MAX366C/D Maxim Integrated, MAX366C/D Datasheet - Page 8

• Manufacturer Part Number: MAX366C/D
• Description: TVS Diode Arrays Signal Line Circuit Protector with Three Independent Protectors
• Manufacturer: Maxim Integrated
• Series: MAX366, MAX367r

Specifications of MAX366C/D

• Polarity: Unidirectional
• Channels: 3 Channels
• Operating Voltage: 0 V to 18 V
• Peak Surge Current: 30 mA
• Termination Style: Through Hole
• Dimensions: 7.87 mm W x 9.91 mm L x 5.08 mm H
• Peak Pulse Power Dissipation: 727 mW

The MAX366/MAX367 V+ and V- pins are normally con-
nected 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 pro-
tector shifts from the higher current capability of the
lower impedance source to the lower current capability
of the higher impedance source.
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 discon-
nects 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.
Signal-Line Circuit Protectors
8
_______________Typical Applications
_______________________________________________________________________________________
Driven Switches
Bipolar Faults
This circuit can be tailored to nearly any rate of turn-
on by selecting the RC time constants in the V+ and
V- pins, without affecting the time constant of the
measuring circuit.
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 pro-
tectors 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.
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 usual-
ly not predictable, and 2) the true resistance is a func-
tion of the applied voltage, which is dramatically altered
by the ohmmeter itself. Autoranging ohmmeters are
particularly unreliable.
Figure 4. Turn-On Delay
_________Testing Circuit Protectors
1
2
3
4
IN1
IN2
IN3
V-
MAX366
Protectors as Circuit Elements
Measuring Path Resistance
OUT1
OUT2
OUT3
V+
8
7
6
5
10 F
10 F
100k
100k
OP AMP
+5V
-5V