AN4218
Application note
Hardware design guideline
power supply and voltage measurement
Introduction
This document provides useful hints and suggestions about the implementation of the
STMicroelectronics 32-bit microcontroller devices in an automotive system. The main focus has been set
on the power supply concept and the connection to signals from different power domains.
Due to the harsh conditions in the automotive environment several precautions have to be taken into
account to ensure the robustness of the system. This is especially important when defining its power
supply concept.
This document shows test cases defined by car makers, which are intended to reproduce the system
behavior in the real automotive environment, it also shows good practices to cope with them as well as
bad practices and their influence on the system robustness.
September 2013
DocID024014 Rev 2
1/26
www.st.com
Contents
AN4218
Contents
1
2
System overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.1
Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.2
Car-battery power supply (VBAT) transients . . . . . . . . . . . . . . . . . . . . . . . 6
Example battery supply test pulses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.2.2
Power-up-reset requirements of the SPC microcontrollers . . . . . . . . . . . 8
Good practices of system power supply . . . . . . . . . . . . . . . . . . . . . . . 10
2.1
3
1.2.1
Microcontroller power supply reactions on VBAT transients . . . . . . . . . . 10
2.1.1
L99PM62GXP block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.1.2
Measurement setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.1.3
Measurement results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Application circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
3.1
Reference circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
3.2
Implementation suggestions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
3.2.1
Measurement of an permanently enabled power-supply (VMEASURE) 16
3.2.2
Bad practices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
3.2.3
Physical layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Appendix A Reference documents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
2/26
DocID024014 Rev 2
AN4218
List of tables
List of tables
Table 1.
Table 2.
Table 3.
Parameters sharp test pulse E11 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
VDD ramp specification (SPC560P34x, SPC560P40x – example only). . . . . . . . . . . . . . . . 9
Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
DocID024014 Rev 2
3/26
List of figures
AN4218
List of figures
Figure 1.
Figure 2.
Figure 3.
Figure 4.
Figure 5.
Figure 6.
Figure 7.
Figure 8.
Figure 9.
Figure 10.
Figure 11.
Figure 12.
Figure 13.
Figure 14.
Figure 15.
Figure 16.
Figure 17.
Figure 18.
Figure 19.
Figure 20.
Figure 21.
Figure 22.
Figure 23.
4/26
Microcontroller with power supply, drivers and physical layer . . . . . . . . . . . . . . . . . . . . . . . 5
Brown out . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Non strictly rising ramp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Slow ramp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Residual voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Test pulse E11 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
VDD ramp-up/ ramp-down (SPC560Bxx, SPC560Cxx, – example only) . . . . . . . . . . . . . . . 9
L99PM62GXP block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Measurement setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Engine cranking pulse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Measurement over the entire pulse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Zoom into the low voltage drop region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
VS voltage ramp up (0.5 V/min) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
VBAT voltage ramp down (0.5 V/min) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Reference circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Voltage divider . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
ISO transients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Negative ISO-pulse simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Protection and low-pass-filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Amplitude and phase over frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Backward current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Bad example circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
CAN-transceiver without reverse protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
DocID024014 Rev 2
AN4218
System overview
1
System overview
1.1
Overview
Figure 1 shows a system, consisting of a microcontroller, a system basis chip, a physical
layer transceiver and load drivers.
The System-Basis-Chip (SBC) generates the power-supply for the other devices in the
system and communicates via serial-parallel interface (SPI) with the microcontroller (SPCµC).
The physical layer transceiver (e.g. standalone CAN-transceiver) is supplied by the SBC
and transfers data from and to the microcontroller via logic-level signals. Through the CANbus it is connected to other CAN-transceivers in the car, which have their own independent
power supply.
Dedicated drivers for high-power loads (light-bulbs, LEDs, door locks, mirror folds, H-bridge
drivers etc.) are also connected to the microcontroller power supply and communicate with it
by SPI.
Several peripherals of the microcontroller are used to monitor voltages like the battery
voltage, either by a logic-level input/output or an analog-to-digital convertor (ADC).
The inductances LS1 to LS4 are the parasitic wire inductances of the supply lines.
Capacitances are added to either protect the supply against distortions or to stabilize the
voltage generated the by voltage controller inside the SBC.
Protection resistors are added at the monitor inputs of the microcontroller.
