Francesco Pallottini

S08MM USB leakage current

Discussion created by Francesco Pallottini on Jul 19, 2011
Latest reply on Jul 21, 2011 by Francesco Pallottini

Hi guys,

(sorry for the bad english)


I have a problem with USB leakeage current. I use a S08MM64, mini-USB connector and my device is SELF POWER.

I connect USB pin number 1 with Ferrite and I connceted a polarized capacitor (4.7uF)  in series to the Ferrite. The voltage between Ferrite and the cap is Vbus and is send to microC port n.59.


Now I want to detach when VBUS is connect (i use the the freescale USB stack AN3582 ) so I decide to connect VBUS with some extarnal PIN of the microC.  I can't connect directly VBUS to extarnal pin beacuse I will burn microC, so I use two resistor connected in parallel with the aim to reduce the voltage. I connect  resistor 1 between the ground and port 1 of resistor 2 , port 2 of resistor 2 is connected with VBUS. Now I connect microC port n.33 with the port 1 of resitor 2.


The value of resistor is:

-RESISTOR n.1 (between ground and resistor n.2 ) 270K

-RESISTOR n.2 (between resistor 1 and VBUS) 470K


I use this value with the aim to reduce current. 


If I don't use the resistor the filter composed by Ferrite and cap seem work fine: infact if VBUS is connected but device is not supplied the VDD pin voltage of the microC is 0.000V. Instead if  I connected the device to the host, so VBUS is supplied, but the device is not supplied VDV voltage of the microC is 600mV.


Where is the mistake? Is there another better way to connect VBUS with the microC?


Thanks in advice