hardware interface between FPGA DE2 board(3.3V) and ADC(5V)

[LF_LF]

HI, i need some technical help on the DE2 board.
I am using DE2 board for my project and i need to interchange signals(SPI) to an ADC. The ADC is 5V for logic high but the max output signal for DE2 board is only 3.3V.
I have tried to use the level/voltage translator(SN7417/SN7407) but it seen like not applicable for my design as i am using 1MHz sample frequency. The SN7417 can convert from 3.3V to 5V till frequency around 5kHz only.
I want to ask those have done the implementation before which ic or translator you are using for high frequency signal like my case?
Due to the sample frequency of the ADC, it need high frequency for it, around 1MHz or 500kHz. Therefore, i need an intermediate for the voltage conversion.
Even for the 5V to 3.3V conversion, i used voltage divider but it also limited to 200kHz. Those more than that will be distorted or gone.Thus, i really need an ic for this bidirectional transmission.
I am very appreciated your help. Thank you in advanced.

 

[karesz]

Hi,
You can find some moderner (bidirectional too) level translators_dedicated for newest FPGA applications.
Sorry, I cannot remember yet for type or vendor_but I did saw new product news over their-i.e. last year...
I guess is from NI, Pericom & nxp to have too,
K.

 

[sameh_yassin99]

Re: hardware interface between FPGA DE2 board(3.3V) and ADC(

Hello LF_LF,

I used a part from Texas instruments "SN74LVC4245A". I used it for a 512kbit/s clock and it was very useful. This part conatins 8 channels , so it is mainly used for transfering data over buses with different voltage levels. However, in my project it was used to transfer several clocks and it was so good. I think it supports rates up to 10 MHz, you should read the data sheet and calculate maximum frequency of operation using Tplh and Tphl between inpt A and output B.


Best Wishes,
Sameh Yassin

 

[wade_hassler]

Re: hardware interface between FPGA DE2 board(3.3V) and ADC(

If the ADC interface is described as 'TTL-compatible', it may work as-is: check the data sheet carefully.

That said, here is a page on 'Bus Switches'
https://www.idt.com/?catID=58730
.. the added propagation delay almost magically low, and they cost
about .66USD singly ( DigiKey item #296-1169-1-ND)

Wade Hassler

 

[LF_LF]

Re: hardware interface between FPGA DE2 board(3.3V) and ADC(

Thanks for anybody above's help.
I found out the sn74lvc244a and SN7417 for conversion of 3.3V to 5V and vice versa,
The waveform is expected at the output of this translator but problem occurred when i connected to ADC( i supply 2 control signals). I doubt if it is the internal structure of ADC that makes the waveform distorted when 2 signals are transferred. No distortion if only 1 connection is made between ADC and translator but there will be if more than 1 lines are connected.

Please refer to attached pictures.
Can anyone let me know why this distortion happen? Is it reallly the internal connected?
Thank you

 

[karesz]

Hi,
Are you sure pls, that your Ev.-Board is problem less to control if you will drive it from normal 5V supplyed logical gates?
Is it not a missed GND wire or some similar in system?
K.

Added after 21 minutes:

Sorry, what is exactly your input pls?
Signals from the 5V ADC logic or you wish to drive the ADC with its outputs from 3V external logic?
Because LVC244A accept 5V to translate on hes outputs for a level between 1.6..to..3.3V, but not in revers direction(not from 5V to lower levels)...
On the data sheet are notes 2/3; current to clamp for max 50mA_ is it not missed in your case?

 

[LF_LF]

Re: hardware interface between FPGA DE2 board(3.3V) and ADC(

Hi,
Are you sure pls, that your Ev.-Board is problem less to control if you will drive it from normal 5V supplyed logical gates?
Is it not a missed GND wire or some similar in system?
K.

Added after 21 minutes:

Sorry, what is exactly your input pls?
Signals from the 5V ADC logic or you wish to drive the ADC with its outputs from 3V external logic?
Because LVC244A accept 5V to translate on hes outputs for a level between 1.6..to..3.3V, but not in revers direction(not from 5V to lower levels)...
On the data sheet are notes 2/3; current to clamp for max 50mA_ is it not missed in your case?

The Ev-Board has the provided 5V, 3.3V and GND pins that i can use straight. I tested with oscilloscope already and it can be trusted.Therefore, i am pretty sure i didn't miss the GND. Then i able to obtain the expected waveforms (these 2 control signals) that i need for ADC.
And now the problem arise as output of voltage translator and input of ADC(another input for conversion of sinewave, not the input of control signals) are seen to have the expected waveform if measure separately. After combine all and measure the intermediate connection between ADC and translator, they are the distorted waveform that i have attached. I really don't know what is happening? Can someone help me?

I used two ic: SN7417 for conversion 3.3V to 5V and LVC244A for 5V to 3.3V. Actually i am waiting the order for 74HCT04 for these two conversion in one-chip.

 

[karesz]

Tnx!
I dont understand the reason for that, seems me as some cross supplying over outputs?
Can you take pls (for test only) two separated `244A for drive your ADC? Maybe so it will function, then I believe that slowly, that your 244A (or ADC?) must be incorrect in function...
K.

Added after 15 minutes:

Maybe you can find a better solution/IC for your level conversion:
Maxim Application Note 3007; Logic-Level Translation
www.maxim-ic.com/app-notes/index.mvp/id/3007
K.
Another possibility is the "Tiny Logic Family" from On Semi/ Faichild & ADIs ADG3233...
In which cases means "bidirectional translating": It operates from two supply voltages, allowing bidirectional level translation, i.e., it translates low voltages to higher voltages and vice versa....

 

[LF_LF]

Re: hardware interface between FPGA DE2 board(3.3V) and ADC(

Thanks karesz. I read through it and i think it should work. However, i am lack of time. This MAX need to order online and it take me 2 working days for the delivering while i need to submit this end of week. Therefore, i try to search if there is any product available at any normal electronics shop.

Have you heard before the pull up transistor? By using PMOS can construct almost same functionality as voltage translator and the important point is MOSFET is available anywhere.

I tried to google it but i cant found any relevant application note. I really don't know how to construct the circuit. Do you have any idea? or anyone else got? Please help....i am running out of time.
Thank you in advanced

 

[karesz]

Hali,
yea, only question is your speed/signal frequency?
You can see in Maxim`s ApplNote too a transistor "CommonEmitter circuit", with remarks "<200Kbps"...
I believe, that basically are all common emitter/source circuits usable for level translating) if you have a serial resistor (Base/Gate) and on the Gate/Base you have to GND another-attenuator + biasing.
QUESTION: did you seen with serial (Schottky?)diodes in the converted outputs?
It must work as a separation form load if your level translator has some atypical behavioral_or the loads(?)...
The voltage drop is not so high that the next logic will not work.
K.

Added after 6 minutes:

Maybe you are spooking over that idea; but I can not open it at home...
http://osdir.com/patents/Electronic-circuitry/Level-shift-circuit-07388402.html

Check it pls:
**broken link removed**
Level Shifting Interfaces for Low Voltage Logic
**broken link removed**

Lo to Hi Noninverting Level Shifter w. NPN transistor, Pw_trans_ni:
http://obrazki.elektroda.pl/51_1270461324.png