Low Supply Voltage. National provides guaranteed perfor-

mance at 2.7V and 5V. These guarantees ensure operation

throughout the battery lifetime.

Rail-to-Rail Output. Rail-to-rail output swing provides maxi-

mum possible dynamic range at the output. This is particu-

larly important when operating on low supply voltages.

Input Includes Ground. Allows direct sensing near GND in

single supply operation.

The differential input voltage may be larger than V

damaging the device. Protection should be provided to pre-

vent the input voltages from going negative more than −0.3V

(at 25˚C). An input clamp diode with a resistor to the IC input

terminal can be used.

2.0 Capacitive Load Tolerance

The LPV321/358/324 can directly drive 200 pF in unity-gain

without oscillation. The unity-gain follower is the most sensi-

tive configuration to capacitive loading. Direct capacitive

loading reduces the phase margin of amplifiers. The combi-

nation of the amplifier’s output impedance and the capacitive

load induces phase lag. This results in either an under-

damped pulse response or oscillation. To drive a heavier ca-

pacitive load, circuit in

Figure 1 can be used.

In

Figure 1, the isolation resistor R

C

margin to the overall system. The desired performance de-

pends on the value of R

value, the more stable V

waveform of

Figure 1 using 100k

Ω for R

C

The circuit in

Figure 3 is an improvement to the one in Figure

1 because it provides DC accuracy as well as AC stability. If

there were a load resistor in

Figure 1, the output would be

voltage divided by R

ure 3,R

techniques to connect V

ing the value of R

LPV321/358/324. C

of phase margin by feeding the high frequency component of

the output signal back to the amplifier’s inverting input,

thereby preserving phase margin in the overall feedback

loop. Increased capacitive drive is possible by increasing the

value of C

3.0 Input Bias Current Cancellation

The LPV321/358/324 family has a bipolar input stage. The

typical input bias current of LPV321/358/324 is 1.5nA with

5V supply. Thus a 100k

Ω input resistor will cause 0.15mV of

error voltage. By balancing the resistor values at both invert-

ing and non-inverting inputs, the error caused by the ampli-

fier’s input bias current will be reduced. The circuit in

Figure

4 shows how to cancel the error caused by input bias

current.

4.0 Typical Single-Supply Application Circuits

4.1 Difference Amplifier

The difference amplifier allows the subtraction of two volt-

ages or, as a special case, the cancellation of a signal com-

mon to two inputs. It is useful as a computational amplifier, in

making a differential to single-ended conversion or in reject-

ing a common mode signal.

DS100920-4

FIGURE 1. Indirectly Driving A Capacitive Load Using

Resistive Isolation

DS100920-75

FIGURE 2. Pulse Response of the LPV324 Circuit in

Figure 1

DS100920-5

FIGURE 3. Indirectly Driving A Capacitive Load with

DC Accuracy

DS100920-6

FIGURE 4. Cancelling the Error Caused by Input Bias

Current

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