8.1.5 Configuring Button or Raw Data Scan Rate
The LDC3114 periodically samples all active channels at the selected scan rate. The device can operate at eight
different scan rates to meet various power consumption requirements, where a lower scan rate achieves lower
power consumption.
In Normal Power Mode, the scan rate can be programmed to 80, 40, 20, or 10 SPS through
Register
NP_SCAN_RATE (Address 0x0D)
. Additionally through NPFSR bit field in the same register 160 SPS rate
can be enabled which overrides the setting of
NPSR
but not the
NPCS
bit fields. The
NPCS
bit field allows to
set the part in continuous sampling mode in Normal Power Mode only. When
NPCS
is set then the settings for
NPSR and NPFSR are ignored.
In Low Power Mode, the scan rate can be programmed to 5, 2.5, 1.25, or 0.625 SPS through
Register
LP_SCAN_RATE (Address 0x0F)
. The mode is selected by setting the LPWRB pin to VDD (Normal Power)
or ground (Low Power). In either mode, each button can be independently enabled through a bit in
Register EN
(Address 0x0C)
.
shows the typical distribution of the scan rates.
Table 8-1. Scan Rates
SCAN RATE (SPS)
LPSR (0x0F)
SETTING
NPSR (0x0D) SETTING
NPCS (0x0D)
SETTING
NPFSR (0x0D)
SETTING
LPWRB PIN SETTING
0.625
b11
Not Applicable
Not Applicable
Not Applicable
Ground
1.25
b10
Not Applicable
Not Applicable
Not Applicable
Ground
2.5
b01
Not Applicable
Not Applicable
Not Applicable
Ground
5
b00
Not Applicable
Not Applicable
Not Applicable
Ground
10
Not Applicable
b11
b0
b0
V
DD
20
Not Applicable
b10
b0
b0
V
DD
40
Not Applicable
b01
b0
b0
V
DD
80
Not Applicable
b00
b0
b0
V
DD
160
Not Applicable
Not Applicable
b0
b1
V
DD
Continuous
Not Applicable
Not Applicable
b1
Not Applicable
V
DD
8.1.6 Programming Button or Raw Data Sampling Window
The sampling window is the actual duration per scan cycle for active data sampling of the sensor frequency.
It is programmed with the exponential parameter, LCDIV, in
Register LC_DIVIDER (Address 0x17)
, and the
individual linear sensor cycle counter SENCYC
n
(
n
= 0, 1, 2, or 3) in Registers SENSOR
n
_CONFIG (
n
= 0, 1,
2, or 3, Addresses
0x20
,
0x22
,
0x24
,
0x26
). For most touch button applications, the button sampling window
should be set to between 1 ms and 8 ms. For sampling rate of 160 SPS, the window has to be less than 6.25
ms. For continuous sampling, the data becomes available at the configured sampling window period rate. The
recommended minimum sensor conversion time is 1 ms. Longer conversion time can be used to achieve better
signal-to-noise ratio, if needed. The active channels in
will sample sequentially if multiple channels
are enabled.
SNOSDD0 – DECEMBER 2021
40
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