SENT “New sensor interface” Allows data-transmission at low cost Petr Kamenicky, Geert Vandensande, Philippe Quarmeau ON Semiconductor Europe What is SENT? Challenges: !!! -Sensor-interface: -Low cost: ON Semi’s Receiver Transmitter CPU Chip VSUPPL - Digital datatransmission at 30 kbits/s Wiring RPULL-UP Rf RTau1 Timer Cf R Input CTau1 Cinput - Low-cost: No receiver, Integrated transmitter -Receiver: - Only passive components at receiver-side - Uni-directional: only from sensor to ECU - Digital input at CPU - Point-to-point: no bus - Clock-drift* error < 0,05us *Clock-drift = variation of nibble length over a message-period at a 3 µs clock tick. - J2716 SAE-standard -Automotive requirements: -SENT: Single Edge Nibble Transmission for Automotive applications - Wiring problems: - Data transmitted as nibbles (4 bits). Maximum of 6 nibbles per message. - Automotive transients: - Wiring short to supply ( reverse battery) - Wiring short to ground ( output-prot.) - Nibble Value (4-bit): 12 13 14 . . . 27 0 1 15 2 ... 27 ticks 17 ticks 22 ticks 14 ticks 20 ticks 12 ticks CRC checksum (13 value) - Pause Pulse or Next Cal. & Synchr. Nibble 6 (0 value) Nibble 5 (8 value) Nibble 4 (2 value) Nibble 3 (10 value) Nibble 2 (5 value) Nibble 1 (15 value) Status & Comm. (0 value) Calibration & Synchronization 12 ticks 25 ticks -Calibration or synchronization pulse: Fixed length for synchronization of receiver (56 clock-ticks). - Status & Communication Nibble defines message format: - Signal freq. content: - Min. pulse-width: 36us – 20% = 29us Corresponding freq. ~ 35 kHz - Falling edge: from 3.8V to 1.1V <6.5us Corresponding freq. ~ 66 kHz Absorber-lined chamber limits: CISPR 25 <21dBµV 150kHz .. 300kHz Implementation: Signal shaping to suppress higher harmonics without impacting: - Pulse-shape - Timing requirements - Signal amplitude For supply-line and signal-line. No Serial Protocol Short Serial Protocol Enhanced Serial Protocol - Checksum-Nibble: 4 bit CRC - Pause-Pulse: to fill-up message to a fixed length (less than 1ms). Goal of SENT? -Low cost -Digital precision: advantage over analog or semi-analog PWM int. -Higher baudrate than LIN. Measurement results: System ESD (8kV contact, 15kV air: C = 330pF, R = 2kΩ) - Radiated Emission, Absorber-lined Chamber -EMC-requirements: - Time measured between falling edges (single edges) - Frame-format: 56 ticks Emission requirement: - ESD-immunity: - Clock Ticks: 0 -Meeting all automotive requirements. - In production as part of sensor-ASIC. -Timing requirements: - 3 wires: 5V, GND, SENT SENT IP: Pegel [dBµV/m] Susceptibility: conducted and radiated class A under 200mA BCI; 4W PDI to supply or SENT wire; 200V/m TEM cell 60 Emission: conducted and radiated 30 50 40 20 Contribution of ON Semiconductor: 10 0 -Participation to SAE- SENT task-force leaded by GM: - Transmitter-def.: push-pull driver. Proposal for external components: Transmitter Receiver Wiring Rsent120 Ω Csent 6.8 nF 560 Ω Cs_emc 6.8 nF 51 kΩ 300k 600k 1M 2M Frequenz [Hz] 3M 5M 10M 30M blue: peak detector green: average detector References: 4.7 kΩ Timer 220 pF Input 2.2 nF 100k CPU Chip 5V Sensor with SENT -10 -SAE J2716 – Information Report FEB2008 Acknowledgements: - Check feasibility of emission requirements at maximum baudrate: 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 Tfall < Trise < 6.5us 18us Tstable > 6us Tstable > 6us 0.5 0.0 000.0E+0 5.0E-6 10.0E-6 15.0E-6 20.0E-6 25.0E-6 30.0E-6 35.0E-6 40.0E-6 - Petr Kamenicky + Brno design team for development of SENT-IP and integration in Sensor-ASIC. - Manu Meyers from Belgium design team for contribution in the early stage of IP-development. - Geert Vandensande from Belgium for support during the SENT feasibility and contribution in the SAE J2716 task force. - Philippe Quarmeau from France for review and presenting this poster at SENSACT 3