WEBENCH® Tools/LM25118-Q1: LM25118-Q1

Arun Nath K.S

Part Number: LM25118-Q1
Other Parts Discussed in Thread: LM25118

Tool/software: WEBENCH® Design Tools

Hi,

I have an LM25118-Q1 IC in one of my board. webench_project_2303220_9.pdf. the only difference I made is that I increased the input capacitor value to 13.3 uF and output capacitor value to 905.14 uF. I assembled the circuit and found that it is not working (no load other than output capacitors). I have probed the output pin and found that a noise of 0.5 v is coming. So I probed other pins and the details are as below.

EN = 13.289 V

Vin = 5.1 V

UVLO = 0.0594 V

HO = 0 V

LO = 0 V

Considering all the above voltages and referring the datasheet i was expecting a current limit situation. so i checked the output for any shorts or capacitor overload. i have removed 704 uF but couldn't find any output. The inductor is getting heated. Please suggest possible reasons and corrections. Also, please help me to identify the issue immediately.

Expecting a fast reply.

Thanks & Regards,

Arun Nath K S

over 7 years ago

0 Youhao Xi over 7 years ago

TI__Guru* 78110 points

UVLO must be greater than 1.23V Typical to operate the circuit. Your UVLO is only 0.059V. Check your Ruv1 and Ruv2 installation.

0 Arun Nath K.S over 7 years ago in reply to Youhao Xi

Prodigy 50 points

hi,

I have removed the resistors and checked the values doubting whether they have misplaced during assembly. but to my surprise, the values are same as in the attached circuit.

0 Youhao Xi over 7 years ago in reply to Arun Nath K.S

TI__Guru* 78110 points

The two resistors form a voltage divider. If everything is okay, you should see the UVLO voltage scaled by the two resistors. If you still see almost 0V, either your circuit board has a short from UVLO pin to GND, or the IC is already damaged.

0 Arun Nath K.S over 7 years ago in reply to Youhao Xi

Prodigy 50 points

I will check whether there is any short at UVLO, if not i will replace the IC and update.

thanks in advance.

0 Arun Nath K.S over 7 years ago in reply to Arun Nath K.S

Prodigy 50 points

Hi,

I have replaced the IC and nothing happened. all the voltages remaining the same i checked UVLO and VCC pin. Pls find the attached figures. below.

Figure 1 : Vin & UVLO

Figure 2 : VIn & VCC

Pls go through the figures and pls suggest some solutions.

Regards,

Arun

0 Youhao Xi over 7 years ago in reply to Arun Nath K.S

TI__Guru* 78110 points

The first scope picture shows clearly your circuit has an error: UVLO should be proportional to VIN but it is pulled down by something. The webech schematic looks correct but your built circuit has an error in UVLO.

0 Arun Nath K.S over 7 years ago in reply to Youhao Xi

Prodigy 50 points

Hi,
I have disconnected UVLO from the pad and now the divider voltage is correct as per designs (3.6 v). Also if the UVLO pin was pulled down by something it should be low from the beginning not after some time(not after approx 50ms). Also the VCC has to follow VIN if VIN < 10 V. We have tried with with 9 v and the second waveform is same. Considering all these i am in a clueless state.

pls help to resolve the issue. Also pls tell the sequntial order of checking, so that i can check in that order and confirm upto which point it is working and from your side you can easily guide me.

thankin you

Arun

0 Youhao Xi over 7 years ago in reply to Arun Nath K.S

TI__Guru* 78110 points

I am afraid you have some connection errors on the board that you built, which will be very hard to debug through e2e post. I would recommend you to order an LM25118 EVM and start from their to get familiar with the part and modify for your use.

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WEBENCH® Tools/LM25118-Q1: LM25118-Q1