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LM3710: LM7310: Minimum set of connections

chris padbury
Prodigy 55 points
Part Number: LM7310
Other Parts Discussed in Thread: LM74700-Q1

I want to use LM7310 as an ideal diode in a space constrained design. I do not require any of the following:

  • a current limiting or monitoring
  • output slew rate control
  • power good
  • OVLO
  • UVLO different to default

Am I correct in thinking that a minimum set of connections could be made in the design of:

  • OVLO (pin 2) connected to GND
  • VIN (pin 5) connected to power source
  • VOUT (pin 6) connected to load
  • GND (pin 8) connected to GND
  • IMON (pin 9) connected to GND

All other pins (EN/UVLO, PG, PGTH, DVDT and DNC) all left disconnected so floating.

The datasheet says in Table 5-1 for EN/UVLO "Do not leave floating", but then in section 7.3.2 it says "The undervoltage protection has a default lockout threshold of VUVP which is fixed internally". This is somewhat contradictory as how else do you use that default?

Also, I wanted to check that it is acceptable to leave PGTH (pin 4) disconnected so floating.

  • 0
    TI__Mastermind 20890 points

    Hi Chris,

    OVLO, IMON, and GND can be connected to GND.

    VIN should be connected to power source.

    VOUT should be connected to the load.

    DVDT and PG can and DNC should be floating.

    PGTH should not be left floating, as comparator inputs can cause the device to draw excessive current if left floating. PGTH can be tied to GND since you are not using PG. Since you are already tying OVLO to GND, it should be easy to connect PGTH to GND.

    EN/UVLO should not be left floating as it does not have input a pullup/down resistor, and thus it would not have any defined state. The section you quoted is saying that the device will be disabled if VIN < VUVP, regardless of the EN/UVLO state. For your application, it looks like the best option is to connect EN/UVLO to VIN directly if VIN < 5V, or through a resistor divider if VIN > 5V, as the maximum recommended voltage of the EN/UVLO pin is 5V.

    Thanks,

    Patrick

  • 0 in reply to Patrick Shalton
    Prodigy 55 points

    Thank you Patrick. That's a disappointment as due to EN/UVLO abs_max I can't connect to VIN (application: 4V to 7.5V) and the potential divider adds greatly to the resulting size of the ideal diode circuit.

    Just to clarify that it would need a potential divider rather than being able to use just a 360k pull-up resistor? Note 2 under the Recommended Operating Conditions table suggests this may be OK, or is it saying the top resistor of the potential divider shouldn't be less than 350k?

    Can you recommend an alternative based on my limited set of needs. I only need ideal diode function (fast response e.g. <= 1.5us) for a rated current up to 5A and voltage up to 7.5V.

  • +1 in reply to chris padbury
    TI__Mastermind 20890 points

    Hi Chris,

    Yes, my apologies - EN/UVLO can be connected to VIN using just a pullup resistor, and a resistor divider is not necessary.

    I will connect you with my colleague for alternative recommendations of ideal diode devices.

    Thanks,

    Patrick

  • 0 in reply to Patrick Shalton
    Prodigy 55 points

    So in summary, the minimum set of connections with this part is:

    • EN/UVLO (pin 1) connected to VIN directly if VIN <=5V or via a 360k resistor if VIN can be higher than 5V
    • OVLO (pin 2) connected to GND
    • PGTH (pin 4) connected to GND
    • VIN (pin 5) connected to power source
    • VOUT (pin 6) connected to load
    • GND (pin 8) connected to GND
    • IMON (pin 9) connected to GND

    Pins 3, 7 and 10 left floating. Some other threads have suggested leaving PGTH floating is OK but I prefer this approach.

    Ignoring any output capacitor, the EN/UVLO resistor (0402) adds about 50% to an otherwise very compact solution of 2mm x 2mm.

    As PG is Open Drain, so I assume there is no issue tying it to GND if that makes routing easier as shown on the right. It's not a requirement though so doesn't form part of the set of minimum connections.

    It's a real shame that the LM7310 part doesn't include a high resistance pullup resistor in die that removes the requirement for an external pullup resistor.

    I think this die with integrated EN/UVLO resistor in an SC70-3 package would be a fantastic simple offering with great market appeal.

  • 0 in reply to chris padbury
    TI__Guru 57737 points

    Hi Chris,

    Kunal from our team will get back to you on your questions related to LM7310. 

    I can help you with Ideal diode controllers like LM74700-Q1. Are you open to using a controller + external FET solution ? What are your current and voltage ratings ?

  • 0 in reply to Praveen GD
    Prodigy 55 points

    Internal FET, 5A, 7.5V with minimal connections.

  • 0 in reply to chris padbury
    TI__Guru 57737 points

    Hi Chris,

    LM73100 is the best solution we have for your requirement. 

    The next best option available is LM74700-Q1 + external FET but this would be a bigger solution size when compared to LM73100