Spartan-3 FPGA Family: Functional Description
DS099 (v3.1) June 27, 2013
Product Specification
54
Additional Configuration Details
Additional details about the Spartan-3 FPGA configuration architecture and command set are available in
UG332: Spartan-3
Generation Configuration User Guide and in application note
XAPP452: Spartan-3 Advanced Configuration Architecture.
Powering Spartan-3 FPGAs
Voltage Regulators
Various power supply manufacturers offer complete power solutions for Xilinx FPGAs, including some with integrated
multi-rail regulators specifically designed for Spartan-3 FPGAs. The
Xilinx Power Corner web page provides links to vendor
solution guides as well as Xilinx power estimation and analysis tools.
Power Distribution System (PDS) Design and Bypass/Decoupling Capacitors
Good power distribution system (PDS) design is important for all FPGA designs, especially for high-performance
applications. Proper design results in better overall performance, lower clock and DCM jitter, and a generally more robust
system. Before designing the printed circuit board (PCB) for the FPGA design, review application note
XAPP623: Power
Distribution System (PDS) Design: Using Bypass/Decoupling Capacitors.
Power-On Behavior
Spartan-3 FPGAs have a built-in Power-On Reset (POR) circuit that monitors the three power rails required to successfully
configure the FPGA. At power-up, the POR circuit holds the FPGA in a reset state until the VCCINT, VCCAUX, and VCCO Bank
4 supplies reach their respective input threshold levels (see
Table 29, page 59). After all three supplies reach their respective
threshold, the POR reset is released and the FPGA begins its configuration process.
Because the three supply inputs must be valid to release the POR reset and can be supplied in any order, there are no
specific voltage sequencing requirements. However, applying the FPGA’s VCCAUX supply before the VCCINT supply uses the
least ICCINT current.
Once all three supplies are valid, the minimum current required to power-on the FPGA is equal to the worst-case quiescent
current, as specified in
Table 34, page 62. Spartan-3 FPGAs do not require Power-On Surge (POS) current to successfully
configure.
Surplus ICCINT if VCCINT Applied before VCCAUX
If the VCCINT supply is applied before the VCCAUX supply, the FPGA may draw a surplus ICCINT current in addition to the
ICCINT quiescent current levels specified in Table 34. The momentary additional ICCINT surplus current might be a few hundred milliamperes under nominal conditions, significantly less than the instantaneous current consumed by the bypass
capacitors at power-on. However, the surplus current immediately disappears when the VCCAUX supply is applied, and, in
response, the FPGA’s ICCINT quiescent current demand drops to the levels specified in Table 34. The FPGA does not use nor does it require the surplus current to successfully power-on and configure. If applying VCCINT- before VCCAUX, ensure
that the regulator does not have a foldback feature that could inadvertently shut down in the presence of the surplus current.
Maximum Allowed VCCINT Ramp Rate on Early Devices, if VVCCINTSupply is Last in Sequence
All devices with a mask revision code ‘E’ or later do not have a VCCINT ramp rate requirement. See Mask and Fab Revisions, Early Spartan-3 FPGAs were produced at a 200 mm wafer production facility and are identified by a fabrication/process
VCCINT ramp rate requirement if and only if VCCINT is the last supply to ramp, after the VCCAUX and VCCO Bank 4 supplies.
Minimum Allowed VCCO Ramp Rate on Early Devices
Devices shipped since 2006 essentially have no VCCO ramp rate limits, shown in Table 30, page 60. Similarly, all devices