Datasheet

Single/Dual/Quad, +1.8V/10µA, SOT23,
Beyond-the-Rails Op Amps
R
L
= 100kΩ TIED TO V
EE
V
IN
= 2.0V
f
IN
= 1kHz
IN
In the region where the differential input voltage
MAX4240-44 fig03
approaches 1.8V, the input resistance decreases expo-
nentially from 45MΩ to 4.4kΩ as the diode block begins
conducting. Conversely, the bias current increases with
the same curve.
1V/div
1V/div
200µs/div
Figure 3. Rail-to-Rail Input/Output Voltage Range
MAX4240–MAX4244
OUT
Rail-to-Rail Output Stage
The MAX4240–MAX4244 output stage can drive up to a
10kΩ load and still swing to within 40mV of the rails.
Figure 3 shows the output voltage swing of a MAX4240
configured as a unity-gain buffer, powered from a single
+2V supply voltage. The output for this setup typically
swings from (V
EE
+ 6mV) to (V
CC
- 8mV) with a 100kΩ
load.
__________Applications Information
Power-Supply Considerations
The MAX4240–MAX4244 operate from a single +1.8V
to +5.5V supply (or dual ±0.9V to ±2.75V supplies) and
100
consume only 10µA of supply current per amplifier. A
high power-supply rejection ratio of 85dB allows the
amplifiers to be powered directly off a decaying battery
90
voltage, simplifying design and extending battery life.
The MAX4240–MAX4244 are ideally suited for use with
most battery-powered systems. Table 1 lists a variety of
typical battery types showing voltage when fresh, volt-
age at end-of-life, capacity, and approximate operating
time from a MAX4240/MAX4241, assuming nominal
conditions for both normal and shutdown modes.
PSRR (dB)
80
70
T
A
= +85°C
T
A
= -40°C
T
A
= +25°C
MAX4240-44 fig04
Although the amplifiers are fully guaranteed over tem-
60
perature for operation down to a +1.8V single supply,
1.0 1.2
1.4 1.6 1.8
2.0
even lower-voltage operation is possible in practice.
SUPPLY VOLTAGE (V)
Figures 4 and 5 show the PSRR and supply current as
a function of supply voltage and temperature.
Figure 4. Power-Supply Rejection Ratio vs. Supply Voltage
Power-Up Settling Time
The MAX4240–MAX4244 typically require 200µs to
12
power up after V
CC
is stable. During this start-up time,
the output is indeterminant. The application circuit
10
T
A
= +85°C
T
A
= +25°C
T
A
= -40°C
MAX4240-44 fig05
should allow for this initial delay.
Shutdown Mode
The MAX4241 (single) and MAX4243 (dual) feature a
low-power shutdown mode. When the shutdown pin
(SHDN) is pulled low, the supply current drops to 1µA
per amplifier, the amplifier is disabled, and the outputs
enter a high-impedance state. Pulling SHDN high or
SUPPLY CURRENT (µA)
8
6
4
leaving it floating enables the amplifier. Take care to
ensure that parasitic leakage current at the SHDN pin
does not inadvertently place the part into shutdown
2
0
1.0 1.2
1.4 1.6 1.8
2.0
mode when SHDN is left floating. Figure 6 shows the
SUPPLY VOLTAGE (V)
output voltage response to a shutdown pulse. The logic
threshold for SHDN is always referred to V
CC
/ 2 (not to
Figure 5. Supply Current vs. Supply Voltage
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