THS4561: Current consumption

Pedaiah G

Part Number: THS4561
Other Parts Discussed in Thread: TINA-TI

Hi,

We are using Three THS4561 Diffrential amplifiers for Single ended to differential ended signal conversion in our design.

Attached Schematics for your reference.

We are generating +5V from Buck converter (Part no: TPS62150AQRGTTQ1) and -5V from Charge pump (LT1054I).

During the operation, We observed drop in Charge pump output and heating of charge pump ( Max sourcing current 100mA).

Then I applied +5V and -5V Externally from power supply to THS4561 Diffrential amplifiers by isolating Buck converter/Charge pump and THS4561 Diffrential amplifiers.

I observed the below results when I applied +5V and -5V to all three Differential amplifiers without applying input and connecting load only 2.1k and 22nF as shown in attached file.

	Current Consumption
Voltage	VS+ = 5V	VS-= -5V
Only -5V applied	X	9.3 mA
Only +5V applied	15.57mA	X
Both +5V and -5V applied	127 mA	127 mA

Queries:

1. What is Actual current consumption by +5V and -5V supply rails of each THS4561 Diffrential amplifier without load ( in my case i connected 2.1k and 22nF) only?

2. In our design as per above results, THS4561 is drawing nearly 40mA of current from external power supply. is this OK?

THS4561.pdf

Thanks and Regards,

Pedaiah G.

over 3 years ago

0 kai klaas69 over 3 years ago

Guru 140200 points

Hi Pedaiah,

the circuit seems to oscillate.

Why is your multi-feedback filter looking so strange? Compare it with the frontpage of datasheet of THS4561. There are some caps missing in your design. Without these caps, especially the feedback caps which serve as phase lead capacitances, the phase margin will be ruined and the OPAmp will oscillate.

Kai

0 Sima Jalaleddine over 3 years ago

TI__Mastermind 28945 points

Hello Pedaiah,

The quiescent current of the device without a load should be under a mA of current from each power supply. I agree with Kai, oscillations from an unstable circuit will cause a large increase in current consumption. As seen in a quick Tina-TI sim below:

As a quick check, try removing the 330Ohm resistors and the 1nF differential capacitor.

Thank you,
Sima

0 Pedaiah G over 3 years ago in reply to kai klaas69

Prodigy 230 points

Hello Kai,

Sorry for the delay in response.

I got the circuit reviewed by internal TI Team.

Please find the below link of Discussion.

https://e2e.ti.com/support/amplifiers-group/amplifiers/f/amplifiers-forum/1002392/ths4551-single-ended-to-differential-conversion/3709833?tisearch=e2e-sitesearch&keymatch=THS4561#3709833

Please do let me know if any modifications.

Thanks and Regards,

Pedaiah G.

0 Pedaiah G over 3 years ago in reply to Sima Jalaleddine

Prodigy 230 points

Hello Sima,

Does Differential op-amp output will oscillate without input?

In my case i have not given any input.

I wanted to under stand why is the circuit drawing 127mA without load.

Thanks and Regards,

Pedaiah G.

0 Sima Jalaleddine over 3 years ago in reply to Pedaiah G

TI__Mastermind 28945 points

Hello Pedaiah,

Yes, the device will oscillate and is unstable even without an input.

Thank you,
Sima

0 Michael Steffes over 3 years ago in reply to Sima Jalaleddine

Guru 48395 points

Yes, quite odd,

1. I think your source is a DAC not an ADC,

2. That RC pole inside the loop is just adding a huge phase shift in the loop - probably oscillating remove the Cap and you should be ok,

3. That extra Rload is unnecessary, remove it

4. What is your real CM control voltage?

...

0 kai klaas69 over 3 years ago in reply to Pedaiah G

Guru 140200 points

Hi Pedaiah,

please follow Sima's recommendation:

Sima Jalaleddine said:
As a quick check, try removing the 330Ohm resistors and the 1nF differential capacitor.

Kai

0 Pedaiah G over 3 years ago in reply to Michael Steffes

Prodigy 230 points

Hello Michael,

Sorry for the delay in response.

1. Yes correct. My source is from DAC.

2. Yes I removed 1nF at the input terminals of THS4561.

3. Yes I removed 2.1K at the output of THS4561.

4. CM control voltage is 0.5V.

After removing 1nF and 2.1k, i can see THS4561 drawing very less current on +5V and -5V supply rails.

I think now circuit looks fine.

Thanks and Regards,

Pedaiah G.

0 Pedaiah G over 3 years ago in reply to kai klaas69

Prodigy 230 points

Hello Kai,

After removing 1nF and 2.1k, i can see THS4561 drawing very less current on +5V and -5V supply rails.

I think now circuit looks fine.

Thanks and Regards,

Pedaiah G.

0 Pedaiah G over 3 years ago in reply to Sima Jalaleddine

Prodigy 230 points

Hello Sima,

sorry for the delay in response.

After removing 1nF and 2.1k, i can see THS4561 drawing very less current on +5V and -5V supply rails.

I think now circuit looks fine.

Can you please share the simulation file for my future reference?

Thanks and Regards,

Pedaiah G.

0 Sima Jalaleddine over 3 years ago in reply to Pedaiah G

TI__Mastermind 28945 points

Hello Pedaiah,

Below is the simulation file in Tina-TI:

THS4561_Pedaiah.tsc

Thank you,

Sima

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THS4561: Current consumption