External 32.768 Khz Low-Power Oscillator - Infineon Cypress WICED CYW43903 Manual

3.3 External 32.768 kHz Low-Power Oscillator

The CYW43903 uses a secondary low frequency clock for low-power-mode timing. Either the internal low-precision LPO or an external
32.768 kHz precision oscillator is required. The internal LPO frequency range is approximately 33 kHz ± 30% over process, voltage,
and temperature, which is adequate for some applications. However, one tradeoff caused by this wide LPO tolerance is a small current
consumption increase during power save mode that is incurred by the need to wake-up earlier to avoid missing beacons.
Whenever possible, the preferred approach is to use a precision external 32.768 kHz clock that meets the requirements listed in
Table 5.
Table 5. External 32.768 kHz Sleep Clock Specifications
Parameter
Nominal input frequency
Frequency accuracy
Duty cycle
Input signal amplitude
Signal type
1
Input impedance
Clock jitter (during initial start-up)
1. When power is applied or switched off.
Document Number: 002-14826 Rev. *G
PRELIMINARY
LPO Clock
32.768
±200
30–70
200–3300
Square-wave or sine-wave
>100k
<5
<10,000
CYW43903
Units
kHz
ppm
%
mV, p-p
–
Ω
pF
ppm
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