MC33989PEG Freescale Semiconductor, MC33989PEG Datasheet - Page 49

• Manufacturer Part Number: MC33989PEG
• Description: SBC-HS
• Manufacturer: Freescale Semiconductor

TX and RX Pins
V2. When V2 is set at 5.0 V, and CAN is in normal mode, RX reports the bus status. When V2 is off RX is low.
Normal Mode and Slew Rate Selection
dominant to recessive transitions. This affect is also the delay time from the TX pin to the bus, and from the bus to RX. The loop
time is thus affected by the slew rate selection.
Minimum Baud Rate
behavior: once TX permanent dominant is detected the CAN driver is off.
Termination
Analog Integrated Circuit Device Data
Freescale Semiconductor
If “CANH minus CANL” is above the threshold, the bus is dominant and RX is set low. This is illustrated in
The TX pin has an internal pull up to V2. The state of TX depends on the V2 status. RX is a push-pull structure, supplied by
The slew rate selection is done via the SPI. Four slew rates are available. The slew rate affects the recessive to dominant and
The following figure is an illustration of the slew rate on CANH, CANL, TX and RX.
As TX permanent dominant is detected after TDOUT (min 200 µs), a minimum Baud rate is required in order to get good
The maximum number of consecutive dominant bits in a frame is 12 (6 bits of active error flag and its echo error flag).
200 µs/12 = 16.7 µs. The minimum Baud rate is 1/6.7 µs = 60 KBaud.
The MC33989 supports the two main types of bus termination:
• Differential termination resistors between CANH and CANL lines.
• Split termination concept, with mid point of the differential termination connected to gnd through a capacitor.
CAN signal with slew rate 0 selected
Figure 35. CAN Driver Operation in Normal Mode
Figure 36. Normal Mode and Slew Rate Selection
2.5V
2.5V
R=60 ohms, CL = CH = 100pF
CANH
TX
CANL
RX
CANH-CANL
CANH-DOM
CANL-DOM
CANH-REC
CANL-REC
CAN signal with slew rate 3 selected
SUPPLEMENTAL APPLICATION NOTES
TYPICAL APPLICATIONS
Figure
35.
33989
49