How to wiring usb 6211 measure curretn

[Sam.Huang]

Hi all

    I have a project need to measure current with usb charger,how to wiring it.

e.g Differential mode direct connect it or shunt resistor and what value of the resistor,thanks in advance!!

[GerdW]

Hi,

when you want to measure current with a device providing only voltage channels then you need to use a shunt resistor!

The value of this resistor is given by required measurement accuracy, voltage range of daq channel, power dissipation of the resistor, influence on USB connection,...

[Sam.Huang]

Thank very much for your reply,just for TWS  earphone charge,only 200mA, what value of the resistor,as photo is OK,thanks!

[GerdW]

Hi sageliuliu,

at 0.1Ohm and 0.2A you measure a voltage of 0.02V: the smallest measurement range of the USB6211 is ±0.2V and so you would only use 1/10 of the possible measurement range (and also limit accuracy).

At the same time the resistor burns 0.004W, way below the given spec of 3W in your image.

When using a resistor of 1Ohm you would get 0.2V at 0.2A (and use the full measurement range of ±0.2V), with a power loss of 0.04W over the resistor: still reasonable values. (You might do the same calculation for resistors of 0.47Ohm or 0.68Ohm…)

Another note: you seem to try to measure the "high side" of the USB power supply: this should be done using two input channels and differential measurement mode. When you would measure the current at the GND line you could go with just one input channel and referenced to GND mode…