1
DA9171A.000
July 31, 1997
MAS9171A
OCTAL PORT PROTECTON
Parallel In, Parallel Out
High Voltage Inputs
Automotive
DESCRIPTION
The MAS9171A is an eight channel protection
circuit for microprocessors in automotive
applications. All inputs are protected against energy
rich pulses according to DIN40839/ISO7637.
Internal analog filters and suitable input threshold
voltages provide the functionality within a noise
spectrum of 150 kHz up to 1 GHz without need of
external filter components. The MAS9171A is
optimized for low current consumption.
FEATURES
APPLICATION
8 digital channels
Supply voltage 3.3 V/5 V
Low supply current
High voltage inputs
Internal analog filter
-40
C to +125
C
SO-18 package
Replacement of protection circuitry in car
electronics and industrial bus systems
BLOCK DIAGRAM
IN1
IN2
IN3
IN4
IN5
IN6
IN7
IN8
OUT1
OUT2
OUT3
OUT4
OUT5
OUT6
OUT7
OUT8
VDD
GND
PROTECT
FILTER
COMP
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DA9171A.000
July 31, 1997
PIN CONFIGURATION
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PIN DESCRIPTION
Pin Name
Pin
Type
Function
GND
1
G
Ground
IN1
2
I
Digital Input 1
IN2
3
I
Digital Input 2
IN3
4
I
Digital Input 3
IN4
5
I
Digital Input 4
IN5
6
I
Digital Input 5
IN6
7
I
Digital Input 6
IN7
8
I
Digital Input 7
IN8
9
I
Digital Input 8
OUT8
10
O
Digital Output 8
OUT7
11
O
Digital Output 7
OUT6
12
O
Digital Output 6
OUT5
13
O
Digital Output 5
OUT4
14
O
Digital Output 4
OUT3
15
O
Digital Output 3
OUT2
16
O
Digital Output 2
OUT1
17
O
Digital Output 1
VDD
18
P
Positive Supply Voltage
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DA9171A.000
July 31, 1997
ABSOLUTE MAXIMUM RATINGS
Parameter
Symbol
Conditions
Min
Max
Unit
Supply Voltage
V
DD
-0.5
7
V
Input Voltage
V
IN
T = 125C, f=100Hz, 5% On
-200
200
V
ESD Voltage
MM (EIAJ ED-4701 Method C-111)
-500
500
V
Output Current (Note 1)
I
OUT
T=125C
5
mA
Ambient Temperature
T
amb
-40
+125
o
C
Storage Temperature
T
Stg
-55
+150
o
C
RECOMMENDED OPERATION CONDITIONS
Parameter
Symbol
Conditions
Min
Typ
Max
Unit
Supply Voltage
V
DD
3.3
5.0
5.5
V
Supply Current
I
DD
V
DD
= 5.0 V
V
IN
1...8
= 0 V
3nA
10
A
ELECTRICAL CHARACTERISTICS
x
Parallel input port
(T=-40C .. +125C,
V
DD
= 3.3V..5.5V
)
Parameter
Symbol
Conditions
Min
Typ
Max
Unit
Input High Voltage (Note 2)
V
IH
V
DD
= 5.0 V
5.0
5.5
6.0
V
Input Low Voltage (Note 2)
V
IL
V
DD
= 5.0 V
2.25
2.75
3.25
V
DC Input Voltage
V
max
Only 1 input at the same time
-100
VDD+100
V
Input Resistance
R
IN1
-1V<V
IN1
<V
DD
x2.25
140
225
320
k
3 dB Frequency of Analog
Filter
fd
100
150
200
kHz
x
Parallel digital outputs
(T=-40C .. +125C,
V
DD
= 5V
)
Parameter
Symbol
Conditions
Min
Typ
Max
Unit
Output High Voltage
V
OH
I
Source
= 3.0 mA
4.1
4.6
V
Output Low Voltage
V
OL
I
Sink
= 3.0 mA
0.35
0.6
V
Signal Rise Time
t
R
no load
50
500
ns
Signal Fall Time
t
R
no load
50
500
ns
Note 1: The sum of all output currents must not exceed 16 mA
Note 2: Typical values of V
IH
/ V
IL
can be calculated as follows:
V
IH
= 1.1 x V
DD
V
IL
= 0.55 x V
DD
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DA9171A.000
July 31, 1997
FUNCTIONS
x
Input protection
The input protection is composed of a high voltage thin film series resistor, a metal-to-metal capacitor to ground
and a Zener diode to GND. The circuit provides the ability of withstanding energy rich voltage pulses as well as
fast transient high voltage bursts without damaging the MAS9171A or devices connected to it.
