con-
verter.
Battery
0.5V ₊
to
6.0V
DC/DC
Converter
2.7V
V_DD
V_BAT1
7.5kΩ
0.125V to 1.5V
2.5kΩ
Host Writes
A/D Converter
Control Register
Start Clock
Power Up Reference
Power Up
A/D Converter
Convert
Battery Input 1
No
Is Data
Averaging Done
Yes
Store Battery Input 1
in BAT1 Register
Battery Input 1
Power Down
A/D Converter
Power Down Reference
Issue Data Available
Turn Off Clock
Done
FIGURE 22. V_BAT1 Measurement Process.
FIGURE 21. Battery Measurement Functional Block Diagram.
The V_BAT2 input is divided down by 2, so it accommodates an
input range of 0.5V to 3.0V, which is represented to the A/D
converter as 0.25V to 1.5V. This smaller divider ratio allows
for increased resolution. Note that the V_BAT2 input pin can
withstand up to 6V, but this input will only provide accurate
measurements within the 0.5V to 3.0V range.
For both battery inputs, the dividers are ON only during the
sampling of the battery input, in order to minimize power
consumption.
Flowcharts which detail the process of making a battery input
reading are shown in Figures 22 and 23.
The time needed to make temperature, auxiliary, or battery
measurements is given by:
(7)
t_READING
= 2.625µs + t_REF

+ N_{AVG }N_BITS
•
1
f_CONV
+ 4.4µs^{}
where t_REF is the reference delay time as given in Table XVII.
Host Writes
A/D Converter
Control Register
Start Clock
Power Up Reference
Power Up
A/D Converter
Convert
Battery Input 2
No
Is Data
Averaging Done
Yes
Store Battery Input 2
in BAT2 Register
Battery Input 2
Power Down
A/D Converter
Power Down Reference
Issue Data Available
Turn Off Clock
Done
FIGURE 23. V_BAT2 Measurement Process.
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