BCM4356XKWBGT Datasheet, PDF (32/195 Pages) Cypress Semiconductor – Single-Chip 5G WiFi IEEE 802.11ac 2×2 MAC/ Baseband/Radio with Integrated Bluetooth 4.1, FM Receiver, and Wireless Charging

BCM4356 Advance Data Sheet
External 32.768 kHz Low-Power Oscillator
External 32.768 kHz Low-Power Oscillator
The BCM4356 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
Nominal input frequency
Frequency accuracy
Duty cycle
Input signal amplitude
Signal type
Input impedance^c
Clock jitter (during initial start-up)
32.768
±200
30 – 70
200–3300^{a, b}
Square-wave or sine-wave
> 100k
<5
< 10,000
a. The LPO_IN input has an internal DC blocking capacitor, no external DC blocking is required.
b. The input DC offset must be ≥ 0V to avoid conduction by the ESD protection diode.
c. When power is applied or switched off.
Unit
kHz
ppm
%
mV, p-p
–
Ω
pF
ppm
Broadcom^®
May 8, 2015 • 4356-DS103-R
BROADCOM CONFIDENTIAL
Page 31