ESD strick to OMAP-L137 w/ SDRAM

Hello,

I use OMAP-L137 with a external clock source and a 32-bit SDRAM. It seems that our system is susceptible to radiated noise during an ESD strike. L137 is uncontrolled during an ESD strike when the device uses the SDRAM. It's no problem except the SDRAM. Could you give me some advice? Do I also need the inpedance control on PCB for EMIFB?

Regards,
Kazu