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TPS2662: e-Fuse Output Issues Near OVP Set Point

Wesley Mandel
Prodigy 40 points
Part Number: TPS2662
Other Parts Discussed in Thread: BQ25628E

Tool/software:

Hello,

I have been trying to implement the TPS2662 e-fuse IC on a board and am encountering some issues. For context, the circuit that this e-fuse is a part of is intended to be a charge base for a portable device. It takes a DC power source and passes it through to the portable device's charge contacts. Below is the circuit I have implemented:

OVP Target: 16.56V

UVLO Target: 5.95V

I limit: 760mA

This circuit is supposed to take in 8V to 15V and pass it though to the output charge contacts. The issue I am encountering is that this circuit is struggling at its maximum output voltage of 15V. The output either perpetually drops in and out or just clamps to ~2.5V.

Generally, if I provide the circuit with 12V input power things behave as expected.

Sometimes this circuit also behaves as expected when there is no load on it. I see the 15V at the output, but once I connect the circuit that is to be charged the efuse activates.

Downstream of this circuit we are using TI's BQ25628E with TI's recommended configuration from its datasheet in the portable device that is being charged. This is in a separate circuit board that is plugged in and removed from the circuit the e-fuse is in.

Another thing I have noted, which I do not want to rely on this in practice is if I touch the set resistors (R5, R6, and R7 in schematic) then I can activate and deactivate the protecting functions. This is not a desirable behavior.

Given all that information, here are the questions I am seeking assistance in answering:

- How can I get this efuse to consistently output 15V without dropping out?

- How do I prevent contact with the set resistors from affecting the efuse behavior?

- Is this device appropriate for a hot-swap charger base application?

Thank You,

Wesley Mandel

  • 0
    TI__Mastermind 21301 points

    Hello Wasley,

    Welcome to E2E.

    Wesley Mandel said:
    - How can I get this efuse to consistently output 15V without dropping out?

    What's the resistance tolerance for R5,R6,R7 resistor. When you are going more than 15V, can you check the OVP pin voltage (TP4)? Is it going above the OVP threshold?

    Please probe VIN, VOUT, IIN and OVP to check what's causing eFuse to go into protection.

    Wesley Mandel said:
    - How do I prevent contact with the set resistors from affecting the efuse behavior?

    You are not supposed to touch the eFuse pins which could cause ESD damage. Moisture on your hand can act as path to short UVLO and OVP by passing the protection.

    Wesley Mandel said:
    - Is this device appropriate for a hot-swap charger base application?

    Yes, This is integrated hot swap eFuse. Through CdVdT cap you can control the slew and inrush current.

    Thanks 

    Amrit 

  • 0 in reply to Amrit Jit
    Prodigy 40 points

    Hello Amrit,

    Amrit Jit said:
    What's the resistance tolerance for R5,R6,R7 resistor. When you are going more than 15V, can you check the OVP pin voltage (TP4)? Is it going above the OVP threshold?

        The resistors are all 1% tolerance. I will get some measurements on a board that is misbehaving today and share the results.

    Amrit Jit said:
    You are not supposed to touch the eFuse pins which could cause ESD damage. Moisture on your hand can act as path to short UVLO and OVP by passing the protection.

    Right, I noticed this while handling the bare boards. I want to avoid touching them, but while putting them in their housings it is easy to come into contact with the sense pins. I agree that these should never be touched due to concerns of ESD and contamination.

    I also noted that when I measured these signals with a multimeter the efuse stopped protecting and opened back up. The steps that lead to this were:

    1) I attempte to connect the device to be charged

    2) the efuse activates

     3) I disconnect the device to be charged, and then measure the signal lines.

    If it is any help the voltage measurement I was getting was roughly 1.1V. I will still be providing more meaningful measurement info later today.

    Amrit Jit said:
    Yes, This is integrated hot swap eFuse. Through CdVdT cap you can control the slew and inrush current.

    Thank you for confirming this. I saw it was hot swap in the datasheet, but wanted to check that my specific application fell under what TI meant. I will see if making CdVdT larger may help with my issues.

    Thank You,

    Wesley Mandel

  • 0 in reply to Wesley Mandel
    TI__Mastermind 21301 points

    Hello Wesley,

    Sure Wiseley. Looking forward to your measurement results.

    Is it possible for you capture in oscilloscope?