Reduce Amplitude obviously

[Linda]

Posted on July 27, 2014 at 15:28

When I using my desktop computer to power the STM32F429i Disco, the PWM out put amplitude is aobut 3v, but when I use a IC LM7805 (change DC form 9V to 5V) to power it, PWM reduce amplitude obviously, even just have 1%.

Please help. Thanks

[Tesla DeLorean]

Posted on July 28, 2014 at 01:52

So 0.03V?

Assume no one here knows how you've wired this up, or the voltages at key test points.

[Linda]

Posted on July 28, 2014 at 17:43

 I have not wired it up with anything yet. Even I wired up with some circuit, the same result.

When I use USB from my desktop computer, the P1(5V) is 4.58, when use LM7805, it is 4.55. not much different. But when test point I should look into? Thnaks

[Tesla DeLorean]

Posted on July 28, 2014 at 18:10

As you're complaining about output voltages from the processor, perhaps start there, and verify the supplies, and outputs of VCAP pins. The voltages across the capacitors might be the easiest to scope.

Where exactly are you injecting your 5V supply? I'd perhaps use the USB USER port, or via diode to the 5V pin on P1