TL494: Oscillator Frequency of TL494

Masami Michino

Part Number: TL494

Dear, All

It is a question about calculation formula of Oscillator Frequency described in TL494 data sheet.
In the data sheet P5 '7.6 Electrical Characteristics, Oscillator Section', the oscillation frequency is described as follows.
Condition: Ct = 0.01 uF, Rt = 12 kOhm
Oscillation frequency 10 kHz (typ.)
However, the equation (3) in the item '9.3.2 Oscillator' in the data sheet P11 is
Fosc = 1 / (Rt * Ct)
It is described as about 8.3 kHz when calculated by this equation.
Therefore, customers want to know the following.

- Is the equation (3) on P11 wrong?
Or is the condition of '7.6 Electrical Characteristics, Oscillator Section' incorrect?

Please let me know.

Thanks, Masami M.

over 7 years ago

0 Benjamin Lough over 7 years ago

TI__Mastermind 26695 points

Hi Masami-san,

Thanks for your interest in TL494. I will look into this discrepancy and get back to you.

Best Regards,
Ben Lough

0 Masami Michino over 7 years ago in reply to Benjamin Lough

Genius 5070 points

Hi Ben-san,

Thanks for your support.
I will wait for your reply.

Thanks, Masami M.

0 Masami Michino over 7 years ago in reply to Benjamin Lough

Genius 5070 points

Hi Ben-san,

Thanks for your support.
Have not you finished investigating my question yet?

Thanks, Masami M.

0 Benjamin Lough over 7 years ago in reply to Masami Michino

TI__Mastermind 26695 points

Hi Masami-san,

I am trying to confirm with the design team but I interpret figure 1 as IC test data for a given set of test conditions and should only be used as guidance. My suggestion is to calculate your switching frequency using equation 8 in the datasheet.

Your customer might also be interest in this design guide for TL494: www.ti.com/.../slva001e.pdf

Best Regards,
Ben Lough

0 Masami Michino over 7 years ago in reply to Benjamin Lough

Genius 5070 points

Hi Ben-san,

I understand.
However, in this answer, the prescribed value of 'Frequency' of '7.6 Electrical Characteristics, Oscillator Section' in datasheet P5 means reference value.
Therefore, it is an interpretation that the value calculated by equation (8) on datasheet P14 is correct.
Is this meaningful?

Thanks, Masami M.

0 Benjamin Lough over 7 years ago in reply to Masami Michino

TI__Mastermind 26695 points

Hi Masami,

Please use the equation F = 1.2/(Rt*Ct) to set the oscillator frequency. This should align with the frequency graph on the TL494 datasheet. I will request the datasheet be updated.

Best Regards,
Ben Lough

Power management

Power management forum

TL494: Oscillator Frequency of TL494