CYW43364 datasheet(13/68 Pages) CYPRESS

13 / 68 page

Document Number: 002-14781 Rev. *C

Page 13 of 68

PRELIMINARY

CYW43364

3.3 External 32.768 kHz Low-Power Oscillator

The CYW43364 uses a secondary low-frequency sleep 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 trade-off 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

4 on page 13.

Note: The CYW43364 will auto-detect the LPO clock. If it senses a clock on the EXT_SLEEP_CLK pin, it will use that clock. If it

doesn't sense a clock, it will use its own internal LPO.

■ To use the internal LPO: Tie EXT_SLEEP_CLK to ground. Do not leave this pin floating.

■ To use an external LPO: Connect the external 32.768 kHz clock to EXT_SLEEP_CLK.

Table 4. 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 impedancea

a. When power is applied or switched off.

>100

kΩ

Clock jitter

<10,000

ppm

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