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PCA9536: Connection with EEPROM

Part Number: PCA9536

Dear E2E,

We would like to use PCA9536 to control the WP of EEPROM & Flash.

And, We would like to let EE_WP# its default is low in order to let EEPROM can be written.

We are not sure if we need to add a pull low resistor (R530), like as 10K or other value?

in addition, Does SPI_WP still need to pull-high resistor (R529)? (Although PCA9536 already has an internal week pull-high?)




  • Hey Jason,

    "We are not sure if we need to add a pull low resistor (R530), like as 10K or other value?"
    Our device has an internal pull up resistor (100k) so it depends if the EEPROM wants to see a high or a low on the line and what voltage is required. With a 10k pull down resistor the device will see about 300mV. If it needs to see something lower, then you will need to use a smaller pull down resistor.

    Doing some light reading on the WP pin, I've found typically the WP pin is pull high (such as with our internal 100k resistor) to protect the device from accidentally writing to it's memory array. The IO Expander allows the WP pin to see low and allow an write if you address it to do so.

    "Does SPI_WP still need to pull-high resistor (R529)?"
    I am not responsible for that device so I do not know it very well.... From what I can see in the datasheet, if there is no active signal on the input then the output will be held in high-Z. You can drive the output (Y) low when you drive the input low. To me, the the pull up resistor is insurance that the device's input will not be floating and accidentally turn on the output. If you have something actively driving the input then this resistor is not needed. I suggest you post on the e2e forum which is responsible for that device to get the expert's opinion on this.

    Lastly, I see that the PCA9536 has some of it's IO pins floating. I would recommend you either pull the unused pins to GND with a pull down resistor or pull up resistor to Vcc if the end equipment/application cares about power consumption. Floating pins can result in unnecessary current consumption.