TPS62872-Q1: How to understand the relation of Vout, I2C config and Vsense(VOSNS/GOSNS)

Hi, 

Thank you for the enquiry. In devices containing the I2C feature, a resistor-to-digital (R2D) converter on the VSET/VID pin is used. This pin reads this resistor value and programs the device. Therefore, the output voltage can be set using the VSEL pin in TPS62872-Q1.

For further explanation on how the I2C interface works, please refer to the following application note, "Methods of output-voltage adjustment for DC/DC converters".

/cfs-file/__key/communityserver-discussions-components-files/196/1373.slyt777_5F00_Methods-of-output_2D00_voltage-adjustment-for-dcdc-converters.pdf

Kind Regards, 

Rameen

Hello Rameen,

Thanks for your fast relay,

Let me explain my confused point furtherly,

In my understanding, during start-up, the output voltage is set by the resistor connected to the Vsel PIN,

and after power on of the SOC and it is able to operate the I2C to adjust the output voltage.

In normal operation, I think the output sense pin (VOSNS/GOSNS) will send back a voltage equal to the output,

but the question is what will happen if the sense voltage is incorrect (caused by external issue e.g., an open connection or something others)?

And actually, an issue happens in our project (the output is higher than the Vsel setting value during start-up and the PG is low) and I want to 

find if the problem is caused by an abnormal sense voltage.

So it's the reason I want to find out what function the sense voltage has for the output voltage.

Hi, 

The sense voltage senses the voltage at the output point (or sense point) which may be a little farther from the actual Vout point of the device. Thus, this compensate for the resistive drop of the power path from the output point to the sense point. The sense lines then sense the voltage at the sense point and feed that back into the device to ensure that the correct voltage is reflected. Another application note you might be interested in can be found below:

www.ti.com/.../slyt467.pdf

On the other hand, I cannot provide feedback on the cause of the issue. Additionally, we have not seen such issues in our circuits. To provide better feedback, I request that you provide more information regarding:

- Schematic/ Layout 

- Waveforms of what you have measured and where you have measured it

- Your test conditions 

Thank you. 

Kind Regards, 

Rameen 

Hello Rameen,

Another question is for the use case of VOSNS/GOSNS pin.

My understanding is that a power voltage and GND signal should be connected from the load side for remote sensing,

and these two signals are routed as peso-differential but not real differential signal.

The hint here the GOSNS must be connected to the ground either the main GND or the ground inside the SOC(the load side)

is my understanding correct or not ?

Hi, 

Normally, the VOSNS/GOSNS may be connected to the terminals of the capacitors before the point of load (your SoC in this case).

Could you please confirm where your caps are connected?

Kind Regards,

Rameen

Hi

These two signals are connected form two dedicated pins inside a SOC (Renesas V3H).

So I ask the required signal type (differential or pseudo-differential ) from the SOC.

Hi, 

Yes, it is differential. 

Kind Regards, 

Rameen 

Hi,

The differential signal I mean with the same amplitude and the reverse phase,

The pseudo-differential I mean with one input(it should be GOSNS) connected to the reference ground.

So, which kind of signal can TPS62872-Q1 support?

This is a key point in our case and I need to confirm with you.

Thank you.