STUSB4500: Is there a way to find out what the maximum source current is?

[pshonsky]

I am looking at using the STUSB4500 as a front end to a sink (battery charger). I understand that I can setup 3 power profiles and if a match is detected with either of those profiles, the corresponding POWER_OKx output will be set. But is there a way to find out what the maximum current is that the source can supply? For example, the TUSB4500 device uses this value in the RDO message...is this value accessible through an I2C message? Otherwise, what good does setting the REQ_SRC_CURRENT bit if we don't know what that value is? I want to use the maximum current without overloading the source.

[Benoit FORET · Accepted solution]

​Hi,

1) if you set REQ_SRC_CURRENT = 0, you can assume that the available current is the current defined in STUSB4500 PDO. This works well for applications whose minimum current value is high and quite stable (Min and Max very close).

2) with REQ_SRC_CURRENT = 1, you can define the PDO current as the minimum value workable for your application, in order to maximize your chance to connect to any power SOURCE, even low power. The benefit is that in case the SOURCE can offer much more, STUSB4500 will book all this power, whatever STUSB4500 PDO current value. The counterpart is that you need to collect this information (available SOURCE current) by software and set your battery charger current limit accordingly. Please download STSW-STUSB003 software library (open source code), and check the Print PDO_from_SRC and Print_RDO functions. it reports the information you are looking for.

Print_PDO_from_SRC

Print_RDO 

 

[pshonsky]

Hi Benoit,

That's perfect! Would have been nice to be able to access through a simple register using the STUSB0002 software for early development purposes, but this will do the trick! Thanks for the quick reply!