Why is it a voltage divider as configuration for the USB2514B in STM32MP157 devkit?

[DMårt]

Why is it a voltage divider as configuration for the USB2514B in STM32MP157 devkit?

I can see in the data sheet that there are two bus configurations abilities.

• I2C EEPROM
• SMBus

I don't know which one should be used. Let's look at the data sheet.

This explains that the pins CFG_SEL[0] and CFG_SEL[1] needs to be low or high before the pin RESET_N goes low.

And the reset can be done through the USB differential lines.

I don't understand this construction. I know that I2C should have a pull-up resistor of 4.7 kOhm, but here we have a 100 kOhm on both GND and 3V3, which makes this a voltage divider.

 

And the data sheet says that 10 kOhm should be the value for pull-up resistors.

Question:

What is the right configuration here if I want to connect my USB hub to my I2C1 ? I'm using I2C1 instead of I2C4 because the HDMI transmitter and PMIC are sharing the I2C4 bus. The reson is that I think this USB hub might use SMBus and PMIC must use I2C4 according to AN5031, so I2C1 must be unique for one I2C device.

Can you also explain the choice of 100 kOhm, and not 4.7 kOhm as the standard?

 

[PatrickF]

HI @DMårt 

did you look at right schematics ?

Regards.

[DMårt]

Hi @PatrickF

 

DNF means Does Not Fit. Does that mens that it could not fit the HW design, or it was removed? So in this case, it's only 100 kOhm pull-downs?

 

I'm looking at the en.mb1272-dk1-c03-schematic.pdf schematics.

STM32MP157D-DK1 - Discovery kit with STM32MP157D MPU - STMicroelectronics

[PatrickF]

Yes, DNF mean Do Not Fit, i.e. component is not populated during board assembly.

The Bill Of Material is the reference for the 'not fitted'

Regards.