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Part Number: TLV70012-Q1
I've found an issue whereby when a TLV70015DSE regulator is used to supply an op amp mid rail bias the reference 1.5V output is not stable and gradually rises to reach a voltage of approximately 2.18V.
On further investigation I found that op amps draw about 0.7uA but believe that the current is sourced from the op amp Vcc via the op amp long tail pair (Vcc= approx 3.0V) that seems to cause the regulator to voltage rise.
To try to prove this I replicated the op amp and replaced with a high value resistor of 2M2 to simulate a similar current. When this resistor was connected to the Vcc rail a similar effect with a rising voltage could be seen.
Note that the same 3.0V rail supplies the input of the TLV70015DSE regulator.
I found that the voltage could be made to return to the correct regulated voltage by connecting a 100k resistor from the 1.5V ref to ground. My thinking behind this was to provide a return current via ground to the regulator.
I would like some help to understand why this is happening as would assume that a regulator would be able to provide a solid voltage source o/p.
As far as I can see the regulator is connected as per recommended in the data sheet and with the recommended decoupling on I/P and O/P of 1uF ceramic capacitor. An outline schematic and circuit of the bal to unbal circuit are attached.
In reply to Jason Song:
In reply to Chris Woolrych:
Just wanted to know if you've any further feedback or answers to my questions on the operation of this part?
The circuitry connected to the positive side of the op-amp is as shown in the schematic snipet. Additionally the VREF connects to an identical op-amp circuit for the other channel.
The measurement was taken at "Node A" as shown on the updated digram attached
Also see diagram showing how 2M2 resistor was connected to VREF.
Vref issue #2.pdf
As you mention in this design we only need a voltage reference.
However since this design was adapted from a previous design and we are already in mass production we don't really want to modify the circuit to change to a voltage reference just now.
Therefore we'd like conformation that the modification we made to add a 100k resistor load from VREF (1.5V to ground to provide some loading for the voltage regulator) that we found prevented the voltage from rising is a viable solution.
Thanks for your conformation.
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