Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
I oftenly hear the terms weak pull-up and strong pull-up resistors.
Could you please give me an example when a strong pull-up is needed, and when a weak pull-up is enough?
Weak pullups are often fine for digital inputs, such as a switch a user might push. A strong pull-up may be needed on something like an I2C bus. If there is a fair amount of capacitance on the line, the pullups may take a long time to pull the line back to a logic HIGH which would limit the maximum bus speed. By increasing the strength of the pullup, the bus is pulled up quicker, and the speed can be increased.
As a very fat thumbed rule of thumb, I start with a 10k pullup and work from there. In battery powered applications I'll try to go up to 100k or more if I can get away with it, and in bus communications I've gone to a couple hundred ohms. Cell phones use pullups in the mega-ohm range.
When you use an EEPROM or a temperature sensor on a 1-wire bus, you need a weak pull-up when the processor is talking to the sensor, but a strong pull-up when the 1-wire device is drawing power.
This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
By continuing to use this site, you are consenting to our use of cookies.