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PSoC™ 4 Forum Discussions

YuCh_3947976
Level 3
Level 3
10 likes given 5 likes given First like received

I have a question about PWM component.

why isn't minimum voltage of PWM around 0? (yellow line)

IMG_20200909101356.jpg

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1 Solution

YuCh,

It seems that the PSoC ground is floating. Please connect o-scope ground to PSoC ground, and check that observed voltage is 0V. It is often recommended to isolate scope from the ground, so that PSoC and scope would be sitting on same ground, and no ground loop is created. The simple way to isolate scope is to remove (tear off) a GND terminal from the AC cord, or use a special pass-through connector w/o GND pin. I always isolate scope when working with PSoC kits.

/odissey1

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9 Replies
LinglingG_46
Moderator
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10 questions asked 5 questions asked 250 sign-ins

1: Could you offer the test project?

2: Please test the impedance of this pin to power and ground.

3: Try to use another pin to test the function.

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please help me to check it,thanks!

I'll test the item you said.

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YuCh,

I looked into your project. I suspect that the pin has been fried, with top FET shorted. Disable PWM and check pin voltage on startup. If it +5V, it is fried.

1. Use onboard LED for testing.

2. Use another pin, and don't forget to add some 200-400 oHm resistror in series with LED.

/odissey1

I just want to generate a PWM output to other device,like function generator

do I need to add a resistor in series on circuit or use another pin?

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Hi

How do you connect the LED on the board?

Because the pin drive mode is Strong, if don't have the series resistance, then the pin have a big chance to be damaged.

pastedImage_0.png

The reference design:

pastedImage_2.png

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if I just want to generate a PWM output,which mode should I select?

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To drive external device the pin should be in strong drive mode. Remove the LED.

Pin 3.0 possibly already damaged. Change to another pin.

What is other device that you want to drive? What is it's input impedance?

/odissey1

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LED driver IC,but I just output to oscilloscope now

I change another pin to output,no matter if resistor is added or not,minimum voltage is -0.5V.

should I do any calibration?

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YuCh,

It seems that the PSoC ground is floating. Please connect o-scope ground to PSoC ground, and check that observed voltage is 0V. It is often recommended to isolate scope from the ground, so that PSoC and scope would be sitting on same ground, and no ground loop is created. The simple way to isolate scope is to remove (tear off) a GND terminal from the AC cord, or use a special pass-through connector w/o GND pin. I always isolate scope when working with PSoC kits.

/odissey1

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