Figure 1. Microcontroller with power supply, drivers and physical layer
/6
9%$7
9,1
/6
9''
9%$7
9287
RSWLRQDO
6%&&RPSDQLRQ
&9%$7
9''
&9%$7
5['
&9''
9%$7
&$1+
3K\VLFDO/D\HU
/6
&$16WDQGDORQH
7['
&$1/
9%$7
0HDVXUHPHQW
,QSXW
63,
53527
,2
0HDVXUHPHQW
,QSXW
9''
,QWHUQDO
/9
5HJXODWRU
325
&LUFXLWU\
9%$7
&$1
&RQWUROOHU
9''
63,
9%$7
WRORDG
/RDG'ULYHU
63,
+6'$663
WRORDG
&'(&
53527
$'&
/HJHQG
*1'
63&0LFUR
9%$7
/V
&9%$7&9%$7
&9''
&'(&
&/3)
%DWWHU\9ROWDJH./.O
3&%VWUD\LQGXFWDQFHVWUDFHV
%DWWHU\6XSSO\&DSDFLWRUV
&6XSSO\&DSDFLWRU
&'HFRXSOLQJ&DSDFLWRUV
&DSDFLWRU/RZ3DVV)LOWHU
59
59
53527
9ROWDJH'LYLGHU5HVLVWRU
9ROWDJH'LYLGHU5HVLVWRU
3URWHFWLRQ5HVLVWRU
("1($'5
DocID024014 Rev 2
5/26
System overview
1.2
AN4218
Car-battery power supply (VBAT) transients
In the following chapters tests are shown used in the automotive industry to check if a
system consisting of a microcontroller and its power supply are able to withstand the harsh
automotive application environment. These tests simulate transients on the battery power
supply. They may happen due to switch-on or switch-off the energy consumers along the
battery supply line with its huge inductance. Since these loads may consume large currents
the magnetic energy stored in the supply cable is huge and its change results in high
induced voltages.
As example requirements from the International-Standard-Organization (ISO) and some
European car manufacturers are described. The influences of these tests have been
measured on a system according to Figure 1, in which a voltage regulator, either standalone or as part of a System-Basis-Chip (SBC), generates out of the battery voltage (VBAT)
the supply voltage for the microcontroller (VDD).
The power-up reset cell of a microcontroller ensures that the microcontroller is put into a
well-defined state, when the supply voltage is switched on. The following conditions on the
microcontroller power supply should be avoided:
Figure 2. Brown out
Figure 3. Non strictly rising ramp
9''
9''
9
9
("1($'5
("1($'5
Figure 4. Slow ramp
Figure 5. Residual voltage
9''
9''
9
9
("1($'5
6/26
DocID024014 Rev 2
("1($'5
AN4218
1.2.1
System overview
Example battery supply test pulses
Example test pulses can be found in test specification defined either by the ISO or various
car makers (see Appendix A: Reference documents).
Engine cranking low voltage on battery-supply
This test is included in all reference documents. It tests the behavior of the system with a
sharp voltage drop and ringing, which can be seen during the engine cranking.
As an example the Volkswagen test specification VW80000: 2009-10, defines the test pulse
E11:
Figure 6. Test pulse E11
("1($'5
Table 1. Parameters sharp test pulse E11
Parameter
Test pulse (sharp)
UB
11.0 V
UT
3.2 V
US
5.0 V
UA
6.0 V
UR
2V
tf
≤ 1 ms
t4
19 ms
t5
≤ 1 ms
t6
329 ms
t7
50 ms
DocID024014 Rev 2
7/26
System overview
AN4218
Table 1. Parameters sharp test pulse E11 (continued)
Parameter
Test pulse (sharp)
t8
10 s
tr
100 ms
f
2 Hz
Ri
0.01 Ω
Pause between test cycles
2s
Number of test cycles
10
As shown in Table 1 the ‘sharp’ pulse E11 on VBAT (UB) drops down to 3.2 V (UT).
Car-battery supply voltage slow ramp-up
This test can be found in all reference documents and is intended to test the device behavior
with a very slow battery voltage ramp (0.5 V/min). A proper power-up-reset has to be
guaranteed.
Car-battery supply voltage slow ramp-down
This test can be found in all reference documents and is intended to test the device behavior
with a very slow battery voltage ramp (0.5 V/min). A proper device shut-down has to be
guaranteed.
Reverse car-battery supply voltage
This tests the system behavior when the power supply is reversed.
1.2.2
Power-up-reset requirements of the SPC microcontrollers
VDD ramp-up/ ramp-down (microcontroller supply)
Figure 7 and Table 2 show as example basic requirements for the microcontroller power
supply (VDD) ramp-up/ ramp-down (for actual values please refer to the associated device
datasheet). The values below are derived from the SPC560B40x/50x, SPC560C40x/50x
datasheet and SPC560P34x, SPC560P40x datasheet (see Appendix A: Reference
documents).
