BCM4339 Preliminary Data Sheet
External 32.768 kHz Low-Power Oscillator
External 32.768 kHz Low-Power Oscillator
The BCM4339 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 that meets the
requirements listed in Table 3.
Table 3: External 32.768 kHz Sleep Clock Specifications
Parameter
LPO Clock
Units
Nominal input frequency
Frequency accuracy
Duty cycle
32.768
kHz
ppm
%
±200
30–70
Input signal amplitude
Signal type
200–1800
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®
November 17, 2014 • 4339-DS106-R
Page 34
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