I2C interface protection, Anyone put values on components for me?

Status
Not open for further replies.
C

calltronics

New Member
I have to reverse engineer this interface to the microchip memory.
Anyone shed anylight on the value of the Zener.
Also the capacitors.
Vcc is 3.3V.
The circuit is part of a battery block that plugs into a defibulator.

Appreciate your help
 
Last edited:
Sort by date Sort by votes
Odd, the part operating range is :



OP, do you know what the Vcc of the EEPROM and that of the MCU ?

Are the caps shown on SDA and SCL parasitic representations, buss approximations,
or real caps ? Odd to see caps added to those lines.......


Regards, Dana.
 
Upvote 0 Downvote

I agree, VERY odd to show capacitors on the I2C bus, good suggestion of possible parasitic capacitance.

Other than that, they would have to be very low values, and no point in them being there.

As for the zener?, that seems pointless as well - although I suppose it could be a vague effort to prevent EEPROM corruption? - if the OP really wants to add one?, then I would suggest 5.6V (assuming 5V Vcc).

However, as always with these posts - it's far too vague, and we need the schematic that it connects to.
 
Upvote 0 Downvote
I agree... with the exception of C4 I wouldn't think installing ANY of those components is going to be a good idea.

Is the memory located on a different board or something?
 
Upvote 0 Downvote
The pull-up resistors aren’t shown.

I have used very small capacitors on I2C lines to protect against very high frequency interference. The time constant of the capacitor and the pull-up resistance has to be much less than the clock frequency. Even if the clock frequency is low, the clock rise time must be fast enough that the slaves can only see one edge.
 
Upvote 0 Downvote
This might of use regarding calculations for the buss, attached.

Regards, Dana.
 

Attachments

  • UM10204-2.pdf
    1.3 MB · Views: 261
Upvote 0 Downvote
The clock and data lines must pull low, through the 100 ohm resistor. The bus will not have good low levels when this part is taking. This reduces the noise margins.
Why only one Zener not two or ever three?
Most designers try to reduce the capacitance on the bus, not add capacitors.
 
Upvote 0 Downvote
Whenever I've used I²C, I've just used pullups to the lowest Vcc and never had a problem.


What is this protection?

Mike.
 
Upvote 0 Downvote
Pommie said:
Whenever I've used I²C, I've just used pullups to the lowest Vcc and never had a problem.


What is this protection?

Mike.
Click to expand...
If you look at the I2C specification, they recommend nothing more than pullup resistors limited in value to a specific range which is intricately detailed in the specification. Anything else you put on the bus you do at your own risk. the people who write specifications usually know what they are doing, and the review process is also self-correcting.
 
Upvote 0 Downvote
You can always use a bidirectional level shifter circuit.
If you don’t want to roll your own, Amazon, Ebay and other E-commerce websites offer a multichannel fully populated board for a few bucks.

 
Upvote 0 Downvote
I don't see any level shifting/voltage translation going on in the original circuit in post 1... just some misguided "interface protection" (whatever that means). We've never been told what that is trying to accomplish.

If it's meant for a mixed-voltage application it doesn't do that very well.
 
Upvote 0 Downvote
took a long time to descover Vcc. It is 3.3V. This circuit is the battery block to connect/plug into a defibulator.
 
Upvote 0 Downvote
Spec on chip :



This spec seems to allow the internal protection diodes to conduct which is not advisable,
so I would clamp at Vin <= Vcc + .7. So worst case a zener value for that.

Protection considerations :




Be aware that LV zeners can add a lot of C to the buss, compromising timing at the higher
speeds. So choose carefully.


Regards, Dana.
 
Upvote 0 Downvote
Status
Not open for further replies.

Similar threads

D
  • Question
Help! Put switch back together on cookerhood
Replies
4
Views
2K
Deebs505
D
F
I2C Interface Tutorial from Hack-A-Day
Replies
4
Views
2K
aliarifat794
A
G
Best way to put voltage taps on 30a wire on transformer secondary winding?
Replies
14
Views
1K
Nigel Goodwin
C
Components for AC-DC rectifier
Replies
13
Views
1K
danadak
P
  • Question
SMPS Inductor values
Replies
3
Views
671
MrAl
M
Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…