These microcontroller supply requirements have to be fulfilled by the voltage regulator
supplying the microcontroller.
8/26
DocID024014 Rev 2
AN4218
System overview
Figure 7. VDD ramp-up/ ramp-down (SPC560Bxx, SPC560Cxx, – example only)
9''B+9
9''B+90$;
G 9''
GW
9325+0$;
32:(583
)81&7,21$/5$1*(
32:(5'2:1
("1($'5
Table 2. VDD ramp specification (SPC560P34x, SPC560P40x – example only)
Symbol
TVDD
Parameter
Slope characteristics on all VDD during power up
with respect to ground (VSS)
DocID024014 Rev 2
Minimum
Maximum
3 V/s
0.5 V/µs
9/26
Good practices of system power supply
AN4218
2
Good practices of system power supply
2.1
Microcontroller power supply reactions on VBAT transients
This section shows the measurements done on a system-basis-chip L99PM62GXP, which
provides the power supply (VDD) to the microcontroller.
In addition to the microcontroller power supply this device provides also an NRESET output,
which should be used to drive the microcontroller NRESET input for achieving maximum
reliability of the microcontroller power-up state.
The measurements have been taken from the STMicroelectronics In-Application-ValidationReport of the L99PM62GXP. This document is available on request.
2.1.1
L99PM62GXP block diagram
Figure 8 shows a typical ST system-basis chip, which contains voltage regulators to
generate the supply for the microcontroller (output V1). Additionally it provides physical
layer interfaces (LIN, CAN), a serial-parallel interface and various high-side and low-side
drivers.
10/26
DocID024014 Rev 2
AN4218
Good practices of system power supply
Figure 8. L99PM62GXP block diagram
9V
/RZ6LGH
P$
2XWSXW&ODPS
7HPS3UHZDUQLQJ
6KXWGRZQ
/RZ6LGH
P$
2XWSXW&ODPS
8QGHUYROWDJH
2YHUYROWDJH
6KXWGRZQ
95(*
9P$
9
9
95(*
9P$
+LJK6LGH
15HVHW
P$
FKDQQHO
3:0*HQHUDWRU
/2*,&
+LJK6LGH
P$
+LJK6LGH
7LPHU
P$
+LJK6LGH
7LPHU
P$
+LJK6LGH
&61
&/.
',
'2
:LQGRZ
:DWFKGRJ
63,
)DLO
6DIH
5(/
5(/
23
23
23BRXW
23
23
23BRXW
287B+6
287
287
287)62
P$
287
:DNH8S,Q
:8
:DNH8S,Q
:8
:DNH8S,Q
:8
&$16XSSO\
/,1
/,138
/,1
6$(-
5['B/1,17
+6&$1
,62
7['B&
5['B&
7['B/
/,1FHUWLILHG
$*1'
&$1B+
63/,7
&$1B/
3*1'
("1($'5
DocID024014 Rev 2
11/26
Good practices of system power supply
2.1.2
AN4218
Measurement setup
Figure 9. Measurement setup
3RZHU
VXSSO\
$
9ERDUG
9EDW
9
9V
&RPSDQLRQ %RDUG
86%
67
2VFLOORVFRSH
3RZHU
VXSSO\
:DYHIRUP
JHQHUDWRU
9
/30*;3
'DXJKWHUERDUG
2XW
2XW
2XW
2XW
2XWB+6
5(/
5(/
9
/RDGV
("1($'5
2.1.3
Measurement results
These measurements show the microcontroller power supply (VDD – V1) and the NRESET
output of the L99PM62GXP, if it is subject to the above defined test pulses.
Engine cranking low voltage
The parameter specification can be found in Table 1.
Figure 10. Engine cranking pulse
("1($'5
12/26
DocID024014 Rev 2
AN4218
Good practices of system power supply
Figure 11. Measurement over the entire pulse
("1($'5
1. Line 1 (RST): NRESET output
Line 2 (V1): microcontroller power supply VDD
Line 3 (VBAT): system power supply (VBAT)
Line 4 (OUT_HS): high-side driver output
Line D4 (CSN): SPI-logic signal chip-select-not
Line D5 (OUT_LS): low-side driver output
Line D7 (FSO): fail-safe state (internal signal)
Figure 12. Zoom into the low voltage drop region
("1($'5
1. Line 1 (RST): NRESET output
Line 2 (V1): microcontroller power supply VDD
Line 3 (VBAT): system power supply (VBAT)
Line 4 (OUT_HS): high-side driver output
Line D4 (CSN): SPI-logic signal chip-select-not
Line D5 (OUT_LS): low-side driver output
Line D7 (FSO): fail-safe state (internal signal)
DocID024014 Rev 2
13/26
Good practices of system power supply
AN4218
During the VBAT drop to 3.2 V, V1 (VDD) goes to 0 V and switches on after VBAT has reached
L99PM62GXP reset threshold. In this case the NRESET output is pulled low and goes to
high 2 ms after V1 has reached the NRESET high threshold.
