SN74AVC4T774: Pull Up resistor calculation

Hari T O0

Hi ,

I am going to use SN74AVC4T774 for convertimg my SPI signal coming from controller which is working on 3.3V to 1.8V.

VCCA side will be 3.3V and VCCB side will be 1.8V. Could you please help me to find out the value of pull up resistor required for OE and DIR signals.

What is the current sinking capability of the device where I can see the current sinking capability in data sheet.

Regards

Hari

over 8 years ago

0 Dylan Hubbard over 8 years ago

TI__Mastermind 48325 points

Hi Hari,

You can use the Ii (current input) spec from the recommended operating conditions which shows the current into the control inputs. With that info and ohms law you can accurately calculate a good pull up to balance the strength of the pull up and power consumption . I would just throw on a 10k and that should work well.

0 Hari T O0 over 8 years ago in reply to Dylan Hubbard

Genius 3820 points

Hi Dylan,

Thank you very much.I am going to use it for SPI. Do I need to connect all "DIR" lines to Vcc

Regards
Hari

0 Dylan Hubbard over 8 years ago in reply to Hari T O0

TI__Mastermind 48325 points

Hi Hari,

It'll depend on how you implement your device. See below:

For SPI will have Clk, CS, MOSI going in one direction and MISO going the other direction. So you'll probably have 3 DIR pins tied high/low and then 1 DIR pin tied to the opposite level of the other 3.

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SN74AVC4T774: Pull Up resistor calculation