Maxim MAX367CPN Signal-line circuit protector Datasheet

19-0326; Rev 0; 12/94
Signal-Line Circuit Protectors
____________________________Features
♦ ±40V Overvoltage Protection
♦ Open Signal Paths with Power Off
100Ω Signal Paths with Power On
♦ 1nA Max Path Leakage at +25°C
♦ 44V Maximum Supply Voltage Rating
♦ Automatic Protection; No Programming or
Controls
______________Ordering Information
PART†
TEMP. RANGE
PIN-PACKAGE
MAX366CPA
0°C to +70°C
8 Plastic DIP
MAX366CSA
MAX366C/D
MAX366EPA
0°C to +70°C
0°C to +70°C
-40°C to +85°C
8 SO
Dice*
8 Plastic DIP
MAX366ESA
MAX366MJA
MAX367CPN
-40°C to +85°C
-55°C to +125°C
0°C to +70°C
8 SO
8 CERDIP**
18 Plastic DIP
MAX367CWN
MAX367C/D
MAX367EPN
0°C to +70°C
0°C to +70°C
-40°C to +85°C
18 Wide SO
Dice*
18 Plastic DIP
MAX367EWN
MAX367MJN
-40°C to +85°C
-55°C to +125°C
18 Wide SO
18 CERDIP**
________________________Applications
† MAX367 available after January 1, 1995.
Process Control Systems
Redundant/Backup Systems
Hot-Insertion Boards/Systems ATE Equipment
Data-Acquisition Systems
Sensitive Instruments
* Dice are tested at TA = +25°C only.
* Contact factory for availability.
Pin Configurations appear at end of data sheet.
___________________________________________________Typical Operating Circuit
ELECTRONICS
PROTECTOR
FAULT!
REMOTE SENSOR
MAX366
+28V
+10V REG.
(SHORT)
8
1
IN1
OUT1
7
2
IN2
OUT2
6
3
IN3
OUT3
5
4
(OPEN)
V+
+12V
SENSITIVE
AMPLIFIER
V-
FAULT!
________________________________________________________________ Maxim Integrated Products
Call toll free 1-800-998-8800 for free samples or literature.
1
MAX366/MAX367
_______________General Description
The MAX366 and MAX367 are multiple, two-terminal circuit
protectors. Placed in series with signal lines, each two-terminal device guards sensitive circuit components against
voltages near and beyond the normal supply voltages.
These devices are used at interfaces where sensitive circuits are connected to the external world and could
encounter damaging voltages (up to 35V beyond the supply rails) during power-up, power-down, or fault conditions.
The MAX366 contains three independent protectors and
the MAX367 contains eight. They can protect analog signals using either unipolar (4.5V to 36V) or bipolar (±2.25V
to ±18V) power supplies. Each protector is symmetrical.
Input and output terminals may be freely interchanged.
These devices are voltage-sensitive MOSFET transistor
arrays that are normally on when power is applied and
normally open circuit when power is off. With ±10V supplies, on-resistance is 100Ω max and leakage is less than
1nA at +25°C.
When signal voltages exceed or are within approximately
1.5V of either power-supply voltage (including when
power is off), the two-terminal resistance increases dramatically, limiting fault current as well as output voltage to
sensitive circuits. The protected side of the switch maintains the correct polarity and clamps approximately 1.5V
below the supply rail. There are no “glitches” or polarity
reversals going into or coming out of a fault condition.
MAX366/MAX367
Signal-Line Circuit Protectors
ABSOLUTE MAXIMUM RATINGS
V+ to V-......................................................................-0.3V, +44V
IN_, OUT_ ..................................................(V- + 44V), (V+ - 44V)
Continuous Current into Any Terminal..............................±30mA
Peak Current into Any Terminal
(pulsed at 1ms, 10% duty cycle)...................................±70mA
Continuous Power Dissipation (TA = +70°C)
8-Pin Plastic DIP (derate 9.09mW/°C above +70°C) ....727mW
8-Pin SO (derate 5.88mW/°C above +70°C).................471mW
8-Pin CERDIP (derate 8.00mW/°C above +70°C).........640mW
18-Pin Plastic DIP (derate 11.11mW/°C above +70°C) ...889mW
18-Pin Wide SO (derate 9.52mW/°C above +70°C) .....762mW
18-Pin CERDIP (derate 10.53mW/°C above +70°C).....842mW
Operating Temperature Ranges
MAX36_C_ _ ........................................................0°C to +70°C
MAX36_E_ _......................................................-40°C to +85°C
MAX36_M_ _ ...................................................-55°C to +125°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10sec) .............................+300°C
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(V+ = +15V, V- = -15V, TA = TMIN to TMAX, unless otherwise noted.)
