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TIDM-BIDIR-400-12: dsp

Kyoungtak Kim
Intellectual 620 points
Part Number: TIDM-BIDIR-400-12
Other Parts Discussed in Thread: CONTROLSUITE

Hi, 

I'm dealing with the ADC circuit for TIDM-BIDIR-400-12. 

In the TIDM-BIDIR-400-12, there is an output voltage sensing circuit. 

It consists of the voltage divider and RC filter I guess. 

The image below is the schematic of the circuit. 

As you can see the image, I guess R21 and R20 work as a voltage divider and R21 and C17 work as an RC filter. 

I want to ask for several things. 

1. What's the intention of the resistor R21 and R20 value? Is it because when the 12v output voltage reached, the designer wants to give the ADC voltage 2.5V? 

2. What's the role of R11 and why that resistor value is 49.9? Is it related to the Input impedance of the f28035 DSP adc port? 

Thanks for your help. 

  • 0
    TI__Guru 71785 points

    Kim,

    Q1)What's the intention of the resistor R21 and R20 value? Is it because when the 12v output voltage reached, the designer wants to give the ADC voltage 2.5V? 

    A1)That is correct, it is the voltage divider to scale the 12V VLV bus to the ADC input range on the F28035 device.  There is a XLS file that contains the math to translate the board level voltages and GUI inputs here: C:\ti\controlSUITE\development_kits\BI_DIRECTIONAL_DC_DC_400_12\v1_00_00_00\Docs\Bi_dir_Calculations.xls  The VLV tab contains the resistor values, as well as the ADC scaling.

    Q2)What's the role of R11 and why that resistor value is 49.9? Is it related to the Input impedance of the f28035 DSP adc port? 

    A2)I don't believe that is the function here, since signal VLV then goes 2nd picture you've attached, i.e. the MCU is going to "see" the kOhm resistors as well.  Looking at the schematic there is Test Points on either side of this resistor; TP4 and TP5.  I suspect this is to provide a measurement point, perhaps for looking at the plant in open loop?

    Best,

    Matthew