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TMCS1126-Q1: Inquiry about Vref voltage condition and Vout waveforms

HOIWOONG JUNG
Prodigy 60 points

Part Number: TMCS1126-Q1

Tool/software:

HI~

Q1) I saw in the data sheet that Vref has 2.5V output from VCC 3.5V to 5V

     Q1-1) Is this condition 3.3V to 5V or is it only satisfied at 3.3V and 5V?

     Q2-1) Is there any data where Vref has been measured under different voltage conditions?

Q2) I measured the Vout waveform while developing the DC-DC converter, and suddenly the voltage drops and then rises

       RED - VOUT , BLUE - CURRENT

     Q2-1) Is there a reason why the VOUT waveform changes with the current change and then suddenly drops?

  • 0
    TI__Mastermind 24265 points

    Hoiwoong, 

    Please find some answers to your questions below:

    Q1 &Q2-1) Can you show me what portion of the datasheet you are questioning here with regard to VREF? The 2.5V output of the reference voltage will actually be bound to the orderable, with A variants outputting 2.5V, B variants 1.65V, and C variants 0.33V respectively. The reference should be stable with respect to supply. As we call out 3.3V and 5V in the global conditions, these are the points that we verify on the device and guarantee performance, but I would expect the performance between these levels to closely adhere to the same performance. Regarding data, we examine the reference for these voltages over temperature, but no, we do not have this data available that we can share here on the forums. 

    Q2) Examining the corresponding current waveform, it appears at the time of the event, there is a small load step. I would expect the drop you are seeing to correspond to the switching voltage present on the input pins of the device, which is known as CMTI:

    At the point the converter is asked to perform this load step, the switching voltage is likely also changing leading to a coupling event as shown in figure 7-3, and the overall cycle by cycle response will need to work this transient out as part of the response.