SPI Maximum Clock Frequency

fmax = 1 / (tsetup + thold + tprop)

Quick answer

This calculator solves f_max = 1 / (t_setup + t_hold + t_prop) for Max Clock Frequency. With Setup Time 10 ns, Hold Time 22 ns, Propagation Delay 47 ns, the result is 12.66 MHz.

Calculator

Max Clock Frequency (MHz)
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Formula

f_max = 1 / (t_setup + t_hold + t_prop)

Description

The maximum SPI (or any synchronous interface) clock frequency is limited by the sum of timing requirements: setup time (how long data must be stable before the clock edge), hold time (how long data must be stable after the clock edge), and propagation delay (trace delay plus driver/receiver delays). The total of these determines the minimum clock period, and the maximum frequency is its reciprocal. In practice, additional margin should be added for jitter, crosstalk, and manufacturing variation.

Variables

  • f_max — Maximum achievable clock frequency (Hz)
  • t_setup — Setup time required by the receiver (s)
  • t_hold — Hold time required by the receiver (s)
  • t_prop — Total propagation delay, driver + PCB + receiver (s)

Practical Notes

SPI has no specified maximum frequency in the protocol itself — it is limited entirely by the device specifications and board design. Typical maximum SPI frequencies: microcontrollers 10-50 MHz, flash memory 50-133 MHz, high-speed ADCs up to 200 MHz. For long SPI buses, propagation delay dominates. A 10 cm trace adds about 600 ps delay. Always check the specific device datasheet for timing diagrams and minimum setup/hold requirements.

Symbols and units

Symbol Meaning Default unit Accepted units
fmax Max Clock Frequency MHz Hz, kHz, MHz, GHz
tsetup Setup Time ns ps, ns, µs, ms, s, min, h
thold Hold Time ns ps, ns, µs, ms, s, min, h
tprop Propagation Delay ns ps, ns, µs, ms, s, min, h

Step by step

  1. 1. What you know: Setup Time 10 ns, Hold Time 22 ns, Propagation Delay 47 ns
  2. 2. The relation: f_max = 1 / (t_setup + t_hold + t_prop)
  3. 3. Substitute: tsetup = 10 ns, thold = 22 ns, tprop = 47 ns
  4. 4. Result: Max Clock Frequency = 12.66 MHz

Worked examples

Minimum range

Given: Setup Time 100 ps, Hold Time 0.22 ns, Propagation Delay 0.47 ns

Result: Max Clock Frequency = 1.266 GHz

Low range

Given: Setup Time 1 ns, Hold Time 2.2 ns, Propagation Delay 4.7 ns

Result: Max Clock Frequency = 126.6 MHz

Typical

Given: Setup Time 10 ns, Hold Time 22 ns, Propagation Delay 47 ns

Result: Max Clock Frequency = 12.66 MHz

High range

Given: Setup Time 100 ns, Hold Time 0.22 µs, Propagation Delay 0.47 µs

Result: Max Clock Frequency = 1.266 MHz

Maximum range

Given: Setup Time 1 µs, Hold Time 2.2 µs, Propagation Delay 4.7 µs

Result: Max Clock Frequency = 126.6 kHz

How Max Clock Frequency changes with Setup Time

Setup Time (input) Max Clock Frequency (result)
1 ns 14.29 MHz
2.5 ns 13.99 MHz
5 ns 13.51 MHz
7.5 ns 13.07 MHz
10 ns 12.66 MHz
15 ns 11.9 MHz
20 ns 11.24 MHz
40 ns 9.174 MHz
70 ns 7.194 MHz
100 ns 5.917 MHz

The same result in other units

Unit Value
kHz 12660
MHz 12.66
GHz 0.01266

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Frequently asked questions

How do you calculate SPI Maximum Clock Frequency?

Use f_max = 1 / (t_setup + t_hold + t_prop). With Setup Time 10 ns, Hold Time 22 ns, Propagation Delay 47 ns, Max Clock Frequency works out to 12.66 MHz.

What is the formula for SPI Maximum Clock Frequency?

The formula is f_max = 1 / (t_setup + t_hold + t_prop). The maximum SPI (or any synchronous interface) clock frequency is limited by the sum of timing requirements: setup time (how long data must be stable before the clock edge), hold time (how long data must be stable after the clock edge), and propagation delay (trace delay plus driver/receiver delays).

What units does SPI Maximum Clock Frequency use?

Max Clock Frequency is shown in kHz, MHz, GHz. Values are held in SI base units internally, so you can mix prefixes without converting by hand.

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