Conclusion
The steep drop of V1 to 0 V in addition with the fast rising slope of V1 after VBAT has
recovered ensures a correct power-up reset of the microcontroller.
The NRESET output goes low to put the microcontroller into reset condition; it goes to high
after V1 has reached the microcontrollers operating region.
The correct power-down / power-up sequence ensures that the microcontroller is always in
a defined state. This is additionally supported by the NRESET signal.
Supply voltage slow ramp-up
Figure 13. VS voltage ramp up (0.5 V/min)
("1($'5
1. Line 1 (RESET): NRESET output
Line 2 (V1): microcontroller power supply VDD
Line 4 (VBAT): system power supply (VBAT)
As long as VBAT is below the L99PM62GXP reset threshold, V1 remains at 0 V. After VBAT
has reached the reset threshold of 3.1 V, V1 is switched on with a fast slope. As soon as the
NRESET threshold is reached NRESET goes to high.
Conclusion
The fast slope of V1 above the power-up-reset threshold of the microcontroller ensures a
correct power-up-reset of the microcontroller, depending only on the capacitors at the V1
node and not on the battery voltage slope.
14/26
DocID024014 Rev 2
AN4218
Good practices of system power supply
The NRESET goes high after V1 has reached the operating region of the microcontroller.
The correct power-up sequence ensures that the microcontroller is always in a defined
state. This is additionally supported by the NRESET signal.
Supply voltage slow ramp-down
Figure 14. VBAT voltage ramp down (0.5 V/min)
("1($'5
1. Line 1 (RST): NRESET output
Line 2 (V1): microcontroller power supply VDD
Line 3 (VBAT): system power supply (VBAT)
Line 4 (OUT_HS): high-side driver output
Line D6 (OUT_LS): low-side driver output
Lines Dx (DI, CLK, CSN): SPI interface signals
As soon as VBAT reaches the NRESET threshold, NRESET goes low and remains there
until VBAT is 0 V.
V1 goes to 0 V with a fast slope, when VBAT is at the power-on-reset threshold of the
L99PM62GXP.
Conclusion
The NRESET goes low after V1 has left the operating region of the microcontroller.
Therefore the microcontroller is always in a defined state.
The fast falling slope of V1 above the power-up-reset threshold to 0 V of the microcontroller
ensures a correct state of the microcontroller during V1 and VBAT switch-off.
DocID024014 Rev 2
15/26
Application circuits
AN4218
3
Application circuits
3.1
Reference circuit
A system containing the microcontroller, the power supply generation, physical layer, load
drivers and a measurement unit for permanent enabled battery supply (e.g. KL30) is shown
in Figure 15.
Figure 15. Reference circuit
/6
9%$7
9,1
/6
9''
9%$7
9287
RSWLRQDO
6%&&RPSDQLRQ
&9%$7
9''
&9%$7
&9''
WR0LFUR
/6
15(6(7
9%$7
&$1+
3K\VLFDO/D\HU
&$16WDQGDORQH
&$1/
WR0LFUR
9%$7
9''
WR0LFUR
90HDVXUH
9''
9%$7
WRORDG
/RDG'ULYHU
+6'$663
,2
,2
WRORDG
59
53527
59
(6'
$'&
$'&
WR,2VWUXFWXUH
LQSXWRXWSXW
EXIIHUV
DOWHUQDWH
IXQFWLRQV
9''&ODPS
&'(&
&/3)
(6'
/HJHQG
*1'
63&0LFUR
9%$7
/V
&9%$7&9%$7
&9''
&'(&
&/3)
%DWWHU\9ROWDJH./.O
3&%VWUD\LQGXFWDQFHVWUDFHV
%DWWHU\6XSSO\&DSDFLWRUV
&6XSSO\&DSDFLWRU
&'HFRXSOLQJ&DSDFLWRUV
&DSDFLWRU/RZ3DVV)LOWHU
59
59
53527
9ROWDJH'LYLGHU5HVLVWRU
9ROWDJH'LYLGHU5HVLVWRU
3URWHFWLRQ5HVLVWRU
("1($'5
3.2
Implementation suggestions
Besides the above mentioned requirements for the microcontroller power supply generation
special care has to be taken on the following system parts.
