PCF8574A: interfacing PCF8574APWR with 74HC4051PW

Hi Nicola,

The PCF8574A has GND floating on pin 15. 

SDA is also left unconnected. 

It looks like SDA and SCL are mixed up. Can we double check pins 2/3/4? 

As for the interrupt pin (/INT), it is recommended to have a PU resistor to VCC if it is being used. 

What voltage is VCC for the PCF8574A? 

Regards,

Tyler

Hi Tyler, 

please dont consider the I2C side but just the one regarding piloting 74HC4051PW  with PCF8574A .

I fixed the pin 15 to gnd, sorry it was just a ctrl+c/ctrl+V errror (thanks).

Regarding the INT pin, im not going to use it so I think I can leave it unconnected , right ?

Regarding the power supply, both Chip are powered at 3,3V.

Can you confirm its all ok ?

I post all the schematic again so that no error will be there.

Thanks a lot.

Nicola

Hi Nicola,

Please allow me to get to you by noon cst tomorrow. 

Regards,

Tyler

Hi Nicola,

nicola gatewers said:

Regarding the INT pin, im not going to use it so I think I can leave it unconnected , right ?

Yes this is fine. The output is open-drain, so leaving it floating is ok. 

nicola gatewers said:

Regarding the power supply, both Chip are powered at 3,3V.

Can you confirm its all ok ?

Yes the implementation looks good for the PCF8574A. 

As for the 74HC4051, I don't support these devices. I will transfer this thread to the MUX team to review that device. 

The VEE connection is the negative power supply. I am not sure this is suppose to be connected to 3.3V supply, but MUX team can further comment. 

Regards,

Tyler

Hi Tyler, thanks for supporting me. I think you are right , i need to connect  VEE pin  to GND since my signal are single ended . Lets wait the answer of your colleagues. Thank a lot.

Hello Nicola,

Just to confirm with you on the schematic for the 74HC4051PW.

The /E, GND and VEE are all tied to ground correct? 
Also it seems all the I/O pins are floating, why is that the case?

Thanks,

Nir 

Hi Nir ,

thanks for reply.

• /E is at GND since I want the chip to be enable all the time
• VEE is at GND since Tyler Townsend warned me about.

I post the whole schematic so that you can check everithings.

• 74HC4051PW will mux 8 analog signal coming from 8 ina138 in single ended mode (0-3v3): if you want i can share the schematic of ina138 also
• Please can you check also the TMUX1308AQPWRQ1 side? With P7,P6,P5 of the PCF8574A  i want also to MUX 8 different uart  driving the  TMUX1308AQPWRQ1 
• Please can you check also the mosfet p-channel side ? i want with P3 switch on/off an I2C ADC

Please let me know in order to cloase the BOM.

Thanks 

Hi Nir Gilgur Tyler Townsend, I have done a modification to the schematic in order to save some BOM . I promise you its last check

Please see the schematic below:

• replaced the 74hcxx with ADS7830 since I see this device has internal buffer . Can you confirm ?
• replaced the PCF85xx with TCA9534DWR since I dont need quasi bidirectional feature
• All chips are powered at 3v3 , also all UARTS are 3v3 logic

Please let me know so that i can close the ticket.

Thanks 

Hello Nicola,

I don't support the ADS7830 part. Please let me loop in the right team.

The TCA9534DWR is a part the TRX team supports. I will let Tyler Townsend to comment on it.

Thanks,

Nir 

Hi All,

do you have an update on this? I have connected a capacitor on pin10 of ADS7830 to ground!

Can you confirm all its ok . I post again the fixed schematic.

Thanks