MIC864 MICREL [Micrel Semiconductor], MIC864 Datasheet - Page 8

• Manufacturer Part Number: MIC864
• Description: Dual 350kHz Rail-to-Rail Operational Amplifier
• Manufacturer: MICREL [Micrel Semiconductor]

Application Information
The MIC864 operational amplifier is optimized for
portable applications such as cell phones, computer
pads, media players, mobile chemical sensors, carbon
monoxide detectors, and smoke detectors. A 2.5V to
5.5V supply voltage range allows operation from the
regulated output of a lithium-ion battery. No-load supply
current is 33µA per channel for long battery life. An input
range 0.2V beyond the supply rails and an output range
to within 15mV of the supply rails (100kΩ load) maximize
dynamic range for improved signal to noise ratios in the
application. High, consistent CMRR and PSRR minimize
power supply noise coupling from adjacent circuitry.
Input protection
The IN- and IN+ inputs of the MIC864 are clamped to
the V+ and V− pins using ESD protection diodes.
Operation of IN+ or IN− beyond (V+) + 0.2V and (V−) −
0.2V is not recommended as this would turn on the ESD
protection diodes and violates the Absolute Maximum
Ratings.
Feedback
Feedback resistors in the 5kΩ and 100kΩ range are
recommended.
requirements must be considered when designing the
feedback network, especially in unity-gain and low-gain
circuits (see “Capacitive and Resistive Loads” section for
further information).
When using high-value feedback resistors, place a low-
value capacitor in parallel with the resistor connected
between IN- and OUT. This capacitor counteracts the
effects of the parasitic capacitance at the IN- pin which
forms a pole that may otherwise degrade stability.
However, a 68pF minimum load capacitance must be
included to ensure stability.
When AC-coupling signals to the MIC864 through a
capacitor, provide a DC-bias current path using a
resistor. Otherwise, there will be no source for supplying
the input bias current and the circuit will stop working.
Micrel, Inc.
March 2012
Load
resistance
and
capacitance
8
Power Supply Bypassing
For single supply operation, connect a 0.1µF ceramic
capacitor between the V+ and V− power supply pins. For
dual supply operation, connect 0.1µF capacitors from V+
to GND and from GND to V−. Place these capacitors
within 0.2in (5mm) of the MIC864. If no large-value
capacitors are nearby then also include 10uF capacitors
connected in similar fashion.
Capacitive and Resistive Loads
The MIC864 is internally compensated for unity-gain
stability with load resistances between 5kΩ and 100kΩ,
and a 100pF load capacitance. A 68pF minimum load
capacitance is required to ensure unity-gain stability
across production and temperature variations. Care
should be taken to observe the minimum load
capacitance requirement in circuits with a gain less than
2, and in circuits with a capacitor connected between the
IN- and OUT pins.
Driving ADCs
ADCs (analog-to-digital converters) typically include
either a capacitive sample-and-hold or a capacitive DAC
at their inputs. During operation, they periodically
connect those capacitors to their inputs while sampling
the input signal. General practice is to place a RC low-
pass filter between the operational amplifier supplying
the input signal and the ADC. The series resistor
between the operational amplifier output and ADC input
limits capacitive loading on the operational amplifier to
prevent instability. The capacitor between the ADC input
and GND minimizes glitches by supplying charge to the
internal ADC capacitors.
M9999-032612-A
MIC864