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TPS2595: TPS259533 eFuse usage

Hossam Moghrabi
Intellectual 270 points
Part Number: TPS2595
Other Parts Discussed in Thread: TPS2117,

Tool/software:

Hello,

I have a 2 DCAP3 buck regulator, one for 3.3v and one for 5v. I hooked their input to TPS2117 power selector IC but this IC is limited to 4 amps while buck regulators short circuit protection only kicks in at 6 amps which will damage TPS2117 as suggested by TI support.

I came up with a simple eFuse circuit based on recommendation of TI support, it is using TPS259533 as in the attached image (high resolution here):

I choose 536 ohms to give me about about 3.69 amps which even when tolerance is added it won't go to 4 amps.

i do not need any fault indication or so function, just cutting the circuit immediately when this current value is reached.

I have chosen a slew rate capacitor of 10 nF but I want to ask if 150p is ok? i don't' have such requirements for slew rate and I have small capacitance before the fuse, pure ceramic caps of total value of around 130 uF X5R so in DC bias will be less.

so my questions for you are:

1- is my circuit correct? will it work as intended without any problem? it won't cause damage to tps2117 at any possibility?

2- can I use 150p on slew rate pin? what effect will it do? what if i just removed it and made it float?

3- my choice of resistor 536 as ILIM resistor, is it correct to give about 3.7 amps typical and even when tolerance of 7.5% won't reach 4 amps?

4- as you see, i have 100k resistor at EN pin to GND to make it always enabled... is this ok? i don't want any over or under voltage protection as that is taken care at buck level.

5- do i need to put thermal vias under it?

6- will it work perfectly fine using this circuit for 3.3v and 5v? i mean using the same circuit twice but changing the input supply.

please answer in details

thanks

  • 0
    TI__Mastermind 23795 points

    Hi! 

    Hossam Moghrabi said:
    1- is my circuit correct? will it work as intended without any problem? it won't cause damage to tps2117 at any possibility?

    Looks fine. This should work as intended. You have some input caps, I would recommend you to add some small value cap like 0.1uF very near the IN pad. 

    Hossam Moghrabi said:
    2- can I use 150p on slew rate pin? what effect will it do? what if i just removed it and made it float?

    Yes, you can keep 150p or floating at the dvdt pin for faster startup time. Since you don't have any output cap, you don't have to worry about the inrush current. 150p will be already very close to floating case in terms of the output voltage slew rate.

    Hossam Moghrabi said:
    3- my choice of resistor 536 as ILIM resistor, is it correct to give about 3.7 amps typical and even when tolerance of 7.5% won't reach 4 amps?

    Yes, this should provide you just around 4A limit even in the worst case.

    Hossam Moghrabi said:
    4- as you see, i have 100k resistor at EN pin to GND to make it always enabled... is this ok? i don't want any over or under voltage protection as that is taken care at buck level.

    This will keep the EN always low. This is fine for this variant of TPS2595.

    Hossam Moghrabi said:
    5- do i need to put thermal vias under it?

    Not necessary for this device but do connect the thermal pad.

    Hossam Moghrabi said:
    6- will it work perfectly fine using this circuit for 3.3v and 5v? i mean using the same circuit twice but changing the input supply.

    Yes, this will work fine for both power rails

    Best Regards,
    Arush