STUSB4500 default power delivery

[Circuit]

Hi 

I am using STUSB4500 using a usb c connector. The usb c connector is connected to XP power ac dc 65w adapter  capable of delivering 20V, upto 3.25A. STUSB4500 is never programmed over I2C and should have its default PDOs. By default settings I mean when it is connected to the XP charger, it should request by default 20V,1A from this source. Since its Req_src_current but is also 0 by default, so it should only demand 20W(20V,1A) from source even though source can deliver upto 3.25A. 
But I desoldered a 0 ohm resistor in the usb vbus path  after STUSB4500 and installed ammeter there and found out that 2A is flowing through vbus instead of 1A. Is this normal?

As I see 20V is being delivered to load but the current is double than what’s requested. One thing worth mentioning is that load connected on the downstream path after STUSB4500 is capable of receiving upto 2.8A.

but I don’t think load should have anything to say here and the STUSB4500 should request only its default 20V, 1A from PGW65 xp charger

[Circuit]

Here is the link for AC DC XP Power PGW65 adapter connected to USB-C Connector using a 100W USB-C Cable: https://www.xppower.com/product/PGW65-Series

[MiBA]

Hi 
The STUSB4500 is a USB-PD controller able to handle all protocol of PD2 power negotiations there no embeded current measurement  so if your system need it you need to add a current sensing or implement current limiter 
on source side usually the source will deliver is max current but here there  is no guarantee  it can stay disconnected 

 

BR 

[Circuit]

Thanks!

 

So right now we have current limit/sense resistor on the load side just after the STUSB4500. This resistor limits the current to 2.8A. And this is what i am seeing that 2.2A is actually going to the load using multimeter.

But again what is the purpose of REQ_SRC_Current then? As described, i have never programmed STUSB4500 before. So, REQ_SRC_Current should be 0 and the sink should not consume more than 20V,1A from the source as default PDO3 Sink shown here:

Or is it something i am misunderstanding here?

[MiBA]

Hi 

With REC_SRC_Current Sink protocol will request the max that source could provide for each PDO  & this is handle by STUSB 4500 but this is up to you to limit the current consumed by your Sink device 

if you are negotiating more than what you are requesting(1 A or Max current given by source PDO ) it could work but this is flexibility given by source application then not guaranteed  
if Vbus drop the the disconnection will append in range of  Vbus - 20% +10%

 that it 

[MiBA]

sorry sentence in wrong  
if you are consuming more than what you are requesting(1 A or Max current given by source PDO ) it could work but this is flexibility given by source application then not guaranteed  
if Vbus drop the disconnection will append when VBUS is out of the range of  negotiated VBUS - 20% +10%

[Circuit]

So If i understood it correctly, does it mean that setting REQ_SRC_Current to 0 or 1 has nothing to say in this case?

My sink device/load after the STUSB4500 is obviously able to consume more current(>1A) than what STUSB4500 has negotiated in its default state(REQ_SRC_Current=0) which is 20V, 1A. So seting REQ_SRC_Current to 0 or 1 becomes irrelevant? However, it does not make much sense looking into this Table 9: 

 

[Didier HERROUIN]

Dear Circuit,

The REQ_SRC_Current parameter is useful when a SINK can accept a higher current that the “typical” one requested in its PDO. In the case of a SOURCE not being able to provide a higher current, the contract can still be agreed (it is not rejected), based on the “typical” current. If the SOURCE can provide more, the SINK will take benefit of this “extra” current. But then, it is up to the SOURCE to provide it.
In your case, setting REQ_SRC_Current to “1” will ask the SOURCE to provide up to 3A (if the load consumes it) as it is able to provide it.