i am designing a pcb in arm lpc1768 in that i am using usb b type connectors db9 female connectors my doubt is that the shield part that is the metal part of usb and db9 should be grounded directly to supply ground are i must use any series capacitor.
kindly help
USB specification says "From Host to Peripheral the shield should be connected from connector to cable in 360 fashion". Shield to GND connection is left to the designer.
Best way is to contact your manufacturer or use manufacturer recommended things.. NXP used Ferrite beads to connect shiled to GND in Host systems (i. e on Connector A side). RC filter on Peripheral side (USB-B connector side).
References are IAR_LPC1768_Eval_Board_Schematic (Host side)" , "Keil_LPC1768_Eval_Board_Schematic(Peripheral side)"....