1. Overview HW design and EMC problems in the praxis System architecture
Actuators
Power supply
Safety concept
Carrier board
Thermal management
Design process
EMC
Basics
Measurement
Design
Mersich András
GS-TC/ENG4-Bp
GS-TC/ENG4-Bp | 01/12/2010 | © Robert Bosch GmbH All rights reserved, also regarding any disposal, exploitation, reproduction, editing, distribution, as well as in the event of applications for industrial property rights.

2. System overview System architecture
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3. Actuators, exercise Actuators It’s all about actuators!!! Exercise:
Switch an actuator, that is supplied by “Vbatt”, on/off via “control”!
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4. Actuators, solutions Actuators Free-wheeling diode: Relay
High-side switch
Low-side switch
Free-wheeling diode:
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5. MOSFET vs. BJT Actuators MOSFET BJT Offset (I=0A) 0V UCEsat
High-side
Low-side
MOSFET BJT
Offset (I=0A) 0V UCEsat
Linearity RDSon nonlinear switch
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6. MOSFET gate driver Actuators
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7. P-channel vs. N-channel FET
Actuators
P-channel vs. N-channel FET
µN = 2…3 * µP
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8. Power supply considerations
Normal operating range: 9 – 16V -40 … +105°C)
Overvoltage: 18V 85°C, 1h)
Jump-start: 24V room temp., 1min)
Step-down DC/DC  Linear stabilizer
EMC noisy zero emission
Dissipation marginal relevant
Components coil simple components
Cost more expensive cheap
Application thorough design off-the-shelf
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9. Safety measures Safety concept Watch-dog
Monitoring internal state (power supply, clock, temperature)
Diagnosis (check weather outputs are what you think they are)
High-active signals, no pull-up
Actuators main relay
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10. Different carrier boards
PCB (FR4)
Flex-foil
LTCC (Low Temperature Co-fired Ceramic)
DBC (Direct Bonded Copper)
PCB LTCC
Temperature ~100°C ~150°C
Layer-R const. only top/bottom
Trans-layer C small bigger
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11. Thermal management - Basics
Over 50% of the electronic system failures are caused by elevated temperatures.
Solutions:
Decrease of component dissipation (design)
Optimised layout and advanced PCB solutions (layout, production)
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12. Heat transfer - Basics Thermal management Forms of heat transfer:
Radiation: emission of photons
Convection: heat transfer by gases or fluids
Conduction: dissipation via solid objects
Vertical: thermovia
Horizontal: copper foil / heat sink
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13. Thermal circuit equivalent
Thermal management
Thermal circuit equivalent
Components on cooling bank
Components without cooling
Rth,J-C depends on:
Component packaging
Rth,C-H depends on:
PCB properties
Layout
Rth,H-A depends on:
Housing dimensions
Air flow
Mounting
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14. Lowering Pdis Thermal management
Use low-consumption components on VDD5
Lowering CPU clock frequency!
Step-down converter???
FETs with low RDSon
FETs with low gate-charge, gate driver
Dissipation of freewheeling diodes (Shottky)
Multi-stage linear stabilizer
Reduce consumption
Reduce losses
Distribute dissipation
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15. Lowering Rth, C-H Thermal management
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16. Thermography Thermal management
Identify hot-spots than measure directly.
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17. Direct Bonded Copper - DBC
Thermal management
Direct Bonded Copper - DBC
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18. Special solutions Thermal management
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19. Design steps Design process Requirement analysis (US vs. JP mentality)
Safety concept
Mechanical design (housing, carrier board, …)
Circuit design (modular concept)
Worst-case analysis
Simulation
Design review FMEA – failure of each and every component DRBFM – modifications to an already available design
Test (initial operation, temperature, EMC, life-cycle, mechanical)
A/B/C-sample
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20. WCA example Design process
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21. EM sources Emission by Immunity against EMC basics Switching of
Mobile phone
Switching of
actuators
Transmission line
Digital
systems
ECUs
Radio stations
Immunity against
Emission by
Ignition
Electro motors
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22. Interference model Coupling Source Receiver EMC basics Ignition
Common battery line
Radio
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23. EMC categories EMC measurements Conducted – Radiated
Emission – Immunity CE RE CI RI
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24. Conducted Immunity (CI)
EMC measurements
Conducted Immunity (CI)
Supply lines: ISO Pulse
Sensor lines: CCC – Capacitive Coupling Clamp DCC – Direct Capacitive Coupling ICC – Inductive Coupling Clamp
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25. Emission, immunity EMC measurements
Measurements in anechoic chamber: LISN (CE) Antenna (RE, RI) Stripline (RE, RI) BCI (RI)
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26. Anechoic chamber EMC measurements
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27. Electrostatic Discharge (ESD)
EMC measurements
Electrostatic Discharge (ESD)
Air
Contact
discharge
HBM MM
CHD
model
Handling: discharge on pins and housing
Active ESD
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28. Critical mesh EMC design Step-down converter
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29. Ground concept, shielding
EMC design
Ground concept, shielding
Use different gnd paths: AGND (analog) DGND (digital) PGND (power)
Connect these together only in a single point!
PGND path similar to supply!
Shield HF signals (SPI, CLK)
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30. Bypass capacitors, grounding concept
EMC design
Bypass capacitors, grounding concept
Gnd
IHF XL XC
ESR
Signal
Via
Block-capacitor
Efficiency of capacitor will be limited by:
Impedance of wiring XL
Impedance of capacitor XC
Parasitic resistor ESR Impedances cause voltage drop  galvanic coupling
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31. Snubber structure EMC design
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32. Slope control, choosing the switching frequency
EMC design
Slope control, choosing the switching frequency
Switching frequency (fundamental frequency and harmonics):
9kHz, 18kHz, 27kHz, 36kHz, 45kHz
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33. Spread Spectrum Clocking (SSC)
EMC design
Spread Spectrum Clocking (SSC)
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