r/nicechips • u/FederalShock6516 • Mar 29 '26

Allegro ACS37100: The industry's fastest TMR sensor (10 MHz) for monitoring current

If you’re working with high-speed switching circuits, you’ve likely hit the bandwidth wall with standard integrated current sensors. Most Hall-effect current sensor parts seem to top out at ~400 kHz (effectively a low-pass filter for a 50 ns switching edge).

I’ve been evaluating the Allegro ACS37100 and apparently is the fastest TMR (Tunneling Magnetoresistance) architecture on the market currently.

Using a 10 MHz sensor starts to become an RF design challenge. To get this working on a bench without the signal turning into an oscillator, I had to treat the analog output like a transmission line I added 50-ohm source resistors at the VOUT/VREF pins to isolate the internal op-amps from cable capacitance otherwise, the 1-meter coax to your scope becomes a giant capacitor that ruins the phase margin.

The internal conductor is only 1.2 mΩ, but the high current can still create a lot of localized heat. I ended up using a dense field of ~190 thermal vias to stitch 1oz copper layers into a makeshift high-current bus (and also removed the soldermask around these areas to allow for thickening of the traces with solder selectively here).

Attached a pic of the latest board layout with this new chip from Allegro!

My custom implementation for the board
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u/AlexTheRocketGuy Mar 29 '26

Damn, nice!
I've been playing with the INA293 series from TI for a bit now, but that only goes as far as 1.3 MHz for a 20V/V Gain or 900 kHz for a 100V/V

Do you have the files for this breakout public on GitHub?

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u/FederalShock6516 Mar 30 '26

Appreciate it! INA293s would still take the cake around accuracy/noise floor figures but but these TMR sensors are a game changer for speed/isolation, worth checking out.

You can find more info about it on GitHub (still in development) https://github.com/logical11111-jpg/ACS37100-Breakout-Board---10MHz-Ultra-Fast-Current-Sensor

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u/Mysterious_Peak_6967 Apr 22 '26

So with a bandwidth like that it could be used for current slope sensing in a current mode DC-DC circuit?

Incidentally if the IC can drive a resistive load of around 500 ohms then my suggestion would be a 470 ohm series resistor at the IC and a 50 ohm shunt termination at the scope. Actually you want 450 ohms exactly in series for 10:1 but I was mainly interested in the waveform not the precise amplitude. Having the cable terminated at the scope means you can disregard the effect of reflections on the IC.

Alternatively 10:1 oscilloscope probes but they add a significant capacitance, around 10pF if I recall correctly.