UC3843: About CCT and RRT recommended range of fosc equation

Hide

Guru 21045 points

Part Number: UC3843

Hi Team,

We understand that UC3843 can set up to 500kHz operation and we would like to set fosc=400kHz.

However, if CCT is 1000pF(=1nF), RRT is 4.3kohm so out of recommended range of RRT(5kohm to 100kohm).

Could you please let us know the recommended combination(CCT and RRT values) for fosc=400kHz?

Regards,

Hide

over 5 years ago

0 Sonal Singh over 5 years ago

TI__Expert 6080 points

Hello Hide,

Figure 10 in datasheet recommends CCT = 1nF and RRT = 6.8K to achieve an oscillator frequency of 400kHz.

Regards,

Sonal

0 Hide over 5 years ago in reply to Sonal Singh

Guru 21045 points

Hi Sonal-san,

If CCT=1nF and RRT=6.8kohm, fosc is around 253kHz by fosc equation.

And, I understand that scale of Fugre10 is incorrect (Position of 5kohm is incorrect).

Is my understanding correct?

If yes, I guess that the recommended range of RRT is incorrect.

Incorrect : 5kohm to 100kohm

Correct: 3kohm to 100kohm

I’d greatly appreciate your verification.

Regards,

Hide

0 Hide over 5 years ago in reply to Hide

Guru 21045 points

Hi Sonal-san,

Would you tell me about the progress on this matter?

I’d greatly appreciate your verification.

Regareds,

Hide

0 Hide over 5 years ago in reply to Hide

Guru 21045 points

Hi Sonal-san,

Would you tell me about the progress on this matter?

I would appreciate your prompt reply.

Regareds,

Hide

0 Sonal Singh over 5 years ago in reply to Hide

TI__Expert 6080 points

Hello Hide,

Thank you for pointing out the discrepancy in the datasheet. The graphs are for general behavior description and I would strongly suggest sticking with the 5Kohm limit on the timing resistor recommendation.

Please use the values below for the 400kHz Fosc: Rt= 5K and Ct=0.86nF following the equation in the datasheet.

Thanks,

Sonal

0 Hide over 5 years ago in reply to Sonal Singh

Guru 21045 points

Hi Sonal-san,

Thank you for the information.

Do you revise a data sheet?

If yes, could you please let us know the update timing?

Regards,

Hide

0 Sonal Singh over 5 years ago in reply to Hide

TI__Expert 6080 points

Hello Hide,

The figure in the datasheet shows a general behavior of the device, I do not think it needs a revision. Please stick to the recommendations.

Regards,

Sonal

0 Hide over 5 years ago in reply to Sonal Singh

Guru 21045 points

Hi Sonal-san,

I understand.

Thank you for kind support.

Regards,

Hide

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UC3843: About CCT and RRT recommended range of fosc equation