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I use SN74AHCT595 for i2s IC

can I connecting unused pin to GND like below Picture ?

enter image description here

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2 Answers 2

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No, that will short the outputs and cause excessive heating in the chip if they attempt to drive high.

The rule for CMOS chips such as 74AHCTxxx is to tie unused inputs to a valid logic level, directly or through a resistor (the latter gives you some flexibility if you later decide to use them it's easier to add a bodge wire), and leave unused outputs open.

If the inputs have an internal pull-up or pull-down then you can leave them open but that's not the case here (nor is it true for most CMOS logic chips in the 4000 or 74xx series).

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    \$\begingroup\$ Okay, I will follow your instruction and let the unused Pin Open. \$\endgroup\$ Oct 23, 2021 at 8:18
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    \$\begingroup\$ Unused outputs just to be clear. QA, QG, QH, QH' are outputs. The others are power pins or inputs. \$\endgroup\$ Oct 23, 2021 at 8:26
  • \$\begingroup\$ okay .......👍👍 \$\endgroup\$ Oct 23, 2021 at 8:34
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All unused inputs must be tied either to Vcc or to GND to ensure proper device operation p.4 SN74AHCT595 datasheet (Recommended Operating Conditions) recommended operating condition note

however outputs should never be pulled above Vcc

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    \$\begingroup\$ I decided to let the unused output pin open. \$\endgroup\$ Oct 23, 2021 at 8:35

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