TPS25750: I2C pull up voltage and voltage / current leakage into I2C pins

Takahiro Saito

Part Number: TPS25750

Hi team,

I have two questions about I2C function below.

1. Can TPS25750 use 1.8V and 3.3V for I2C pull up voltage?

2. Could you check if there is no voltage / current leakage to I2C_SDA and SCL pins from external pull-up voltage when TPS25750 I2C function is disabled?

Regards,

Saito

over 5 years ago

0 Adam Mc Gaffin over 5 years ago

TI__Mastermind 30000 points

Hello,

We recommend connecting the LDO_3V3 to the I2C channels for pullup. LDO_1V8 is not designed to drive external loads, but instead is used as an internal reference

As far as the leakage current for the I2C channels, this stated within the datasheet. I've highlighted the relevant portion in the image below for your reference.

0 Takahiro Saito over 5 years ago in reply to Adam Mc Gaffin

TI__Expert 5585 points

Hi Adam-san,

>LDO_1V8 is not designed to drive external loads, but instead is used as an internal reference.

Is it able to use an external 1.8V power supply for I2C pullup instead of LDO_1V8?

Regards,

Saito

0 Takahiro Saito over 5 years ago in reply to Takahiro Saito

TI__Expert 5585 points

Hi Adam-san,

>As far as the leakage current for the I2C channels, this stated within the datasheet. I've highlighted the relevant portion in the image below for your reference.

I understood the leak voltage from pullup supply to I2C pins.

How about voltage leakage to any other pins from I2C pull up supply through I2C pins?

Some other competitor devices leak the voltage to the other pin from I2C pins. So, I just want to check it.

Regards,

Saito

0 Adam Mc Gaffin over 5 years ago in reply to Takahiro Saito

TI__Mastermind 30000 points

Hello,

Is it able to use an external 1.8V power supply for I2C pullup instead of LDO_1V8?

No, you must connect the I2C pullup resistors to LDO_3V3

How about voltage leakage to any other pins from I2C pull up supply through I2C pins?

You must use LDO_3V3 when connecting to the I2C pullup resistors. As the datasheet states, when LDO_3V3 is used on the I2C pullups, there is a maximum leakage current of 3uA

0 Takahiro Saito over 5 years ago in reply to Adam Mc Gaffin

TI__Expert 5585 points

Hi Adam-san,

It's too bad the device can't use 1.8V pull-up for I2C because it takes extra cost for a level shifter. That's customer's a key requirement.

> How about voltage leakage to any other pins from I2C pull up supply through I2C pins?

Is it able to use other 3.3V external pull-up voltage for I2C bus? I think this is okay. My question is whether any voltage leakage shows up on any other pins when TPS25750 is powered off and 3.3V external pull-up voltage is ON.

Regards,

Saito

0 Adam Mc Gaffin over 5 years ago in reply to Takahiro Saito

TI__Mastermind 30000 points

Hello,

The I2C pins must be pulled up to LDO_3V3. You cannot replace LDO_3V3 with an external 3.3V supply for the purpose of the I2C pullup resistors. The internal configuration of the device has LDO_3V3 enabled on initial boot so that the TPS25750 can load the binary from the external EEPROM without problems.

0 Takahiro Saito over 5 years ago in reply to Adam Mc Gaffin

TI__Expert 5585 points

Hi Adam-san,

So, if there are multiple slave devices on the same I2C bus like below. Other I2C slave devices have to use LDO_3V3 pull up.

If TPS25750 isn't powered up, other I2C slave device can't work, is that correct?

Regards,

Saito

0 Adam Mc Gaffin over 5 years ago in reply to Takahiro Saito

TI__Mastermind 30000 points

That is correct. All I2C slave devices will be connected to TPS25750 LDO_3V3 that share the same I2C channel as the TPS25750.

There should be no instance when the TPS25750 is not powered and other slave devices are powered. In a normal scenario, the TPS25750 will be powered by the system from VIN_3V3. In a dead battery condition, the TPS25750 will be powered from VBUS.

0 Takahiro Saito over 5 years ago in reply to Adam Mc Gaffin

TI__Expert 5585 points

Hi Adam-san,

Now, I'm clear. Thank you for clear explanation.

Originally, customer wants to ask us if the backdrive voltage happens from SDA/SCL to other pins.

But, if LDO_3V3 is an only source for I2C pull up, the case that TPS25750 is powered off and other I2C device's SDA/SCL pin have some voltage will never happen. So, I think customer will understand this situation.

I will appreciate your help if I need further help for this.

Regards,

Saito

0 Takahiro Saito over 5 years ago in reply to Takahiro Saito

TI__Expert 5585 points

Hi Adam-san,

Sorry for open the thread again.

Before answering it to customer, I would like to know why only LDO_3V3 is allowed as an I2C pull-up supply.

Why isn't external 3.3V supply allowed as a I2C pull-up supply?

Regards,

Saito

0 Adam Mc Gaffin over 5 years ago in reply to Takahiro Saito

TI__Mastermind 30000 points

The internal configuration of the device has LDO_3V3 enabled on initial boot so that the TPS25750 can load the binary from the external EEPROM without problems. If you use an external 3.3V supply other than the LDO_3V3, it must have 3.3V present by the time the TPS25750 boots up and is ready to load the configuration. If this is not the case, and the TPS25750 boots before the pullup resistors are ready, then the TPS25750 will not be able to boot up properly and could get into an abnormal state. That is why we recommend connecting it to LDO_3V3 so that the customer does not have to worry about this timing requirement

0 Takahiro Saito over 5 years ago in reply to Adam Mc Gaffin

TI__Expert 5585 points

Hi Adam-san,

Thank you for your clear explanation. If customer wants to use the external I2C supply, I will ask them to power up before booting TPS25750.

When an external I2C supply is used before powering up TPS25750, is there any leak voltage to any other pins through SDA/SCL pins from?

Regards,

Saito

0 Hari Patel1 over 5 years ago in reply to Takahiro Saito

TI__Genius 12700 points

Hi Saito-san,

No you shouldn't have any leakage to the other I2C pins if they are not configured or also connected to the external 3.3V supply. If so, it would be minimal as the Table that Adam uploaded showed of +/-3uA.

Thank you,

Hari

0 Takahiro Saito over 5 years ago in reply to Hari Patel1

TI__Expert 5585 points

Hari-san,

I greatly appreciate your support!

Regards,

Saito

0 Jiang Boqian over 5 years ago in reply to Takahiro Saito

Intellectual 655 points

Hi Saito,

It is possible to use external I2C pull up voltage if you know that there's no internal TVS diode from I2C pin to VDD of your IC(TPS25750 in this case).

Usually you can get this information from datasheet's absolute maximum ratings or recommended operating conditions. If there's something like VDD+0.3 for maximum SDA or SCL voltage, you know there's a diode from SDA or SCL to VDD. In this case, you cannot use external I2C pull up voltage, because there will be leakage current from external pull up voltage through pull up resistance and internal diode to VDD, and will power up your VDD if it is not powered.

P.S. I see now you became one of the TI, can you have a try? Don't leave unsolved problems...

0 Takahiro Saito over 5 years ago in reply to Jiang Boqian

TI__Expert 5585 points

Hi Jiang-san,

>there's no internal TVS diode from I2C pin to VDD of your IC(TPS25750 in this case).

Thank you for additional answer. I have wanted to get this information. So, I now fully understand there is no lakage path to TPS25750's other pins.

Regards,

Saito

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TPS25750: I2C pull up voltage and voltage / current leakage into I2C pins