TPS922055DMTREVM: Output doesn't work bellow 10 V (operating range 4,5-60V)

Some more information: when starting lowering input voltage from 12 V down, it is also visible on the LEDs, that power goes down (so output current drops) and between 9 and 10 V LEDs are completely turned off.

I also tried with a single LED and behaviour is exactly the same as with 2 LEDs in parallel. Also PWM duty cycle doesn't change anything.

Hi Gregor,

Sorry. I am currently out of office. I will reply to you next Monday when I am back to office. Thanks for your understanding.

Best Regards,

Steven

Hi Gregor,

Sorry for the late response.

Please check the UVP resistor divider settings of the evaluation board. You can refer to this E2E FAQ - [FAQ] How to design the UVP resistor divider for TPS922055 / TPS922054 / TPS922053 / TPS922052? - Power management forum - Power management - TI E2E support forums

Best Regards,

Steven

Many thanks, will try tomorrow and let you know about the result.

Hi Gregor,

You are welcome. Please feel free to let me know if you have any question.

Best Regards,

Steven

Dear Steven, thanks for your help. I did change UVP resistors to 2M and 10k and now I get it working up to 6,5 V, however power starts to derating at approx. 7,6 V (approx. 1,6 V above LED voltage). Is there any way to compensate that in a way that I would get full power at lower voltages? (target application is 2S LiIon powered and I'd need like 0,5 V more)

HI Gregor,

Gregor Macek said:

I did change UVP resistors to 2M and 10k

Please double check the value of your UVP resistor divider.

Gregor Macek said:

Is there any way to compensate that in a way that I would get full power at lower voltages? (target application is 2S LiIon powered and I'd need like 0,5 V more)

Please leave the UVP pin floating, connect the TEMP pin to GND and have another try.

Best Regards,

Steven

Hi, did that, there's basically no changes, same Vin points, where LED current starts dropping.

Hi Gregor,

Please check if the SW pin has any switching behavior when the current starts to drop. I assume the power FET will be constantly on at this moment. Please also check the voltage of the LED string and VIN at this moment. 

Best Regards,

Steven

Vin at test pins on board, when this starts to happen is at 7,145 V where LED output voltage is 5,289 V. At this moment waveform on SW pin changes significantly, correct.

Normal waveform, Vin > 7,2 V

Derating starts, Vin<7,2 V

However, we meet with our client yesterday and they say that derating at lower voltages shouldn't be such a problem and that we can proceed with the product design using those ICs. Anyway, if we could get it work at full power like 0,5 V lower from our current treshold, that would be great.

I am about to start the design today (ALU, 1L), is it ok if I send you the design afterwards for a review?

Regards,

Gregor 

By the way, are there Altium files avalible for the devboard? (I know we got them for some BQ, when we designed some BMS in the past)

Another question: do you think that WE 74439387100 coil would do the job? (next alternative is WE 74439369100, which should be ok, but is still quite big for the design we are into)

Hi Gregor,

You can refer to this E2E thread on how the IC will behave when Vin is very close to the Vout - TPS922055: Maximum output duty cycle (minimum difference between Vin and Vout) - Power management forum - Power management - TI E2E support forums

Gregor Macek said:

Vin at test pins on board, when this starts to happen is at 7,145 V where LED output voltage is 5,289 V. At this moment waveform on SW pin changes significantly, correct.

I assume a lot of voltage drop is on the DCR of the inductor, current sense resistor, the power path on the PCB and also the wires connecting to the LED. Using inductor with smaller DCR, increasing the width of you power trace or using thicker connection wires may help.

Gregor Macek said:

I am about to start the design today (ALU, 1L), is it ok if I send you the design afterwards for a review?

Sure. I can help with the design review. We can talk through e-mail if you prefer.

Best Regards,

Steven

Hi Gregor,

Yes. The design files for the EVM are available. I can send them to you through e-mail.

I have sent you a friendship request through this E2E forum. After you accept it, I will send you my e-mail address and then we can continue the talk there.

Best Regards,

Steven

Hi Gregor,

Here is a calculation tool for your reference that may help you sizing the correct components for this chip - [FAQ] Is there a calculation tool for TPS922055 / TPS922054 / TPS922053 / TPS922052? - Power management forum - Power management - TI E2E support forums

Whether the inductor is appropriate will be mainly based on your design requirements and how you design the circuit (especially the switching frequency and output current ripple requirement).

Best Regards,

Steven

Hi, done - sent you my email adress via private message.

Hi Gregor,

I have sent you my e-mail address through private message. Let's continue the talk through e-mail. Thanks.

Best Regards,

Steven