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

4.7 nFAULT and FG pin

nFAULT, FG are digital output pins with IO structure as shown in Figure 4-3. These are open drain pins that need a pull-up resistor for proper operation. MCF831xC provides an option of internal pull-up resistor to AVDD that can be enabled by setting PULLUP_ENABLE to 1b. If a logic level (MCU IO power rail) other than 3.3V is needed for FG, nFAULT signals, then PULLUP_ENABLE need to be set to 0b and an external pull-up resistor to required voltage level need to be connected.

nFAULT and FG IO Equivalent Circuit Figure 4-7 nFAULT and FG IO Equivalent Circuit

When used, these pins need to be pulled up (either internally or externally) to required logic level.

When unused, these pins need to be left floating.

Note: Internal pull-up resistors for FG, nFAULT are available only in MCF831xC and not in MCF831xA. In MCF831xA, FG needs an external pull-up to AVDD (even when unused) for normal operation.
Table 4-3 MCF831xC IO Pin Recommendations
Pin Recommendation When Used Recommendation When Unused
SPEED
BRAKE, DIR, DRVOFF
EXT_WD, EXT_CLK
SCL, SDA
nFAULT, FG
DACOUT