Document Number: 002-14826 Rev. *G
Page 15 of 65
PRELIMINARY
CYW43903
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. External 32.768 kHz Sleep Clock Specifications
Parameter
LPO Clock
Units
Nominal input frequency
32.768
kHz
Frequency accuracy
±200
ppm
Duty cycle
30–70
%
Input signal amplitude
200–3300
mV, p-p
Signal type
Square-wave or sine-wave
–
Input impedance
1
1. When power is applied or switched off.
>100k
<5
Ω
pF
Clock jitter (during initial start-up)
<10,000
ppm
