• State TI Thinks Resolved
  • Locked Locked
  • Replies 4 replies
  • Answers 1 answer
  • Subscribers 30 subscribers
  • Views 551 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Original question:

PGA411-Q1: Exciter signal output waveform distortion problem

PGA411-Q1: Excitation and AFE questions

Yassine DAMOH
Prodigy 70 points
Part Number: PGA411-Q1

Hello,

I have a couple of questions regarding the PGA411-Q1.

1- Excitation :

a) When using the internal Excitation circuit to have the 7VRMS differential output,and using an external op amp as follower to supply the primary coil with the needed current. What protection should be added between the OEx pins and the External Op amp?

b) is it possible to use external power op amp, amplifying an OEx output of minimum 4VRMS to 7VRMS.

if yes, can i use a zener diode in the Vext pin to adjust the supply voltage to 12V (for 4VRMS Mode)  (I imagine, the pga411-q1 would have less power consumption in this case)

For the Vexts pin, should it have the voltage used for supplying the external op amp or the one used to supply the internal one

The IEx pins,  could they receive an excitation voltage of 7VRMS knowing that the PGA is working with 4VRMS Mode

c) Does the PGA have a under-modulation detection/Correction feature? in case of multiple poles resolver, the Sin/Cos reading at high speeds would probably be distorted.

2- Analog front End,

a) How can we set the cutoff frequency of the differential mode capacitor ? or it depends on the how much the actual Sin/Cos voltage is distorted? (Same question for the excitation feedback capacitors)

b) For the Open circuit operations, the available documentation clearly states that the Pulldown and Pullup resistors of the AFE should pull the Osin/Ocos Voltage out of the normal operation range (Higher than 75%Vcc and lower than 25%Vcc). but i couldnt find any combination of resistors, that would be able to pull the signal above 75%Vcc. in fact it would always trigger the lower open circuit threshold.

c) What if the OVIZL threshold is the same as the OOPENTHL threshold? may it cause any fault detection problems ? 

Thanks for the support

Yassine

  • 0
    TI__Mastermind 23810 points
    Yassine,

    1.
    (a) I cannot speak to the protection needed for the external op amp. The PGA411 OEx outputs will continue to have diagnostics for over/undervoltage and overcurrent conditions, but they will not necessarily detect if there is a short circuit on the op amp output.

    (b) You can do this. Alternatively, you could use the PGA411 ORS single-ended output instead of the OEx outputs. In this mode, the PGA411 will use much less current consumption.

    Are you asking if the VEXT can be used to supply the external op amp by placing a zener in-between? This should be possible, but the current limits of the boost will still need to be followed. Since the current limits are sized for the current output capabilities of the PGA411 excitation output, you could run into issues.

    VEXTS should always be connected to VEXT.

    (c) Can you describe what the waveforms would look like in this case? I do not believe that the PGA411 would detect such a case, but I can double check if you provide more details about the condition.

    2.
    (a) Equation 19 in the datasheet shows the calculation for the cut-off frequency. You should set the cut-off to be above your excitation frequency, by about 10kHz to 20kHz. For instance, for an excitation of 10kHz, it will work well if your cut-off frequency is between 20kHz and 30kHz.

    (b) You will not trigger both of these conditions with a single AFE configuration. Triggering only the lower threshold is perfectly fine. You just need to make sure that when an open circuit condition occurs that one of the faults is triggered.

    (c) There will not necessarily be problems with that. OVIZL looks at the single-ended IZx pin voltages while OOPENTHL looks at the differential output (it looks at an internal signal, but you can see a buffered version on OCOS/OSIN). Additionally, it is not a problem if a typical signal crosses the OOPENTHL threshold because the deglitch time is so long.
  • 0 in reply to Clancy Soehren
    Prodigy 70 points

    Clancy,

    Thank you for the quick and detailed response.

    Regarding the under-modulation question, the below graphs shows angle variation & Sin/Cos reading for low and high speed with the same excitation frequency.

    • For Low Speed : (angle variation)

    • Cosine Reading

    • For High Speed (Angle Variation)

    • Cosine reading

    Remark : these graphs were plotted using the same time scale.

    Thank you in advance 

  • 0 in reply to Clancy Soehren
    Prodigy 70 points
    Followup question is in the comment below
  • 0 in reply to Yassine DAMOH
    TI__Mastermind 23810 points
    This is for a multi-pole resolver correct? You should see that the angle output is correct as long as you stay within the datasheet specified speed (72,000 electrical RPM for 12 bit mode). It may be difficult to see on an oscilloscope, but if the signals are demodulated, they will revert to typical sin/cos signals.