PARAMETER
SYMBOL
Analog Signal Range
Fault-Free Analog Signal Range
VIN, VOUT
VIN, VOUT
Analog-Signal Output
Range (Fault)
VOUT
TEMP.
RANGE
MIN
(Note 1)
V+ = 15V, V- = -15V (Note 2)
All
All
VIN = V+ or V-,
100kΩ < ROUT < 1000MΩ (Note 1)
All
CONDITIONS
MAX
UNITS
(V+ - 40)
-11
(V- + 40)
11
V
V
(V- + 3)
(V+ - 1.5)
V
+25°C
V+ = 15V, V- = -15V, VIN = ±10V,
IOUT = 1mA
Analog-Signal-Path Resistance
R(IN-OUT)
V+ = 5V, V- = -5V, VIN = ±2V,
IOUT = 1mA
Signal-Path Resistance Match
∆R(IN-OUT)
62
C, E
M
125
VIN = ±10V, IOUT = 1mA
Signal-Path Leakage
(Power Off)
IIN(OFF)
V+ = V- = 0V, VIN = ±35V,
VOUT = open circuit
Signal-Path Leakage
(without Fault Condition)
IOUT(ON)
VIN = VOUT = ±10V
Signal-Path Leakage
(with Fault Condition)
IIN(ON)
VIN = ±25V, VOUT = open circuit
Signal-Path Leakage
(with Overvoltage)
IIN(OFF)
V+ = V- = 0V, VOUT = 0V,
VIN = ±35V
62
C, E
100
125
M
Ω
150
+25°C
C, E, M
+25°C
C, E, M
+25°C
C, E, M
+25°C
C, E, M
+25°C
C, E, M
+25°C
C, E, M
85
100
+25°C
V+ = 10V, V- = -10V, VIN = ±5V,
IOUT = 1mA
TYP
140
350
-10
-1000
-1
-100
-10
-1000
-10
-1000
400
7
10
10
1000
1
100
10
1000
10
1000
+25°C,
C, E, M
0
±18
V
+25°C,
C, E, M
±2.25
±18
V
+25°C
C, E, M
-1
-10
1
10
µA
Ω
nA
nA
nA
nA
POWER SUPPLY
Power-Supply Range
V+, V-
Power-Supply Range
(without Fault Condition)
V+, V-
Power-Supply Current
I+, I-
R(IN-OUT) < 1000Ω (Note 2)
Note 1: Guaranteed, but not tested.
Note 2: See Typical Operating Characteristics curves for fault-free analog signal range at various supply voltages.
