BCM4354 Data Sheet
External 32.768 kHz Low-Power Oscillator
External 32.768 kHz Low-Power Oscillator
The BCM4354 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 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 which meets the
requirements listed in Table 4.
Table 4: External 32.768 kHz Sleep Clock Specifications
Parameter
LPO Clock
Unit
Nominal input frequency
Frequency accuracy
Duty cycle
32.768
kHz
ppm
%
±200
30–70
Input signal amplitude
Signal type
200-3300
mV, p-p
–
Square-wave or sine-wave
Input impedancea
> 100k
< 5
Ω
pF
Clock jitter (during initial start-up)
< 10,000
ppm
a. When power is applied or switched off.
Broadcom®
October 15, 2014 • 4354-DS109-R
Page 30
BROADCOM CONFIDENTIAL
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