Crystal Start-Up Waiting Time Setting - Realtek RTL8762C Hardware Instructions

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The smaller the CL is, the larger the frequency offset step of each internal capacitor is.

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For crystal with CL=12/15pF, external capacitor is needed to make the frequency offset

within 30~35KHz before performing calibration.

4.2 Crystal start-up waiting time setting

The start-up waiting time is to ensure that the crystal oscillator has sufficient start-up time. When

the crystal start-up time is greater than the start-up waiting time set by the IC, the SW will crash.

The IC crystal start-up time can be set by MP TOOL, and the start-up time is directly related to the

value of XTAL capacitor. The larger the XTAL capacitor is, the longer time the crystal oscillator

start-up takes. In addition, the PCBA crystal start-up time can be measured by an oscilloscope.

The crystal start-up time test procedure is as follows:

Set up the corresponding test platform as shown below, the steps are as follows:

1. Tightly twist two DuPont lines together to form a twisted pair, one of which is soldered to

the xo pin of 40MHz XTAL (the gray DuPont line in Figure 1), and the other one is not

connected (the red DuPont line in Figure 1).

2. Connect Micro USB to EVB Mother Board as power supply.

3. Connect the oscilloscope probe to the red DuPont line (the one that is not connected to xo

pin) in the twisted pair.

After the corresponding test platform is built according to the operation steps above, the EVB is

state, observe the waveform on the red DuPont line, which is coupled from the waveform of

40MHz XTAL xo pin on the gray DuPont line in the twisted pair, and measure the corresponding

start-up time (it is suggested to set the horizontal axis scale to 500ms first, and then adjust the

horizontal axis to 500us after the waveform is captured). The result is as shown in the figure below.

The start-up time is about 2T=750*2=1500us=1.5ms. Note that the external capacitor connected to

Figure 1 crystal start-up time test platform

RTL8762C Evaluation Board User Manual

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