2
_______________________________________________________________________________________
Signal-Line Circuit Protectors
TRANSFER CHARACTERISTICS
(BIPOLAR SUPPLIES)
V+ = +3V,
V- = -3V
5
0
V+ = +5V,
V- = -5V
-5
V+ = +10V, V- = -10V
OUTPUT
LOAD = 1MΩ
-35
-25
-15
MAX366/7-03
15
V+ = 15V
10
V+ = 10V
5
V+ = 5V
0
-5 0 5
15
25
35
0
5
10
15
20
25
30
35
PATH RESISTANCE vs. INPUT VOLTAGE
(BIPOLAR SUPPLIES)
PATH RESISTANCE vs. INPUT VOLTAGE
(BIPOLAR SUPPLIES)
V± = ±3V
500
V± = ±10V
1E+04
1E+03
V± = ±5V
V± = ±3V
450
V± = ±15V
1E+05
400
V± = ±15V
350
V± = ±10V
300
250
200
150
V± = ±5V
100
1E+02
MAX366/7-05
INPUT VOLTAGE (V)
VIN > (V+ - 35V)
1E+06
1E+01
V+ = 25V
20
INPUT VOLTAGE (V)
1E+08
1E+07
OUTPUT LOAD = 1MΩ
V- = 0V
V+ = +15V, V- = -15V
PATH RESISTANCE (Ω)
-15
25
OUTPUT VOLTAGE (V),
INPUT & OUTPUT CURRENT (µA)
10
-10
PATH RESISTANCE (Ω)
MAX366/7-02
V+ = +15V, V- = -15V
V+ = +10V, V- = -10V
MAX366/7-04
OUTPUT VOLTAGE (V),
INPUT & OUTPUT CURRENT (µA)
15
TRANSFER CHARACTERISTICS
(SINGLE SUPPLY)
50
Circuit of Fig. 6
-15
-10
-5
0
0
5
INPUT VOLTAGE (V)
10
15
Circuit of Fig. 6
-15
-10
-5
0
5
10
15
INPUT VOLTAGE (V)
_______________________________________________________________________________________
3
MAX366/MAX367
__________________________________________Typical Operating Characteristics
(V+ = +15V, V- = -15V, TA = +25°C, unless otherwise noted.)
____________________________Typical Operating Characteristics (continued)
(V+ = +15V, V- = -15V, TA = +25°C, unless otherwise noted.)
PATH RESISTANCE vs. INPUT VOLTAGE
(SINGLE SUPPLY)
PATH RESISTANCE vs. INPUT VOLTAGE
(SINGLE SUPPLY)
10M
V+ = 10V
1M
V+ = 35V
V+ = 15V
10k
1k
MAX366/7-07
450
PATH RESISTANCE (Ω)
V+ = 25V
100k
500
MAX366/7-06
1G
100M
PATH RESISTANCE (Ω)
V+ = 10V
400
V+ = 15V
350
V+ = 25V
300
250
V+ = 5V
200
V+ = 35V
150
100
100
V+ = 5V
10 Circuit of Fig. 6
1
50
V- = 0V
10
V- = 0V
Circuit of Fig. 6
0
1
100
100
10
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
OVERVOLTAGE RAMP
MAX366 FREQUENCY RESPONSE
MAX366-TOC9
0
-2
SOURCE = 50Ω
LOAD = 50Ω
V+ = 5V
V- = -5V
-4
LOSS (dB)
MAX366/MAX367
Signal-Line Circuit Protectors
-6
-8
-10
-12
V+ = 5V, V- = -5V
CHAN 1: INPUT OVERVOLTAGE RAMP ±7V, 2V/div
CHAN 2: OUTPUT; OUTPUT LOAD = 1000Ω, 2V/div
4
10
100
1k
10k 100k 1M
FREQUENCY (Hz)
_______________________________________________________________________________________
10M 100M
Signal-Line Circuit Protectors
PIN
NAME*
MAX366
MAX367
1, 2, 3
1, 2, 3
IN1, IN2, IN3
–
4–8
IN4–IN8
FUNCTION
Signal Inputs 1, 2, 3
Signal Inputs 4–8
4
9
V-
–
10–14
OUT8–OUT4
Negative Supply Voltage Input
Signal Outputs 4–8
5, 6, 7
15, 16, 17
OUT3, OUT2,
OUT1
Signal Outputs 1, 2, 3
8
18
V+
Positive Supply Voltage Input
* Inputs and outputs are names for convenience only; inputs and outputs are identical and interchangeable.
___________Background Information
When a voltage outside the supply range is applied to
most integrated circuits, there is a strong possibility they
will be damaged or “latch up” (that is, fail to operate properly even after the offending voltage is removed). If an
IC’s input or output pin is supplied with a voltage when the
IC’s power is off, and power is subsequently applied, the
device may act as an SCR and destroy itself and/or other
circuitry. Such “faults” are commonly encountered in
modular control systems where power and signals to interconnected modules may be interrupted and re-established at random. They can happen during production
testing, maintenance, start-up, or a power “brownout.”