3.2.1
Measurement of an permanently enabled power-supply (VMEASURE)
Since VMEASURE is permanently supplied, while the supply for the microcontroller system
(VBAT) can be turned off, it must be made sure, that the power-up functionality of the
microcontroller is not influenced.
Additional the microcontroller pins have to be protected against ISO-pulses, which may
damage the microcontroller. These ISO-transients are defined in ISO 7637-2:2011(E).
Note:
The calculations and values used are examples only. For the actual values please refer to
the latest datasheet of the used device.
Calculation of RV1/2 for ADC
The voltage divider has to be dimensioned such that no overvoltage condition at the analogto-digital-convertor (ADC) input can occur. Especially it must be ensured, that the voltage at
the ADC is never higher than at the VDD, which supplies the ADC pin.
16/26
DocID024014 Rev 2
AN4218
Application circuits
For further information please consult the actual datasheet of the used microcontroller.
Figure 16. Voltage divider
9''B+9
90HDVXUH
,2
59
(6'
9$'&
59
$'&
9''&ODPS
WR,2VWUXFWXUHLQSXWRXWSXW
EXIIHUVDOWHUQDWHIXQFWLRQV
(6'
63&0LFUR
*1'
("1($'5
Example 1:
Maximum VADC = 5.0V
Maximum VMEASURE = 40V
R V2
5.0V
--------------------------------- = -----------40V
( R V1 + R V2 )
Insertion of a series protection resistor (RPROT)
The series resistor RPROT prevents current injection spikes into the microcontroller and its
ESD-diodes if an ISO-transient occurs.
These ISO-transients are defined in ISO 7637-2:2011(E).
The values used in the following calculations are examples only. Please consult the actual
datasheet of the used device for the latest requirements.
DocID024014 Rev 2
17/26
Application circuits
AN4218
Figure 17. ISO transients
,627UDQVLHQW
9''+9
9''B+9
3RVLWLYH,62
7UDQVLHQW
90HDVXUH
,2
59
(6'
53527 9$'&
$'&
59
9''&ODPS
WR,2VWUXFWXUHLQSXWRXWSXW
EXIIHUVDOWHUQDWHIXQFWLRQV
(6'
1HJDWLYH,62
7UDQVLHQW
63&0LFUR
*1'
("1($'5
Example 2:
ISO-pulse 3b generates a maximum voltage of 100 V and uses an interior resistor of 50 Ω
(RI) at pin VMEASURE. Neglecting RI this leads to:
5V
100V ⋅ ----------- = 12.5V
40V
at the ADC-pin.
This voltage is clamped to VDD + 0.7 V (typical ESD-diode drop). With VDD = 5 V this clamp
voltage is 5.7 V.
The maximum injected current at any pin derived from the absolute maximum ratings is
10 mA, so the series protection resistor (RPROT) has to be at least
12.5V – 5.7V
R PROT = ---------------------------------- = 680Ω
10mA
to clamp the positive pulse.
For the negative ISO-Pulse the calculation is similar: the ISO-Pulse 3a generates a negative
voltage of -150 V over 50 Ω (RI). Neglecting RI the resulting voltage before RPROT is
5V
– 150V ⋅ ----------- = – 18.75V
40V
18/26
DocID024014 Rev 2
AN4218
Application circuits
This is clamped to -0.7 V by the internal ESD-diode to ground, so RPROT has to be at least
– 18.75V – ( – 0.7V )
R PROT = -------------------------------------------------- = 1.805kΩ
– 10mA
As can be seen from above calculations, the negative ISO pulse requires a series protection
resistor of at least 2 kΩ to limit the injected current to the absolute maximum ratings. If the
injected current has to be limited to ±5mA the required series protection resistor has to be at
least 4 kΩ.
A larger resistor is recommended to cover the worst-case conditions.
This calculation applies for low-impedance voltage dividers at VMEASURE.
A simplified calculation can be used for higher resistive RV1:
•
For the positive ISO-pulse:
100V – 5.7V
R V1 = --------------------------------- = 9.42kΩ
10mA
•
For the negative pulse:
– 150V – ( – 0.7V )
R V1 = --------------------------------------------- = 14.93kΩ
– 10mA
So for RV1 > 15 kΩ (30 kΩ for 5mA injection current), the series protection resistor can be
omitted, but it protects the microcontroller input in case of a damaged RV1.
Figure 18 shows a simulation of a negative 150 V ISO pulse. ‘V(meas)’ is the voltage at the
VMEASURE pin, ‘V(adc)’ at VADC and ‘Ix(xuc:IO)’ the current that flows out of the
microcontroller pin.
The resistor divider uses RV1= 15 kΩ and RV2= 2.2 kΩ.
