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LM5069: how to set PWR pin resistance, Timer pin capacitance, Sense pin Connection and etc.

jinsu kim
Prodigy 80 points
Part Number: LM5069

Hi Team

My customer has some question about LM5069.

He use LM5069 as Load switch. Input voltage range is 50 ~ 80V , Output current is max 20A.

Schematic is here.

 

 Questions

 1. My customer use external current sensor. So he doesn't want to use Rsns. Is the schematic correct under this condition ?

 2. He doesn't use current limit function. Let me know how to set PWR pin resistance, Timer pin capacitance, Sense pin Connection and etc.

3. When Input is 50V, Output voltage is 50V and Vgs is 12V, But when input is 70V, output voltage 63V and Vgs is 3V (No load condition)

   As Input  rises above 60V, the Vgs  gradually drops. Let me know Why Vgs drops and How can solve this problem.

  • 0
    TI__Guru** 105531 points

    Hi Kim,

    Thanks for reaching out!

    I will look into it and reply by tomorrow.

    BR, Rakesh

  • 0 in reply to Rakesh
    TI__Guru** 105531 points

    Hi Kim,

    Since it is high power design, I suggest to use the protection features of the LM5069 device.

    If you intend to use LM5069 as load switch, do the following

    1. Short Vin & Sense pins and connect to source/supply

    2. Leave Timer pin OPEN

    3. Leave PWR pin OPEN

    The GATE voltage drop is to the OVP trigger. Adjust the OVP threshold or disable the OVP feature and check. Also, check with load. If you still see the issue, please share Vin, Vout, GATE, input current waveform

    BR, Rakesh

  • 0 in reply to Rakesh
    Prodigy 80 points

    Hi. Rakesh

    Thank you for your reply. 

    And I solve gate voltage drop issue. when the gate is connected differential probe(ADP305), gate voltage drop occurs.

    In the opposite case, Output voltage operates normally.

    I have additional questions about this. 

    I know LM5069 gate source current is low (typ. 16uA). 

    1. Is the Impedance of the probe causing the gate voltage drop?

    2. Why does the gate voltage drop only occur at high voltages(above 60V)?

    3. How can I measure Vgs?

  • 0 in reply to jinsu kim
    TI__Guru** 105531 points

    Hi Kim,

    We have seen this issue of gate voltage drop when the gate is connected using differential probes. The impedance of the probe would effect the voltage.

    I suggest to measure GATE pin, MOSFET Source pin voltages using two probes and use math function in the scope to measure Vgs.

    Best Regards,

    Rakesh

  • 0 in reply to Rakesh
    Prodigy 80 points

    Hi Rakesh 

    I'll try your suggestion.

    Thank you.