External Current Limiting Circuit Recommendation for STUSB1600

[TIENHUA]

Hi Sir,

I am reviewing the application schematic of the STUSB1600 in a dual-role Type-C design. I understand that when STUSB1600 operates as a Source, the output current can be configured through the CC_CAPABILITY_CTRL register.

However, I did not see an explicit current limiting component in the provided schematic. I would like to ask whether ST has any recommended external circuit solutions to further enforce current limitation, such as a preferred power switch or current limiting IC that is compatible with this setup.

Additionally, I would like to confirm: if we only configure the CC_CAPABILITY_CTRL register without any external current limiting components, would the actual output current still exceed the configured 1.5A limit in certain conditions? If so, could you provide a reference circuit diagram or recommendations for suitable current limiting components that ensure proper current regulation?

[Peter BENSCH]

Unfortunately, you have misunderstood the abbreviation CC - it does not stand for Constant Current, but for Configuration Channel.

According to the data sheet, section 5.1.10, byte CC_CAPABILITY_CTRL at address 0x18 is used for:

When operating in source power role, this register allows the advertising of the current capability to be changed as defined in the USB Type-C standard specification and the VCONN supply capability.

The exact meaning of the individual parts of this byte can be found directly below in table 26 of the data sheet.

Does this answer your question?

Regards
/Peter

[TIENHUA]

Hi Peter,

I understand that CC_CAPABILITY_CTRL in the STUSB1600 is used to advertise the available current capability (e.g., 1.5A) to the connected sink, but it does not actually enforce a hard limit on the VBUS output current.

If a sink device attempts to draw 3A, what mechanism prevents VBUS from exceeding the configured 1.5A limit? I noticed that the STUSB1600 reference schematic does not include any explicit current limiting components.

Does ST recommend a specific power switch, eFuse, or current-limiting IC that should be used with the STUSB1600 to enforce a strict current limit? Or is there an integrated feature in the STUSB1600 that helps regulate the actual output current?

I am designing a Type-C source application without an MCU, so I would like to implement proper current limitation using only hardware components. If possible, could you provide a reference schematic or component recommendations?

Thanks in advance!

[Peter BENSCH · Accepted solution]

The STUSB1600 does not provide the option of limiting the current and trusts that a sink will not draw more current than it has requested..

If you want to realise a pure USB-C source, you can use the STUSB4761, which can realise a current limit with an external shunt.

Regards
/Peter

[TIENHUA]

Hi Peter,

Thank you for your response. Could you please clarify how the current limiting function can be implemented with the STUSB1600 based on the PCB circuit design, or is it completely not feasible to implement? I would appreciate any insights you can provide on how this can be achieved within the existing design. Thank you!

[Peter BENSCH]

As the STUSB1600 has no current limiting function, it must be realised independently of this. I do not currently have a proposal for this.

Regards
/Peter