10.1.5.2.1 Output Driver AC Characteristics
The timing definitions necessary to specify the maximum operating frequency of an output driver are given in the following figure.
T: Period of the digital output signal
f = 1 / T: Frequency of the digital output signal
tHIGH: Time during which the output waveform is greater than VDD / 2
tLOW = T - tHIGH: Time during which the output waveform is less than VDD / 2
d = tHIGH / T: Output waveform duty cycle
VO: Output waveform amplitude
- tR < 0.75 / fMAX and tF < 0.75 / fMAX
- d: the duty cycle of the output waveform is between 45% and 55%
- VO: the output waveform amplitude is greater than 95% VDD
The fMAX parameter indicates the speed limit of an output driver across various operating conditions: supply voltage range, load capacitance, drive strength and slewrate programming. The effective maximum output frequency of a specific output line may be limited by the peripheral that drives this line.
- Output load: 10 pF capacitor to ground
- Two VDD ranges:
- 1.7V < VDD < 1.9V
- 3.0V < VDD < 3.6V
- Two Drive settings: 0 and 1
- Two Slewrate settings for the GPIO type: 0 and 1. The DDRIO drivers do not have slewrate settings and rather use an autocalibration setting. See DDR/SDR I/O Calibration.
For the GPIO drivers, the table below gives the recommended Drive and Slewrate settings depending on the output switching frequency and the two commonly used VDD ranges (1.8V and 3.3V). Other settings are possible but they may lead to excessively fast rise and fall times (tR, tF), with a potentially negative impact on the electromagnetic emissions of the application.
For the DDRIO drivers, it is recommended to use Drive = 0 if the VDD range is 3.0V to 3.6V, and Drive = 1 if the VDD range is 1.7V to 1.9V.
| VDD Range | Low-speed fGPIO ≤ 50 MHz(1) | High-speed 50 MHz ≤ fGPIO ≤ 150 MHz(1) |
|---|---|---|
| 1.7V – 1.9V | Drive = 1, Slewrate = 1 | Drive = 1, Slewrate = 0 |
| 3.0V – 3.6V | Drive = 0, Slewrate = 1 | Drive = 0, Slewrate = 0 |
- This is an indicative value. See tables Output Driver AC Characteristics (1.7V < VDD < 1.9V) and Output Driver AC Characteristics (3.0V < VDD < 3.6V) for accurate maximum frequency specifications.
| Symbol | Parameter | I/O Type | Conditions | Min | Max | Unit |
|---|---|---|---|---|---|---|
| tR or tF | Rise or fall time(1)(4) | Any | CL = 10 pF | – | – | – |
| GPIO | Drive = 0, Slewrate = 0 | 0.9 | 4.0 | ns | ||
| Drive = 1, Slewrate = 0 | 0.8 | 2.8 | ns | |||
| Drive = 0, Slewrate = 1 | 3.0 | 12.0 | ns | |||
| Drive = 1, Slewrate = 1 | 1.6 | 5.6 | ns | |||
| DDRIO | Drive = 0 | 1.2 | 3.1 | ns | ||
| Drive = 1 | 1.0 | 2.6 | ns | |||
| fMAX | Maximum frequency(2)(3)(4) | Any | CL = 10 pF | – | – | – |
| GPIO | Drive = 0, Slewrate = 0 | 90 | – | MHz | ||
| Drive = 1, Slewrate = 0 | 130 | – | MHz | |||
| Drive = 0, Slewrate = 1 | 25 | – | MHz | |||
| Drive = 1, Slewrate = 1 | 50 | – | MHz | |||
| DDRIO | Drive = 0 | 90 | – | MHz | ||
| Drive = 1 | 100 | – | MHz |
- Measured between VO = 10% VDD and VO= 90% VDD
- fMAX = 0.75 / (tR+tF). Frequency numbers are rounded for legibility.
- fMAX may be limited by the peripheral that drives the I/O line.
- Simulation data
| Symbol | Parameter | I/O Type | Conditions | Min | Max | Unit |
|---|---|---|---|---|---|---|
| tR or tF | Rise or fall time(1)(4) | Any | CL = 10 pF | – | – | – |
| GPIO | Drive = 0, Slewrate = 0 | 0.9 | 2.0 | ns | ||
| Drive = 1, Slewrate = 0 | 0.8 | 1.8 | ns | |||
| Drive = 0, Slewrate = 1 | 3.0 | 6.6 | ns | |||
| Drive = 1, Slewrate = 1 | 1.6 | 3.3 | ns | |||
| DDRIO | Drive = 0 | 0.9 | 2.0 | ns | ||
| Drive = 1 | 0.8 | 1.7 | ns | |||
| fMAX | Maximum frequency(2)(3)(4) | Any | CL = 10 pF | – | – | – |
| GPIO | Drive = 0, Slewrate = 0 | 150 | – | MHz | ||
| Drive = 1, Slewrate = 0 | 170 | – | MHz | |||
| Drive = 0, Slewrate = 1 | 50 | – | MHz | |||
| Drive = 1, Slewrate = 1 | 75 | – | MHz | |||
| DDRIO | Drive = 0 | 140 | – | MHz | ||
| Drive = 1 | 160 | – | MHz |
- Measured between VO = 10% VDD and VO= 90% VDD
- fMAX = 0.75 / (tR+tF). Frequency numbers are rounded for legibility.
- fMAX may be limited by the peripheral that drives the I/O line.
- Simulation data