I currently work with two FPGAs, Microchip/Microsemi ProASIC3E and AMD/Xilinx Zynq-7020.

In their datasheets, the recommended minimum operating frequency is 1.5 MHz for the A3PE ProASIC3E chip. The minimum frequency for the Zynq chip is not mentioned.

While I can understand the limit of maximum speed the FPGA can clock at, as there are timing issues and stray capacitance issues at overclocked speeds, I do not understand the requirement for minimum clock speed for FPGAs.

Would such FPGAs work if they are clocked at, say, a few hundred kilohertz?

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    \$\begingroup\$ Might be due to PLLs or internal charge pumps. You’d have to contact the manufacturer to get the lowdown methinks. \$\endgroup\$
    – Kartman
    Commented Apr 6, 2022 at 7:17
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    \$\begingroup\$ Note that you can always use a higher-frequency input clock and then divide it to any arbitrary low speed to clock internal logic. There is no minimum frequency for the internal primitives (LUTs, etc.). But as already commented the PLL will have minimum frequency requirements. \$\endgroup\$
    – TypeIA
    Commented Apr 6, 2022 at 7:26

1 Answer 1


In their datasheets, the recommended minimum operating frequency is 1.5MHz for the A3PE ProASIC3E chip.

Actually, it's fIN_CCC that's specified as 1.5 MHz min in the datasheet for ProASIC3E Flash Family FPGAs.

That's the Clock Conditioning Circuit (CCC) input frequency. A ProASIC3E CCC contains a PLL and other clock circuitry. PLLs have a frequency range that they can lock to, which here is 1.5 MHz to 350 MHz.

The standard clocked logic circuits within FPGAs/CPLDs are registers (flip-flops/latches) and block RAM. There's no IC minimum input frequency for registers, just a rise/fall time requirement. Block RAMs typically don't have a minimum either.

Some FPGAs contain 'hard IP' blocks: dedicated circuitry rather than programmable logic. Some of these, such as internal ADCs, have required clock frequency ranges. Others, such as SPI or some CPUs, again have no minimum clock frequency.

  • \$\begingroup\$ Thanks for the accurate answer. This was what I was looking for. Does the microblaze hard IP also have a required clock frequency range? \$\endgroup\$ Commented Apr 7, 2022 at 5:32
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    \$\begingroup\$ @abunickabhi, you're welcome. Microblaze is a soft IP processor, there is no hard version of it. It has no minimum frequency that I know of. \$\endgroup\$
    – TonyM
    Commented Apr 7, 2022 at 8:36

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