how to test WCO's precision at PSoC4100S

[Anonymous]

Our product using psoc4100s as MCU, but the ILO is not accurate and we use WCO to replace it. Now how to test the precision of WCO at PSoC4100S.

1, using WDT timer?

WDT timer is based on LFCLK, which is from ILO. would you help confirm that WDT from ILO or WDT from WCO.

2, using timer0 or timer1 or timer2?

If timer using WCO as source clock, we want set timer and in timer-isr to driver "one pin" in high state, hardware test the time of the pin from low state to high state.

Does this method is accurate enough when test the precision of WCO?

3, any other methods to test WCO's precision?

thanks.

[HaoW_21]

Hi Qipan,

Here are the answers to your question.

1. WDT clock source is ILO, not WCO.

2. You can use timer0, timer1 or timer2 to check WCO frequency indirectly, but that is different from accuracy here. You just measure its frequency with oscilloscope.

Actually WCO accuracy depends mostly on the crystal you have used.

Hao

[Anonymous]

thanks, hao!

BTW, can we disable ILO and LFCLK to save power when using WCO.

[HaoW_21]

Hi Qipan,

No, you can not disable ILO for PSoC4100S Plus. First LFCLK should always have a clock source;  Second, WCO is not a clock input for LFCLK on this chip. We do have other PSoC4 series like PSoC4200L that has WCO for clock input for LFCLK.

Hao

[Anonymous]

OK, thanks very much.

[RyanZhao]

Hi Qipan,

ILO spends very low power, as ILO AC spec is not very narrow.

And you can see in datasheet, the deep sleep current is typically 2.5uA, of course with ILO active.

Thanks,

Ryan

[Anonymous]

OK, thanks.

[Anonymous · Accepted solution]

Hi,

We recommend ECS-.327-12.5-39-TR which we have used in Kit CY8CKIT-149

www.cypress.com/cy8ckit-149

There are 2 ways.

1. Configure your PSoC clock configuration to work in WCO mode. Then probe the WCO pin to DSO.

2. Configure your PSoC clock configuration to work in WCO mode. Then connect TCPWM to clock and change the duty cycle. You should see clean low jitter clock.

Do note for point 1, use a small gnd wire of the probe.