I am using FPGA 3.3 V outputs to drive 16x4 character LCD (5 V). I went through the data sheet 74LS245 and found this can be operated at Vcc 5 V and accept input voltages from 2 V. I am confused because data sheet has not mentioned the output voltage up to 5 V, will this IC suitable for my application?

  • \$\begingroup\$ Check LCD specs. Most likely has same TTL input thresholds and hence work straight off your 3.3V FPGA if you set its outputs in CMOS mode \$\endgroup\$ – carloc Jul 23 '17 at 18:04

It does mention it. Search for VOH You will find that it is inadequate: It will only guarantee that VOH is above 2 volts under worst condition, and above 2.7 volts under "good" conditions.

Typically you'd want to take a look at the 74HCT245. It has a higher guaranteed output but a 2 volt input threshold even when driven at 5 volts.

  • \$\begingroup\$ will this ( 74HCT245) IC suitable for my application?3.3V inputs at VCC 5V to get 5V outputs? \$\endgroup\$ – iopertyki Jul 22 '17 at 21:41
  • \$\begingroup\$ @iopertyki 74LSxxx is TTL and input threshold is 1.5V (between 0&1) and 74HCTxxx uses same input threshold in CMOS with full output swing unlike true TTL, while 74HCxxx like most CMOS input threshold is Vcc/2 +/-x%, so YES 'HCT' it will work. T designates TTL input thresholds of 1.5V is centred enough on 3.3V ok. \$\endgroup\$ – Sunnyskyguy EE75 Jul 23 '17 at 2:19

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