The MAX366/MAX367 are designed to protect delicate
input and output circuitry from overvoltage faults up to
±40V (with or without power applied), in devices such as
op amps, analog-to-digital/digital-to-analog converters,
and voltage references. These circuit protectors automatically limit signal voltages and currents to safe levels without degrading normal signal performance, even in very
high-impedance circuits. They are powered by the power
supply of the protected circuit and inserted into the signal
lines. There are no control lines, programming pins, or
adjustments.
Unlike shunt diode networks, these devices are lowimpedance FETs that become high impedance during a
fault condition, so fault current and power dissipation are
extremely low. Equally important, leakage current during
normal and fault conditions is extremely low. In addition,
unlike most discrete networks, these parts protect circuits
both when power is off and during power transitions.
_______________Detailed Description
Internal Construction
Figure 1 shows the simplified internal construction of
each protector inside the MAX366/MAX367. Each circuit
consists of two N-channel FETs and one P-channel FET.
All the FETs are enhancement types; that is, the N channels must have approximately 1.3V of positive gate voltage in order to conduct, and the P channel must have
approximately 2V of negative gate voltage in order to
conduct.
During normal operation, V+ is connected to a positive
potential and V- is connected to a negative potential.
Since their gates are tied to V+, transistors Q1 and Q3
conduct as long as their sources are at least 1.3V below
V+ (the N-channel gate threshold.) Transistor Q2’s gate
is tied to V-, so it conducts as long as its source is 2V or
more above V- (the P-channel gate threshold.)
VP
IN
OUT
Q2
N
N
Q1
Q3
V+
Figure 1. Simplified Internal Structure
_______________________________________________________________________________________
5
MAX366/MAX367
______________________________________________________________Pin Description
MAX366/MAX367
Signal-Line Circuit Protectors
As long as the signal is within these limits, all three transistors conduct and a low-resistance path is maintained
from the IN to OUT pin. (Note that, since the device is
symmetrical, IN and OUT pins can be interchanged.)
When the signal is beyond the gate threshold of either
Q2 or Q1/Q3, the path resistance rises dramatically.
When power is off, none of the transistors have gate
bias, so the circuit from IN to OUT is open.
Normal Operation
In normal operation, the protector is placed in series
with the signal line and the power supplies are connected to V+ and V- (see Figure 2). V- is ground when
operating with a single supply. When power is applied,
each protector acts as a resistor in the signal path.
Any voltage source on the “input” side of the switch will
be conducted through the protector to the output. (Note
that, since the protector is symmetrical, IN and OUT
pins can be interchanged.)
If the output load is resistive, it will draw current, and a
voltage divider will be formed with the internal resistance
so the output voltage will be lower than the input voltage.
Since the internal resistance is typically less than 100Ω,
high-impedance loads will be relatively unaffected by the
presence of the protector. The protector’s path resistance is a function of the supply voltage and the signal
voltage (see Typical Operating Characteristics).
MAX366
4
VVIN
1
V-
V+
IN1
OUT1
8
7
V+
VOUT
ROUT
VLOW
Power Off
When power is off (i.e., V+ = V- = 0V), the protector is a
virtual open circuit, and all voltages on each side are
isolated from each other up to ±40V. With ±40V applied
to the input pin, the output pin will be 0V, regardless of
its resistance to ground.
Fault Conditions
A fault condition exists when the voltage on either signal pin is within about 1.5V of either supply rail or
exceeds either supply rail. This definition is valid when
power is applied and when it is off, as well as during all
the states as power ramps up or down.
During a fault, the protector acts as a variable resistor,
conducting only enough to sustain the other side of the
switch within about 1.5V of the supply rail. This voltage
is known as the “fault knee voltage,” and is not symmetrical. It is approximately 1.3V down from the positive
supply (V+ pin) or approximately 2.0V up from the negative supply (V- pin). Each fault knee voltage varies
slightly with supply voltage, with output current, and
from device to device.
During a fault condition, all the fault current flows
from one signal pin through the protector and out
the other signal pin. No fault current flows through
either supply pin. (There will be a few pico-amps of
leakage current from each signal pin to each supply
pin, but this is independent of fault current.)
During the fault condition, enough current will flow to
maintain the output voltage at the fault knee voltage, so
the fault current is a function of the output resistance
and the supply voltage. The output voltage and current have the same polarity as the fault.