Figure 18. Negative ISO-pulse simulation
9PHDV
9
9
9
9
9
9
9DGF
P9
P9
P9
P9
P9
P9
,[[XF,2
P$
P$
P$
P$
P$
P$
PV
PV
PV
PV
PV
PV
PV
PV
PV
PV
PV
*$3*&)7
As can be seen in Figure 18 the current out of the microcontroller with a negative ISO-pulse
of 150 V does not increase above 10 mA.
Please refer to the latest datasheet of the used device for further information. Especially a
possible impact on the accuracy of the analog-to-digital-convertor has to be taken into
account.
DocID024014 Rev 2
19/26
Application circuits
AN4218
Low pass filter
The low-pass filter, which consists of RPROT and CLPF, has to be dimensioned such that the
bandwidth of the ADC is not exceeded, since otherwise aliasing-artifacts may be observed.
Figure 19. Protection and low-pass-filter
9''+9
9''B+9
90HDVXUH
,2
59
(6'
9$'&
53527
$'&
&/3)
59
9''&ODPS
WR,2VWUXFWXUHLQSXWRXWSXW
EXIIHUVDOWHUQDWHIXQFWLRQV
(6'
63&0LFUR
*1'
*$3*&)7
Figure 20 shows a simulation of the frequency (amplitude damping and phase) at VADC with
RV1 = 15 kΩ, RV2 = 2.2 kΩ, RPROT = 680 Ω and CLPF = 1 nF. The input voltage is 15 V with
an AC-Amplitude of 1 V (the voltage divider-by-8 causes an initial 18dB reduction).
Figure 20. Amplitude and phase over frequency
9DG F
G %
G %
G %
G %
G %
G %
G %
G %
G %
G %
G %
G %
G %
.+]
.+]
.+]
0+]
0+]
*$3*&)7
Divider disconnection switch
A switch at VMEASURE avoids backward supplying from a powered VMEASURE source to the
unpowered microcontroller through the ESD diode of the input pin.
20/26
DocID024014 Rev 2
AN4218
Application circuits
Figure 21. Backward current
9''+9
9''B+9
%DFNZDUG&XUUHQW
ZKLOH9''+9 9
DQG90($685(DSSOLHG
90HDVXUH
6ZLWFK
,2
59
53527
59
(6'
9$'&
$'&
&/3)
9''&ODPS
WR,2VWUXFWXUHLQSXWRXWSXW
EXIIHUVDOWHUQDWHIXQFWLRQV
(6'
63&0LFUR
*1'
*$3*&)7
With a current flowing through the ESD-diode, the voltage at pin VADC would be one VBE
(0.7 Vtyp) higher than VDD-HV, thus violating the absolute maximum rating of 0.3 Vmax.
3.2.2
Bad practices
An example of a badly designed VMEASURE measurement interface is shown in the
Figure 22.
The circuit does not contain a protection resistor RPROT and no low-pass-filter.
DocID024014 Rev 2
21/26
Application circuits
AN4218
Figure 22. Bad example circuit
/6
9%$7
9,1
/6
9''
9%$7
9287
,,1-
RSWLRQDO
,,1-
6%&&RPSDQLRQ
&9%$7
9''
&9%$7
&9''
WR0LFUR
/6
15(6(7
9%$7
3K\VLFDO/D\HU
&$1+
&$16WDQGDORQH
&$1/
WR0LFUR
9%$7
9''
WR0LFUR
90HDVXUH ./
9''
9%$7
WRORDG
/RDG'ULYHU
+6'$663
,2
WRORDG
59
,0($685(
,,1-
(6'
$'&
$'&
59
9$'&
WR,2VWUXFWXUH
LQSXWRXWSXW
EXIIHUV
DOWHUQDWH
IXQFWLRQV
9''&ODPS
&'(&
(6'
/HJHQG
*1'
63&0LFUR
9%$7
/V
&9%$7&9%$7
&9''
&'(&
%DWWHU\9ROWDJH./.O
3&%VWUD\LQGXFWDQFHVWUDFHV
%DWWHU\6XSSO\&DSDFLWRUV
&6XSSO\&DSDFLWRU
&'HFRXSOLQJ&DSDFLWRUV
59
59
9ROWDJH'LYLGHU5HVLVWRU
9ROWDJH'LYLGHU5HVLVWRU
*$3*&)7
Calculation of RV1/2 for ADC
The calculation for the voltage divider is done in the same way as for the example with
RPROT.
In addition to this, also the ADC-protection regarding ISO-transients has to be taken into
account.
