LM5143: External SYNC Support

Hello Eldo

Let me check internally about how much variation can be expected over 5 °C to 75 °C.

Regards

Onkar Bhakare

Hello Onkar,

Okay. Thank you.

Kind regards,

Eldho

Hello Eldho

I have written to responsible engineer. I'll get back to you once I hear him.

Thank you

Regards

Onkar Bhakare

Hello Onkar,

Okay. Thank you.

Kind regards,

Eldho

Hello Eldho

Kindly expect some delay as responsible engineer doesn't work in my time zone.

Thank you

Regards

Onkar Bhakare

Hello Onkar,

Okay. Thank you for letting me know.

Kind regards,

Eldho

Hello Eldho

I checked with responsible engineer. We don't have data for 5 to 75 degC. Would 25 to 150C work?

Thank you

Regards

Onkar Bhakare

Hello Onkar,

Thank you for your continued support.

As I mentioned in the original post, the temperature range of our application is limited. Is there any data available for a temperature value between 25°C and 150°C? If not from silicon measurements, at least from simulations? We are particularly interested to know, how much variation to expect in the internal oscillator frequency from temperature variation alone - of ± 20°C around room temperature. From my time at TI as a design engineer, I would expect the variation to be much lower for a limited temperature variation of ± 20°C around room temperature, unless all of the variation in the internal oscillator frequency is accounted by process and/or supply variations. But I would expect, some sort of trim to be there to account for the process variation. The supply voltage is more or less constant in our application.

Thank you and kind regards,

Eldho

Hello Eldho

I have requested for test data of 25 to 150 degC. I hope to get it from engineer tonight. I'll share with you Tommorow IST.

Thank you

Regards

Onkar Bhakare

Hello Onkar,

Okay. Thank you very much for providing this information.

Kind regards,

Eldho

Hello Eldho

Let me know if you need further help. Kindly close the thread if your query has been resolved.

Thank you

Regards

Onkar Bhakare

Hello Onkar,

One follow-up question: If most of the variation in the internal oscillator frequency can be attributed to process variations, can we use a trim option (say 3 or 4 bits) to fine tune the external resistor RRT to center the internal oscillator frequency to the mid of the synchronisation range needed for the application (190 kHz to 250 kHz)? This way, can we work around the ± 11.4% variation of the internal oscillator frequency?

Thank you and kind regards,

Eldho

Hello Minkle

Minkle Eldho Paul said:

If most of the variation in the internal oscillator frequency can be attributed to process variations, can we use a trim option (say 3 or 4 bits) to fine tune the external resistor RRT to center the internal oscillator frequency to the mid of the synchronisation range needed for the application (190 kHz to 250 kHz)?

Yes, Minkle that can be done. If I understand correctly, you will measure frequency set by nominal value RT and then adjust it for bringing to the center of the mentioned frequency range. However, it won't help during synchronization, as RT plays no role when external clock is given, device simply ignores RT.

Thank you

Regards

Onkar Bhakare

Hello Onkar,

Yes, that is what I meant. I understand that RT plays no role when external clock is given and that device simply ignores RT. But in the datasheet it says the range of the synchronization frequency has to be within ± 20% of the programmed frequency (presumably set by RT). Hence the concern with the process variation of the frequency set by RT. It would be indeed great, if we could avoid this trim option entirely and the device can synchronize to external frequency in the range 190 kHz to 250 kHz. Could you please clarify that with the design team?

Kind regards,

Eldho

Hello Eldho

Based on the information mention in EC table. I feel applied frequency should be within -+20 of typical frequency set by RT resistors. However, I clarify this with the designer

Thank you

Regards

Onkar Bhakare

Hello Eldo

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Let me know if you need further help

Thank you

Regards

Onkar Bhakare