DC-DC converter with over current indication output.

hi, Kiran,

If the normal input voltage is 36V I suggest a 60V grade buck and leave some buffer.

LMR36015-Q14.2-V to 60-V, 1.5-A ultra-small synchronous step-down converter

LMR38020-Q1Automotive SIMPLE SWITCHER® power converter 4.2-V to 80-V, 2-A, synchronous buck converter

Also put some 36V grade device in case need.

LMR33620-Q13.8-V to 36-V, 2-A synchronous step-down voltage converter

LMQ66420-Q1Automotive, 36-V, 2-A low-EMI synchronous step-down converter with 1.5-µA IQ

Elena

Hi Elena,

Thank you for your suggestions. 

Basically the required buck converter will be used in different sections in my design with different current limits say 500mA, 1A etc. Hence, I am looking for the buck converter which has function to set the output current limit (something like setting the ILIM using external strap resistor) and current monitoring function to indicate the over current fault when the output current drawn more than the current limit set. Unfortunately the suggested buck converters doesn't have this feature. Does the TI has any automotive buck converters which has the function as mentioned above?

Thanks in Advance

Kiran

hi,Kiran,

The device all have C protection, and current limit is fixed .please refer to one LM5145, if this is what you want .

www.ti.com/.../lm5145-q1.pdf

Elena

Hi Elena,

Yes I am looking for converter similar to  LM5145, but needed a fault output function to indicate fault condition whenever there is overcurrent or short circuit on the load happens. 

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Thanks in Advance

Kiran

Hi Elena, 

I am using LMR38020-Q1 for the design and the external current sense circuit for over current protection. I have chosen the LMR38020SQDDARQ1 part for the design considering the light load efficiency of this part. Is there any advantage considering the other option LMR38020FSQDDARQ1 over the chosen one given my requirements? 

My plan is to use the same design for the 12V and 15V application by adjusting the feedback resistor value. The design for 12V is shown below

For the 15V application, the feedback resistor, 6.9K will be replaced by 7.15K. I aim to keep the inductance value constant. Could you please review it and let me know if there's room for improvement in the design? The output power requirements are: 1) 15V@500mA 2) 12V@1.5A. The plan is to use the same inductance for both the design and adjust the current limits using the external current sense circuit. 

Additionally, I've selected the INA300-Q1 for current sensing for overcurrent protection. I have a few queries on the INA300 design. Should I create a new query for that, or can we continue in the same thread? Please advise.

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Thanks in Advance

Kiran

I will reply to you next Monday.

hi,Kiran

LMR38020FSQDDARQ1 is FPWM mode, with will have a fixed frequency across all loading condition. 

Without F LMR38020SQDDARQ1 is a PFM mode, this will have a higher light load efficiency, you can refer to DS Efficiency plot to compare.

You can start with 12V 1.5A to calculate the inductor, also follow DS recommend example is good start. For 15V 500mA  rail, the current is less than 12V rail, so there is no risk to trigger HS current limit, a smaller inductor can be good to use here as current ripple is acceptable.

Please check the Vout ripple if is as you required . Cout can reserved a place when you doing hardware, that's convenient for debug.

And do you need EN connect to Vin ,I see here is external control right? 

Make sure VCC is <50V, I saw input cap is 50V, or suggest to 100V since LMR38020 is a 80V device.

PG is open if you not use this function . If need, pull high to a supply with a resistor .

Other look good to me.

Elena

 INA300-Q1 , you can submit a new thread, sorry for I am not belong to that product team.

you can also keep in one thread, I will forward this question to  INA300-Q1 product team, after you have no question about LMR38020.

Both is good for me ,let me know your prefer.

Thank you.

Elena

Hi Elena, 

Thanks for the reply. I have raised a new thread for the INA300-Q1 related query. 

Elena Gao said:

You can start with 12V 1.5A to calculate the inductor, also follow DS recommend example is good start. For 15V 500mA  rail, the current is less than 12V rail, so there is no risk to trigger HS current limit, a smaller inductor can be good to use here as current ripple is acceptable.

Yes, I have followed the same approach. For the 12V @1.5A configuration, the calculated inductance value is 33.33uH at a 0.4 ripple constant for a 36V input, using the formula specified in the datasheet.

For 15V application, I have retained the same 33uH since the current is less than that of 12V. If I consider only 500mA , the calculated inductance would be around 109uH. Is there any impact or constraint associated with using 33uH here instead of 109uH?

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Thanks in Advance 

Kiran