MAX366CSA Maxim Integrated Products, MAX366CSA Datasheet - Page 7

• Manufacturer Part Number: MAX366CSA
• Description: IC SIGNAL-LINE CIRC PROT 8-SOIC
• Manufacturer: Maxim Integrated Products

Specifications of MAX366CSA

• Voltage - Clamping: ±40V
• Technology: Mixed Technology
• Power (watts): 471mW
• Number Of Circuits: 3
• Applications: General Purpose
• Package / Case: 8-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Voltage - Working: -

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 pack-
age 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.
Single-supply operation is a special case. Signals can-
not go to ground, since from 0V to approximately +2V is
a fault condition.
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 op-
amp inputs), a small leakage current flows from the
input to the output during fault conditions. This current
is typically below a nano-ampere (<10
output resistance is high enough, it can cause the out-
put 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 sup-
ply 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 high-
impedance FET-input amplifiers that lack input protection
diodes. Such amplifiers are fragile and are normally
Extremely Low-Current Operation
Single-Supply Output Operation
_______________________________________________________________________________________
-9
A) but, if the
Signal-Line Circuit Protectors
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.
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 volt-
age. 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 neg-
ative 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 inter-
changeable, 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.
Figure 3. High-Impedance Transfer Characteristic
-1
-2
-3
-4
5
4
3
2
1
0
-30
V+ = +5V
V- = -5V
R
OUT
-20
= 100M
INPUT VOLTAGE (V)
-10
Low-Voltage Operation
0
10
20
30
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