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Lukasz Przenioslo
Lukasz Przenioslo
Associate III
October 16, 2017
Question

Push-pull vs open drain

  • October 16, 2017
  • 2 replies
  • 2556 views
Posted on October 16, 2017 at 12:43

Hello there,

I have noticed that in the newer STM32 chips it is possible to configure the GPIO's in 2 kinds of output states:

  • Push-pull
  • Open-drain

I was wondering which option is drawing less current for driving simple ON/ OFF logic at low frequency? Is it better to use Push-pull without internal pull-up/ pull-down or open-drain + internal pull-up?

I would appreciate all help.

#gpio-open-drain #push-pull
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2 replies

Nesrine M_O
Nesrine M_O
Associate
October 16, 2017
Posted on October 16, 2017 at 13:02

Hi

Przenioslo.Lukasz

,

I recommend you to have a look to

http://www.st.com/content/ccc/resource/technical/document/application_note/group0/13/c0/f6/6c/29/3b/47/b3/DM00315319/files/DM00315pdf/jcr:content/translations/en.DM00315pdf

application note.

-Nesrine-

AvaTar
AvaTar
Senior III
October 16, 2017
Posted on October 16, 2017 at 14:03

The 'Open Drain' configuration is a requirement for some use cases.

This means, the Drain (or the Collector with BJT) is left open, and needs an exernal load to VDD  (or VCC).

OD outputs form a 'wired OR', if connected together.

For example, the I2C bus requires both bus pins (SDA, SCL) to be configured as Open Drain.

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