MAX9943 데이터 시트보기 (PDF) - Maxim Integrated
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MAX9943 Datasheet PDF : 11 Pages
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MAX9943/MAX9944
High-Voltage, Precision, Low-Power Op Amps
Detailed Description
The MAX9943/MAX9944 are single/dual operational
amplifiers designed for industrial applications. They
operate from 6V to 38V supply range while maintaining
excellent performance. These devices utilize a three-
stage architecture optimized for low offset voltage and low
input noise with only 550μA supply current. The devices
are unity gain stable with a 1nF capacitive load. These
well-matched devices guarantee the high open-loop gain,
CMRR, PSRR, and low voltage offset.
The MAX9943/MAX9944 provide a wide input/output
voltage range. The input terminals of the MAX9943/
MAX9944 are protected from excessive differential
voltage with back-to-back diodes. The input signal current
is also limited by an internal series resistor. With a 40V
differential voltage, the input current is limited to 20mA.
The output can swing to the negative rail while delivering
20mA of current, which is ideal for loop-powered system
applications. The specifications and operation of the
MAX9943/MAX9944 family is guaranteed over the -40°C
to +125°C temperature range.
Application Information
Bias Current vs. Input Common Mode
The MAX9943/MAX9944 use an internal bias current
cancellation circuit to achieve very low bias current over
a wide input common-mode range. For such a circuit to
function properly, the input common mode must be at
least 300mV away from the negative supply VEE. The
input common mode can reach the negative supply VEE.
However, in the region between VEE and VEE + 0.3V,
there is an increase in bias current for both inputs.
Capacitive Load Stability
Driving large capacitive loads can cause instability in many
op amps. The MAX9943/MAX9944 are stable with capacitive
loads up to 1nF. The Capacitive Load vs. Resistive Load
graph in the Typical Operating Characteristics gives the
stable operation region for capacitive versus resistive loads.
Stability with higher capacitive loads can be improved
by adding an isolation resistor in series with the op-amp
output, as shown in Figure 1. This resistor improves the
circuit’s phase margin by isolating the load capacitor from
the amplifier’s output.
Power Supplies and Layout
The MAX9943/MAX9944 can operate with dual supplies
from ±3V to ±19V or with a single supply from +6V to +38V
with respect to ground. When used with dual supplies,
bypass both VCC and VEE with their own 0.1μF capacitor
INPUT
MAX9943
RISO
OUTPUT
CL
Figure 1. Capacitive Load Driving Circuit
1.5kΩ
1.5kΩ
Figure 2. Input Protection Circuit
to ground. When used with a single supply, bypass VCC
with a 0.1μF capacitor to ground. Careful layout technique
helps optimize performance by decreasing the amount of
stray capacitance at the op amp’s inputs and outputs. To
decrease stray capacitance, minimize trace lengths by
placing external components close to the op amp’s pins.
Output Current Capability
The MAX9943/MAX9944 are capable of driving heavy
loads such as the ones that can be found in loop-powered
systems for remote sensors. The information is transmitted
through ±20mA or 4mA–20mA current output across
long lines that are terminated with low resistance loads
(e.g., 600Ω). The Typical Application Circuit shows the
MAX9944 used as a voltage-to-current converter with a
current-sense amplifier in the feedback loop. Because
of the high output current capability of the MAX9944, the
device can be used to directly drive the current-loop.
The specifications and operation of the MAX9943/MAX9944
family is guaranteed over the -40°C to +125°C temperature
range, However, when used in applications with ±15V
supply voltage (see Figure 3), the capability of driving more
than ±20mA of current is limited to the -40°C to +85°C
temperature range. Use a lower supply voltage if this
current must be delivered at a higher temperature range.
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