Rainbow Electronics MAX9618 - Manual (Page 7)

High-Efficiency, 1.5MHz
Op Amps with RRIO
MAX9617/MAX9618
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Detailed Description
The MAX9617 (single) and MAX9618 (dual) are preci-
sion, low-power op amps ideal for signal processing
applications. These devices use an innovative autozero
technique that allows precision and low noise with a
minimum amount of power. The low input offset voltage,
CMOS inputs, and the absence of 1/f noise allows for
optimization of active filter designs.
The MAX9617/MAX9618 achieve rail-to-rail performance
at the input through the use of a low-noise charge pump.
This ensures a glitch-free, common-mode input voltage
range extending from the negative supply rail up to
the positive supply rail, eliminating crossover distortion
common to traditional n-channel/p-channel CMOS pair
inputs, reducing harmonic distortion at the output.
Autozero
The MAX9617/MAX9618 feature an autozero circuit that
allows the device to achieve less than 10FV (max) of
input offset voltage and eliminates the 1/f noise.
Internal Charge Pump
An internal charge pump provides an internal supply typi-
cally 1V beyond the upper rail. This internal rail allows the
MAX9617/MAX9618 to achieve true rail-to-rail inputs and
outputs, while providing excellent common-mode rejec-
tion, power-supply rejection ratios, and gain linearity.
The charge pump requires no external components, and
in most applications is entirely transparent to the user.
The operating frequency is well beyond the unity-gain
frequency of the amplifier, avoiding aliasing or other sig-
nal integrity issues in sensitive applications.
Applications Information
The MAX9617/MAX9618 low-power, low-noise, and pre-
cision operational amplifiers are designed for applica-
tions in the portable medical, such as ECG and pulse
oximetry, portable consumer, and industrial markets.
The MAX9617/MAX9618 are also ideal for loop-powered
systems that interface with pressure sensors or strain
gauges.
Capacitive-Load Stability
Driving large capacitive loads can cause instability in
many op amps. The MAX9617/MAX9618 are stable
with capacitive loads up to 400pF. Stability with higher
capacitive loads can be improved by adding an isolation
resistor in series with the op-amp output. This resistor
improves the circuit’s phase margin by isolating the load
capacitor from the amplifier’s output. The graph in the
Typical Operating Characteristics gives the stable oper-
ation region for capacitive load versus isolation resistors.
Power Supplies and Layout
The MAX9617/MAX9618 operate either with a single sup-
ply from +1.6V to +5.5V with respect to ground or with
dual supplies from Q0.8V to Q2.75V. When used with
dual supplies, bypass both supplies with their own 0.1FF
capacitor to ground. When used with a single supply,
bypass V
DD
with a 0.1FF 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 capaci-
tance, minimize trace lengths by placing external com-
ponents close to the op amp’s pins.
Figure 1. Typical Application Circuit: Sallen-Key Active Lowpass Filter
Chip Information
PROCESS: BiCMOS
MAX9617 ADC
+5V
V IN