Application Notes

Ground Sensing And Rail To Rail

The input common-mode voltage range of the LMV72xA series extends 300mV

beyond

the supply rails. This is achieved with a complementary input stage—a N-channel input

differential pair in parallel with a P-channel differential pair. For normal operation, inputs

should be limited to this range. The absolute maximum input voltage is 500mV beyond the

supplies. Inputs greater than the input common-mode range but less than the maximum input

voltage, while not valid, will not cause any damage to the op-amp. Unlike some other op-

amps, if input current is limited, the inputs may go beyond the supplies without phase

inversion, as shown in Figure 13. Since the input common-mode range extends from (VS− −

0.1V) to (VS+ + 0.1V), the LMV72xA op-amps can easily perform ‘true ground’ sensing.

Fig. 13 No Phase Inversion with Inputs Greater Than the Power-Supply Voltage

A topology of class AB output stage with common-source transistors is used to achieve

rail-to-rail output. For light resistive loads (e.g. 100kΩ), the output voltage can typically

swing to within 5mV from the supply rails. With moderate resistive loads (e.g. 10kΩ), the

output can typically swing to within 10mV from the supply rails and maintain high open-loop

gain.

The maximum output current is a function of total supply voltage. As the supply voltage

to the amplifier increases, the output current capability also increases. Attention must be paid

to keep the junction temperature of the IC below 150℃ when the output is in continuous

short-circuit. The output of the amplifier has reverse-biased ESD diodes connected to each

supply. The output should not be forced more than 0.5V beyond either supply, otherwise

current will flow through these diodes.

Capacitive Load And Stability

The LMV72xA can directly drive 1nF in unity-gain without oscillation. The unity-

gain

follower (buffer) is the most sensitive configuration to capacitive loading.

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10MHz, RRIO CMOS Operational Amplifiers

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