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PGA309 OWB Bit Stuck On

David McCarty
Prodigy 30 points
Other Parts Discussed in Thread: PGA309

I am unable to clear the OWD bit in the external EEPROM.

I am also unable to read from or write to the EEPROM.

My output is at high impedance and I am reading the reference voltage on the output.

I am programming through the ONE wire PRG line and cycling power. TEST pin is pulled low. Therefore, the PGA309 writes the EEPROM table through I2C.

The procedure that I am using is CMD VDUT_OFF, Wait 0.5 seconds, CMD WAKE_UP_ONE, Read or Write to EEPROM Table.

For Write, I send ONE 0x55 0x02 [Address: 0xLowByte 0xHighByte] then ONE 0x55 0x08 [Data: 0xLowBye 0xHighByte] for each 2-byte word of the first part of the EEPROM table.

For Read, I send ONE 0x55 0x02 [Address: 0xLowByte 0xHigh Byte] then ONE 0x55 0x20 R R for each 2-byte word of the first part of the EEPROM table.

At this point, I am uncertain of the contents of address 0 & 1 (TI Flag) or the checksum of the first part of the EEPROM table.

Are there any procedures for resetting or initializing the EEPROM table to FFFF's or any other method to clear the table/OWD bit?

  • 0
    TI__Mastermind 27715 points

    Hello David,

    Is this the same issue you were able to resolve by removing power to the pull-up resistors on the instrumentation side? If so, I will mark this question as resolved.

    For the sake of completeness, here is the proper PGA309 start-up sequence for OWD=1 mode:

    1. Power is cycled on the device, and within a few milliseconds we write to the device. This can be done with the command "CMD WAKE_UP_ONE"
    2. Once communications are established we wipe the first byte of the EEPROM. The voltage output will remain disabled for 1 second after the last communication is issued.
    3. After one second the PGA309 will try to read the EEPROM. The TI flag has been erased, so the EEPROM format is no longer valid and the output will be disabled.
    4. The output will remain disabled until valid information is written into the EEPROM.

    If you do not cycle power, you will have issues with OWD=1. The goal of OWD is to disable the one-wire interface shortly (milliseconds) after power-up. The only way to enable the one-wire interface is to disable this feature. The "CMD WAKE_UP_ONE" command cycles power and immediately communicates with the device; this allows you to establish communications even when OWD=1.

    Best regards,

    Ian Williams
    Linear Applications Engineer
    Precision Analog and Sensing Products