AN2760 Datasheet, PDF (10/14 Pages) STMicroelectronics – Using clock distribution circuits in smart phone system design

Cell phone system design with STCD10x0 clock solution
Figure 5. Connection of the DC-CUT capacitor and bias
VCC
VCTCXO
0.1μF
OUT
DC-CUT
R1
MCLK
R2
STCD1020
STCD1030
STCD1040
AN2760
ai13957
2.4
Connecting STCD10x0 outputs to application modules
The output channels of the STCD10x0 are biased at half of V_CC internally by design. 1µF
DC-CUT capacitors are required at each of the outputs in most applications.
2.5
Power-down sequence
If the STCD10x0 shares the same power supply with TCXO (clock source), it is suggested
to power up the TCXO before enabling each of the clock outputs since normally it will take
several milliseconds for the TCXO to stabilize its output.
If the STCD10x0 uses different power supplies with TCXO, it is not recommended to power
down V_CC of STCD10x0 since it only consumes standby current which is no more than 1µA
(when no clock output is enabled, the STCD10x0 enters standby mode). If shutdown of the
STCD10x0 is preferred, the following power-down steps must be followed:
1. Shut down clock source TCXO output
2. Disable EN pins, pull low
3. Shut down STCD10x0 power V_CC
If the power-down sequence is not strictly followed as above, the user may find the clock
output waveform viewed at the condition of TCXO active with output, V_CC of STCD10x0
shutdown, and EN pins active. This possibility is illustrated in Figure 6.
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