FPGA Central

Hi ng,

i'm currently building a serial controller between a 5V FPGA and a 3.3V
microcontroller. Maybe someone of you can tell me, if there exists any
common electronic component which can convert digital signals at ~ 1MHz with
high level varying from 3.0 to 5.0 Volt and should output a signal with high
level at 3.3Volt . (low level is always 0V)

first i tried to build a simple voltage divider with two resistors, which
was only acceptable with stable 0V Low /5V High input... the other problem
is a fixed input capacitor at the 3.3V device of 50pF which - in combination
with my voltage divider - passed only low frequencies.

thanks in advance,
Stefan

Stefan Oedenkoven <[email protected]> wrote:
> Hi ng,
>
Hi Stefan!
> i'm currently building a serial controller between a 5V FPGA and a 3.3V
> microcontroller. Maybe someone of you can tell me, if there exists any
> common electronic component which can convert digital signals at ~ 1MHz with
> high level varying from 3.0 to 5.0 Volt and should output a signal with high
> level at 3.3Volt . (low level is always 0V)
>
Please look for "voltage translator". There are some ICs available for
this purpose. You can also build them with two transtors in common base
configuration. If you google for transistor voltage translator you
should find it, if I am wrong just send me a mail.

Best regards,

Christoph
>
>

Stefan,
TI do a CB3T family. What do you mean by common? They're common as muck in
my designs!
http://focus.ti.com/lit/an/scda008/scda008.pdf
Cheers, Syms.
"Stefan Oedenkoven" <[email protected]> wrote in message
news:[email protected]..
> i'm currently building a serial controller between a 5V FPGA and a 3.3V
> microcontroller. Maybe someone of you can tell me, if there exists any
> common electronic component which can convert digital signals at ~ 1MHz
with
> high level varying from 3.0 to 5.0 Volt and should output a signal with
high
> level at 3.3Volt . (low level is always 0V)

Stefan Oedenkoven wrote:

> Hi ng,
>
> i'm currently building a serial controller between a 5V FPGA and a 3.3V
> microcontroller. Maybe someone of you can tell me, if there exists any
> common electronic component which can convert digital signals at ~ 1MHz with
> high level varying from 3.0 to 5.0 Volt and should output a signal with high
> level at 3.3Volt . (low level is always 0V)
>
> first i tried to build a simple voltage divider with two resistors, which
> was only acceptable with stable 0V Low /5V High input... the other problem
> is a fixed input capacitor at the 3.3V device of 50pF which - in combination
> with my voltage divider - passed only low frequencies.
>
> thanks in advance,
> Stefan

Two options:
a) A lot (most new familes?) of CMOS Logic devices ( TI, Philips,
Fairchild et al ) have overdrive tolerance, so poered from 3.3V, they do
not mind 5V overdrive on IPs.
Use a set of these, powered, and in the direction as needed.

b) New are level converters, with dual Vccs, from TI, and IIRC
Fairchild. These are a more precise solution, and will give
lower Icc levels. Driving a 5V powered TTL threshold gate with >2.4V hi,
works in the Logic sense, but it does draw IP buffer current, so
if you are worried about static Icc, the level converters can be
a better solution.

-jg