System Controller Suspend Mode Exit Induced VDD Surge Current

SmartFusion2 and IGLOO2 devices support system controller suspend mode for safety critical applications. Customers using this feature can force the system controller to exit suspend mode to support system controller features including device reprogramming. Exiting suspend mode is accomplished by driving the JTAG TRSTn pin high. Exiting the device from system controller suspend mode, after device is fully operational, temporarily disables the FPGA core which results in a current surge on VDD. This surge current is for a very short duration and is normally handled by bulk decoupling capacitors on the VDD power plane in a typical system. The magnitude of this surge current is similar to the surge resulting from a DEVRST_N assertion (Table 1).

The surge current can be kept within acceptable limits by adhering to VDD decoupling capacitors requirements per Microchip-recommended board design guidelines as shown in Table 2.