Electronic – Difference between 32 KHz clock output load vs. clock input impedance requirement

clockimpedance

I have a WiFi chip that requires a input impedance of > 100 kohms and < 5 pF as seen in the requirements table found in the datasheet below.

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I'm confused if this 5 pF requirement correlates to the output load of the clock I'm using.

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Am I confusing things here? I feel like 15 pF output load violates the 5 pF input impedance requirement.

Another question is, how do I know if my output impedance is greater than 100 kohms, do I just place a 100 kohm resistor to do that job?

Any help is appreciated. Very new to this sort of stuff.

Link to Clock datasheet

Best Answer

I have a wifi chip that requires a input impedence of >100kohms and <5pF

You are misunderstanding the datasheet. That means that the input impedance of the clock input will be greater than 100 kΩ, and have a load capacitance of less than 5 pF.

This means that you need a clock source with a significantly lower output impedance than 100 kΩ, and can tolerate at least a 5 pF capacitive load. Luckily, just about every clock source, including your clock source, is able to drive this input.

Edit:

However, note the input signal amplitude specified: 200-1800 mV. The 3.3 V output from the oscillator exceeds this. A voltage divider should be fine, the 32 kHz signal is slow enough that a voltage divider is not an issue.

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