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I know that linear voltage regulators are more accurate at holding the required voltage but the boost converter i am using seems to keep a pretty steady one. the voltage will of course be within the chips requirements. what would be the main drawbacks of not using one?

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is a voltage regulator required for atmega328p when powering from boost converter at a set voltage?

No it is not.

The ATMega is "just" some logic circuits in a chip.

So is the CPU in your PC and in your smartphone. Both of these are powered directly from switched regulators (usually buck converters but that doesn't matter that much) and they work fine!

As long as you keep the supply voltage of the ATMega chip within the specified limits (see the manufacturer's datasheet, from my memory it is 1.8 V to 5.5 V) then it will work as long as there is not too much variation (ripple) on the supply.

To keep the ripple in check, any boost, buck and linear regulator has at least one decoupling capacitor across its output. The ATMega chip also needs it's own decoupling capacitor. It is good practice to place at least one near each supply pin.

The accuracy of the supply voltage is not that relevant. The logic will work just as well at 3.456 V as it will on 3.3000 or 5.0000 Volts.

The only exception can be if you use the build-in ADC of the ATMega. This ADC can use the supply voltage as its reference voltage. If the supply is not accurate then the ADC's output data will not be accurate either.

There is a build-in more accurate reference for the ADC that can improve this. You can also use an external reference voltage if you like.

Also if you would use the PWM output function, filter the PWM signal and want it to be accurate then also it will be as (in)accurate as the supply voltage.

But in general, if you need this then you would know and take precautions.

Oh and there is no reason to assume that switched regulator (boost or buck) are in any way less accurate than linear regulators. It depends on the model (chip, circuit) you're using and if you calibrate it or not (measure the voltage with a known accurate meter and then adjust to the right voltage). Both linear and switched can be as bad or good as the other.

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  • \$\begingroup\$ "The logic will work just as well at 3.456 V as it will on 3.3000 or 5.0000 Volts." - Not if you want certain clock speeds, it won't ;) For example, at 2.7V, the 328P only guarantees reliable operation at 10MHz (see Electrical Characteristics > Speed Grades in the datasheet). More generally, there will be a lower bound (determined by clock speed in this case), and upper bound (determined by what the transistors can tolerate). Stay within the bounds, and you're fine. \$\endgroup\$ – marcelm Sep 4 '18 at 15:36
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    \$\begingroup\$ @marcelm And since we're nit-picking, there is also a brown out detection on the ATMega which has a threshold voltage setting which resets the chip if the supply drops below a certain value. For common Arduinos it is often set to 2.7 V while the chip can reliably work at 1.8 V if you keep the clock frequency low enough. I have a reprogrammed Arduino here set to the lowest brown-out voltage so that it can run down 2 AA cells down to below 2.0 V which increases battery life. \$\endgroup\$ – Bimpelrekkie Sep 4 '18 at 16:08
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If you just have an all digital circuit, there are little drawbacks (some ICs do not react very well to voltage ripple, but those can be fixed with a RC combination on the supply usually).

One thing which might be an issue is also the ramp up of the voltage for the chips. You should make sure it starts fast enough for all the chips. This can be improved by the linear regulator, but there are also other ways to accomplish that (voltage monitor).

If you are planning on using the ADC (mixed analog and digital design), you might want to evaluate if the readings are within your required range of noise. Even then you can use the boost converter to power the digital part and the linear regulator for the analog one.

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One thing which might be an issue is also the ramp up of the voltage for the chips. You should make sure it starts fast enough for all the chips. This can be improved by the linear regulator, but there are also other ways to accomplish that (voltage monitor).

I would also enable the Brown Out Detector in the microcontroller. That will keep the chip in reset state until the power supply voltage gets high enough. There are a couple of voltage levels that can be selected: Off, 1.8V, 2.7V, and 4.3V typical, +/- 0.1 to 0.2V.

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