TPS54200: LED

Hi, Sim,

Can you provide more information like input voltage range(min and max for 6V and 12V), LED current ripple(max), and input voltage ripple(max)?

You can also refer to 8.2 Typical Application in datasheet for the detailed calculation process.

Thanks.
Regards,
Kenneth

Hi Kenneth,

1. input voltage range for 6V : 4.5 ~ 8v , for 12V : 9v~15v

2. Led current and voltage ripple, don't have this number but you can refer the web page for LED : http://ledjoy.co.kr/product/detail.html?product_no=447&cate_no=104

 -> you can give typical parameters for normal condition.

Best regards,

Wave.

Hi Kenneth,

I made my EXEL sheet to get these parameters.

But, I have a problem to put conditions into this file.

There's no mention in the manual in terms of Rf(resistor for FB pin)

How can I choose Rf which looks being related to pole frequency?

In the manual, it chooses any number under 1KHz I think.

There's no any formula for it.

Best regards,

Wave. 

Hi, Wave,

As you can see from 8.2.1.2.4, suggested frequency of pole is 2 kHz in analog dimming mode:

So you can use 2kHz for fPOLE and select RF<1 Kohm, like 910ohm, then CF can be calculated by Equation 13.

Hope this helps.

Thanks.

Regards,

Kenneth

Hi Kenneth,

Yes, I read it of course.

My question is that it only says I can choose any number under 1Kohm but not exactly.

Why does it choose 910 instead of other parameters?

Also, I can see another mention of it in the second example which is more suitable for my case, just on/off mode.

At this case as PWM mode, it chooses 4KHz as Fpole and 475ohm instead 910 at the first time, but it also suggests that 200 ohm for faster response, 10Khz.

So I think it would be a formula associated in between since decreasing resistance makes higher frequency.

Best regards,

Wave.

Hi, Wave,

Understand. Let me check with design team.

Since the team is on Chinese public holidays, I'll reply you on Apr 8th(UTC+08:00).

Thanks for your understanding.

Regards,
Kenneth

Hi, Wave,

The recomanded role is set to compensate the zero of the internal circuit.

As you can see from datasheet 8.2.1.2.4, "Suggested frequency of pole is 2 kHz in analog dimming mode, and 4 kHz in PWM dimming mode".

If you want to get a faster loop response, you can also choose a pole a little higher than the suggested ones. Then you can choose the RF and CF to set the pole.

Moreover, we also provide Transient Models in TPS54200 product folder, which you can take for reference.

Hope this solves your problem.

Thanks.

Regards,

Kenneth