EECS 373 On Operational Amplifiers and Other Means of Manipulating Voltage and Current

Schedule updates I’ll have office hours and a review session between the last day of class and the final. – Exam review, likely Sunday late afternoon. HW6 will be assigned on April 3 rd. – Practice final—can’t assign until last topic talk is done. Topic talks**** Short (50 min?) lecture: Design Expo stuff: poster, video etc. information 10:30am-1:30pm Op-amps

Once you’ve done your topic talk… Send me your slides – Pdf is fine, but I’d prefer power point (and both is better yet). Don’t believe I have the two from Tuesday yet.

Other Administrivia? And yes, Merriam-Webster accepts that as an English word.

Analog—the bane of the computer engineer In embedded systems, you often need to deal with voltages and currents. – Often the outputs you have don’t match the inputs you need. Generally the current or voltage is too small Sometimes the voltage is too big. Sometimes the values are in the wrong range. Today we’ll touch on some ways of manipulating these values. – This is intended to give you some idea what options are out there Often the details are tricky and/or annoying. We expect you may need to ask for help…

Examples of where you might have problems. You have 5V for power, but some devices need 3.3V for power. You are using a device that generates too little current for your ADC, you may want to amplify the current but hold the voltage constant. You may be using a UART or other serial bus where one device wants 3.3V or 1.7V and the other wants 5V. You may be driving a motor that needs but you can only drive what do you do?

What are DC converters? DC converters convert one DC voltage level to another. – Very commonly on PCBs Often have USB or battery power But might need 1.8V, 3.3V, 5V, 12V and -12V all on the same board. – On-PCB converters allow us to do that Images from from

DC converters Probably the most common problem is dropping power from 5V to 3.3V. – Often because we’ve got a device that wants 3.3V as Vcc and everything else wants 5V. The generic term for a device used to change voltages is “DC converter” – But when dropping it is sometimes called a “voltage regulator”. – Specific types are called “linear regulator”, “Low Dropout (LDO)”, and “Switching regulator”

Different types of DC converters Linear convertersSwitching converters Simpler to design Low-noise output for noise- sensitive applications Can only drop voltage – And in fact must drop it by some minimum amount – The larger the voltage drop the less power efficient the converter is (All voltage dropped is converted to heat). Can be significantly more complex to design – **Don’t use for project** Can drop voltage or increase voltage – “buck” and “boost” respectively Generally very power efficient – 75% to 98% is normal

Linear regulator 1.Input 2.Ground 3.Output 1 2 3

Linear regulators and capacitors Specification for regulators almost always include required capacitors – If you don’t have them, your output may get noisy and cause all kinds of problems including reseting your chips. Too big is better than too small. – May have required capacitor types (ceramic, etc.) Be sure to check (most linear regulators don’t…)

Op-amps We’ll briefly talk about using op-amps to do a few basic things. – Current buffering – Threshold detection – Etc. I’m not going to talk much about single supply vs. dual supply. – gle_supply_opamp_and_dual_supply_opamp is helpful though. gle_supply_opamp_and_dual_supply_opamp

Very idealized basics

Voltage comparator Can change the ground input to any voltage. – Often just goes down to ground rather than –Vcc.

Voltage follower How does this work?

And a bunch of others

Current to voltage and back. Where would we have used a current-to-voltage device?

Additional reading – Used for the last 4 slides.

Serial bus issues There are devices that can convert data between voltage levels automatically. – TXS0102 – It uses two separate power supply rails, with the A ports supporting operating voltages from 1.65 V to 3.6 V while it tracks the V supply, and the B ports supporting operating voltages from 2.3 V to 5.5 V