Current monitor chips

We're using a shunt resistor and an INA241 in one product. It claims to work to -5 volts on the shunt. The product is in development still, FPGAs and code and such, so I can't swear it works well.

Our current is bipolar so zero current parks the INA output halfway up.

I'm using a 10-amp Hall chip on another product and it seems to be nice. You may be running nanoamps.

John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics

I have just used vanilla op-amps for low side sensing, nothing gaudy. Just curious why you mentioned chopper amp kickout, how high value are your shunt resistors?

That ZXCT family is interesting, thanks, accurate but not fast.

Nice part. Of course it ought to be for $3. ;)

That "enhanced PWM rejection" part worries me slightly--sounds like it might have some kickout, which I really do not want. The 0.01% accuracy and CMR (166 dB!) are pretty cool though. I'll get a few to try out.

Nah, not this time. Generally 50 uA - 5 mA per photodiode. It's a differential laser noise canceller with some nice comfort features.

I ordered some of these to try out:

Should be here in the depths of the deepfreeze next week. We'll see!

Cheers

Phil Hobbs

About 20 to 100 ohms, depending on the minimum gain of the sense amp family. They're hanging in midair, though, between the photodiode and a ~1-ohm bootstrap. I'm bypassing them with 470 nF or so, and the sense amp's input resistors are theoretically about 100k, so the kickout should theoretically be pretty low. On the other hand, some customers are going to be looking at the output with a spectrum analyzer....

I could use an op amp and a transistor to do the sensing and generate a current output to do the level shifting all in one go, but it's really hard to get good enough CMR using discrete resistors. It's also five or six extra parts per sensor, and I need three of them. I'll certainly do that if I have to.

Cheap, too!

Cheers

Phil Hobbs

I can sell them to you for $2.

The PWM thing sounds like filtering or spike rejection. We're using it in a barely-filtered 500 KHz 50-volt h-bridge output and the resulting ADC noise is pretty good.

What bw do you need?

I'll email you our schematic.

Stay warm!

John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics

I've been known to hang an opamp+pfet current source up there, hanging on the shunt, shooting a copy of the current down to ground. No matched resistors.

Takes a mess of parts.

John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics

The DS says that when it detects an edge, it freezes its output for 1 us, which sounds like it has switches in the input structure.

There shouldn’t be any edges to trigger that behavior, but I have a nasty suspicious mind. ;)

Sure, I’d be interested.

Working that little problem right now.

Cheers

Phil Hobbs

We'll need some "global warming" to do that. Phil's likely to be a bit colder than me - I'm near Long Island Sound, he's about 40 miles north. Ed

Around here, survival gear is a sweat shirt, socks optional.

John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics

So’s sunscreen. ;)

Cheers

Phil Hobbs

Sun? I think we had a bit of that a couple of weeks ago.

John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics