I am trying to send a signal from an Altera DE2 FPGA to a detector so that I can gate it on and off. The FPGA uses 3.3V logic while the detector uses 5V logic, so I need to increase the voltage on the signal. I am thinking I should use a logic level converter, like this one from SparkFun: (https://www.sparkfun.com/products/12009)

However, I am concerned about the amount of current that will be going into the detector. In the datasheet for the detector (picture below) on the bottom row, it mentions the sink current being < 1.6mA and the source current being < 5.5mA.

Will using this LLC push too much current into the detector? If so, what other method should I use to increase the voltage of the signal without putting too much current into the device? I was also thinking of using an op amp to increase the voltage, one that has a low output current. Which method would be better?

Gating Threshold


1 Answer 1


The Sparkfun logic level converter outputs voltage, not current. It can output a maximum of 220 mA to an output that is drawing that current, but will not "push" a current anywhere. It should probably be safe to use for this task.

That being said, a more appropriate part for this task would be a buffer IC, like the 74HC244 (octal tristate buffer, 3.3V CMOS compatible inputs when running at 5V). There's nothing wrong with the Sparkfun level shifter, but this part should be easier to source and use in a professional design.

  • \$\begingroup\$ The "T" in 74HCT224 indicates that the inputs are TTL level. The outputs are CMOS. \$\endgroup\$ Sep 14, 2016 at 23:10
  • \$\begingroup\$ Would using the IC buffer be like using the LLC, just connect the ground, Vcc (5V), then my input and output wires? \$\endgroup\$
    – Cody495
    Sep 15, 2016 at 0:15
  • \$\begingroup\$ @PeterBennett Whoops. I always get that mixed up. 74HC should be fine here, though. \$\endgroup\$
    – user39382
    Sep 15, 2016 at 3:19
  • \$\begingroup\$ @Cody495 Nearly! You'd have to pull the output enable lines low (tie them to ground) and tie off any unused inputs. Otherwise it's basically the same though. \$\endgroup\$
    – user39382
    Sep 15, 2016 at 3:21

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