Voltage specification for externally provided clock signal (MCX A185 VLH)

[wyss-11]

I can not find the max. voltage allowed at the EXTAL48M pin for the MCXA185VLH MCU in the datasheets.

I know from the LPCxxx families of microcontrollers that the oscillator input is very picky about this amplitude (0.85Vpp or similar). 

Can I feed an externally generated 3.3V oscillator clock signal directly to the EXTAL48M pin? 

[wyss-11]

Thanks for your post. 

Yes, the datasheet specifies Vec (Externally provided input clock amplitude) with max. voltage as VIH. But as VIH is 0.7xVDD, this would mean that with VDD=3.3V, Vec max. would be 2.31V only. 

So either this datasheet specification is wrong, or Vec max. is really 2.31V in case of VDD=3.3V?

[carlos_o · Accepted solution]

Hi @wyss-11 

The VEC specification refers to the minimum voltage levels required by the external oscillator input to recognize valid low and high states.

When VDD = 3.3 V, 2.31 V is the minimum voltage that will be detected as a valid high level.

[carlos_o]

Hi @wyss-11 

Thanks for your post!

MCXA18 does have an EXTAL48M input voltage definition, but it is specified indirectly through the standard input thresholds VIH/VIL relative to VDD, not as a separate fixed EXTAL48M voltage value.

The datasheet only stands the Peak-to-peak amplitude of oscillation as typical value of 0.6V.

When VDD is 3.3 V, EXTAL48M can be driven by a 3.3 V external oscillator as long as the clock meets the VIH/VIL thresholds and does not exceed the VDD + 0.3 V input limit.