3.3 V level shifter

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bananasiong

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Hi,
What is suitable to be used to level shift from 5 V to 3.3 V? I'm doing interfacing of a PIC (5 V) with 3.3 V devices via SPI or IIC. Is there any level shifter that can meet the requirement apart from resistive voltage divider?

Thanks
 
You can probably work without a level shifter.

If it is IIC you should be using pull ups to 3.3V and you can use that for 5V -> 3.3V
The two levels are:-
Pull down to 0V
No pull down and voltage is pulled up to 3.3 V

Going the other way, if you go into a TTL level input the 0 and 3.3V will be fine. It will probably be fine even into a shmitt-trigger input that has a typical threshold of bellow 3.3V at all temperatures.

If you are using SPI, you can allways use pull-ups to 3.3V.
 
Hi,
Just wonder, if I don't pull up but just connect the output pin of the PIC through a voltage divider into the IIC pins, is it possible?
Or if I use CMOS buffer like 4050 which has the voltage range of 3 V to 15 V will be better? As Papabravo suggested, but it is just a single buffer.

I'm doing the interfacing between a PIC with MAX9850. Apart from the IIC, there're some other pins used for the audio data, that's why I'm looking for an single IC to level shift the PIC's output to ~3.3 V.

Thanks
 
It's an older post here and if you search for 3.3V you'll come across others.

I've yet to test it but if it works it'll be the basis for the Squid kit (a 3.3 / 5V LM317 supply plus level shifter for the Inchworm & Junebug kits.
**broken link removed**
 
bananasiong said:
I'm doing the interfacing between a PIC with MAX9850. Apart from the IIC, there're some other pins used for the audio data, that's why I'm looking for an single IC to level shift the PIC's output to ~3.3 V.
Click to expand...

I would choose a modern PIC that can run off 3.3 V and get rid of the 5 V supply. The I2C interface is shown on page 13 of the datasheet, they suggest 10k pull-up resistors.
 
A lot of the PICs have a LF version. There was even a 16LF628. Also, most PICs will run at 3.3V at a reduced maximum clock rate. But if you still want to do a 3.3-5V level shift, MicroChip uses the 74VHCT125 in their example circuits.
 
eng1 said:
I would choose a modern PIC that can run off 3.3 V and get rid of the 5 V supply. The I2C interface is shown on page 13 of the datasheet, they suggest 10k pull-up resistors.
Click to expand...

Some PICs won't run at max frequency at less than 4.5V such as the 18F4550. Many I2C and SPI devices are have 5V versions anyway.
 
blueroomelectronics said:
Some PICs won't run at max frequency at less than 4.5V such as the 18F4550. Many I2C and SPI devices are have 5V versions anyway.
Click to expand...
There are PICs (with the MSSP) that can run at 8 MHz with Vdd > 2 V (such as the 16f887) or up to 40 MHz with 2.7 < Vdd <3.6 V.

Bananasiong, could you tell us what frequency (min.) can the PIC run at?
Are there other parts that require 5 V logic, such as an LCD?
 
Hi,
I'm using PIC18F2331. I know that there is LF version for this PIC, but I need to run it at 5 V because I don't want to reduce the AD clock speed.

I planned to use PIC24FJ, but C is really

Thanks
 
Ha, unfortunately no..
Seems I have to use a CMOS buffer, since I have I2C pins and also the data and the clock pins for the audio signal.
*EDIT: It is the MAX9850 audio DAC
 
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