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Button Sampling Window: set by
LCDIV, SENCYC
n
, and
f
SENSOR
n
Scan Rate: set by NPSR,
LPSR, and LPWRB pin
IN0
IN1
IN2
IN3
Figure 8-6. Configurable Scan Rate and Sampling Window
The LDC3114 is designed to work with LC resonator sensors with oscillation frequencies ranging from 1 MHz to
30 MHz.
calculates the exact definition of the sampling window.
n
n
t
n
f
LCDIV
SAMPLE
SENSOR
Number of Sensor Oscillation Cycles
Button Sampling Window
Sensor Frequency
128
SENCYC
1
2
,
0, 1, 2, or 3
u
u
(7)
where:
•
t
SAMPLE
is the sampling window in µs
• SENCYC
n
and LCDIV are the linear and exponential scalers that set the number of sensor oscillation cycles
•
f
SENSOR
n
is the sensor frequency in MHz
In
, LCDIV (0 to 7, default 3) is the exponential LC divider that sets the approximate ranges for all
channels, and SENCYC
n
(0 to 31, default 4) is the linear sensor cycle scaler that fine-tunes each individual
channel. Together they set the number of sensor oscillation cycles used to determine the sampling window.
For example, if the LC sensor frequency is 9.2 MHz, and it is desirable to get 1-ms sampling window, then this
can be achieved by setting SENCYC
n
= 17 and LCDIV = 2.
Alternatively, from the sampling window and sensor frequency, the LCDIV can be read off from
Function of Sensor Frequency and Button Sampling Window
. For example, 1-ms sampling window
and 9.2-MHz sensor frequency intersect in the region closest to where LCDIV = 2. Then SENCYC
n
can be
calculated accordingly.
SNOSDD0 – DECEMBER 2021
Copyright © 2021 Texas Instruments Incorporated
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