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Original question:

TMCS1101: TMCS1101A4U supply voltage 3,3 V recommended?

TMCS1101-Q1: TMCS1101A1UQDRQ1

CY
Prodigy 65 points
Part Number: TMCS1101-Q1
Other Parts Discussed in Thread: TMCS1101

Hi,


We measure a full bridge primary input current with TMCS1101A1UQDRQ1.

Output goes to the CPU ADC input. Primary current is 25 Amps maximum. We supply the chip with 3.3V. When there is no or small current flowing through the IC, supply current is OK. But when we draw more than 1 Amps, TMCS supply current increases as the primary input current increase (this goes to 100 mA's). We tried this with multiple chips. Is there anything we miss wrto design?  

Thanks,
MA

  • 0
    TI__Mastermind 28640 points

    Hello Celil,

    I do not see anything that brings up issues.  The things I would investigate is the 25A is high and the 30A we specify is with the EVM which dissipates a lot of heat.  I assume your layout also has enough copper to dissipate the heat?  https://www.ti.com/lit/an/sboa400/sboa400.pdf may be help if this is the case this is a concern.

    Is this the only item connected to the 3.3V, or have you already isolated the current to the TMCS1101.  

  • 0 in reply to Javier Contreras4
    Prodigy 65 points

    Hi Javier,

    Thanks for your reply. We did not work the chip at 25 Amps yet, so could not be related to that. We change the chip with a new one, and the result is the same. 

    And yes, we isolated the issue to TMCS. After we disconnect TMCS supply pin from the circuit, everything is fine.  

    We increased the 3.3V decouple capacitor and it did not work. I could not find any spec related design mistake etc.

    There is a cutout at the bottom of the chip, does this might trigger something?

  • 0 in reply to CY
    TI__Mastermind 28640 points

    Hello CY,

    Do you see any issues at the output.  The 100 ohm resistor and 1nF cap should be fine and I would not expect any issues but checking to make sure there are no oscillations.  Anything else hanging on the output node to worry about.

    The cutout should not be an issue unless the is some way the input is coupling to the supply somehow on the PCB.  I would expect the cutout to help.  Can you share a layout.  I do not  think it is the issue but another look in case.