FUNCTIONAL DESCRIPTION
INTRODUCTION
FUNCTIONAL DESCRIPTION
INTRODUCTION
The 33661 is a Physical Layer component dedicated to
automotive LIN sub-bus applications.
performance, and safe behavior in case of LIN bus short-to-
ground or LIN bus leakage during low power mode.
The 33661 features include slew rate selection for
optimized operation at 10 kbps and 20 kbps, fast baud rate
for test and programming modes, excellent radiated emission
Digital inputs are 5.0 V and 3.3 V compatible without any
external component required.
The INH output may be used to control an external voltage
regulator or to drive a LIN bus pullup resistor.
FUNCTIONAL PIN DESCRIPTION
POWER SUPPLY PIN (VSUP)
DATA INPUT PIN (TXD)
The VSUP supply pin is the power supply pin for the
33661. The pin is connected to a battery through a serial
diode for reverse battery protection. The DC operating
voltage is from 7.0 V to 27 V. This pin sustains standard
automotive voltage conditions such as 27 V DC during jump-
start conditions and 40 V during load dump. Supply current in
the Sleep mode is typically 8.0 µA.
The TXD input pin is the MCU interface to control the state
of the LIN output. When TXD is LOW, LIN output is LOW;
when TXD is HIGH, the LIN output transistor is turned OFF.
The threshold is 3.3 V and 5.0 V compatible. The baud rate
selection (normal or Slow mode) is done at device wake-up
by the state of the TXD pin prior to a HIGH level at the EN pin
(see Figures 7 through 12, pp. 10–11).
DATA OUTPUT PIN (RXD)
GROUND PIN (GND)
The RXD output pin is the MCU interface, which reports
the state of the LIN bus voltage. LIN HIGH (recessive) is
reported by a high voltage on RXD; LIN LOW (dominant) is
reported by a low voltage on RXD. The RXD output structure
is a CMOS-type push-pull output stage.
In case of a ground disconnection at the module level, the
33661 does not have significant current consumption on the
LIN bus pin when in the recessive state. (Less than 100 µA is
sourced from LIN bus pin, which creates 100 mV drop
voltage from the 1.0 kΩ LIN bus pullup resistor.)
The low level is fixed. The high level is dependant on the
EN voltage. If EN is set at 3.3 V, RXD VOH is 3.3 V. If EN is
set at 5.0 V, RXD VOH is 5.0 V.
LIN BUS PIN (LIN)
This I/O pin represents the single-wire bus transmitter and
receiver.
In the Sleep mode, RXD is high impedance. When a wake-
up event is recognized from WAKE pin or from the LIN bus
pin, RXD is pulled LOW to report the wake-up event. An
external pullup resistor may be needed.
Transmitter Characteristics
The LIN driver is a low-side MOSFET with internal
overcurrent thermal shutdown. An internal pullup resistor with
a serial diode structure is integrated so no external pullup
components are required for the application in a slave node.
An additional pullup resistor of 1.0 kΩ must be added when
the device is used in the master node.
ENABLE INPUT PIN (EN)
The EN input pin controls the operation mode of the
interface. If EN = 1, the interface is in Normal mode, with
transmission path from TXD to LIN and from LIN to RXD both
active. The threshold is 3.3 V and 5.0 V compatible. The high
level at EN defines the VOH at RXD. The Sleep mode is
entered by setting EN LOW while TXD is HIGH. Sleep mode
is active after the tSD filter time (see Figure 14, 11).
Voltage can go from -18 V to 40 V without current other
than the pullup resistance. The LIN pin exhibits no reverse
current from the LIN bus line to VSUP, even in the event of
GND shift or VPWR disconnection.
The transmitter has two slew rate selections: 20 kbps
(normal slew rate) and 10 kbps (slow slew rate). The slow
slew rate can be used to improve radiated emissions.
INHIBIT OUTPUT PIN (INH)
The INH output pin may have two main functions. It may
be used to control an external switchable voltage regulator
having an inhibit input. The high drive capability also allows it
to drive the bus external resistor in the master node
application. This is illustrated in Figures 18 and 19, 17.
Receiver Characteristics
The receiver thresholds are ratiometric with the device
supply pin.
In Sleep mode, INH is turned OFF. If a voltage regulator
inhibit input is connected to INH, the regulator will be
disabled. If the master node pullup resistor is connected to
INH, the pullup resistor will be disabled from the LIN bus.
33661
Analog Integrated Circuit Device Data
Freescale Semiconductor
12
FREESCALE [ Freescale ]