The maximum input fault voltage is 40V from the “opposite-polarity supply rail.” This means the input can go
to ±35V with ±5V supplies or to ±25V with ±15V supplies. The fault voltage is highest (±40V) when the supplies are off (V+ = V- = 0V).
Using the circuit of Figure 2, the approximate fault currents are as follows:
1) For positive faults:
I(F) ≈ (V+ - 1.3V - VLOW) ÷ ROUT
2) For negative faults:
I(F) ≈ (V- + 2V + VLOW) ÷ ROUT
where VLOW is the terminating voltage at the far end of
ROUT. VLOW = 0V when ROUT is grounded.
Figure 2. Application Circuit
6
_______________________________________________________________________________________
Signal-Line Circuit Protectors
Single-Supply Output Operation
Single-supply operation is a special case. Signals cannot go to ground, since from 0V to approximately +2V is
a fault condition.
Extremely Low-Current Operation
Figure 3 shows the typical high-impedance transfer
characteristics with a 100MΩ load. Compared to the
transfer characteristic at 1MΩ (see Typical Operating
Characteristics), the two knees are closer to the supply
voltages and the slopes of the flat portions of the curve
(fault conditions) are steeper. As the load resistance is
increased even further, the positive and negative knees
increase, and the slopes in fault conditions increase
even more. Eventually, at some extremely high output
resistance (e.g., Tera ohms), the output voltage can
exceed the supply voltage during fault conditions. This
is due to extremely low leakage currents from the input
to output.
When the protector’s output side is connected to very
high-resistance, very low-current loads (such as opamp inputs), a small leakage current flows from the
input to the output during fault conditions. This current
is typically below a nano-ampere (<10-9A) but, if the
output resistance is high enough, it can cause the output voltage to exceed the supply voltages during fault
conditions.
This condition can be self-correcting, however, if the
high-resistance load has protection diodes to the supply rails (either external or internal to the op amp).
These diodes conduct the leakage current to the supply
rails and safely limit the output voltage. An alternative is
to add a high-value resistor to ground in parallel with
the load. This resistor may be as low as 1000MΩ; its
value must be determined experimentally at the highest
anticipated operational temperature.
The fault protectors will not normally be used with highimpedance FET-input amplifiers that lack input protection
diodes. Such amplifiers are fragile and are normally
OUTPUT VOLTAGE (V)
4
MAX366/7-fig03
5
V+ = +5V
V- = -5V
ROUT = 100MΩ
3
2
MAX366/MAX367
The current through each protector should never exceed
30mA. Always calculate the power dissipated by all the
protectors in worst-case conditions (maximum voltage
and current through each protector) to ensure the package dissipation limit is not reached.
With single-supply operation, grounded loads will have
zero voltage (and current) whenever the input voltage is
below approximately 2V. In effect, both the IN and OUT
pins are in fault condition.
A special case arises when power is off: The part is in a
perpetual fault condition but no fault current flows
because all the internal FETs are off.
1
0
-1
-2
-3
-4
-30
-20
-10
0
10
20
30
INPUT VOLTAGE (V)
Figure 3. High-Impedance Transfer Characteristic
reserved for use when ultra-low leakage (pA) is needed.
The MAX366/MAX367 have nano-amperes of leakage,
which would negate the low leakage of the unprotected
amplifier.
Low-Voltage Operation
The MAX366/MAX367 “operate” with supply voltages
all the way down to 0V, but what they do to the signal is
not obvious. With a total supply voltage of 3.5V, the
protector is in a fault condition with nearly any input that
is not close to 2.0V. Below 3.5V (including power off),
the protector is perpetually in a fault condition (i.e., high
impedance).
When the supply voltage(s) ramps up (and/or down)
from zero, the signal path is initially in a fault condition
(open), until the supply voltage passes the input voltage. The output starts at zero and is delayed from
reaching the input voltage as the part comes out of the
fault condition. If the supply voltage exceeds about
3.5V, but never exceeds the input voltage, the output
will follow the supply, always remaining about 1.3V
below the positive supply voltage or 2V above the negative supply voltage. If the input voltage subsequently
comes out of the fault condition, the output returns to
the input value. This set of conditions is exactly
reversed when power ramps down to zero.
