USB suspend mode in uPSD 3234

[h239955_stm1_st]

Posted on May 27, 2005 at 05:18

USB suspend mode in uPSD 3234

[h239955_stm1_st]

Posted on May 17, 2011 at 12:06

Dear all,

According to the usb spec, when in suspend mode, the current should be less than the 500uA. I'm using a 3234 to develop a USB keyboard. Is there any one who knows that How can I meet the spec? and How to force the USB into the suspend mode to test?

[thomasthanner9]

Posted on May 17, 2011 at 12:06

Hello,

getting a device into suspend mode is quite simple. A look at the USB spec tells that a device has to enter suspend mode automatically after it sees an IDLE upstream bus state for more than 3.0ms. The device has to enter suspend mode at least 10ms after that idle condition. IDLE bus mode means for a LOW speed device D+ low and D- high.. So to get the uPSD into suspend mode (at least the USB state machine part of the controller) you simply have to disconnect the USB data lines from the device. The required Pull-Up resistor on D- will hold the upstream port in IDLE state. Putting the uPSD into power down state after detecting the suspended USB state should get the power consumption down to the required limits. The most difficult part will be to get the device out of suspended state. Regarding to the USB spec any non idle condition on the bus has to take the device out of suspended state within 20 ms. I know that this was not a full solution to your problem. But maybe it helps a step further.