CALIFORNIA MICRO DEVICES
Applications Benefits
CMV7101
that can be damaged if currents in excess of 5 mA when
the input voltage exceeds the rail by 0.3 volt. Damage
can be precluded by inserting a limiting resistor, Rs, in
series with the input whose recommend value may be
calculated from:
1.0 Packaging
The most obvious benefit to using the CMV7101 is the
SOT package, which has been widely accepted as the surface
mounting of choice. The SOT23 footprint not only saves
space on the PCB but also provides a low profile for
applications such as the PCMCIA, type III cards which
require heights less than 0.056 Inches (1.43 mm).
Vin - (V+ - 0.3 V)
Rs >
(1)
5 mA
For V+ equal to 2.2 volts, and Vin equal to a maximum of
5 volts, Rs should be chosen for a value of 500 Ω or
greater.
1.2 Signal Integrity
As systems have become smaller and higher functionality
is demanded of them, spacing between traces has
diminished as well. This can result in increased sensitivity
to noise, pick-up, and cross talk. Due to its small size, the
CMV7101 may be placed in close proximity to the signal
source minimizing the above problems, and since it is a
single device, routing traces to a multiple amplifier such as
dual or quad avoids running long traces reducing cross
talk.
2.1 Output Current and Power Dissipation
The CMV7101 is capable of sinking or sourcing output
currents in excess of 50 mA and voltages nearly equal to
the supply voltage. The device does not have internal short
circuit limiting, but it is capable of withstanding an indefinite
short circuit without sustaining damage. Clearly the
maximum power dissipation will occur under these
conditions:
The Rail to Rail Inputs and Output allow the amplifier to
operate on a low supply voltages while maintaining signal
tracking integrity and large output voltage swings (relative
to the supply rail).
Pdiss = (V+ - Vout) * Iout
(2)
Where: Pdiss = Power dissipated by the chip
V+ Supply Voltage
Vout = The Output Voltage
=
1.3 Low Distortion
Even when operated from a 2.2 volt supply, the CMV7101
still exhibits very low distortion thanks to its large open
loop gain and unique circuit design making it suitable for
application in many audio systems.
Furhermore,
TJ = TA + θJA
(3)
Where TA = The Ambient Temperature
1.4 Low Supply Current and High Output Current
θJA = The thermal impedance of the package
The supply current required by CMV7101 of 300 µA coupled
with its ability to sink and source large currents of 50 mA
make it unique in its class. Clearly, the low supply current
provides longer operation in battery operated systems while
the high output current assures that circuits with capacitive
loads will starter faster. The high output current also
eliminates the need for a buffer, such as an emitter follower,
in the loop with the amplifier for applications demanding
large load currents.
For a short circuit on the output with V+ equal to 3 volts
and an output current of 50 mA, the power dissipation per
equation (2) would be 150 mW. Assuming a worst case
ambient of 85 °C, the junction temperature would be
134 °C well below the maximum junction rating of 150 °C.
2.2 Input Considerations
The CMV7101 exhibits an input impedance which is typically
in excess of 1 Tera W making it an excellent choice for
applications requiring high source impedance such as
buffering photo diodes, high impedance transducers, or
long time constant integraters. A high source impedance
usually dictates a large feedback resistor, Rf, but the parallel
combination of Rf and Rs in parallel with the input
capacitance of the amplifier (typically 3 pF) creates a parasitic
pole which can erode the phase margin of the amplifier.
The recommended fix is to bypass Rf with a small capacitor
thus canceling the pole at the inverting input. The formula
Applications Information
2.0 Input Common Mode and Output Voltage
Considerations
The CMV7101 will accommodate input common mode
voltages equal to both rails, and input signals that exceed
the rails will not cause phase inversion of the output.
However, ESD diode clamps are provided at the inputs
©2000 California Micro Devices Corp. All rights reserved.
3/00
215 Topaz Street, Milpitas, California 95035
Tel: (408) 263-3214
Fax: (408) 263-7846
www.calmicro.com
6
CALMIRCO [ CALIFORNIA MICRO DEVICES CORP ]
