• State
  • Locked Locked
  • Replies 3 replies
  • Subscribers 49 subscribers
  • Views 287 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

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.

TLV4111: Using a Op Amp as Voltage Follower to limit voltage drop

Rafael
Prodigy 10 points
Part Number: TLV4111
Other Parts Discussed in Thread: OPA521

Hello Texas Instruments team,

Please, when using TLV4111 as a volage follower, can i connect the Vdd pin to the input pin of the op amp ?

I have this question because this component is only rail-to-rail at the output.

If this doesn't work, is there an operational amplifier that can provide a similar current, is rail-to-rail input/output and could be used as a voltage follower with a 5V source ?

My application is :

I want to supply 5 V to different loads that are switched in the milisecond range.

The current provided to this impedances variates from 100 mA to 150 mA and they are not always activated.

My problem is that this impedance switch causes a variational voltage drop on my 5V line.

To solve this problem I thought about using an operational amplifier working as a voltage follower between the 5V and the impedances variation.

Best regards,

Rafael

  • 0
    Guru 140200 points

    Hi Rafael,

    so you want to give 5V to the input of TLV4111 being wired as voltage follower, want to power it from the same 5V supply and want to drive a load which can vary between 100mA and 150mA?

    Kai

  • 0 in reply to kai klaas69
    Prodigy 10 points

    Hello Kai,

    Exactly, would this be possible to do using this op amp ?

    Rafael

  • 0
    TI__Guru 51701 points

    Hi Rafael,

    My problem is that this impedance switch causes a variational voltage drop on my 5V line.

    If you only have 5Vdd available in your board, TLV4111 is unable to source the 5Vdc @150mA load for the application as voltage follower.

    To accomplish this, you will need to following scenario. 

    1. The Vdd applied  to an op amp is able to source more than 150mA at the application's operating temperature range. It the 5Vdd will droop if it is connected to 33.3Ohm load, then this will not work. In other words, your 5V source voltage has to have 5*150mA + IR pwr losses =  0.75W + IR pwr loss (efficiency issue). 

    2. You are likely required to have higher single supply voltage rail to source up to 150mA from an op amp, say 6V or higher to generate 5Vdc @150mA. It is possible to use parallel op amplifiers to improve the output voltage compliance, but I do not like to use the parallel op amp topology to this type of application (you still have to meet requirements in condition 1). 

    3. You may use power amplifier, like OPA521 (low cost power amplifier), but it will require higher voltage. 

    4. We may be able to boost the 5V source supply voltage and use the higher voltage to drive another suitable op amp for 5Vdc up to 150mA (need more circuitry).  

    5. Use relay to do this msec switching at 5Vdd. 

    Please let me know what options you have and I will simulate one for you. 

    Best,

    Raymond