Our customer ran into issue that this USBDCD module doesn’t work correctly at very low/dead battery level, especially when the battery is disconnected (the module sometimes reported the Wall Charger as USB Host). And the app note mentions that “this module assumes that the battery is good”. We use this module to detect different type of Charger (either Wall of Host) to configure different charging current to the battery.
Please see attached schematics and snippets of the K21 refererence manual(deadbattery.rtf) for reference.
Please see snippets of the K21 refererence manual(deadbattery.rtf) and the attachment (sheet2) for schematic, related to VBUS IN of 100mA/500mA.
FW is programed with this sequence:
1) Start with 100mA.
2) Check for VBUS, if VBUS connected, use USB Charger Detect to figure out whether the device is connected to USB Host or USB charger.
3) If the connection is USB Charger, bump the current charge to 500mA.
4) If the connection is USB Host, Issue the command to the USB controller to pullup the USB D+ line and Enable test Application (USB interface).
How is the battery level affect the USBDCD?