DS90UH927 Pull up resistor for PDB/IDx/SCl/SDA

Ryuuichi machida

Hi,

I would like you to confirm about below.

According to datasheet, there is following description.

In case of "PDB", I understood that specification of LVCMOS buffer of "PDB" is only 3.3V. so user need to drive by VDD33 or VDDIO(case of VDDIO=3.3V).

However, in case of pins which are related to I2C, I understood that user can use both 1.8V and 3.3V for I2C. So if user set VDDIO to 1.8V, then user need to pull up by 1.8V via pull-up resistor.

Is my understanding correct ?

(I'm not sure why TI described only 3.3V for I2C. (If user will set VDDIO to 3.3V, then user need to pull up 3.3V. In other words pulled up voltage depend on VDDIO....))

Best Regards,

Machida

over 8 years ago

0 Ryuuichi machida over 8 years ago

Guru 12650 points

Hi,

Could you please give me your reply ?

Best Regards,
Machida

0 Mark Sauerwald88474 over 8 years ago

TI__Genius 13475 points

VDDIO will set the levels used by the LVCMOS I/O on the device. It is possible to use the device with 1.8V VDDIO for the CMOS I/O pins, but to still use 3.3V on the I2C control bus, in this case you would have VDDIO=1.8V and would have pullup resistors on SDB and SDA which go to 3.3V.

0 Ryuuichi machida over 8 years ago in reply to Mark Sauerwald88474

Guru 12650 points

Mark-san,

Thank you for your reply.
Do you mean even if user use VDDIO=1.8V, 3.3V(I guess this comes from VDD33) exists on I2C bus of DS90UH927 internally ?

BR,
Machida

0 Mark Sauerwald88474 over 8 years ago in reply to Ryuuichi machida

TI__Genius 13475 points

The I2C bus is an open drain bus, so the chip output does not need to pull the bus high to 3.3V, only to tolerate the 3,3V bias on it's input when the bus pin is in the high state.

0 Ryuuichi machida over 8 years ago in reply to Mark Sauerwald88474

Guru 12650 points

Hi Mark-san,

Thank you for your reply.

understood.

Best Regards,

Machida

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DS90UH927 Pull up resistor for PDB/IDx/SCl/SDA