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CMV1030

MICROPOWER RRO Operational Amplifier

California Micro Devices => Onsemi 

CMV1030

Applications Information

1. Input Common Mode Range and Output

Voltage Considerations

The CMV1030 is capable of accommodating an input

common mode voltage equal to one volt below the

positive rail and all the way to the negative rail. It is also

capable of output voltages equal to both power supply

rails. Voltages that exceed the supply voltages will not

cause phase inversion of the output, however, ESD

diode clamps are provided at the inputs that can be

damaged if static currents in excess of ±5mA are

allowed to flow in them. This can occur when the

magnitude of input voltage exceeds the rail by more

than 0.3 volt. To preclude damage, an applications

resistor, Rs, in series with the input is recommended as

illustrated in Figure 1 whose value for Rs is given by:

VIN - (V+ + 0.3 V)

RS > ——————————

5mA

For V+ (or V-) equal to 2.2 volts and V equal to 10 volts,

IN

RS should be chosen for a value of 2.5KΩ or greater.

is indefinitely shorted to ground. In general:

PDISS = (V+ –VOUT)*IOUT + IS*V+

Where: PDISS = Power dissipated by the chip

V+ = Supply voltage

VOUT = The output voltage

IS = Supply Current

The contribution to power dissipation due to supply

current is 200µW and is indeed negligible as stated

above.

The primary contribution to power dissipation occurs in

the output stage. V+ – VOUT would equal

5V – 0V = 5 V, and power dissipation would be equal to

35mW.

TJ = TA + θJA* PDISS

Where: T = The ambient temperature

A

θJA = The thermal impedance of the package

junction to ambient

The SOT23 exhibits a θJA equal to 325°C/W. Thus for our

example the junction rise would be about 11.4 which is

clearly not a destructive situation even under an ambient

temperature of 85°C.

3. Input Impedance Considerations

Figure 1.

2. Output Current and Power Dissipation

Considerations

The CMV1030 is capable of sinking and sourcing output

currents in excess of 7mA at voltages very nearly equal

to the rails. As such, it does not have any internal short

circuit protection (which would in any event detract from

its rail to rail capability). Although the power dissipation

and junction temperature rise are small, a short analysis

is worth investigating.

Obviously, the worst case from a power dissipation point

of view is when the output is shorted to either ground in

a single rail application or to the opposite supply voltage

in split rail applications. Since device only draws 60µA

supply current (100µA maximum), its contribution to the

junction temperature, TJ, is negligible. As an example, let

us analyze a situation in which the CMV1030 is oper-

ated from a 5 volt supply and ground, the output is

"programmed" to positive saturation, and the output pin

The CMV1030 exhibits an input impedance typically in

excess of 1 Tera Ω (1 X 10 12 ohms) making it very

appropriate for applications involving high source

impedance such as photodiodes and high output

impedance transducers or long time constant integra-

tors. High source impedances usually dictate large

feedback resistors. But, the output capacitance of the

source in parallel with the input capacitance of the

CMV1030 (which is typically 3pF) create a parasitic pole

with the feedback resistor which erodes the phase

margin of the amplifier. The usual fix is to bypass, RF, as

shown in Figure 2 with a small capacitor to cancel the

input pole. The usual formula for calculating CF always

results in a value larger than that is required:

1

1

—————— ≥ ——————

2Π RS CS

2Π RF CF

Since the parasitic capacitance can change between the

breadboard and the production printed circuit board, we

favor the use of a "gimmick", a technique perfected by

TV technicians in the 1950’s. A gimmick is made by

taking two lengths (typically about a foot) of small gauge

wire such as AWG 24, twisting them together, and then

after baring all ends soldering the gimmick across RF.

With the circuit operating, CF is "adjusted" by clipping

short lengths of the gimmick off until the compensation

is nominal. Then simply remove the gimmick, take it to

an impedance bridge, and select the capacitor accord-

©2000 California Micro Devices Corp. All rights reserved.

215 Topaz Street, Milpitas, California 95035 

8

Tel: (408) 263-3214

Fax: (408) 263-7846

www.calmicro.com

10/19/2000

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