PCA9698 OE pin not working with frequencies over 600Hz

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PCA9698 OE pin not working with frequencies over 600Hz

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cferrer3
Contributor I

While using the IO expander PCA9698DGG and applying a 1khz square signal to the OE the output pin doesn't disable the output pin. At 300Hz the OE toggles the output pin but with a delay and jitter in the falling edge (of the output), the raising edge switches properly. At low frequencies the OE pin enable/disable works fine.

The system is supplied by 5V (4.8V measured), and the OE pin is driven by a atmega328p output pin, configured as pushpull.

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cferrer3
Contributor I

Dear G.W,

Thanks for the reply, I could share the Altium schematics, please let me know if it would be useful.

I can describe the conditions of the test:

The Duty Cycle in the 1kHz PWM was set to 50%, attached you can find pictures of the described behavior. Sorry for the quality, but because of quarantine I can't access any other scope.   The 3 pictures attached were measured with a 166Hz square wave, 50% duty cycle. There seems to be a delay between the OE rising edge (OE is negated) and the falling edge of the selected output pin. Changing the polarity of OE by software, by using the OEPOL bit in the  MODE SELECTION REGISTER seems to have no effect, the delay is still present on the falling edge of the selected output pin.   The delay is aprox 1-1.5ms long (pictures are taken with some persistence so they are not 100% accurate). Changing duty cycle does not affect the delay, just the relative position of it. Because the delay is larger than 1ms the maximum switching frequency is limited by it, faster than that it doesn't switch off.   There seems to be a 80us jitter (peak to peak) on the falling edge of the output pin (delay). The supplied voltage is 5VUSB, 4.9V in the Vdd pins of the PCA9698, 4.7-4.8V measured at the output pin when the OE is selected . 2x100nF capacitors, one in each Vdd pin, together with a 33uF capacitor are used to decouple each IC. Seven PCA9698  are used in a 150x300 board, the output conditions for all the pins (250 pins) is a 10kOhm load.

0.5msM.jpg1msM.jpeg2msM.jpg

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guoweisun
NXP TechSupport
NXP TechSupport

I see your case-

00295869

You can update based on that case.

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212 Views
guoweisun
NXP TechSupport
NXP TechSupport

Hi

1:Please share with your schematic.

2:Please also give us the test waveform  about OE and output channels .

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