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TPL1401: Can TPL1401 be used as a 200k digital Pot to adjust the RT pin of UCC28086

Bright Robert
Intellectual 300 points
Part Number: TPL1401
Other Parts Discussed in Thread: UCC28086, , TPL0102-100

Hi, 

I want to enquire whether the TPL1401DSGT can be used a a digital potentiometer to adjust the RT pin (frequency) of PWM controller such as UCC28086. If not, do you have any Digpot of upto 200k upwards that can be used to adjust the RT pin of UCC28086?

Kind regards,

Bright

  • 0
    TI__Intellectual 1635 points

    Hello Bright, 

    Thank you for reaching out. 

    Since the RT pin needs a true resistor, TPL1401 can not be used there. TPL1401 has an output buffer, hence it outputs voltage based on the internal resistance.

    We do not have any digipots in our portfolio unfortunately that can do more than 100k Ohm. 

    Thank you, 

    illia Volkov

  • 0 in reply to Illia Volkov
    TI__Mastermind 29898 points

    Hi Bright, 

    I agree with Illia here. One other suggestion to consider is using a both channels of a two channel digipot, such as the TPL0102-100, in series to achieve the 200k. 

    Best,

    Katlynne Jones

  • 0 in reply to Katlynne Jones
    Intellectual 300 points

    Hi illia and Katlynne,

    Thank you for the swift reply. 

    I have further inquiry;

    1) The supply voltage of the proposed digpot IC is 2.7 - 5.5V. I need digpot IC that operates on 1.8V - 5.5V  to allow me to supply 1.8V- 2V maximum to the IC, this is because, the RT pin of the UCC28086 is 2V absolute maximum (see the datasheet of UCC28086, page 3, 4, 7). Kindy review the RT pin of UCC28086  see if it will work with 2.7V without damaging the RT pin if TPL0102-100 will be used 

    2) How do I make the connection in series? A sketch/diagram would be helpful.

    ucc28086.pdf

    Kind regards,

    Bright

  • 0 in reply to Bright Robert
    Intellectual 300 points

    Kindly check if the connection diagram marked in red is correct. 

  • 0 in reply to Bright Robert
    TI__Mastermind 29898 points

    Hi Bright, 

    VDD is required to be 2.7V to 5.5V, but the HA input can have any input from 0 to VDD. So the limit of the RT pin should not be affected by the required supply range of the TPL. 

    Your figure for connecting the two channels in series is correct. The voltage at RT will be V = (resistance of digipot) * (current flowing from RT). I'm not seeing the current expected from RT in the datasheet, but given that the datasheet is recommending to use resistor values in this range then there should be no issue. 

    Best,

    Katlynne Jones 

  • 0 in reply to Katlynne Jones
    Intellectual 300 points

    Hi Katlynne,

    Thank you for the response. 

    The current at RT pin of UCC28086 is mentioned in Page 3 on the absolute maximum rating, which is about -100uA to100uA

    Also, I intend to connect a 430K R before connecting the dual channel digpot. 

    Kind regards,

    Bright

  • 0 in reply to Bright Robert
    TI__Mastermind 29898 points

    Hi Bright, 

    The absolute maximum rating is what the pin can tolerate, but that's not the current of the pin during operation. Looking at this section of the datasheet again, it looks like the voltage of RT is fixed to ~1.5V. In that case the current through RT is set by the chosen resistor value. As long as the total resistance value you're connecting to RT is within the recommend range then this configuration should be ok. 

    Best,

    Katlynne Jones

  • 0 in reply to Katlynne Jones
    Intellectual 300 points

    Hi Katlynne,

    Thank you