Since the input and output pins are identical and interchangeable, predicting whether or not the part is in a
fault condition is easy: If either IN or OUT exceeds V+
or V-, a fault condition exists and the current that flows
will be just enough to cause the other signal pin (OUT
or IN) to approach the appropriate supply rail.
_______________________________________________________________________________________
7
MAX366/MAX367
Signal-Line Circuit Protectors
Bipolar Faults
The MAX366/MAX367 V+ and V- pins are normally connected to a circuit’s most positive and most negative
power supplies. When a circuit has multiple power
supplies (such as ±5V and ±12V) and the MAX366/
MAX367 V+ and V- pins are connected to the lower
supply, it is possible to have fault conditions on both
sides of the signal path at once, if both sides of the
switch have paths to higher voltages. If the polarity of
these faults is the same, the signal path will be open
and there is no conflict.
If the IN and OUT pins are driven in opposite polarities
from low-impedance sources, the lower of the two
impedances will overcome the higher impedance, just
as if the protector were not present. (Make sure the
current does not exceed the 30mA absolute maximum
rating.) As the lower impedance source approaches
and exceeds the fault knee voltage, the protector will
conduct enough current to maintain the other signal pin
near the fault knee voltage. This means when the fault
knee voltage is reached, the current through the protector shifts from the higher current capability of the
lower impedance source to the lower current capability
of the higher impedance source.
_______________Typical Applications
Driven Switches
The MAX366/MAX367 have low supply currents
(<1µA), which allows the supply pins to be driven
directly by other active circuitry, instead of connected
directly to the power sources. In this configuration,
the parts can be used as driven fault-protected
switches with V+ or V- pins used as the control pins.
For example, if the V- pin is grounded, you can turn
the V+ pin on and off by driving it with the output of a
CMOS gate. This effectively connects and disconnects three or eight separate signal lines at once. (If
bipolar signals or signals that go to ground are being
switched, the V- pin must be driven simultaneously to
a negative potential.) Always ensure that the driving
source(s) does not drive the V+ pin more negative
than the V- pin.
Figure 4 shows a simple turn-on delay that takes
advantage of the MAX366’s low power consumption.
The two RC networks cause gradual application of
power to the MAX366, which in turn applies the input
signals smoothly after the amplifier has stabilized.
The two diodes discharge the two capacitors rapidly
when power is turned off.
8
+5V
MAX366
V+
8
10µF
1
IN1
OUT1
7
2
IN2
OUT2
6
3
IN3
OUT3
5
4
100k
OP AMP
V-
10µF
100k
-5V
Figure 4. Turn-On Delay
This circuit can be tailored to nearly any rate of turnon by selecting the RC time constants in the V+ and
V- pins, without affecting the time constant of the
measuring circuit.
Protectors as Circuit Elements
Any of the individual protectors in a MAX366 or MAX367
may be used as a switched resistor, independent of the
functions of other elements in the same package. For
example, Figure 5 shows a MAX366 with two of the protectors used to protect the input of an op amp, and the
third element used to sequence a power supply.
Combining the circuits of Figures 4 and 5 produces a
delayed action on the switched +5V, as well as smooth
application of signals to the amplifier input.
_________Testing Circuit Protectors
Measuring Path Resistance
Measuring path resistance requires special techniques,
since path resistance varies dramatically with the IN
and OUT voltages relative to the supply voltages.
Conventional ohmmeters should not be used, for two
reasons: 1) the applied voltage and currents are usually not predictable, and 2) the true resistance is a function of the applied voltage, which is dramatically altered
by the ohmmeter itself. Autoranging ohmmeters are
particularly unreliable.
_______________________________________________________________________________________
Signal-Line Circuit Protectors
MAX366/MAX367
SWITCHED +5V
P
100mV
+5V
MAX366
V+
1
IN1
OUT1
7
2
IN2
OUT2
6
3
IN3
OUT3
5
4
A
8
MAX366
100k
VIN
OP AMP
V-
4
IN_
V-
OUT_
V+
VOUT
8
V+
ADJUSTABLE ANALOG VOLTAGE
V-
PATH RESISTANCE = 100mV/A
-5V
Figure 5. Power-Supply Sequencing
Figure 6. Path-Resistance Measuring Circuit
Figure 6 shows a circuit that can give reliable results.
