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Original question:

Are there amplitude adjustable chip when feeding a PWM signal?

TPL0501-100: Using Digital Potentiometer to control the gain of an Op Amp

David__
Genius 3585 points
Part Number: TPL0501-100
Other Parts Discussed in Thread: TPL0102-100, MSP-EXP430FR2355,

Hi, I have tested this Op Amp gain controlling application using an analog potentiometer and I saw the changing gain using an oscilloscope.

Instead of using an analog potentiometer, I want to use a digital potentiometer to control the gain of a signal.

1. From this example,

What is the range of V_I? Can I apply 40V to the High or Low terminal pins?

I couldn't find this from the datasheet.

2. Just like the first picture, I was thinking of shorting the wiper terminal to the high or low terminal.

If I do this, can I control the resistance(high terminal - low terminal) from 0 to 100k Ohms?

I used other digital potentiometers but those didn't work when I shorted it.

Instead of the first application, I want to use this digital potentiometer to control the gain.

If there is an alternative way instead of shorting the two terminals, I wish to hear about it, please.

  • 0
    TI__Genius 14220 points

    Hi David,

    Thank you for your query. Please find my answers below:

    David__ said:

    1. From this example,

    What is the range of V_I? Can I apply 40V to the High or Low terminal pins?

    I couldn't find this from the datasheet.

    TI: This information has been provided in section 6.1 of the datasheet. The maximum voltage allowed for every resistor terminal is VDD.

    David__ said:

    2. Just like the first picture, I was thinking of shorting the wiper terminal to the high or low terminal.

    If I do this, can I control the resistance(high terminal - low terminal) from 0 to 100k Ohms?

    I used other digital potentiometers but those didn't work when I shorted it.

    David__ said:

    The TPL0501 has a floating resistor configuration. it can be used in a gain control configuration for an opamp as long as the maximum voltage at each terminal is not exceeded. 

    Instead of the first application, I want to use this digital potentiometer to control the gain.

    If there is an alternative way instead of shorting the two terminals, I wish to hear about it, please.

    You can refer to the application circuit provided for TPL0102-100. This circuit explains your use-case.

    Hope that answers your question.

    Regards,

    Uttam Sahu

    Applications Engineer, Precision DACs

  • 0 in reply to Uttam Sahu
    Genius 3585 points

    Hello, .

    Uttam Sahu said:
    The maximum voltage allowed for every resistor terminal is VDD.

    I see thanks for your reply. Also, appreciate that you recommended an alternative product.

    I'm a bit confused since I'm new with the digital potentiometers.

    Uttam Sahu said:
    The TPL0501 has a floating resistor configuration. it can be used in a gain control configuration for an opamp as long as the maximum voltage at each terminal is not exceeded. 

    0.

    I'm using the MSP-EXP430FR2355's SAC(Smart Analog Combo) - DAC example with a high pass filter.

    I will apply 50 ~ 2kHz square wave signals which have positive 1.2V & negative 1.2V amplitude to the Op Amp's positive input(+, V_I).

    Can the TPL0102-100 or TPL0501-100 handle negative voltages as well? I checked the absolute max rating and I want to double check this.

    1. I'm using a rail-to-rail Op Amp configuration (positive 10V, negative 10V). Then setting the Vss of TPL0102-100 is mandatory?

    I can't search the usage.

    2. What do you mean by "floating resistor configuration"? I couldn't find an explanation related to that.

    Are you meaning there are some categories when purchasing a digital potentiometer?

    3. What's the difference between TPL0501-100 vs TPL0102-100?

    Besides the number of channels or negative power supply I can't really tell the difference.

    4. Can I apply the above (Figure 31) schematic when using TPL0501-100 as well? Or is this for TPL0102-100 only (or other special/non-floating digital potentiometers?

  • 0 in reply to David__
    TI__Mastermind 46290 points

    Hello David,

    David__ said:

    Can the TPL0102-100 or TPL0501-100 handle negative voltages as well? I checked the absolute max rating and I want to double check this.

    1. I'm using a rail-to-rail Op Amp configuration (positive 10V, negative 10V). Then setting the Vss of TPL0102-100 is mandatory?

    I can't search the usage.

    As the Absolute Maximum Ratings table indicates, the voltage at either Vh, Vl, or Vw terminals must be within 0.3V of the positive and negative rails in order to prevent the internal ESD cells from becoming forward biased and conducting. Really, you should stay well within the supply rails because even though the cells will not fully forward-biased until closer to 0.3V, you will begin to see the "elbow" of the diode curve and therefore experience some leakage current. To maintain linear operation, you should stay within the supply rails.

    The supply rails for the op-amp are not relevant. What is relevant is the input signal and exact gain configuration.

    David__ said:

    2. What do you mean by "floating resistor configuration"? I couldn't find an explanation related to that.

    Are you meaning there are some categories when purchasing a digital potentiometer?

    Conventionally digital potentiometers are described with two operational modes - "voltage divider" and "rheostat". Page 14 of the datasheet (TPL0102 datasheet) describes the rheostat modes with floating configurations for Vl or Vh.

    David__ said:

    3. What's the difference between TPL0501-100 vs TPL0102-100?

    Besides the number of channels or negative power supply I can't really tell the difference.

    Probably the chief-most difference is that TPL0501 uses an SPI interface while TPL0102 uses an I2C interface.

    David__ said:
    4. Can I apply the above (Figure 31) schematic when using TPL0501-100 as well? Or is this for TPL0102-100 only (or other special/non-floating digital potentiometers?

    Both devices can operate in either configuration. You can look for the rheostat descriptions I mentioned.