Effects of the bad VMEASURE implementation
Sensitivity to ISO transients
Any ISO pulse voltage (e.g. +100 V, - 150 V) applied to pin VMEASURE is applied to the
device pin and its ESD protection diode directly via RV1. If RV1 is not high resistive enough
(see example above), the microcontroller might be damaged.
Sensitivity to Electro-Magnetic-Injection (EMI)
All EMI-distortions at the pin VMEASURE are coupled into the microcontroller pin via the
voltage divider and may distort the microcontroller. A capacitor at the microcontroller pin
improves this by adding a low resistive path to ground for high frequencies.
Residual voltage at VDD in power down condition
A residual voltage at VDD might happen if the current flowing from VMEASURE to VDD via the
microcontroller ESD protection diode is not actively sunk to ground.
Since the VDD-net supplies other components in the system (e.g. physical layer, high load
drivers etc.) they will get affected as well.
Absolute maximum ratings of the ESD-protection diode
In power down condition the absolute maximum voltage rating (e.g. 0.3 V) as well as the
absolute maximum current rating (e.g. 75 µA) may constantly be violated. The voltage and
currents given above are examples only, for the actual values please refer to the associated
datasheet.
22/26
DocID024014 Rev 2
AN4218
Application circuits
System reliability
The ESD-diodes inside of the microcontroller are designed for short discharge pulses only,
not to sustain a constant current over time. Therefore the maximum continuous voltage drop
over them is specified in the absolute maximum ratings to be not higher than 0.3 V. In this
case only a very limited current is flowing through them.
A continuous current may lead to a degrading effect on these diodes over time.
3.2.3
Physical layer
Physical layer interfaces such as CAN-transceiver and LIN-transceivers may not have a
reverse protection from the physical layer to its power supply, which may be connected to
the microcontroller-supply (VDD-HV). Since the physical layer is driven by other members on
the bus this may lead to residual voltages while the microcontroller is not supplied.
CAN-transceiver without reverse protection show the backward current through an
unprotected CAN-biasing net to the unpowered microcontroller-supply (VDD). In a carnetwork the CAN-bus is expected to be always supplied even while the microcontroller is
not.
Figure 23. CAN-transceiver without reverse protection
9%$7
9,1
/6
9''+9
9287
&9''
6%&&RPSDQLRQ
&,1
&95(*
15(6(7
WR0LFUR
9''
9''+9
9''
9''B+9
(6'
%DFNZDUG&XUUHQW
ZKLOHWKH&$1%XV
&$1+&$1/LV
VXSSOLHG
&$1+
,2
WR,2VWUXFWXUHLQSXWRXWSXW
EXIIHUVDOWHUQDWHIXQFWLRQV
&$1/
(6'
9''&ODPS
3K\VLFDO/D\HU
&$16WDQG$ORQH
63&0LFUR
*1'
*$3*&)7
DocID024014 Rev 2
23/26
Reference documents
Appendix A
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
AN4218
Reference documents
32-bit Power Architecture® based MCU for automotive powertrain applications
(SPC560P34x, SPC560P40x — Doc ID 18078)
32-bit MCU family built on the embedded Power Architecture® (SPC564A74B4,
SPC564A74L7, SPC564A80B4, SPC564A80L7 — Doc ID 15399)
32-bit MCU family built on the Power Architecture® for automotive body electronics
applications (SPC560D30x, SPC560D40x — Doc ID 16315)
32-bit MCU family built on the Power Architecture® for automotive body electronics
applications (SPC560B40x, SPC560B50x, SPC560C40x, SPC560C50x —
Doc ID 14619)
32-bit MCU family built on the Power Architecture® for automotive body electronics
applications (SPC560B54x, SPC560B60x, SPC560B64x — Doc ID 15131)
32-bit MCU family built on the Power Architecture® for automotive body electronics
applications (SPC564Bxx, SPC56ECxx — Doc ID 17478)
32-bit Power Architecture® microcontroller for automotive SIL3/ASILD chassis and
safety applications (SPC56EL60x, SPC56EL54x, SPC564L60x, SPC564L54x —
Doc ID 15457)
32-bit Power Architecture® microcontroller for automotive SIL3/ASILD chassis and
safety applications (SPC56EL70L3, SPC56EL70L5, SPC564L70L3, SPC564L70L5 —
Doc ID 023953)
32-bit Power Architecture® based MCU with 320 KB Flash memory and 20 KB RAM for
automotive chassis and safety applications (SPC560P34L1, SPC560P34L3,
SPC560P40L1, SPC560P40L3 — Doc ID 16100)
32-bit Power Architecture® based MCU with 576 KB Flash memory and 40 KB SRAM
for automotive chassis and safety applications(SPC560P44L3, SPC560P44L5,
SPC560P50L3, SPC560P50L5 — Doc ID 14723)
32-bit Power Architecture® based MCU with 1088 KB Flash memory and 80 KB RAM
for automotive chassis and safety applications (SPC56AP60x, SPC56AP54x,
SPC560P60x, SPC560P54x — Doc ID 18340)
32-bit Power Architecture® based MCU for automotive powertrain applications
(SPC563M64L5, SPC563M64L7 — Doc ID 14642)
Power management IC with LIN and high speed CAN (L99PM62GXP, Doc ID 15136)
14. ISO 7637-2:2011(E)
15. ISO16750-2:2006
16. BMW GS95024-2-1
17. Renault 36-00-808 / 2010
18. VW 80000: 2009-10
24/26
DocID024014 Rev 2
AN4218
Revision history
Revision history
Table 3. Document revision history
Date
Revision
Changes
04-Mar-2013
1
Initial release.
