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INA199-Q1: Sensing accurancy with several kHz oscillation

Gene Qiu
Intellectual 1720 points
Part Number: INA199-Q1
Other Parts Discussed in Thread: INA210

Hi team, 

When using INA199A-Q1 in DCDC for output current sensing after inductance with 0.1 mΩ sensing resistor,   

1. in the case of small current, like 2-3A, the output has a few kHz (3.3kHz) oscillation.

2.When load on with 45A, output should be calculated as 225mV (with 50V/V gain), while the waveform is triangular wave with 13.5kHz frequency. Why it is triangular, the mid-point is ~225mV

Best Regards,

Gene

  • 0
    TI__Mastermind 32395 points

    Hey Gene,

    Thanks for the waveforms. Well it is hard to say why it is triangular. Could the DCDC output current contain a 13.52 kHz output ripple?

    100 uOhm shunt resistor is pretty small. Aside from the AC error, there could be a DC error if the sensing lines for shunt resistor are including solder resistance that is in the main DCDC conduction path.

    Best,
    Peter

  • 0 in reply to Peter Iliya
    TI__Mastermind 32395 points
    Hey Gene,

    Additionally, their could be an output ripple if the load capacitance is greater than 1nF (without isolation resistor). If their is some isolation resistance, the load capacitance can be greater than 1nF, but if it is too large then this RC network could be causing resonance with the closed-loop output impedance of the INA210.

    Best,
    Peter