I wonder about the maximum current supply capability of a USB debug adapter. The user manual (https://www.silabs.com/Support%20Documents/TechnicalDocs/USB_Debug_Adapter_UG.pdf) has the following statement:
With the default settings, the USB Debug Adapter can supply up to 100 mA to a target system.
It sounds like that there could be more current drawn from the 5V supply. Has anyone further information about if it's really possible and if the modification is software or hardware? I assume it's only the maximum current field of the USB descriptor.

Regards,

In a phrase "You do not know how much you can draw from a USB port beyond the guaranteed 100 mA."

the key phrase is 'could' not 'can'
if the PC is so equipped an USB device can after enumeration draw 500mA.
A PC must be equipped to draw up to 500mA from a port, otherwise it would violate the USB spec. I assume the 100mA restriction is due to that the debug adapter will enumerate with maximum current of 100mA.

In a phrase "You do not know how much you can draw from a USB port beyond the guaranteed 100 mA."
That's why each device must enumerate with it's maximum current consumption so that the host can decide to allow the enumeration with higher current.
I think the DA has a transistor in the power line to switch power on/off. That's why the option "power target after programming" can be selected for the USB DA.

Regards,

1) USB power supply (VBUS)
- USB spec guarantees 500mA (five units load) for each PC USB port (root hub)
- Self-powered hub also supplies 500mA for each port.
- Bus-powered hub reduces the max into 100mA for each port.

2) bMaxPower setting on the configuration descriptor of UDA.
I remember bMaxPower is 100mA (I'll check it afterward)

100mA is better choice than 500mA for UDA - it ensures enumeration.
In the real world, if a device of 100mA bMaxPower would draw 500mA from USB bus, PC doesn't complaint of.

3) Capacity of MOSFET switch on UDA, voltage drop across series resistor
The MOSFET is NDS352AP, according to the schematic on the UDA User's Guide.
It's a Fairchild product http://www.fairchildsemi.com/ds/ND/NDS352AP.pdf
- I_D: 0.9A max
- R_DS: 0.5 - 0.7 Ohm max

3 Ohm resistor (R30) is inserted across VBUS to the MOSFET.
When you draw 500mA, the voltage drop across R30 goes to 1.5 V. It'll heat up with 0.75W consumption.

After all, do it at your own risk, as usual [ ]

ReneK wrote:
There is also a current limitation circuit built into the DA, as you can see in the user's guide on page 4:
Argh, I've overseen that current limitation
Thanks for pointing me to it.

Tsuneo wrote:
100mA is better choice than 500mA for UDA - it ensures enumeration.
Okay, ensuring proper enumeration is a point.

In the real world, if a device of 100mA bMaxPower would draw 500mA from USB bus, PC doesn't complaint of.
But the mainboard will do - hopefully with foldback mechanism

After all, do it at your own risk, as usual
Na, no need. It would be nice if 500mA could be drawn from DA, but it doesn't matter for development, just one additional cable for power supply. And I prefer one additional cable rather than a boiling DA

Regards,