CMV7101 Ver la hoja de datos (PDF) - California Micro Devices => Onsemi

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CMV7101

CMV7101 Low Power, Low Voltage OPAMP with RRIO, SOT23-5

California Micro Devices => Onsemi 

CALIFORNIA MICRO DEVICES

CMV7101

for calculating invariably results in a value larger than

optimum,

1

>

1

(4)

2 Rs

2 Rf

2.4 Power Supply Decoupling

The CMV7101 is not prone to oscillation without the use

of power supply decoupling capacitors, however to

minimize hum and noise pick-up, it is recommended that

the rails be bypassed with 0.01 µF capacitors.

Since the parasitic capacitance is bound to change

between the breadboard phase and the production printed

circuit board, we recommend the use of a “gimmick”

which is made by twisting two lengths (about a foot) of

insulated wire (such as AWG 24) that are bared at both

ends. The gimmick is soldered across Rf . With the circuit in

operation, Cf is adjusted by clipping short lengths until the

compensation is nominal. Then simply measure the

capacitance of the gimmick on an impedance bridge.

Typical Application

3.0 Low Power and Supply Voltage Single Rail Oscillator

Operational amplifiers have been used for years to generate

frequency stable oscillators, but the circuit shown in Figure

3 provides a stable frequency operating from a single supply

voltage and drawing a mere 300 µA. For (R1 + R2) ÷ R1 =

0.473, the period, T, of the oscillator is given by:

Figure 1. Input Capacitance Compensation

T = 2 Rf C1

(5)

Where: Rf is the feedback resistor, C1 is the capacitor

The period is easily adjusted by varying Rf. R3 ensures that the

circuit will start on a single rail by forcing A1’s output to the

positive rail. R4’s value is not critical but should be a factor of

10 greater than the parallel combination of R1 and R2.

The circuit lends itself to a variety of applications such as

battery operated toys where a LED is required to flash at a

periodic rate. The high output current of the CMV7101 assures

that the LED will have sufficient current to turn it on.

2.3 Capacitive Load Considerations

The CMV7101 is capable of driving capacitive loads in excess

of 100 pF without oscillation. However, significant peaking

will result. The easiest way to minimize this problem is to

use an isolation resistor as shown in Figure 2.

R1

R1 + R2

= 0.473

Figure 2. Isolating a Capacitve Load

Figure 3. Single Rail Oscillator

© 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

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