Question on Microcontroller Voltage

[FreshmanNewbie]

I have this Microcontroller and using the USB interface of the MCU (PA24 & PA25).

On page 44 of the datasheet, it is mentioned like, the acceptable voltage for the MCU for the power rails would be 1.7V to 3.63V.

I am working on a Low Power USB device. So, I am using 1.8V for the Microcontroller Power Supply rails.
The micro is powered from 1.8V, and uses the micro's internal linear regulator for the 1.2V VCore (not using SW).

Laptop connected to the USB device. USB Type A to USB Type C cable. When I try to bootload via USB, I have issues.
When VDD (of MCU) drops below 1.75V, USB drops out. When VDD is > 2V, then no issues. Note that the micro doesn't reboot when USB drops out, and scoping the USB data lines seems to show the host still pinging every 1ms.

While debugging, I checked page 1884 on datasheet, an it mentions for USB, All operating voltage should be 3.3V.

Can someone please confirm what this means? Our board is designed for 1.8V. Does it mean for USB to work we need to power the micro from 3.3V?

The datasheet earlier says it can run down to 1.71? Which is correct?

Also is USB the only peripheral that won't work at 1.8V, or should we be concerned about other parts of the micro that won't work correctly when running the micro at what seems within the recommended voltage range?

 

[barry]

I can explain it to you, but I can’t understand for you.

You yourself found in the data sheet where it EXPLICITLY SAYS “THE OPERATING VOLTAGE MUST BE 3.3V”.

Which part of that don’t you understand?

 

[KlausST]

Can someone please confirm what this means? Our board is designed for 1.8V. Does it mean for USB to work we need to power the micro from 3.3V?

The datasheet earlier says it can run down to 1.71? Which is correct?

Both is correct.

The microcontroller (functionally) runs with supply voltage down to 1.7V.

But to be USB compatible it needs to be able to output USB signals with a certain voltage level. Thus it needs enough supply voltage to do so.

***
Let´s say you want to connect a 3.3V external SPI device. Here also you need to ensure proper signals levels ... thus you can´t work with 1.8V.
The same is with USB.

Chapter 54.15 of the datasheet tells you also the requirements for the clock ... if you want to run USB....

***
Maybe you can use a USB level shifter like TXS0202.

Klaus

 

[FreshmanNewbie]

Both is correct.

The microcontroller (functionally) runs with supply voltage down to 1.7V.

But to be USB compatible it needs to be able to output USB signals with a certain voltage level. Thus it needs enough supply voltage to do so.

***
Let´s say you want to connect a 3.3V external SPI device. Here also you need to ensure proper signals levels ... thus you can´t work with 1.8V.
The same is with USB.

Chapter 54.15 of the datasheet tells you also the requirements for the clock ... if you want to run USB....

***
Maybe you can use a USB level shifter like TXS0202.

Klaus

My doubt is, even with such voltage levels, I am able to program on certain occassion. If a total of 50 times I program, I am getting 5 times success. How can this happen?

--- Updated Mar 7, 2024 ---

I can explain it to you, but I can’t understand for you.

You yourself found in the data sheet where it EXPLICITLY SAYS “THE OPERATING VOLTAGE MUST BE 3.3V”.

Which part of that don’t you understand?

My doubt is, even with such voltage levels, I am able to program on certain occassion. If a total of 50 times I program, I am getting 5 times success. How can this happen?

 

[FreshmanNewbie]

[Crossposted thread merged with previous same topic thread]
I have this Microcontroller, https://ww1.microchip.com/downloads.../SAM-D5x-E5x-Family-Data-Sheet-DS60001507.pdf, where they mention the acceptable voltage levels in between 1.7V to 3.63V.

But under USB section, page 1884, they mention for USB, we need 3.3V.

But for other peripherals like, I2C, ADC, SPI, I didn't see such mention of required voltages.

So my questions:

1. If I give 1.8V as Vcc to the MCU, I can work with other peripheral perfectly fine except USB? Or what peripherals will be affected or the ones I need to take care if I use 1.8V as Vcc?

2. While researching more on this, I found on page 1846 that , "Note: Note: The PA24 and PA25 pads do not have Drive Strength capability.". These are USB datalines. What does it mean that they don't have drive strength capability?

