PGA308: 1 wire communication wave issue

Arking Chiu

Intellectual 790 points

Part Number: PGA308

Hi Team

customer use STM32 to communicate with PGA308.

they found PGA308 cannot pull low enough.

is there any ideal to slove it?

over 7 years ago

0 Alex Davis over 7 years ago

TI__Expert 6520 points

Hi Arking,

I suspect this may be due to the 10mA current limit on the Dout pin of the PGA308. Could you provide details of any circuitry on the PGA308's Dout pin, as well as pullup resistance on the 1-wire line? A schematic would be very helpful.

0 user5121996 over 7 years ago in reply to Alex Davis

Prodigy 60 points

Our schematic diagram is shown in the figure above

0 Alex Davis over 7 years ago in reply to user5121996

TI__Expert 6520 points

I don't see anything in that schematic that looks like it should be causing the problem. What is connected on the controller side? As I mentioned above, I'd guess that the value for the pullup resistor on the one wire bus is too small, exceeding the 10mA current limit on the PGA308's one-wire output.

0 user5121996 over 7 years ago in reply to Alex Davis

Prodigy 60 points

1W pin, pull resistor 10K, power 3.3V, our project flying line to EVM development board, register read and write are normal. The main control is STM32.

0 Alex Davis over 7 years ago in reply to user5121996

TI__Expert 6520 points

Looking at the levels in the scope image you posted above, it looks like the pullup resistance is 100 ohms. This could be caused by the PGA308 enabling its output while configured in 3 wire mode. Typically in this mode, there's a small window of time after power-up during which you can communicate with the device. After that time, the output is enabled and remains enabled until the part is power-cycled.

If the device is being used in a 4-wire mode (separate vout and 1-wire), then there must be something else pulling the 1-wire bus high through about 100 ohms.

0 user5121996 over 7 years ago in reply to Alex Davis

Prodigy 60 points

Hi Alex,
I can read and write the most of PGA308‘s register but PGA308_REG__ALRM = 0x09 and PGA308_REG__OTPS = 0x0A . I setup the other registers with default parameters.

0 user5121996 over 7 years ago in reply to user5121996

Prodigy 60 points

Hi Alex：

When we debug PGA308, we find that when VS=3.34V, VREF=3.25V, registers ZDAC and GDAC can write data,but we read the other data! When the VS voltage is adjusted to the 3.27V voltage, the registers ZDAC and GDAC can read and write the same data. What is the correspondence between VS and VREF voltage, and how does this affect the register read and write of 1W? Or is there a problem in the timing of 1W?

0 Alex Davis over 7 years ago in reply to user5121996

TI__Expert 6520 points

I've replied to this in another post here: e2e.ti.com/.../632920

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PGA308: 1 wire communication wave issue