TIDA-01226: LED drive circuit design issues

Hi JingMingJun,

Could you kindly mention which version of Firmware you are using? We'll be looking into this and get back to you shortly.

Thanks & Regards,
Hirak.

Hello JingMingJun,

Could you please also confirm you are talking about C129 and C123? C129 is the .01uF cap for the PLLs and C123 is the decoupling cap on VDD. I wouldn't expect either of these to need changing for new LEDs.

Thanks,
Kyle

Hi Hirak

Thank you for your reply.
I am using the firmware downloaded from the TI website, the name is:
TIRef_DPP3439_p47-1080P-TRP_v1p5p1-PAD3005-AC-Only.exportedproject

Thanks & Regards,
JingMingJun

Hello Kyle

I am very sorry to have given the wrong circuit number.
The correct circuit numbers are C321 and C370, which are used between the GATE and SOUCE of the LOW SIDE and HIGH SIDE FETs in the LED driver circuit.

Thanks & Regards,
JingMingJun

Hi JingMingJun,

Thanks for clarifying. Could you please upload a schematic of the LED driver part of your circuit?

Thanks,
Kyle

Hi Kyle

The schematic of the LED driver part has been uploaded, please check.

Since the circuit number is back annotated, it is different from the TI schematic.

Thanks,

JingMingJun

CHP_RJBC1047_TIcomfirm_190416.rar

Hi JingMingJun,

Could you kindly reupload the schematic in PDF format? We are having difficulties viewing it.

Thanks & Regards,
Hirak.

Hi Hirak

Hi JingMingJun,

On your schematic I see that R595 (9mOhm) has been replaced with R42||R479 (6mOhm) so the drive current will increase. Have you accounted for that?

Thanks & Regards,
Hirak.

Hi Hirak

Because I have used different LED light sources which need a current of up to 25A,

so I changed the resistance to 6 milliohms based on the simulation calculation of the COMPOSER GUI.

Thanks & Regards,
 JingMingJun

Hi JingMingJun,

Can you kindly explain more on the behavior? Do you observe changing the constant drive current or introduction of abnormal spikes in drive current in some intervals or any other kind of behavior?

Thanks & Regards,
Hirak.

Hi Hirak
I am sorry, what you are asking is the reason for changing to 6 milliohm resistance?
The reason is just to increase the current output to 25A.
Thanks & Regards,
JingMingJun

With a 9 milliohm resistor, the current output can only be up to 16A.

Hi JingMingJun,

I understand the reason for changing resistance to 6mOhm. When you say changing the capacitor changes drive current, did you capture current waveforms with different values of capacitors? Can you kindly post those waveforms?

Thanks & Regards,
Hirak.

Hi Hirak

Yes, kindly capture the waveform under your use case with different capacitor values and send it to us. This will help us debug the underlying issue!

Thanks & Regards,
Hirak.

Hi JingMingJun,


Do you still need the answer to your question? I'll be temporarily closing this thread due to inactivity. You can reopen anytime.

Thanks & Regards,
Hirak.

Hi Hirak

I am very sorry to reply so late.

First of all, I need to correct my previous explanation errors.

"For example, when the C123 and C129 are changed, the driving current of the LED light source is changed..."

should be

"For example, when the C321 and C370 are changed, and when the driving current of the LED light source is changed..."

The reason I want to change the capacitor is that I can't buy a 4300pF (reference design) capacitor.

The reason for changing the current is to use an LED light source that requires a current of 25A.

It is not that changing the capacitance causes a change in current.

Hi Hirak

Hi JingMingJun,

Could you kindly try to further increase the gain (0x25h) and see if it solves the problem?

Thanks & Regards,
Hirak.

Hi Hirak

It seems that the effects of 03h, 07h, 0Bh, and 0Fh are the same and are optimal,but still not enough.

Thanks & Regards,
JingMingJun

Hi Hirak

In fact, I have redesigned the 25A product based on TI's reference design TIDA-01226, including schematics, PCBs and cooling systems.

>as it only has a single HS/LS FET configuration

what does this mean? Is there an insurmountable flaw or risk in my design?

Thanks & Regards,

JingMingJun

Hi Kyle

>If your board was fully designed for the current then you should be good. Note the TI design your referenced was only for 16A maximum.

Regarding the LED light source drive circuit, I used the same or equivalent components as the TI reference design. The components in the TI reference circuit are also capable of supporting outputs up to 25A. Also under my cooling conditions, no components exceeding the temperature specification were found.
This should be fine, right?

>For high current we use a dual high side and dual low side FET configuration to split the current between to FETs. If your FET can handle the current then you should be fine.

Hello JingMingJun,

Are you having issues with your current design? If your components are appropriately specified (and derated as you judge appropriate) and you aren't seeing issues there may be no issue with your approach.

Thanks,

Kyle

Hi JingMingJun,

Do you still need the answer to your question? I'll be temporarily closing this thread due to inactivity, you can reopen anytime. 

Thanks & Regards,

Hirak.