If there is no activity on the USB lines (D+ and D-) for 3ms the USB LS and FS devices are suspended by the host.
If the device is bus powered device
Once the host is set to standby mode the device will not receive any power. To avoid this uncheck the box that is checked in the attachment shown "USB_power_management". Identify the root hub to which the device is connected and uncheck the box as mentioned above in the power management section of device manager. In this case if the device is a low speed USB device the hos keeps on sending "Keep Alive packets" which will not allow the device to go to suspend.
To avoid the above things
1. make the device as self powered device
2. Put the PC to standby
A firmware similar to the one attached may be developed. The functionality of the firmware is as follows
1. If there is no activity on D+,D- lines for 3ms the device goes to suspend mode(low power mode). Put the host to standby and measure the current consumption during this time.
2. Wake up the host and see that the USB activity is resumed.