FlexRay Standard Transceiver
1 General Description
This document is subjected to change without notice.
The AS8221 is a high speed automotive bus driver fully conforming
to the FlexRay Electrical Physical Layer Specification V2.1 Rev B.
The AS8221 operates as a bi-directional interface between the
FlexRay Communication Controller and the twisted-pair copper
The AS8221 provides an optimized host controller interface
consisting of three low-active pins. The Enable (EN) and Standby
(STBN) input pins for mode handling by the microcontroller and the
Error (ERRN) out pin where system, chip failures or status
information are signalled to the microcontroller. Signalling logic high
on the Enable and Standby pin the device will enter NORMAL mode
in case no fault condition is given and in this mode the device is fully
operational meaning FlexRay communication is possible.
Additionally a RECEIVE-0NLY mode is implemented, which can be
accessed by the microcontroller where only FlexRay streams can be
received in order to avoid unwanted disturbances on the FlexRay
bus while listening to the bus traffic. In the low-power modes
(STANDBY and SLEEP mode) very low power consumption is
In case of undervoltage at one of the supply voltages (VBAT, VCC,
and VIO) the device will change its mode to a low-power mode
(either STANDBY or SLEEP mode) and the device will signal an
error accordingly. In case of low voltage is detected on both VBAT
and VCC the device will enter the POWER-OFF mode, where no
operation is possible. A safe mechanism from the low-power modes
to POWER-OFF mode and vice versa is implemented ensuring that
no deadlock can happen during the startup phase.
Ensuring application in safety critical environments a two wire bus-
guardian interface is implemented where additional monitoring
circuitries on the electronic-control-unit can activate and deactivate
the transmitter and additionally on the receive enable output (RxEN)
in low-power modes the wake conditions and in normal power
modes the received FlexRay streams can be monitored.
A thermal sensor circuit with an integral shutdown mechanism
prevents damage to the device in extreme temperature conditions.
The symmetrical transient control for the high- and low-side driver for
both the bus-minus (BM) and bus-plus (BP) line allows an ideal
balance of communications over different network topologies, with
excellent EMC performance.
2 Key Features
Compliant with FlexRay Electrical Physical Layer Specification
V2.1 Rev. B
Data transfer up to 10 Mbps
Excellent EMC performance. High common mode range ensure
Interface for Bus Guardian or supervision circuits
Automatic thermal shutdown protection
Supports 12V and 24V systems with very low sleep current
Integrated power management system
- Two inhibit pins for external voltage supply control
- Local wake-up input
- Remote wake-up capability via FlexRay bus in low-power
Supports 2.5, 3, 3.3, 5 V microcontrollers, automatic adaptation
to digital interface levels
Protection against damage due to short circuit conditions on the
bus (positive and negative battery voltage)
Operating temperature range -40ºC to +125ºC
Lead-free SSOP20 package
The AS8221 FlexRay Standard Transceiver is best fitting for
automotive FlexRay nodes where bus wake-up and voltage regulator
control for voltage supplies is needed.
The device addresses all ECUs connected to the permanent battery
supply (clamp 30). The AS8221 can be used as only ECU wake-up
component with very low power consumption in SLEEP mode.
1 - 43