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Current monitor for LED driver

Other Parts Discussed in Thread: LMP8640, INA210, INA219

Hi,

I am designing a adjustable current-feedback switching regulator for driving LED's. The switcher works at 500KHz, output is max. 3A dc at 6V dc. I want to monitor output average current for display. My logic (12-bit ADC) runs at 3.3V. Output current ripple is expected to be about 10mA p-p.

I was looking at the wide selection (86 chips!) of shunt monitors and I want to ask specifically about the LMV8640.

Looking at the datasheet I noticed:

Page 4 of the datasheet (2.7 V characteristics) says "Minimum output voltage = 80mV" for the 100V/V option.  Is that with zero shunt current? I contrast this with Fig.15 on page 10, which shows a 25mV Vout for zero Vsense. What output will I get at 100mA if I use a 10 milliohm shunt? How about 50mA?

Also there is no mention of input filter. If I use one, will it degrade the accuracy, offset, output, if so by how much? 

I would be grateful if anyone could explain the above, and perhaps suggest a way to measure switcher output current with tolerable accuracy (<5% error) solely for display purposes. 

 Bas

  • Sorry for the typo, I believe that's the LMP8640, not LMV....my bad.

  • 6 days later.

    So I came to the conclusion that the LMP8640 is practically not much use at the lower range of sensing due to its input offset times gain.

    I will probably choose one of the INA210 "zero-drift" series using input and output filters. Offset in microvolts. I think just for measuring for average current display, I don't need that much bandwidth. I want to get a more stable result.

    I also had a look at the INA219 with 12-bit ADC, sample averaging and I2C. Wow! At first sight this seemed absolutely great, but there is no mention of bandwidth in the entire datasheet. Conversion time almost 600us. Averaging time up to 68ms.  More hours of programming.  Maybe use in a future version, I need my beauty sleep now.

    Again, thanks in advance to anyone who does offer advice in this forum.