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LM7480-Q1: Circuit is not turning on

May
Genius 9880 points
Part Number: LM7480-Q1
Other Parts Discussed in Thread: LM7480, LM5051

Hi,

Customer is encountering problem with the IC, details below.

"I would like to use the 7480 to control an ideal diode on the ground side of a circuit. All of the application diagrams show pin2 "A" tied to the source of the first mosfet. However the application notes say that "A" must be at least ~2.4 volts or DGATE will not activate. Rather than tying "A" to the source of the first mosfet, can I just apply 2.4v to enable the circuit?

In my test circuit I connected "A" to the source of the first mosfet but the circuit is not turning on. OV, EN, VS, CAP, and GND are all at their expected voltages, however DGATE and HGATE are off.



The application note I am referring to is on page 15 of the datasheet.

Additional Information:
1. Tried replacing the chip and the mosfets.
2. As configured in the provided circuit diagram the voltages for the low side LM7480-Q1 are: Pin1: 0.723v, Pin2: 0.723v, Pin3: 0.723v, Pin4: 0.664v, Pin5: 0v, Pin6: 28v, Pin7: 0v, Pin8: 0v, Pin9: 0v, Pin10: 28v, Pin11: 28v, Pin12 0.53v.
3. I am attempting to create an ideal diode on the ground side of a circuit and thus the voltage passing through the mosfet's needs to be 0v.
4. A and VSNS of the lower LM7480 are connected to the ground of the upper LM7480. This is intended as the desired turn on behavior is for the lower LM7480 to turn on 1st

Regards,
Maynard

  • 0
    TI__Guru 57737 points

    Hi Maynard,

    LM7480-Q1 is not designed to be used on the low side/ GND side of the power path. The VS pin needs to be > 3V and VA needs to be > V(A_PORR) for the device to operate successfully. In case you connect these pins to a separate voltage source, the whole purpose of using this device is defeated.(device will no longer be able to detect reverse current flowing through the Mosfet)

  • 0 in reply to Praveen GD
    TI__Genius 9880 points

    Hi Praveen,

    Thank you for the information, customer have follow up question.


    Can you recommend a alternative device which is capable of being used on the low side/GND side of a power path?

    Regards,
    Maynard

  • 0 in reply to May
    TI__Guru 57737 points

    Hi Maynard,

    Can you let us know which below protection features are required by the customer. 

    1. ORing (Reverse Current Blocking)
    2. Input Reverse Polarity Protection
    3. Over voltage Protection
    4. Forward current Blocking
  • 0 in reply to Praveen GD
    TI__Guru 57737 points

    Hi Maynard,

    We only have one device in our portfolio which can operate on low-side. It is LM5051. This device is an ORing controller which offers only reverse current protection. This device does not offer the following features. 

    1. Input Reverse Polarity Protection
    2. Over voltage Protection
    3. Forward current Blocking