TPSM33625: 36Vin Rating Buck

One more question, what's the max. duty cycle of TPSM33625?

Regards

Brian

Hi Brian,

The issue is not with heat but with the lower limit. When operating at 5.4 VIN, the part will be subject to dropout, but this phenomena is not covered in the scope of the webench model. The max duty cycle of this device is dependent on your operating conditions. Please see this thread and section 7.4.3.5 of the datasheet for more details. In any case, it does not look like 5.4 VIN will allow for a 5 VOUT.

Can you please outline what is needed of this design (AUTO or FPWM, Switching Frequency) and I can recommend a new part.

Thank you,

Joshua Austria

so, TPSM33625 doesn't work with this condition, right?

Here please find the device requirements. 

FPWM

Switching freq > 400K

5.5Vin to 5Vout/2.1A

Ambient 85degree

Vin:5.4~5.6V

Vo:5V/2.15A

Low cost device

Regards

Brian

Hi Brian,

At 400 kHz and 2.1 A out, a 5.4 VIN - 5 VOUT may be difficult for a Wide VIN part to support without entering dropout. Can I ask why a Wide VIN part is being considered instead of a likely better fit with the Low VIN profile bucks at TI?

Thank you,

Joshua Austria

That is for the FuSa power consideration.

The power tree is :

24Vin to 5.5Vout by LM76002

5.5Vin to 5Vout by TPSM33625 (This one needs > 24V voltage derating against the 24V is shorted to 5.5Vin rail inside the LM76002 as it's not FuSa compliant device)

5Vin to 3.3V/1.3V by TLV62569/

Regards

Brian

Also, customer has done the test on the TPSM33625EVM with 5.5Vin to 5Vout/0.5A-1.5A. However, we found the random switching on the SW node pin. Is that normally? what is the reason it's not regular switching?

Is TPSM33625 able to do the 5.5Vin to 5Vout/0.5A-1.5A? What else converter or power module with >28V rating you suggested? thanks. 

thanks. 

TPSM33625 EVM 實測結果.pptx

Hi Brian,

Like noted before, the device's datasheet states that this condition is not supported, so your results may vary when operating the part like this. The random switching is due to the device not having sufficient input voltage to support its output and thus the part operates in dropout where the device switching frequency folds back to try and support the high duty cycle required without violating its timing characteristics as specified in the datasheet EC table. 

Is there a reason that the customer cannot do a 5.4 -> 3.3 or 1.3 V application? I believe this device has a better chance at consistently supporting this at load.

Thank you,

Joshua Austria

Hello Joshua,

Thanks. Regarding to the SPEC of TPSM33625, with the condition of the 300KHz freq setting, 5.4Vin - 5.5Vin and 5Vout, the calculated min off-time > 85nS that is specified in d/s. Why is it violating the SPEC? We're confused about it! Is the reason drop voltage caused by internal Rds(on) of the high side SW? How about the resistance of high side switch and Inductor? Very Thanks. 

The reason behind is related to the FuSa SIL3 requirement as i mentioned early. The 5.5V to 5V converter is for the single fault shorting with 24V from LM76002 not to damage the downstream devices. 

One more questions, customer is more interested in TPSM33625 on this design. Could you help to feedback on below question!

1. If output voltage is set at 5V, and output current load is 200mA, 500mA, 1A and 1.5A, how about the minimum input voltage at 300KHz freq?

2. also, If input voltage is set at 5.5V, how about the max. output voltage with current load 200mA/500mA/1A/1.5A?

Customer would like to know the device capability and optimize the design. Very thanks. 

Regards

Brian