This circuit uses a 100mV voltage source and a lowvoltage-drop ammeter as the measuring circuit, and an
adjustable supply to sweep the analog voltage across
its whole range. The ammeter must have a voltage
drop of less than one millivolt (at any current) for accurate results. (A Keithley Model 617 Electrometer has a
suitable ammeter circuit, appropriate ranges, and a
built-in voltage source designed for this type of measurement.) Measurements are made by setting the
analog voltage, measuring the current, and calculating
the path resistance. The procedure is repeated at
each analog voltage and supply voltage.
It is important to use a voltage source of 100mV or less.
As shown in Figure 4, this voltage is added to the VIN
voltage to form the VOUT voltage. Using a higher voltage could cause the OUT pin to go into a fault condition prematurely.
In 50Ω systems, signal response is reasonably flat up
to several megahertz (see Typical Operating
Characteristics). Above 5MHz, the response has several minor peaks, which are highly layout dependent.
Because the path resistance is dependent on the supply voltage and signal amplitude, the impedance is not
controlled. Adjacent channel attenuation up to 5MHz is
about 3dB above that of a bare IC socket, and is due
entirely to capacitive coupling.
Pulse response is reasonable, but because the impedance changes rapidly, fast rise times may induce ringing
as the signal approaches the fault voltage. At very high
amplitudes (such as noise spikes), the capacitive coupling across the signal pins will transfer considerable
energy, despite the fact that the DC path is a virtual open
circuit.
High-Frequency Performance
_______________________________________________________________________________________
9
MAX366/MAX367
Signal-Line Circuit Protectors
__High-Voltage Surge Suppression
These devices are not high-voltage arresters, nor are they
substitutes for surge suppressers. In systems that use
these forms of protection, however, the MAX366/MAX367
can fill a vital gap. Figure 7 shows a typical circuit.
Although the surge suppressers are extremely fast shunt
elements, they have very soft current knees. Their clamp
voltage must be chosen well above the normal signal
levels, because they have excessive leakage currents as
the knee is approached. This current can interfere with
normal operation when signal levels are low or impedances are high. If the clamp voltage is too high, however,
the input can be damaged.
Using a MAX366/MAX367 after the surge suppresser
allows the surge-suppresser voltage to be set above
the supply voltage (but within the overvoltage limits),
dramatically reducing the effects of leakage (Figure 7).
During a surge, the surge suppresser clamps the input
This protects the
voltage to roughly ±10V.
MAX366/MAX367, but the MAX366/MAX367 still disconnect the signal from the op amp well within the ±5V
supply.
_________________Pin Configurations
+5V
MAX366
V+
8
1
IN1
OUT1
7
2
IN2
OUT2
6
3
IN3
OUT3
5
4
OP AMP
V-
-5V
SURGE SUPPRESSERS
(+10V)
Figure 7. Surge-Suppression Circuit
___________________Chip Topography
IN1
TOP VIEW
IN1
18 V+
1
8 V+
IN3 3
16 OUT2
IN2 2
7 OUT1
IN4 4
15 OUT3
IN3 3
6 OUT2
IN5 5
14 OUT4
5 OUT3
IN1
1
IN6 6
13 OUT5
MAX366
IN7 7
12 OUT6
DIP/SO
IN8 8
11 OUT7
V- 4
V+
17 OUT1
IN2 2
V- 9
OUT1
IN2
0.112"
(2.84mm)
OUT2
IN3
10 OUT8
MAX367
DIP/SO
OUT3
V-
0.085"
(2.16mm)
TRANSISTOR COUNT: 21
SUBSTRATE CONNECTED TO V+
10
______________________________________________________________________________________
Signal-Line Circuit Protectors
D
E
DIM
E1
A
A1
A2
A3
B
B1
C
D1
E
E1
e
eA
eB
L
A3
A A2
L A1
0° - 15°
C
e
B1
eA
B
eB
D1
Plastic DIP
PLASTIC
DUAL-IN-LINE
PACKAGE
(0.300 in.)
