2
\$\begingroup\$

I am trying to figure out how to use an SN75441ONE h-bridge. I have it hooked up like this:

enter image description here

Pins 1, 8 and 16 are connected to the positive rail (+5 V). Pins 4, 5, 12 and 13 are connected to ground. Everything else is left alone. My expectation is that since all the input pins are LOW (here unconnected), the output pins should also be LOW. However, the output pins are all HIGH. What is going on here?

\$\endgroup\$
3
\$\begingroup\$

From the input circuit show in the datasheet I expect a non-connected input to behave as a 1 (current must be sunk to drive it low), exactly what you are experiencing.

\$\endgroup\$
  • \$\begingroup\$ My apologies for not marking your answer as accepted. You were very helpful. \$\endgroup\$ – azani Dec 25 '12 at 23:40
3
\$\begingroup\$

Your inputs are floating and not in a definite 'low' state. Using pulldown resistors around 1M\$\Omega\$ between the negative rail and the input pins will pull them low, while protecting \$V_{cc}\$ from ground when you input a high.

\$\endgroup\$
1
\$\begingroup\$

Your input pins are not low, they're floating - they aren't at a defined state. Try connecting your inputs to ground.

\$\endgroup\$
0
\$\begingroup\$

Check each pin. Are V+,Gnd top/bot rails connected? enter image description here

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.