Reset Controller
UG0331 User Guide Revision 15.0
647
21.2.2
VDD Power-Up to Functional Time
The core supply voltage VDD is connected to the appropriate source and VDD is monitored by the
power-on reset circuitry to check if it reaches the minimum threshold value and initiates the system
controller to release the device from reset. This scenario provides power-up to functional time data when
only the FPGA fabric and the FPGA I/O are used with all supplies ramped up except VDD, which is
ramped up at the last. The required power-on reset delay is set using the Libero SoC tool.
The design uses a fabric counter that starts to operate when POWER_ON_RESET_N is deasserted. The
LSB of the counter output is connected to a latch and given to an output buffer, which is then connected
to an input buffer of the fabric using external loopback. This input is used for stopping the counter from
incrementing. The counter stops as soon as the counter's LSB bit transitions to logic HIGH. The power-
up to functional time is measured from the VDD supply ramp to transition of the fabric buffer output.
The following figure shows the characterization test design setup used for obtaining the VDD power-up to
functional timing values.
Note:
In this test design setup, PLL is not used and instead clock for the fabric is directly fed from the RC
oscillator. If PLL is used in the design then the Power-up to functional time will get impacted because of
PLL lock assertion time.
Figure 280 •
VDD Power-up to Functional Time Design Setup
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