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TLE2426: Output voltage

Amir Eshraghi
Expert 1230 points
Part Number: TLE2426
Other Parts Discussed in Thread: TL081

Hi

I have quick questions regarding TLE2426IDR. We are using this virtual ground to our transimpedance amplifier so we do not have to use rail to rail power supply.

The issue is when  VCC or ground change (Due to high load on circuit board) the TLE2426 output to change which cause  amplifier output to change too.

I have attached below graph to see what happen to amplifier output every time VGND voltage change. This mostly happen if any thing high load turns on in the pcb such as heater.

I want to know is it possible to keep VGND output steady.

  • 0
    Guru 140200 points

    Hi Amir,

    the TL081 cannot run with a 3.3V single supply voltage.

    What sensor do you have? Can you tell a bit more about your application?

    Kai

  • 0 in reply to kai klaas69
    Expert 1230 points

    Hi Kai,

    Sorry for the confusion the op-amp in the diagram is not part number I am using(MCP6V02-E/SN). 

    The sensor we are using is oxygen sensor which gerenrate 1nA - 100uA of current.

    As I described before we are using TLE2426 as our virtual ground, but the problem is TLE2426 Vout shift when a large load turns on. (Load can be in different voltage from vin of TLE2426).

    I am using 15V vin to my pcb and reduce voltage  to desire voltage of transimpedance amplifier. All my loads are connected to 12V supply. 

    Please let me know if you need more information.

    Thank you

  • 0 in reply to Amir Eshraghi
    TI__Mastermind 47656 points

    Hi Amir,

    What is the %load_regulation in your 12V switching power supply? 

    I was wondering when the heater is turned on, the 12V power supply droops significantly, and interrupts the 5V switching regulator, which TLE2426 is operating on. 

    Are 5V and 12V switching power supplies generated from the same SW supply? The TLE2426's input voltage is specified between 4-40V. I was wondering if 5V supply droops below 4V when heater is on. If this is the case, connect TLE2426 op amp to 15V rail. 

    Best,

    Raymond

  • 0 in reply to Raymond Zhang1
    Expert 1230 points

    Hi

    I am using LM34936RHFR as my  12v regulator and when max load of 3A turns on it only drop 500mV. 

    My problem is even when I have 500mA load on my supply which cause 5mV change in 12v supply cause change on my TLE2426 due to voltage divider.

    The main supply goes to 12V regulator and then 12V output connect to 5V regulator.

    I have check the output does not drop under 4V.

    Thank you

  • 0 in reply to Amir Eshraghi
    TI__Guru* 93105 points

    Hello Amir,

    The TLE2426 is basically a precision resistive divider followed by a precision op amp. If the voltage applied to TLE2426 Vi input pin or to the common changes, that changes the output voltage from the input divider, and the supply voltage applied to the precision op amp. Therefore, the TLE2426 output will reflect a change in either Vi, or common.

    I set the TLE2426 model up in TINA and tried connected a capacitor from the Vi pin to ground, and then a capacitor each to the Vi and common pins. The single cap shows a long response time, and the dual caps follow the supply glitch. I don't see any way to keep that from occurring with the TLE2426 design.

    TLE2426_SplitCaps_02.TSC

    Regards, Thomas

    Precision Amplifiers Applications Engineering

  • 0 in reply to Thomas Kuehl
    Expert 1230 points

    Hi Thomas 

    Thanks for quick reply again. You answered my questions by the simulation, but how come you connect the vin bypass capacitor to pin 8 instead of ground.

    Thank you

  • 0 in reply to Amir Eshraghi
    TI__Guru* 93105 points

    Hi Amir,

    The usual connection of the TLE2426 "noise reduction" or bypass capacitor is from the "IN" pin to ground. However, using that connection results in a long RC time constant that delays when the "OUT" voltage comes up to full level. Connecting one capacitor from the positive supply line to "IN" and another from "IN" to "COMMON" eliminates the RC time constant and that may be desirable. The differences can be seen in the TINA plots I provided in my earlier response.

    Regards, Thomas

    Precision Amplifiers Applications Engineering