Figure 2-5. Use Of The Batcntl Pin; Battery Control Feature - Sharp LH79524 User Manual

LH79524/LH79525 User's Guide
Four comparison periods are necessary for a 4-bit ADC. Generally, an N-bit SAR ADC
requires N comparison periods and will not be ready for the next conversion until the
current conversion is completed.
Another feature of SAR ADCs is that power dissipation scales with the sample rate. By
comparison, flash or pipelined ADCs usually have constant power dissipation as opposed
to sample rate. This SAR ADC feature is especially useful in low-power applications or
applications where data acquisition is not continuous.

2.1.6 Battery Control Feature

The battery control pin (BATCNTL) allows control of external battery circuits by the SoC.
An external resistor divider allows monitoring the external battery voltage, as shown
in Figure 2-5. External switches Q1 and Q2 connect the voltage divider to
the battery. These switches are driven by the BATCNTL pin, which remains HIGH for the
duration of the measurement. R1 and R2 should be chosen so that during normal opera-
tion (with BATCNTL LOW), the voltage at VBAT is somewhere within the common mode
input range of the ADC. For example if the battery voltage is 6 V nominal, choose R1= 300
kΩ and R2 = 100 kΩ to give IN+ = 1.5 V at a load of only 15
Note that the BATCNTL pin is only active when making the measurement on that particular
ADC channel. All other times BATCNTL is LOW.
Software can easily configure the ADC for battery voltage measurement. Program the
PC:BATLOC field to correspond to the channel to which the battery voltage measurement
is connected. When HW:INP (the + Input Mux selection) equals the value in PC:BATLOC,
the BATCNTL pin goes HIGH and loads the battery through the external switch as shown
in Figure 2-5. In addition, PC:BATEN, the Battery Control Enable signal, must be pro-
grammed to 1. When the BATCNTL pin is not required to go HIGH, for example when the
ADC is used in a general purpose application, PC:BATLOC should be programmed so that
it will never equal any of the inputs that will be used in the application e.g. 0b1111. Also
the PC:BATEN can be programmed to 0 to disable this function.
R1
VBAT
Q1
+
_
R2
BATTERY
Q2

Figure 2-5. Use of the BATCNTL Pin

Version 1.0
Analog-to-Digital Converter/Brownout Detector
μ
LH79524/LH79525
AN x
IN+
MUX
CTCLK/INT4/BATCNTL
A on the battery.
10
A/D
LH79525-119
2-7