DIM PINS
D
D
D
D
D
D
DIM
D
0°-8°
A
0.101mm
0.004in.
e
B
A1
E
C
H
L
SO
SMALL OUTLINE
PACKAGE
(0.150 in.)
INCHES
MAX
MIN
0.200
–
–
0.015
0.175
0.125
0.080
0.055
0.022
0.016
0.065
0.045
0.012
0.008
0.080
0.005
0.325
0.300
0.310
0.240
–
0.100
–
0.300
0.400
–
0.150
0.115
A
A1
B
C
E
e
H
L
8
14
16
18
20
24
INCHES
MAX
MIN
0.069
0.053
0.010
0.004
0.019
0.014
0.010
0.007
0.157
0.150
0.050
0.244
0.228
0.050
0.016
DIM PINS
D
D
D
INCHES
MIN
MAX
0.348 0.390
0.735 0.765
0.745 0.765
0.885 0.915
1.015 1.045
1.14 1.265
8
14
16
MILLIMETERS
MIN
MAX
–
5.08
0.38
–
3.18
4.45
1.40
2.03
0.41
0.56
1.14
1.65
0.20
0.30
0.13
2.03
7.62
8.26
6.10
7.87
2.54
–
7.62
–
–
10.16
2.92
3.81
MILLIMETERS
MIN
MAX
8.84
9.91
18.67 19.43
18.92 19.43
22.48 23.24
25.78 26.54
28.96 32.13
MILLIMETERS
MIN
MAX
1.35
1.75
0.10
0.25
0.35
0.49
0.19
0.25
3.80
4.00
1.27
5.80
6.20
0.40
1.27
INCHES
MILLIMETERS
MIN MAX
MIN
MAX
0.189 0.197 4.80
5.00
0.337 0.344 8.55
8.75
0.386 0.394 9.80 10.00
21-0041A
______________________________________________________________________________________
11
MAX366/MAX367
________________________________________________________Package Information
MAX366/MAX367
Signal-Line Circuit Protectors
___________________________________________Package Information (continued)
DIM
D
0°- 8°
A
e
B
0.101mm
0.004in.
A1
C
L
A
A1
B
C
E
e
H
L
INCHES
MAX
MIN
0.104
0.093
0.012
0.004
0.019
0.014
0.013
0.009
0.299
0.291
0.050
0.419
0.394
0.050
0.016
DIM PINS
E
Wide SO
SMALL OUTLINE
PACKAGE
(0.300 in.)
H
D
D
D
D
D
16
18
20
24
28
INCHES
MIN MAX
0.398 0.413
0.447 0.463
0.496 0.512
0.598 0.614
0.697 0.713
MILLIMETERS
MIN
MAX
2.35
2.65
0.10
0.30
0.35
0.49
0.23
0.32
7.40
7.60
1.27
10.00
10.65
0.40
1.27
MILLIMETERS
MIN
MAX
10.10 10.50
11.35 11.75
12.60 13.00
15.20 15.60
17.70 18.10
21-0042A
DIM
E1
E
D
A
0°-15°
Q
L
L1
e
C
B1
B
S1
S
CERDIP
CERAMIC DUAL-IN-LINE
PACKAGE
(0.300 in.)
A
B
B1
C
E
E1
e
L
L1
Q
S
S1
INCHES
MIN
MAX
–
0.200
0.014
0.023
0.038
0.065
0.008
0.015
0.220
0.310
0.290
0.320
0.100
0.125
0.200
0.150
–
0.015
0.070
–
0.098
0.005
–
DIM PINS
D
D
D
D
D
D
8
14
16
18
20
24
MILLIMETERS
MIN
MAX
–
5.08
0.36
0.58
0.97
1.65
0.20
0.38
5.59
7.87
7.37
8.13
2.54
3.18
5.08
3.81
–
0.38
1.78
–
2.49
0.13
–
INCHES
MILLIMETERS
MIN
MAX MIN MAX
–
0.405
–
10.29
–
0.785
–
19.94
–
0.840
–
21.34
–
0.960
–
24.38
–
1.060
–
26.92
–
1.280
–
32.51
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
12 __________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 (408) 737-7600
© 1994 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.