0

I am using the MIC29300 https://www.microchip.com/wwwproducts/en/MIC29300 in my circuit to generate a 5V signal to my ADC (works fine now)

Would it be possible to grab that 5V line and have it provide the power for my Raspberry Pi 3 Model B+? Would it cause voltage fluctuations and affect my ADC? Should I just use another IC?

George
  • 99
  • 7
  • Ah, I feel jealous that you are using MIC 2930x LDO, which is 10 times more expensive than the cheapie LM2596 I have been using all these years. I know MIC2930x is industrial grade, with the following non LM2596 features: (a) Low dropout voltage, (b) Low ground current, (c) Accurate 1% guaranteed tolerance, (d) Extremely fast transient response, (e) Reverse-battery and load dump protection, (f) Zero-current shutdown mode, (g) Error flag signals output out-of-regulation. – tlfong01 Feb 18 '20 at 02:40
  • References:MIC2930x 5-Lead TO-220 Fixed Voltage High-Current Low Dropout Regulators http://ww1.microchip.com/downloads/en/DeviceDoc/MIC2915x-30x-50x-75x-High-Current-Low-Dropout-Regulators-DS20005685B.pdf – tlfong01 Feb 18 '20 at 02:41
  • The IC you’re using looks good. What about the LTM8063? I imagine that they all function the same. The MICa to give out a ton of heat, which is not the best. However, they provide with a clean circuit which is a big pro, but maybe it’s an overkill for powering the pi. I’ll want to try and use a switching circuit to power on the PI and see if the 5V line from the pi is good enough for my adc to have a stable reference. Although it might have some internal management for that anyway. – George Feb 18 '20 at 10:29
  • Just a quick reply. (1) Switcher regulator such as LM2596 has high efficiency. In other words, if Vin = 12V, Vout = 5V won't lost much power as heat. On the other hand LDO efficieny depends on Vin, If Vin = 6V, then not much heat generated. But if Vin = 24V, then the chip might be very hot. I have tried other switching regulator 10A. 12V etc, they don't heat up much. I don't use LTM8063, because there are no cheap modules around :) – tlfong01 Feb 18 '20 at 10:46
  • In case you have not read the following: (1) LDO Wikipedia https://en.wikipedia.org/wiki/Low-dropout_regulator, (2) Switched-mode power supply Wikipedia: https://en.wikipedia.org/wiki/Switched-mode_power_supply – tlfong01 Feb 18 '20 at 11:15
  • And my answer to the following question shows my other 5V 14A PSU, not much heat generated. My answer also has a list of references: https://raspberrypi.stackexchange.com/questions/102115/slight-dip-on-the-gpio-5v-line-when-leds-are-on. – tlfong01 Feb 18 '20 at 11:19
  • LDO efficiency is low, but noise is also low. So one solution is to use switcher to first step down to say 6V, then use LDO to do second level step down to 5V. Or use a switcher PSU but a huge cap to filter/by pass ripples/noises. You might like to read my answer to the following question where I use a huge 10,000uF cap to reduce noise: https://raspberrypi.stackexchange.com/questions/98832/raspberry-pi-zero-w-solar-power-setup. – tlfong01 Feb 18 '20 at 11:34
  • @tlfong01 I will have a LDO at the input of my circuit, doing a 12V to 11.5 V conversion, so that the signal coming into my signal is clean. Would adding a buck afterwards add noise to the system? or if the signal coming in is clean I should be okay? – George Feb 18 '20 at 13:42
  • Yea I have already looked at that for some inspiration. Thank you – George Feb 18 '20 at 13:43
  • (1) "12V to 11.5 V" is a bit marginal, because if your Vin falls to 11.8V then 0.2V dropout might not be enough. Of course you need to read the datasheet. (2) Actually I have been too lazy to read more tutorials: (3) LDO Basics - TI: http://www.ti.com/lit/ml/slyy151a/slyy151a.pdf, And actually it depends a lot on the ADC, If your ADC is 16 bit, and you only need 12 bit resolution, then you can afford more noise and less requirement on voltage. – tlfong01 Feb 18 '20 at 14:01
  • 1
    I have a US$300 digital scope, so I usually use it to display the waveforms. And I am mostly prototyping, not mass production, so I usually afford time, space, and money to over kill. Sometimes I just show off, eg, that I have a 10,000uF cap, to make my bad friends feel jealous. – tlfong01 Feb 18 '20 at 14:03
  • Hmm i see. My ADC is the MAX1204, and every bit counts to be honest with you. What I'm going to do is power on the pi with a power supply to see how much current it draws during the operation I want it to do. Afterwards, if my existing LDO is enough, then I might stick to that. Low noise is what I need, however thermal management cannot be ignored. to be honest, my 12 - 11.5 is not to bad, as long as it stays over 10.8V or so, my circuit will be able to work just fine. – George Feb 18 '20 at 14:10
  • Let us continue this discussion in chat. – tlfong01 Feb 18 '20 at 14:13

1 Answers1

0

You COULD use a linear regulator if you have a large enough heatsink because any linear regulator will dissipate lots of heat.

Whether the voltage would be stable and sufficiently clean depends on the circuitry you put around the regulator.

I wouldn't use a linear regulator switch mode power supplies are preferable.

PS I don't know why you would want to use a separate regulator with an ADC - most have precision internal references, which are temperature stabilised.

Milliways
  • 59,890
  • 31
  • 101
  • 209
  • The ADC I am using is the MAX1204 and requires a 5V power supply. I believe the internals reference is set at 4.096 V (which works great) but I still need to power the device with a 5V line. – George Feb 17 '20 at 23:01
  • Would you recommend this IC: https://www.analog.com/media/en/technical-documentation/data-sheets/LTM8063.pdf ? – George Feb 17 '20 at 23:06
  • What is wrong with the 5V pin on the Pi - that is what the rest of us would use. – Milliways Feb 17 '20 at 23:09
  • I could give it a shot. I was under the impression that the raspberry pi has a noisy environment which is why I didn't want to try and use it's power supplies. The ADC has an internal reference, but I was also under the impression that it depends on how clean the VDD signal is. Garbage in = Garbage out.

    And I just wanted to show you. Some people like to have the links.

     – George Feb 17 '20 at 23:19
  • Sorry, I will be more careful next time. – George Feb 17 '20 at 23:24