TL594: Resolution and sensitivity of input error amplifier or IN+ and IN- inputs of PWM generator IC

Lavanya Ayyalasomayajula

Part Number: TL594

I would like to know the resolution and sensitivity of the IC TL594CD inputs like, what is the minimum difference between the IN+ and IN- inputs that the IC can sense to generate non-zero output pulse and what is the incremental difference in inputs that leads to output pulse width change. Similarly is there a minimum output pulse width that can be generated and the incremental step size of the pulse width.

I want to use the IC for inverter output voltage control in a variable voltage DC-DC power supply control. The variation needed in output voltage is 25% to 100% with incremental step of 0.33%. And the targeted accuracy of the output voltage is <0.5% of the set value. The maximum operating frequency would be around 240kHz.. I would like to know if these requirements can be met using TL594CD or any alternate PWM IC.

over 3 years ago

0 Hong Huang over 3 years ago

TI__Guru 60375 points

Hi,

On the op-amp, please look at page 5 of the datasheet for specs.

On the min pulse width, please look at page 6 (switching characteristics). The min pulse width can estimated from there.

0 Lavanya Ayyalasomayajula over 3 years ago in reply to Hong Huang

Prodigy 40 points

Dear Hong Huang,

Thank you so much for you response. But could you please be more specific about what parameter in page5 answers my query on the resolution and sensitivity. Also how do I arrive at the minimum pulse width and incremental step size based on the switching characteristics of page 6.

Thanku

0 Hong Huang over 3 years ago in reply to Lavanya Ayyalasomayajula

TI__Guru 60375 points

Hi,

Page 5, amplifier, input offset voltage and current.

Page 6, 6.6, switching characteristics. The min pulse width should be greater than rise time + fall time. If less, the pulse starts to disappear.

0 Lavanya Ayyalasomayajula over 3 years ago in reply to Hong Huang

Prodigy 40 points

Hi Hong Huang,

Thank you. I think I am good with the resolution part of the question. Could you please clarify on the sensitivity and the incremental step size of the output pulse ?

Thanks,

Lavanya

+1 Hong Huang over 3 years ago in reply to Lavanya Ayyalasomayajula

TI__Guru 60375 points

Hi,

TL594 is an analog device. If you use it in a closed loop converter, the control object (i.e., in most time, your converter output voltage) accuracy depends on your loop DC gain.

If you use it in a open loop control, and use the IC op-amp for your control, and if the IC op-amp also open, the datasheet shows the minimum gain of op-amp is 70dB.

The above are the basis for an analog control device when you consider its sensitivity. Practically saying, in a typical application of switch mode converter, you can literally think the step is continuous which is different from a digital controller.

0 Lavanya Ayyalasomayajula over 3 years ago in reply to Hong Huang

Prodigy 40 points

Dear Hong Huang,

Thank you for your quick replies. I think I will have to go through some reading to understand your answers better. Appreciate if you can suggest any good sources.

Regards,

Lavanya.

0 Hong Huang over 3 years ago in reply to Lavanya Ayyalasomayajula

TI__Guru 60375 points

Hi,

It sounds like you may need to compare an analog circuit and a digital circuit on the differences between them, you can search the web, and there are many articles. But to me, in practice, an analog circuit, we are not talking about the step size as the signal is continuous. But a digital circuit, a step size is a base to affect everything else.

You may also refresh your analog amplifier knowledges.

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TL594: Resolution and sensitivity of input error amplifier or IN+ and IN- inputs of PWM generator IC