I am planning to use a STUSB4710 and use the reference schematic from it's datasheet (Figure 7). There is a connection between the STUSB4710 with the ST1S14's feedback pin. Is this how they communicate with each other to get for example 20V or 15V onto the VBUS line?
The data sheet of the STUSB4710 says in section 2.3.10:
SEL_PDO [5:2]
These 4 output signals are asserted (active low) respectively when PDO2, PDO3, PDO4 and PDO5 are selected by the attached sink. These signals are used to pilot the power management unit.
Active low here means an open drain output, so that the connections of SEL_PDOx to the resistor chain R2...R6 visible in Fig 7 short-circuit the respective resistors to GND. This influences the voltage divider, which derives the feedback voltage from the output voltage of ST1S14, so that the desired output voltage results. The function is also listed under Fig 7, but it is somewhat misleading because GPIO0...GPIO3 are mentioned, but they are assigned to the pins SEL_PDO2...SEL_PDO5.
In Table 11 you will find the corresponding calculation of the resistors, which simplifies the use of another switching controller.
In this respect, the ST1S14 is only an example of a switching regulator whose feedback can be set and thus programmed via the SEL_PDO, whereby the respective output current is not affected by this.
Does it answer your question?
Regards
/Peter
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