Level Shifer

[Astro02]

I need a level shifter to Translate 3.3v(Rpi gpio) to 2.6v
(i need to use openocd, for some jtag test )
can i use this circuit appling 3.3 to hight side and 2.6 to low side (TMS,CLK,TDI)
and can be used to translate 2.6v to 3.3v with the same connection(TDO)

[PeterO]

The issue would be that 2.6V may not be enough to turn the FET on when the low side pulls down to "0",

The data sheet says spread of Gate threshold voltage min=0.8V typ=2.1V max=3V so some examples might not work.

PeterO

[Astro02]

thanks can you tell me a circuit or a breadboard integrated circuits to do this work(i know that txb010x or tbs010x but i don't know how solder a tssop package)

[PeterO]

I would only be doing the same google searches that you can do
PeterO

[Astro02]

I have googled a lot, i thinked that you know some chip, thank anyway

[PeterO]

I have googled a lot, i thinked that you know some chip, thank anyway

No sorry.. I've only needed to use the circuit you showed for 3v3 to 5v shifting.
PeterO

[klricks]

Google works for me.
https://www.sparkfun.com/products/12009

[Astro02]

i live in italy and i wan't pay up to 20€ for a 2€ chip
i have already foud this https://www.sparkfun.com/products/11771
thanks anyway

[PeterO]

Google works for me.
https://www.sparkfun.com/products/12009

Same circuit, but different FET with much lower gate threshold voltage, so it will work at the lower voltages Astro02 required.

If you can get the FETS you can build the circuits up yourself.

PeterO

[Astro02]

exists a breadboard equivalent of bss138(i hate smd component are difficult to solder)
Edit:
Anyone know if
I also need to level translate the jtag nRST and tRST?
Edit2: the sot-23 package can be soldered with normal iron solder

[Astro02]

can CD40109B or CD4504B or SN74LVC245ADWR or 74hc244 do this work?

[Laurens-wuyts]

Wouldn't a voltage divider work here?

Laurens

[Astro02]

wikipedia mean:For direct current and relatively low frequencies, a voltage divider may be sufficiently accurate if made only of resistors;

in my applicatiom will be a cpu, a rapberry pi and the the frequency of jtag is 5mhz

[Laurens-wuyts]

the frequency of jtag is 5mhz

Oops, I didn't think of that.

Laurens

[Astro02]

i found 74HC4050N can be used for this ?

[pksato]

Voltage divider can work on GHz band.
Just choose a low reactance packaging (SMT).
Common carbon film resistor can be used above 5MHz.
Just test, it cost only few cents (or free).
Use high current (8mA) to maintain low RC constant.
R1=82
R2=330

Oscilloscope Probe is a voltage divider, and work on hundreds of MHz.

[Astro02]

thanks, but i don't want make a disaster, i need to connect the raspberry with open ocd,to a old phone to load a bootloader into it, it has a msm7227 cpu whit a arm1136 core that can accept max2.6V
i also need to convert 2.6 to 3.3 for tdo(return data)

[Laurens-wuyts]

2,6V shouldn't be a problem to connect to the 3,3V pins. They will detect it fine.
You can check your voltage after the voltage divider with a multimeter. Just connect the 3.3V side to the 3.3V pin on the raspberry pi.

Laurens

[pksato]

Voltage divider is safe, if proper connected.
Or replace R2 (GND side) for a zener diode.
Minimum voltage to RPi recognize as high is near 2V. Device to RPi not need level shifter.
If is official jtag, probable have a protection to avoid danger voltages.

[Astro02]

i'll try when arrive my raspberry,
the trasfer rate of voltage divider is comparable to a level shifter(5-20Mbps)?
if i use a zener diode the R1 is the same of voltage divider

[Cancelor]

I use these >>> http://www.ebay.co.uk/itm/4-channel-Bi- ... Sw~OdVYXxJ

They are bi-directional and can also converter 2.8V and 1.8V devices.

In your case just connect Vhigh to the RPi 3.3v and Vlow to 2.8v

Cheap as chips, but you will have to wait a long time for delivery from China.

[Astro02]

I use these >>> http://www.ebay.co.uk/itm/4-channel-Bi- ... Sw~OdVYXxJ

They are bi-directional and can also converter 2.8V and 1.8V devices.

In your case just connect Vhigh to the RPi 3.3v and Vlow to 2.8v

Cheap as chips, but you will have to wait a long time for delivery from China.

this is the same as https://www.sparkfun.com/products/12009
use the schematic on first post but with bss138 mosfet

[hampi]

By my experience that circuit works between 3.3 V and 3.0 V (Q3 and Q4 in circuit diagram)

https://github.com/oh7bf/RaspiPwr12V/bl ... pwr12V.pdf

You could just try if it works down to 2.7 V too.

[Astro02]

the 74HC541 or 74hc4050 works?
(i hate smd component are too small )
what is the difference of a hex level shifter and a level shifter?
what is the tree-state output?

[PeterO]

Hex means there are 6 of them in each packace
Tri-state means each output pin has 3 states: Pulled High (1) or Pulled Low (0) or High Impedance.

PeterO