Part Number: PCA9536
I got feedback from customer that rigister #2 data of PCA9536 is 0x01 read at power up stage without any writing. it didn't match the describtion in datasheet as default setting as 0x00. any reason will cause register #2 change the default setting?
In reply to Max Robertson:
In reply to Ching Su:
Hey Ching Su,
"What function is for register 0x3?"
-Register 0x03 is the configuration register of the device. It determines whether the device's ports are outputs or inputs.
Were you able to confirm your device was powering up correctly? We have a power on reset errata on the datasheet on page 20 section 9.1. Please confirm there are no issues with this. If you are able to get a scope shot of the device's Vcc during power up, it may provide us with clues. Also are you able to show us a picture of the schematic?
In reply to Bobby Nguyen:
Please kindly see attached picture for VCC power on reset and PCA9536 schemtic
PSU0_PG and PSU1_PG is from daughter board
Daughter board schemtic↓
Main board schemtic↓
Thank you very much
Posted thier schematic.
In reply to Jason Dai:
Thank you for the additional information.
Looking at the o-scope shot, your Vcc waveform looks good when it is ramping up but during the ramp down it begins to slow down. The ramp down itself looks like a capacitor discharging; a colleague of mine ran into this issue of the internal registers sometimes changing from default state during POR before; due to this ramp down slewing. In his case, I believe he was able to resolve this problem by placing a pull down resistor on Vcc to allow for a faster slew rate when powering down.
1) Can you remove the 1uF and 10uF capacitors next to the device from Vcc? It is affecting the ramp down slew rate of our device.
2) Please add a pull down resistor on Vcc to GND (next to our device) and check to ensure Vcc ramps down faster. I would probably try a value like 10k and work my way down (lower) and checking the Vcc pin on the o-scope until it looks similar to the rise time. [Lower will have faster fall times at the expense of power consumption]
-After adding the pull down resistor, please check the default states of the registers again
On my end, I will discuss this problem with my colleague when he gets back from vacation, on Tuesday, to double check with him on how he resolved the past issue. (Very similar to your case)
customer is busy on other task and they will update the result next week.
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