this post was submitted on 26 Jun 2023
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TI's MSPM0L1105 chip offers 32MHz and 4kB SRAM + 1x OpAmp for $0.39 / 1k quantities. (self.technology)
submitted 1 year ago by dragontamer to c/technology
2 comments fedilink hide all child comments
 

https://www.ti.com/product/MSPM0L1105

Microcontrollers are always kind of interesting to me. Lets see how many others in [email protected] are interested in these tiny chips!

Earlier this year, TI has added a number of Cortex-M0+ chips to their lineup. At the absolute bargain-bin is the MSPM0L1105 (of the MSPM0 line). Prices seem to have started coming in at Digikey at ~$1.60 @quantity 1, though TI offers much lower prices in bulk quantities as expected.

The Cortex M0+ is the smallest ARM, lacking many features familiar to desktop or phone users. Its too small to run Linux, but its more of a Arduino competitor. The focus is on the smallest price possible, as well as ease of use for the Electrical Engineer and programmer.

One of the coolest things going on with modern uCs is that OpAmps are being offered as part of the package these days. OpAmps are perhaps the oldest "computers", designed to give the EE an easy-to-use negative feedback loop. OpAmps can implement analog-logic, arithmetic over voltage rather than discrete values like digital enthusiasts are familiar with. The voltage itself is the value, and thus you can multiply, divide, add, subtract, logarithm or exponent, derivative or integrate by just adding resistors, capacitors, or diodes to the correct location on the circuit.

With the 12-bit ADC and an OpAmp (probably most commonly to be used as a filter), this should provide a wide variety of simple applications at very low costs. At 39-cents, this device basically costs the same as another opamp (except this device includes a full blown CPU + ADC Converter).

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[–] photon 1 points 1 year ago (1 children)

Thanks for posting this! I’m particularly excited about the use of the opamp as a transimpedance amplifier, converting a current from a photodiode to a voltage, then being able to feed that signal straight into the ADC. Depending on the performance, this could simplify my design work significantly.

I found some basic documentation on that here - https://www.ti.com/lit/an/slaae81/slaae81.pdf?ts=1689294975621

[–] dragontamer 2 points 1 year ago* (last edited 1 year ago)

IIRC, a low side (relative to ground) is straightforward. But high side current sensing (measuring and amplifying the current measurement where one resistor side is NOT tied to ground/zero volts) has some subtle accuracy issues.

Note that worst case CMRR is 44db, so 1mA at 0V and 1mA at 3V will have a ~0.03V difference. CMRR is that non-ideal property where the change of Voltage that the OpAmp operates at will kinda sorta leak out to the output / results.

Operating at near 0V will minimize this error. Or the Chopper-mode will cut down on that if you must do high side current sense.

There are lots of different opamps for a reason, they all have tradeoffs. This TI one is chopper mode which should have better CMRR than a lot of others IIRC.