INA240: Triangular waveform observed at the output of the Amplifier

Nisha Lemos

Part Number: INA240

We have used INA240A3 as a current shunt amplifier. However, the output is displaying abnormal behavior. The output of the amplifier is a 1.3Vpp triangular wave @2.5V offset for 0 current.

I am attaching the designed schematics and the acquired waveform. Could you please check and revert on these issues.

over 2 years ago

0 kai klaas69 over 2 years ago

Guru 140200 points

Hi Nisha,

you should urgently remove C8 from the output of INA240.

Also, what is the input signal?

Kai

0 Nisha Lemos over 2 years ago in reply to kai klaas69

Prodigy 70 points

Hi Kai,

SRP and srn are connected to a 0.1mohm shunt resistor.

Nisha

0 Peter Iliya over 2 years ago

TI__Mastermind 31735 points

Hello Nisha,

I am looking into this and will respond shortly.

Best,

Peter

+1 Peter Iliya over 2 years ago in reply to Nisha Lemos

TI__Mastermind 31735 points

Hey Nisha,

The 100nF output capacitor (C8) is most likely creating instability/oscillation with INA240's inductive output impedance. The maximum recommended output capacitor (with no isolation resistance) is 1nF. So you should either reduce C8 to 1nF (assuming no extra load capacitance at OUT node) or place an isolation resistor in between OUT and C8. For a 100nF capacitor, Riso>100Ω, but this may reduce signal BW beyond what is acceptable.

Sincerely,

Peter

0 kai klaas69 over 2 years ago in reply to Nisha Lemos

Guru 140200 points

Hi Nisha,

Nisha Lemos said:
SRP and srn are connected to a 0.1mohm shunt resistor.

Yes, but what is the signal across the shunt resistor? Can you show a scope plot?

Kai

0 Nisha Lemos over 2 years ago in reply to kai klaas69

Prodigy 70 points

The shunt resistor is connected in line with the battery to measure battery current. Currently no load is attached and the battery current is zero.

0 kai klaas69 over 2 years ago in reply to Nisha Lemos

Guru 140200 points

Hi Nisha,

then the INA240 is oscillating because of the huge capacitive load of 100nF. Please solve the issue as recommended above.

Kai

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INA240: Triangular waveform observed at the output of the Amplifier