pca8885 NXP Semiconductors, pca8885 Datasheet - Page 15

• Manufacturer Part Number: pca8885
• Description: Capacitive 8-channel Proximity Switch With Auto-calibration And Very Low Power Consumption
• Manufacturer: NXP Semiconductors

NXP Semiconductors
PCA8885
Objective data sheet
10.4.1 Clock generation and frequency adjustment
All bits in this register can be written and read with the write-clock and read-clock
commands.
The PCA8885 contains an integrated oscillator as main clock source. The oscillator runs
nominally at f
can be tuned (see
The values of m can be varied in the range 0.5  m  1.75, where m = 1.0 corresponds to
the default value of FRQF[2:0] = 100.
The internal clock frequency (f
where the values for n are 1, 4, 16, or 64 and can be selected with FRQC[1:0]. The sensor
sampling frequency (f
The eight sensors are sampled sequentially, which results in a default sensor sampling
rate of f
In secondary-chip mode, the internal clock generator is stopped, and the circuit is clocked
from the CLK_IN input pin.
The tuning of the oscillator frequency and the programmable clock divider (see
allows changing the sensor sampling rate, the adjustment of the reaction time and the
power consumption of the PCA8885 over a wide range.
Fig 6.
f
f
f
s
osc
clk
=
=
=
f
clk
s
f
m
= 1 kHz.
osc
Oscillator block diagram
8 

n 
f
FRQF[2:0]
osc(nom)
osc nom
OSC
All information provided in this document is subject to legal disclaimers.

Equation

= 128 kHz. With the values of FRQF[2:0], the oscillator frequency
Rev. 1 — 24 November 2011
s
) is derived from the internal clock frequency with
Capacitive 8-channel proximity switch with auto-calibration
1).
f
osc
clk
/4
) is derived from the oscillator frequency with
f
osc
/4
/4
f
osc
/16
/4
f
osc
/64
FRQC[1:0]
013aaa314
PCA8885
© NXP B.V. 2011. All rights reserved.
Equation
CLK
Equation
Figure
3:
15 of 43
6)
(1)
(2)
(3)
2: