F l e x R a y S t a n d a r d Tr a n s c e i v e r
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
wiring.
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
achieved.
In case of undervoltage at one of the supply voltages (V
BAT
, V
CC
,
and V
IO
) 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 V
BAT
and V
CC
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
excellent EMI
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
modes
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
3 Applications
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.
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AS8221
Data Sheet - A p p l i c a t i o n s
Figure 1. AS8221 FlexRay Standard Transceiver Block Diagram
VIO
AS8221
Bus
Failure
Detector
STBN
EN
ERRN
VIO
Host
Controller Interface
RxD
TxD
TxEN
Communication
Controller
Interface
BP
Internal Logic (IL)
Transmitter
BM
BGE
RxEN
VBAT
VBAT
Bus
Guardian
Interface
Receiver
INH1
INH2
Power Supply
Interface
Wake-Up
Detector
VBAT
VIO
VCC
GND
WAKE
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AS8221
Data Sheet - C o n t e n t s
Contents
1 General Description.................................................................................................................................................................... 1
2 Key Features ............................................................................................................................................................................... 1
5 Absolute Maximum Ratings....................................................................................................................................................... 7
NORMAL Mode .......................................................................................................................................................................... 16
8.6 Power On/Off Events.............................................................................................................................................................................. 17
8.7.2 Local Wake-Up Event ................................................................................................................................................................. 18
8.8 System Description................................................................................................................................................................................. 19
8.9.2 State Transitions due to Under Voltage Detection...................................................................................................................... 20
8.9.3 State Transitions due to Voltage Recovery Detection ................................................................................................................ 20
8.11 Loss of ground ...................................................................................................................................................................................... 23
Bus Error (BUSERR) ................................................................................................................................................................ 23
BP Open Line (BP_OL) ............................................................................................................................................................ 23
BM Open Line (BM_OL) ........................................................................................................................................................... 23
BP Short Circuit to GND (BP_GND) ......................................................................................................................................... 24
BM Short Circuit to GND (BM_GND)........................................................................................................................................ 24
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AS8221
Data Sheet - C o n t e n t s
8.12.9 Short Circuit between BP and BM (BP_BM)............................................................................................................................. 24
8.12.10 Over Temperature (OT) .......................................................................................................................................................... 24
8.12.12 Error Flag (ERROR) ............................................................................................................................................................... 24
8.13 Status Flags Description....................................................................................................................................................................... 24
8.13.1 Local Wake Flag (LWAKE) ....................................................................................................................................................... 24
8.13.2 Remote Wake Flag (RWAKE) .................................................................................................................................................. 24
8.13.3 Power on Flag (PWON) ............................................................................................................................................................ 25
8.14 Error Flags and Status Flags Read-Out ............................................................................................................................................... 25
8.14.1 Error and Status Flag Bit Order ................................................................................................................................................ 25
8.15 Bus Driver............................................................................................................................................................................................. 26
8.15.1 Bus States ................................................................................................................................................................................ 26
8.18.1 Bus Activity and Idle Detection (only in NORMAL and RECEIVE-ONLY mode) ...................................................................... 30
8.18.2 Bus Data Detection (only in NORMAL and RECEIVE-ONLY mode)........................................................................................ 30
8.18.3 Receiver Test Signal................................................................................................................................................................. 32
8.19 Test Circuits .......................................................................................................................................................................................... 33
11 Ordering Information .............................................................................................................................................................. 43
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AS8221
Data Sheet - P i n A s s i g n m e n t s
4 Pin Assignments
Figure 2. Pin Assignments SSOP20 Package
INH2
INH1
EN
VIO
TxD
TxEN
RxD
BGE
STBN
Reserved
1
2
3
4
5
6
7
8
9
10
20
19
18
17
n.u
VCC
BP
BM
GND
WAKE
VBAT
ERRN
RxEN
n.u
AS8221
16
15
14
13
12
11
4.1 Pin Descriptions
Table 1. Pin Descriptions
Pin Name
INH2
INH1
EN
V
IO
TxD
TxEN
RxD
BGE
STBN
Reserved
Not used
RxEN
ERRN
V
BAT
WAKE
GND
BM
BP
V
CC
Not used
Pin Number
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
DO
DO
S
AIO
S
AIO
AIO
S
Digital Output.
Receive data enable output
Digital Output.
Error diagnosis output and wake status output
Supply Voltage.
Battery supply voltage
Analog Input.
Local wake-up input
Ground
Analog Input/Output.
Bus line Minus
Analog Input/Output.
Bus line Plus
Supply voltage.
Pin Type
AIO
AIO
DI_PD
S
DI_PD
DI_PU
DO
DI_PD
DI_PD
A/DIO_PD
Description
Analog Output.
Inhibit 2 output for switching external voltage regulator
Analog Output.
Inhibit 1 output for switching external voltage regulator
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