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MSP430G2553 Pullups


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Hi All,

 

Been a while since ive posted, but have picked up a little BLDC project again.

 

I have designed a PCB for this BLDC controller im making, but have put pull-down resistors on the hall sensor inputs instead of pull-ups, which are what I need for the particular motors I want to drive. Stupid mistake.

 

The manufacturers own BLDC controller uses 20k pull ups on their controllers, and I note the MSP430G2553's internal pull ups are 35k (20k-50k). If i were to just leave off the pull-downs on my PCB and use the internal pull ups, are they generally good enough to do the job?

 

Ive never used the MSP internal pull-ups/downs before so dont know what to expect.

This would save getting some new boards made, ill fix it with the next revision.

 

EDIT: Maybe an important bit of info. The hall sensors are 5V, so I have a voltage divider dropping the level to 3.3V. This is jointly acting as the pulldown. (5v through 270R to MSP430, pulled to ground via 470R). 

 

Thanks!

 

Alec

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Ok I've been doing some thinking/testing and I think the internal pullups will work. A question remains however. What effect will the voltage divider which precedes the pullup have? I'm trying to nut it out, and all I can conclude is that the low resistance resistor in the VDiv which is attached to ground will fight with the high resistance pull up, the result being the input is pulled low.

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