50.5.2.1 Output Driver AC Characteristics

The timing definitions necessary to specify the maximum operating frequency of an output driver are given in the figure below.

Figure 50-4. Timing Definitions of a Digital Output Signal

t: Period of the digital output signal

f = 1 / t: Frequency of the digital output signal

t_HIGH: Time during which the output waveform is greater than V_DD/2

t_LOW = t - t_HIGH: Time during which the output waveform is less than V_DD/2

d = t_HIGH / t: Output waveform duty cycle

In Output Driver AC Characteristics, Output Load = 10pF, 3V < VDD3V3 < 3.6V, the maximum operating frequency f_MAX guarantees that the driver’s output waveform fulfills the following characteristics :

t_R < 0.75 / f_MAX and t_F < 0.75 / f_MAX
d: the duty cycle of the output waveform is between 45% and 55%

The f_MAX parameter indicates the speed limit of an output driver across various operating conditions: supply voltage range, load capacitance, slew rate programming. The effective maximum output frequency of a specific output line may be limited by the peripheral that drives this line.

The table below gives the AC output characteristics of the output drivers in the following conditions:

Output load: 10pF at the pin
VDD3V3 range: 3V < VDD < 3.6V
Four slew rate settings programmable in the PIO Controller user interface

Table 50-11. Output Driver AC Characteristics, Output Load = 10pF, 3V < VDD3V3 < 3.6V
Symbol	Parameter	I/O Type	Conditions			Unit
Symbol	Parameter	I/O Type	Slew Rate	Min	Max	Unit
t_R	Rise time ^{(2, 3)}	PIOA/B/C/D IOs	Fast	1.76	3.1	ns
			Medium Fast	4.1	9.5
			Medium	6.3	14
			Slow	8.6	19.6
t_F	Fall time^{(2, 3)}	PIOA/B/C/D IOs	Fast	1.88	3.5	ns
			Medium Fast	4.9	10
			Medium	7.6	15.2
			Slow	10.3	20.8
f_MAX	Maximum frequency^{(1, 2, 3)}	PIOA/B/C/D IOs	Fast	–	65	MHz
			Medium Fast	–	20
			Medium	–	15
			Slow	–	10

Note:

f_MAX may be limited by the peripheral that drives the I/O line.
Measured between 10% and 90%.
Simulation data.