External Crystal Drive Level Too High S9KEAZN64AMLC

[amitsinhaEM]

Hello, 

We are using the MCU S9KEAZN64AMLC in our design with an external crystal (ECS-160-12-37BQ-CTN-TR, load capacitance 12 pF).

We observed that the crystal drive level is about three times the recommended 100 µW.

Currently, we are using HGO = 1 (high gain) in our code because the ESR of the external crystal is 150 Ω.

Could you please advise which setup is correct, high gain (HGO = 1) or switch to low gain (HGO = 0) for this crystal? 

If HGO=1 is correct why drive level of crystal too high?

[amitsinhaEM]

We are using the same setup still drive level is too high. 

[Pablo_Ramos]

Hi @amitsinhaEM,

According to the datasheet, and given the crystal's ESR of 150 Ω, your setup should be configured with High Range and High Gain Mode.

Screenshot 2025-08-26 123729.png

Set the oscillator control register as follows:

OSC_CR[RANGE] = 1 (High frequency range)

OSC_CR[HGO] = 1 (High gain mode)

Please ensure that both the RANGE and HGO bits in the OSC_CR register are properly set.

Best Regards,

Pablo

[amitsinhaEM]

Hi @Pablo_Ramos,  

We are using the same setup still drive level is too high.

OSC_CR[RANGE] = 1 (High frequency range)

OSC_CR[HGO] = 1 (High gain mode)

[Pablo_Ramos]

Hi @amitsinhaEM,

Can you help me with the following test?

Start with HGO = 0 (low-gain mode) and test for stability. If the oscillator fails to start or shows instability, switch to HGO = 1.

Best Regards,

Pablo

[amitsinhaEM]

Hi @Pablo_Ramos in both the cases crystal is stable and working fine. Only difference is in case of HGO=1 drive level is too high and in case of HGO=0 drive level is withing the recommended limit. ESR of external crystal is 150 Ohm. 

[Pablo_Ramos]

Hi @amitsinhaEM,

What may be happening is that when the configuration is set to high-gain mode (HGO = 1), the crystal is being overdriven, as you can observe.

If the crystal operates stably in low-gain mode (HGO = 0), please use that configuration.

Best Regards,

Pablo

[amitsinhaEM]

Thanks, but what is the correct way to choose drive level? 

[Pablo_Ramos]

Hi @amitsinhaEM,

For Drive Level evaluation, it is advisable to collaborate closely with the crystal supplier and consider utilizing the circuit evaluation services they typically offer.

Best Regards,

Pablo

[amitsinhaEM]

@Pablo_RamosSo, does this mean there is no standard method to define the drive level after selecting the external crystal, and that we need to send the board to the crystal manufacturer for circuit evaluation?

[Pablo_Ramos]

Hello, 

I apologize for the delay; I was not able to locate any other information available on the request to share. 

I apologize for the inconvenience this might cause you. 

Regards, 

Pablo 

[amitsinhaEM]

Thanks