The values for R

zero attributed to C

attributed to C

pole on the transfer function is compensated for by the pres-

ence of the zero, and that the ROC is maintained at 20 dB/

decade. For the circuit shown in Figure 2 the values of R

C

maintaining stability for different values of C

phase margins obtained, are shown in Table 1. R

are 10 k

Ω, R

(1)

TABLE 1.

C

R

C

Phase Margin (°)

0.5

680

10

17.4

1

680

20

12.4

1.5

680

30

10.1

The LMV641 is capable of driving heavy capacitive loads of

up to 1 nF without oscillating, however it is recommended to

use compensation should the load exceed 1 nF. Using this

methodology will reduce any excessive ringing and help

maintain the phase margin for stability. The values of the

compensation network tabulated above illustrate the phase

margin degradation as a function of the capacitive load.

Although this methodology provides circuit stability for any

load capacitance, it does so at the price of bandwidth. The

closed loop bandwidth of the circuit is now limited by R

C

Compensation by External Resistor

In some applications it is essential to drive a capacitive load

without sacrificing bandwidth. In such a case, in the loop com-

pensation is not viable. A simpler scheme for compensation

is shown in Figure 3. A resistor, R

tween the load capacitance and the output. This introduces a

zero in the circuit transfer function, which counteracts the ef-

fect of the pole formed by the load capacitance, and ensures

stability. The value of R

pending on the size of C

sired. Values ranging from 5

Ω to 50Ω are usually sufficient to

ensure stability. A larger value of R

with less ringing and overshoot, but will also limit the output

swing and the short circuit current of the circuit.

20203360

FIGURE 3. Compensation by Isolation Resistor

Typical Applications

ANISOTROPIC MAGNETORESISTIVE SENSOR

The low operating current of the LMV641 makes it a good

choice for battery operated applications. Figure 4 shows two

LMV641s in a portable application with a magnetic field sen-

sor. The LMV641s condition the output from an anisotropic

magnetoresistive (AMR) sensor. The sensor is arranged in

the form of a Wheatstone bridge. This type of sensor can be

used to accurately measure the current (either DC or AC)

flowing in a wire by measuring the magnetic flux density, B,

emanating from the wire.

20203341

FIGURE 4. A Battery Operated System for Contact-Less Current Sensing Using an Anisotropic Magnetoresistive Sensor

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