Has anyone ever damaged a reset pin by omitting the diode?

Go To Last Post
18 posts / 0 new
Author
Message
#1
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

I put one in everything I design, but I wonder, is it really necessary.  When is the last time one without this died?  And if it does fail from not having a diode, what is the typical failure mode?

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0


I assume your talking about this:

Well in all of my applications, the reset pin was left floating so the internal pull up keeps the pin high, I have never used any of the external parts.   YMMV!

Jim

 

 

(Possum Lodge oath) Quando omni flunkus, moritati.

"I thought growing old would take longer"

 

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 1

The diode is not there for protection, it is there to quickly discharge the capacitor when the power goes off.

#1 Hardware Problem? https://www.avrfreaks.net/forum/...

#2 Hardware Problem? Read AVR042.

#3 All grounds are not created equal

#4 Have you proved your chip is running at xxMHz?

#5 "If you think you need floating point to solve the problem then you don't understand the problem. If you really do need floating point then you have a problem you do not understand."

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Connection of RESET Pin on AVR Devices | AVR® Microcontroller Hardware Design Considerations

 

...

 

ESD protection diode is not provided internally from Reset to VCC in order to allow HVPP. If HVPP is not used, it is recommended to add an ESD protection diode externally from Reset to VCC. [zener alternative]

...

"Dare to be naïve." - Buckminster Fuller

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

alank2 wrote:
And if it does fail from not having a diode, what is the typical failure mode?
MOSFET gate oxide punch through or the RESET-to-GND ESD suppressor shorts

RESET has an internal low pass filter; one way to increase ESD tolerance is to add a low pass filter (R-C-R, time constant at pin is 100ns approx) into a Schmitt trigger input (AVR input that's not RESET, RESET can be slow, debugWIRE cannot be slow)

Connection of RESET Pin on AVR Devices | AVR® Microcontroller Hardware Design Considerations

...

 

To protect the Reset line from further noise, connect a capacitor from the RESET pin to ground. This is not directly required since AVR devices internally have a low-pass filter to eliminate spikes and noise that could cause reset. Using an extra capacitor is an additional protection. However, such extra capacitor cannot be used when DebugWIRE or PDI is used.

 

...

 

"Dare to be naïve." - Buckminster Fuller

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

I thought the diode was there to provide some protection that the reset pin lacked because it was how HV programming was done.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

If you have auto-reset functionality with a capacitor in series with the reset line, you can get voltage doubling by toggling the line on the other side of the capacitor. I'll assume 10V will put the AVR into HV programming mode? A diode will prevent this.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

It sounds like the consensus is if you don't use a capacitor, then the diode is not necessary.  Agree?

 

Also, is the build in pullup strong enough to eliminate the need for an external 10K pullup?

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

alank2 wrote:
Also, is the build in pullup strong enough to eliminate the need for an external 10K pullup?

Depends on the environment it runs in, low noise - not needed, high noise - needed, you decide what is high/low.

 

Jim

 

 

(Possum Lodge oath) Quando omni flunkus, moritati.

"I thought growing old would take longer"

 

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Also, if the diode is there, you can NEVER use High Voltage Programming!

 

Jim

 

Until Black Lives Matter, we do not have "All Lives Matter"!

 

 

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

The Arduino has that quesionable auto-reset circuit, and it turned out that without the diode it could cause voltage spikes on RESET that would put the chip into high-voltage programming mode, which caused problems.

(hmm...  https://forum.arduino.cc/index.p... )

 

It doesn't (usually?) DAMAGE the reset pin (which, after all, is designed to accept higher voltages to activate HVPP.)  But having the chip go into HVPP mode unexpectedly is not a good thing!

 

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

alank2 wrote:

I thought the diode was there to provide some protection that the reset pin lacked because it was how HV programming was done.

 

Yes, so the question is how exposed is your reset pin to external ESD events ?

Usually, reset pins are more buried than GPIO pins so need less protection.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

I  have never used the diode (but used a 4K7 pullup), about 8,000+ boards with AVRs in the field in almost 20 years.

John Samperi

Ampertronics Pty. Ltd.

www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

alank2 wrote:
Agree?
Conditionally yes (correct layout of the reset signal on the PCB)

alank2 wrote:
Also, is the build in pullup strong enough to eliminate the need for an external 10K pullup?
Usually yes though a MPLAB PICkit 4 has excellent drive.

 


AN_1619 AVR040: EMC Design Considerations

[PDF pages 16 and 17]

4.9.2. Reset Pin Protection

...

If high ESD protection of Reset is not required, or is achieved by other components, the diode may be omitted.

...

2: Finding PCB Layout Defects with the Fischer EFT Pulser - YouTube (2m25s)

High Frequency Measurements Site Index

 

"Dare to be naïve." - Buckminster Fuller

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Never used a diode or a capacitor on the RESET line myself.  Only odd resets I've seen have been in situations when other bizarre things were going on in the power supplies.  S.

 

Edited to add:  But yes, I do ALWAYS use an external pullup resistor, from 4.7k to 15k - ish.  S.

Last Edited: Wed. Sep 2, 2020 - 11:01 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Thanks guys - I'm going to start skipping the diode and just use a 10K pull up.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

I've never used a pull-up. Certainly, in known high-noise situations, a pull-up is warranted, but never smaller than 10K if you want to use a common programmer.

 

Jim

 

Until Black Lives Matter, we do not have "All Lives Matter"!

 

 

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

though not debugWIRE :

Release Notes for MPLAB® Snap
In-Circuit Debugger & Device (Non-Production) Programmer

MPLAB® X IDE v5.40

__firmware__

 

May 14, 2020

...

 

11.2   AVR UPDI/PDI/TPI Support

A 1K ohm pull-up resistor must be installed between the MPLAB Snap ICD ICSP connector's (PCB reference designator J4) pin 4 (PGD) and pin 2 (VDD) to allow proper programming/debugging support for AVR parts that support the UPDI/PDI/TPI interface.

Note: If this 1K ohm pull-up resistor is not installed a 'PDI physical timed out. (25)' message will be issued for various operations in the MPLAB X IDE or MPLAB X IPE GUI.

 

...

 

edit : an inexpensive AVR STK500v2 ICSP that would have an issue with strong pull-ups :

Pololu - 1.1. Supported AVR microcontrollers

[last paragraph]

The programmer is incompatible with some AVR boards that have extra components on their programming pins. The programmer’s I/O pins are protected by 470 Ω resistors, so pull-up or pull-down resistors on those lines that have a value below 5 kΩ might prevent the programmer from properly communicating with the AVR. For example, the programmer does not work with the Arduino Nano due to the 1 kΩ pull-up resistor on its reset line.

 


https://www.avrfreaks.net/forum/mplab-snap?page=2#comment-2987696

Pololu USB AVR Programmer v2.1

 

"Dare to be naïve." - Buckminster Fuller

Last Edited: Thu. Sep 3, 2020 - 06:16 PM