 

[KlausST]

Hi,

you are outside the specified range. It may work or it may not work. It may work with the one USB partner, but not with the other. It may work on current temperature but not at a different temperature. It may work today, but it may not work tomorrow.

Specification tells you the condition for RELIABlY working.

Let´s say there is a bungee rope specified for 80 kg persons. If you use it on a person with 120kg .. you (and the person) have to live with the consequences.

Klaus

 

[KlausST]

Hi,

Every device´s datasheet tells VOL, VOH, VIL, VIH .. all devices need to match. It´s a very basic rule.
(especially for one that has several years of experience in electronics.)

Klaus

 

[FreshmanNewbie]

Hi,

Every device´s datasheet tells VOL, VOH, VIL, VIH .. all devices need to match. It´s a very basic rule.
(especially for one that has several years of experience in electronics.)

Klaus

For USB lines, PA24 and PA25, they do not have Voh and Vol, right? Can you please explain on this

 

[KlausST]

Hi,

I have this Microcontroller

THIS is a datasheet for several different microcontrollers. Thus we don´t know which microcontroller exactly you use.

****

For USB lines, PA24 and PA25, they do not have Voh and Vol, right? Can you please explain on this

I´d say these are the USB signals (not used as general purose outputs). Thus they are specified differently:
in chapter 54.9 it says:
4. The USB pads, PA24 and PA25, are compliant to the USB standard in USB mode.

In chapter: 54.15:
The USB on-chip buffers comply with the Universal Serial Bus (USB) v2.0 standard. All AC parameters
related to these buff ers can be found within the USB 2.0 electrical specifications.

Indeed .. when using them as USB signals .. this is all you need to know. You don´t need to care about drive strength, voltage levels, currents.
(If you want to do a compliance test, you need to refer to USB standard specification)

Klaus

 

[FreshmanNewbie]

Hi,

THIS is a datasheet for several different microcontrollers. Thus we don´t know which microcontroller exactly you use.

****


I´d say these are the USB signals (not used as general purose outputs). Thus they are specified differently:
in chapter 54.9 it says:
4. The USB pads, PA24 and PA25, are compliant to the USB standard in USB mode.

In chapter: 54.15:
The USB on-chip buffers comply with the Universal Serial Bus (USB) v2.0 standard. All AC parameters
related to these buff ers can be found within the USB 2.0 electrical specifications.

Indeed .. when using them as USB signals .. this is all you need to know. You don´t need to care about drive strength, voltage levels, currents.
(If you want to do a compliance test, you need to refer to USB standard specification)

Klaus

Thank you for the information.

ATSAME53N20A this is the device I am using. I wasn't able to find anything else that will not work with 1.8V.
I2C, SPI, ADC, DAC etc., don't mention that they will require 3.3V. I hope it is fine that they will work 1.8V.

Hence, I believe only USB requires 3.3V, right?

 

[KlausST]

Hi,

I2C, SPI, ADC, DAC etc., don't mention that they will require 3.3V. I hope it is fine that they will work 1.8V.

My thoughts:
Your microcontoller has several supplies.
You need to check which supply is responsible for what.

--> There is VDDIO .. it is responsible for the IOs (signal voltage levels).

--> Then the datasheet tells you what signal level you may expect at which drive current.

And this needs to comply with your connected devices. Nothing new. (At least it should be common knowledge for an electronics designer. It´s a standard procedure.)

And I´ve never seen an I2C device that reliably works with 1.8V levels. (This does not mean they don´t exist. I´ve just not seen any)
In either case YOU (as the designer) need to confirm that your connected devices are compatible.

As already mentioned: there are ready to buy level converters .. for various interfaces and various conditions.

Klaus

--- Updated Mar 7, 2024 ---

added:

Microchip supports you. datasheet says:

Section 60: Schematic checklist.

also:

USB Host and Device Interface recommendations can be found in the “Basic 32-Bit MCU Design and
Troubleshooting Checklist” guide, available on the Microchip web site, www.microchip.com/.

Also they provide an evaluation board, any you may request for schematics / documentation.

Klaus