View Full Version : Voltage Level Translation from TI

September 25th, 2013, 01:36 AM
32 bit, 5V TTL to 3.3V CMOS
Texas Instruments CD4504B (http://www.ti.com/product/cd4504b)

There are two versions, it is the latter I will use for my 8bit ISA Projects...

September 25th, 2013, 08:27 AM
Um, are you certain you have the right part? The 4504 dates from the 1970s and I don't believe has a 3.3V rating, but is used to shift from TTL to CMOS (high-voltage). Propagation times are glacial. If you're operating at a high-level of 5V, the tprop is somewhere around a half a microsecond!

There are much better solutions for this!

September 25th, 2013, 08:43 AM
Take a look at this document from TI- I'm going to take a guess that you're using an MSP430, but the technical information should be accurate for all 3-3.6V microcontrollers:

"Interfacing the 3-V MSP430 to 5-V Circuits"

September 25th, 2013, 08:50 AM
I generally use quick switches for ISA cards such as this one:


Of course quick switches just diode clip to the lower voltage. If you want level promotion from 3.3V to true 5V levels, you can use something like this:


With .25 ns propagation and fast logic on the other side (modern PLDs), I've actually found cases where modern logic is too fast. The PCJr for example presents the /WR latch strobes ahead of the data on the bus due to slight differences in prop times of the strobe verses data buffers. Old latches with slow setup times don't have a problem but I had to loop the strobe inside the PLD to artificially delay it a few nanoseconds.

September 25th, 2013, 09:27 AM
If this is for interfacing an MCU to the bus, there are MCUs taking independent supply rails for the interface and internal logic with 5V-tolerant receivers. My guess is that you're going to have to latch data off the bus, however, so the 74VLC may be a good approach. You can also do the bus interface in traditional 5V logic, dropping the VIH levels only when you get to the MCU interface--or use an MCU with 5V tolerant inputs and ignore the shifting issue entirely.

Microchip, some years back, published a document that discusses various ways to skin the 3.3-to-5V cat.

Bottom line is that you'll probably have to go SMD to do it, but there are many very good solutions out there.

September 25th, 2013, 11:15 AM
Thank you, didn't notice the prop time...I will find another chip out on the internet...somewhere...;-)

September 25th, 2013, 11:32 AM
Try using octopart.com. You can search for a very wide variety of parts by function.

September 26th, 2013, 02:02 AM
The MAX3002 runs at 20ns prop time...