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Original question:

LM5116: Voltage Drops Under Load on LM5116-Based 60V to 6.5V Regulator

LM5116: LM5116 - Start up Issue

Ritesh Yadav
Prodigy 30 points
Part Number: LM5116
Other Parts Discussed in Thread: LM5146

Tool/software:

Dear Sir,

When 12V battery is connected at output and then input is given to converter, IC does not provide the pulses to high side gate. But this problem does not occur with  LM5146.

Input Voltage Range 35-72V

Please find the attached waveform with the below descriptions.

 

1.       Input Voltage (VIN)                             ->   Yellow, 10V/dev

2.       Output Voltage (O/P V)                     ->   Green, 2V/dev

3.       Boot Capacitor (BST_CAP)                 ->   Pink, 2V/dev

4.       Lower Gate Drive (LO)                        ->   Orange, 2V/dev

5.       Higher Gate Drive (HO)                      ->    Red, 2V/dev

We are looking forward your quick response.

Thanks & regards

  • 0
    TI__Expert 5305 points

    Hi Ritesh Ji,

    Please share the schematics with me. 

    Thanks,

    Best Regards.

    Taru

  • 0 in reply to Taru Kapoor
    Prodigy 30 points

    Please find the schematics

    Thanks

  • 0 in reply to Ritesh Yadav
    TI__Expert 5305 points

    Hi ritesh Ji,


    Can you probe the HB-SW using a differential probe? I want to check if the V(HB-SW) is greater than the HB-to-SW threshold.

    Thanks,

    Best Regards.

    Taru

  • 0 in reply to Taru Kapoor
    Prodigy 30 points

    Hi Taru, 

    As per the internal diagram of I, voltage between HB -SW will always be less than 3V at starting  if 12 V is connected at output . If I am correct. This will create the issue .

    Waveform is attached previously

    We do not want to connect extra circuit.

    Thanks 

    Ritesh

  • 0 in reply to Ritesh Yadav
    TI__Expert 5305 points

    HHi Ritesh Ji,

    The waveform that you have shared is not very clear - please send a clearer image. 

    What is the output voltage that you have configured? 

    Furthermore, I see the boot cap being quite high in your case - 2.2uF - can you check with a smaller value? 0.1uF is a good starting point. You can see that the converter is trying to start up - my guess is that the Cboot is quite large and is not getting charged enough to start switching. 

    Thanks,

    Best Regards,

    Taru