The resistance of each input to ground is approx. 225 kOhms. Each input is protected against electrostatic
discharge (ESD) according to Machine Model EIAJ ED-4701 Method C-111 (+/-500 kV, 200 pF, 0 Ohms).
The device has been specially designed for high decoupling between Inputs and Power Supply or Outputs to
prevent voltage overswing when applying test pulses according to DIN40839/ISO7637.
For a given ambient temperature the maximum pulse length is limited by the maximum silicon temperature of
T=150C.
x
Analog filter
The input protection is followed by a passive low pass filter of 2nd order with a 3 dB frequency of 150 kHz. This
filter is used to block high frequency components coupled through capacitive coupling clamps or electromagnetic
field.
x
Comparator
The output signal of the analog filter of each channel is pulse-shaped by a Schmitt-Trigger Comparator with
strong output drivers. The output stage works with non-overlapping clocks to reduce current spikes at the Supply
Pins caused by change of output level.
x
Input levels
The Ouput OUTx is "High" if the corresponding input voltage VINx > 5.5 V and "Low" if VINx < 2.75 V (typical
values).
Fig 1.: Input Channel of MAS9171A
100
K
1
K
125
K
125
K
6.8V
6.8V
9pF
4pF
to Comparator
IN 1....8
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DA9171A.000
July 31, 1997
APPLICATION INFORMATION
GENERAL
In the late 70ties microcontrollers have been introduced into most of the low cost applications in the field of
consumer, industrial and automotive. Lowest cost 8-Bit microcontrollers are used in modern computer
monitors for user programmable adjustment of the picture geometrie. A modern car can carry up to 40
microcontrollers that control motor managment, air condition, wipers, brakes, instruments,......
The increased density of complex electronic systems results in high electromagnetic fields with a wide
frequency spectrum in the environment. Examples for typical noise sources are DC-Motors, ignitors,
discharge lamps, switch-mode supplies and all different kinds of transmitters like mobile phones and radio
stations. The requirements on EMI immunity are defined in several DIN, ISO and IEC standards.
Design-Engineers have to think of how to protect sensitive components like microcontrollers against
overvoltage pulses. Especially pulses with short rise times might cause problems because most of the
standard components are not designed to work properly at frequencies above the cut-off frequency.
In addition the layout of the PCB is very critical at high frequencies. Filters components have to be placed
very closely to the connectors leading to external wires that may work as antennas. It is quite common that a
lot of filter and protection components have to be designed in at a very late phase of the project when starting
EMI measurements with pre-production parts. This can cause delays to the product introduction phase and
therefore it is very important to think about the limits of sensitive components already with the first Prototypes.
INPUT PROTECTION FOR MICROCONTROLLERS
A typical protection circuit for a digital input of a
HCMOS microcontrollers consists of one series
resistor, one or two block capacitors to Vss and
two clamping diodes to Vss/Vdd.
The series resistor shall limit the maximum current
into the internal protection diodes to a value below
the latch-up current of the input structure (typ.
25mA). Together with the capacitor it builds up a
1th order RC-filter.The purpose of the filter is to get
a stable signal within the sampling period of the
microcontroller without need of software filtering.
For resistor values > 100 kOhms however, the
leakage current of the port may cause unwanted
dropout
Vdd
uC
P1
Vin
Fig.2 : Discrete protection circuit
voltage which is not any longer neglectible to the input voltage. Over the full temperature and supply voltage
range this can cause severe tolerance problems. Those inputs need extra clamping diodes to the Vss/Vdd
and a lower value series resistor.
Most of 0805/1204 SMD resistors are specified for voltages < 200V. For higher voltages two resistors in
series are recommended. Especially for applications with a lot of input ports the protection circuitry around
the microcontroller consumes a big amount of board space and therefore makes the board layout very
difficult even when using SMD components. Each component is a potential source of an error in production
and must be tested with In-circuit testers.
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