SLLA643 August   2024 MCF8315C , MCF8315C-Q1 , MCF8316C-Q1

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Power Pin Design Recommendations
    1. 2.1 VM
    2. 2.2 Charge Pump: CPH, CPL, CP
    3. 2.3 Buck Converter: FB_BK, SW_BK, GND_BK
    4. 2.4 AVDD
    5. 2.5 DVDD
    6. 2.6 PGND, AGND, DGND
    7. 2.7 Thermal Pad
  6. 3MCF831xC Buck Regulator Overview
    1. 3.1 Buck Regulator Mode of Operation
    2. 3.2 Buck Regulator Output Voltage
    3. 3.3 Buck Power Sequencing
    4. 3.4 Buck Inductor Selection
    5. 3.5 MCF831xC Operation Without Buck Regulator
  7. 4MCF831xC IO Pins Design Recommendations
    1. 4.1 SPEED Pin
    2. 4.2 BRAKE, DIR, DRVOFF pins
    3. 4.3 EXT_CLK, EXT_WD
    4. 4.4 ALARM
    5. 4.5 DACOUT1, DACOUT2
    6. 4.6 SDA, SCL
    7. 4.7 nFAULT and FG pin
  8. 5MCF831xC PCB Schematic and Layout Recommendations
    1. 5.1 Single Ground Plane
    2. 5.2 Single Ground with AVDD Shorted to FB_BK
    3. 5.3 Two Grounds
  9. 6Summary
  10. 7References

4.6 SDA, SCL

SDA, SCL are digital input (SDA has dual function of output also) pins with IO structure as shown in Figure 4-6. The input path has a buffer with hysteresis followed by a 50ns glitch filter to suppress noise.

SCL, SDA IO Equivalent Circuit Figure 4-6 SCL, SDA IO Equivalent Circuit

The output path is an open drain that needs an external pull-up resistor to AVDD for I2C communication. The pull-down drive strength (Slew rate) can be configured using SLEW_RATE_I2C_PINS to optimize between timing requirements, EMI and cross talk. Default pull-down drive strength is 4.8mA and this can drive up to 400pF bus capacitance. If system has a lower bus capacitance, a lower pull-down drive strength can be selected. Pull-up resistor depends the I2C clock frequency and bus capacitance [2].

Table 4-2 I2C Pins Drive Strength
SLEW_RATE_I2C_PINS Pull-Down Drive Strength (mA)
00b 4.8
01b 3.9
10b 1.86
11b 30.8

When used, these pins need to be directly connected to the external MCU with an external pull-up resistor to AVDD.

When unused, these pins need to be left floating.