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TPS4811-Q1: TPS4811 Rdson sense

Stas Shamanin
Intellectual 450 points
Part Number: TPS4811-Q1
Other Parts Discussed in Thread: TPS4800-Q1, TPS4810-Q1, TPS4813-Q1, LM74930, TPS4812-Q1

Tool/software:

Hi!

I have a design with multiple TPS48110-Q1.

I want to use it as simple high side switch with 1 MOSFET.

I don't really need to measure current accurately, but I do care about power dissipation.

I see in datasheet there is possibility to measure current with Rdson.

I have inductive loads (blowers) that is why I consider this schematic:

As MOSFET I want to use IAUCN08S7N013ATMA1 1.3 mOhm

The problem I see:

1. Rdson may change dramatically, I have a load maximum 15A. Should I calculate SC trip point for maximum expected resistance (2.5mOhm)? Or for expected maximum working temperature conditions like 2mOhm?

2. RImon output. I want to have some information regarding current, even if it is not accurate. But I see there may be too high voltage up to 6.5V on output especially when fet is opened.

2. What are your general thoughts to use Rdson as current sense? I don't care to buy sense resistor, I just want to save dissipation power.

Thanks!

Stas

  • 0
    Intellectual 450 points

    Also it is quite strange with RDSON sensing, in absolute max ratings it is claimed 0.3V max CS+ to CS-:

    But if I do RDSON sensing according to 8.3.3 in off state it may be up to 100V between CS+ and CS-

    Something strange here

  • +1 in reply to Stas Shamanin
    TI__Mastermind 28220 points

    Hi Stas,

    This is a known issue in the data sheet, that section mentioning Rdson sensing is from the TPS12000-Q1/TPS48000-Q1 data sheet and was erroneously included. TPS4811(0)-Q1 can't support Rdson sensing. But you can use a small CS resistor instead to save the power dissipation and have a more accurate ISCP threshold, or use TPS4800-Q1.

    Thanks,

    Patrick

  • 0 in reply to Patrick Shalton
    Intellectual 450 points

    Hi!

    As I see PTPS48000QDGXRQ1 is preview status and not available to buy.

    I am in design stage, I am ready to put it in, but I need 20 ICs for prototypes in coming month and like 300 available to buy in coming 6 month for production.

    Is there other high side switch with rdson measurement that is in production?

    Also I found out you released pretty big family of that controllers, and I don't understand features they provide like LPM with two parallel paths.

    Is there any presentation that highlights specific use for these products, so I can understand how it can benefit my design?

    Thanks.

    Stas

  • 0 in reply to Stas Shamanin
    TI__Mastermind 28220 points

    Hi Stas,

    For Rdson sensing, we have TPS4813-Q1 which we just released. There is also TPS4810-Q1, but it is currently out of stock as well. But let's follow up on this via email.

    As to the different features available for these devices, please see below for the presentation from our New Product Update webinar a while back. It includes common end equipment, family comparisons, links to app notes, and feature set overviews. LPM is important because the device and system Iq can be greatly reduced in system low power states such as key off where only a weak load needs to be driven, especially when multiple controllers are used in a single system.

    High Side Switch Controller Webinar.pptx

    Over email we can discuss this more as well.

    Thanks,

    Patrick

  • 0 in reply to Patrick Shalton
    Intellectual 450 points

    Hi!

    I think now I understand why TPS4813 was released.

    Maybe you can help me with selection.

    In my application I have only switch of inductive load, but in general for other projects also I want to select one IC with:

    1. OV/UV/SCP/RPP Switch

    2. Current sense

    3. Pre-charge or other technology for capacitor loads

    4. Can be used for load dumps for voltages higher than 100V like LM74930

    Thanks!

  • 0 in reply to Stas Shamanin
    TI__Mastermind 28220 points

    Hi Stas,

    Sorry for the delay on this, and Happy New Year!

    TPS4800-Q1 was recently restocked on ti.com.

    As to the requirements, it looks like TPS4812-Q1 would be the best fit, though none of the HSS controllers can take load dumps >100V like LM74930. Could it work for your application?

    Or, if you need the 200V capability of LM74930, would that part work instead?

    Thanks,

    Patrick

  • 0 in reply to Patrick Shalton
    Intellectual 450 points

    Hi!

    Happy New Year!

    1. I see that regarding load dumping best fit is LM74930.

    As I see, it is because Rsns goes after back-mosfet, that may serve as OV-protection.

    I am just not sure if it is ok to use LM74930 as switch, but I don't see a problem, just want to confirm it.

    Just short (or use MODE low) forward MOSFET and it looks like I can use LM74930 as load switch with load-dump feature.

    2. Also I see you started to implement RDS-sense in TPS48xx controllers, but in the same time you replaced IMON output.

    I agree, that RDS-sense is completely not precise, but it is always nice to have current feedback even if it is not accurate.

  • 0 in reply to Stas Shamanin
    TI__Mastermind 28220 points

    Hi Stas,

    Apologies for the delay. Yes as you mentioned, LM74930 can be used as a switch as you described.

    Thanks for the feedback about RDS sense!

    Thanks,

    Patrick