17-Sep-2013
2
Updated Disclaimer.
DocID024014 Rev 2
25/26
AN4218
Please Read Carefully:
Information in this document is provided solely in connection with ST products. STMicroelectronics NV and its subsidiaries (“ST”) reserve the
right to make changes, corrections, modifications or improvements, to this document, and the products and services described herein at any
time, without notice.
All ST products are sold pursuant to ST’s terms and conditions of sale.
Purchasers are solely responsible for the choice, selection and use of the ST products and services described herein, and ST assumes no
liability whatsoever relating to the choice, selection or use of the ST products and services described herein.
No license, express or implied, by estoppel or otherwise, to any intellectual property rights is granted under this document. If any part of this
document refers to any third party products or services it shall not be deemed a license grant by ST for the use of such third party products
or services, or any intellectual property contained therein or considered as a warranty covering the use in any manner whatsoever of such
third party products or services or any intellectual property contained therein.
UNLESS OTHERWISE SET FORTH IN ST’S TERMS AND CONDITIONS OF SALE ST DISCLAIMS ANY EXPRESS OR IMPLIED
WARRANTY WITH RESPECT TO THE USE AND/OR SALE OF ST PRODUCTS INCLUDING WITHOUT LIMITATION IMPLIED
WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE (AND THEIR EQUIVALENTS UNDER THE LAWS
OF ANY JURISDICTION), OR INFRINGEMENT OF ANY PATENT, COPYRIGHT OR OTHER INTELLECTUAL PROPERTY RIGHT.
ST PRODUCTS ARE NOT DESIGNED OR AUTHORIZED FOR USE IN: (A) SAFETY CRITICAL APPLICATIONS SUCH AS LIFE
SUPPORTING, ACTIVE IMPLANTED DEVICES OR SYSTEMS WITH PRODUCT FUNCTIONAL SAFETY REQUIREMENTS; (B)
AERONAUTIC APPLICATIONS; (C) AUTOMOTIVE APPLICATIONS OR ENVIRONMENTS, AND/OR (D) AEROSPACE APPLICATIONS
OR ENVIRONMENTS. WHERE ST PRODUCTS ARE NOT DESIGNED FOR SUCH USE, THE PURCHASER SHALL USE PRODUCTS AT
PURCHASER’S SOLE RISK, EVEN IF ST HAS BEEN INFORMED IN WRITING OF SUCH USAGE, UNLESS A PRODUCT IS
EXPRESSLY DESIGNATED BY ST AS BEING INTENDED FOR “AUTOMOTIVE, AUTOMOTIVE SAFETY OR MEDICAL” INDUSTRY
DOMAINS ACCORDING TO ST PRODUCT DESIGN SPECIFICATIONS. PRODUCTS FORMALLY ESCC, QML OR JAN QUALIFIED ARE
DEEMED SUITABLE FOR USE IN AEROSPACE BY THE CORRESPONDING GOVERNMENTAL AGENCY.
Resale of ST products with provisions different from the statements and/or technical features set forth in this document shall immediately void
any warranty granted by ST for the ST product or service described herein and shall not create or extend in any manner whatsoever, any
liability of ST.
ST and the ST logo are trademarks or registered trademarks of ST in various countries.
Information in this document supersedes and replaces all information previously supplied.
The ST logo is a registered trademark of STMicroelectronics. All other names are the property of their respective owners.
© 2013 STMicroelectronics - All rights reserved
STMicroelectronics group of companies
Australia - Belgium - Brazil - Canada - China - Czech Republic - Finland - France - Germany - Hong Kong - India - Israel - Italy - Japan Malaysia - Malta - Morocco - Philippines - Singapore - Spain - Sweden - Switzerland - United Kingdom - United States of America
www.st.com
26/26
DocID024014 Rev 2