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L9638
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4 FUNCTIONAL DESCRIPTION
The L9638 is a monolithic bus driver designed to provide bidirectional serial communication in Local In-
terconnect Network (LIN).
In addition to the integrated physical layer (specified in LIN specification rev. 2.0), further control in- and
output functions simplify various system requirements like controlled power saving modes or additional
external wake up capability.
4.1 Operating modes
There are four possible modes of operation: normal, standby, sleep and short circuit. The transitions be-
tween the various operation modes are described in the diagram.
4.2 Standby mode
This mode is reached after power up the system or due to a received wake-up condition from sleep mode.
The device is able to receive at RxD, but could not transmit any data. This prevents the disturbance of the
LIN bus line due to a not correctly working µC. Entering the standby mode, the INH output will set to HIGH
by simultaneous switching off the internal pull down resistor to reduce the current consumption. This al-
lows the control of connected power supply devices.
Therefore for systems, that will be controlled only by the LIN bus line (particular ECUs, that works as slave
node) a power management can easy build up on that function. It is recommended to power up the sys-
tem before the communication will start, otherwise additional delay times have to be regarded.
Because of integrated filtering of external WUP input, the INH output can alternatively be used to simplify
a software filtering procedure to detect an external edge sensitive signal by connecting INH versus a se-
ries resistor to an interrupt capable input of the µC.
4.3 Normal mode
This mode can only be reached from standby or sleep mode by setting the EN input to HIGH. Transmis-
sion and receiving of data stream via the LIN line is possible. An integrated pull up resistor in series with
a diode at LIN provides either required recessive state (HIGH) as well as a protection against reverse pow-
er supply. In master node application, a LOW ohmic resistor in series with a diode has to be connected
externally between LIN and battery to allow the maximum transmission rate.
The receiver converts the battery supply related signal at LIN to a logic supply compatible output at RxD.
Integrated filter in addition with the supply voltage related threshold and hysteresis provide optimal noise
suppression.
The transmitter shifts the logic supply related data stream at TxD to battery level at LIN. A read back func-
tion is possible by evaluating the mirrored state from the LIN line at the output RxD.
4.4 Short circuit mode
The L9638 provides a special operation mode for shorted LIN bus lines to ground. In that case, the whole
LIN network is blocked. If the protocol handler in the µC detects a "time out" condition, that could be un-
ambiguously identified as a short to ground condition in the bus line, the whole LIN node could be discon-
nected from the network by setting EN input to LOW.
This will switch INH output from active HIGH to LOW. Additionally RxD output, that remains in the domi-
nant state and maybe block the µC will set to HIGH ohmic state.
The L9638 won't accept any transition at TxD. This short circuit mode will be stable until the dominant state
on LIN will be cleared. In that case, the device will switch to the sleep mode. According to that, the current
consumption of a blocked LIN network will be reduced to the resulting short circuit current in the LIN line.
Especially for sporadically happening shorts due to damaged cable isolation, the LIN network will be au-
tomatically reset. Therefore no special power up procedure is required.
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