Application Information

CIRCUIT DESCRIPTION AND ADVANTAGE OF THE

LMV951

The LMV951 utilizes an internal voltage generator which

allows for rail to rail input and output operation from 1 to 3V

supplies. An internal switching frequency between 10 MHz

and 15 MHz is used for generating the internal voltages.

The bipolar input stage provides rail to rail input operation

with no input bias current phase reversal and a constant

input offset voltage over the entire input common mode

range.

The CMOS output stage provides a gain that is virtually

independent of resistive loads and an output drive current in

excess of 35 mA at 1V. A further benefit of the output stage

is that the LMV951 is stable in positive unity gain at capaci-

tive loads in excess of 1000 pF.

Battery Operated Systems

The maximum operating voltage is 3V and the operating

characteristics are guaranteed down to 1V which makes the

LMV951 an excellent choice for battery operated systems

using one or two NiCd or NiMH cells. The LMV951 is also

functional at 0.9V making it an appropriate choice for a

single cell alkaline battery.

Shutdown Capability

While in shutdown mode, the LMV951 typically consumes

less than 50 nA of supply current making it ideal for power

conscious applications. Full functionality is restored within 3

µs of enable.

Small Size

The small footprint of the LMV951 package is ideal for high

density board systems. By using the small 6-Pin SOT23

package, the amplifier can be placed closer to the signal

source, reducing noise pickup and increasing signal integrity.

Power Supply Bypassing

As in any high performance IC, proper power supply bypass-

ing is necessary for optimizing the performance of the

LMV951. The internal voltage generator needs proper by-

passing for optimum operation. A surface mount ceramic .01

µF capacitor must be located as close as possible to the V

+

and V

ESR and a self resonant frequency above 15 MHz. A small

tantalum or electrolytic capacitor with a value between 1 µF

and 10 µF also needs to be located close to the LMV951.

DRIVING CAPACITIVE LOAD

The unity gain follower is the most sensitive op amp configu-

ration to capacitive loading; the LMV951 can drive up to

10,000 pF in this configuration without oscillation. If the

application requires a phase margin greater than those

shown in the datasheet graphs, a snubber network is rec-

ommended. The snubber offers the advantage of reducing

the output signal ringing while maintaining the output swing

which ensures a wider dynamic range; this is especially

important at lower supply voltages.

The chart below gives recommended values for some com-

mon values of large capacitors. For these values R

Ω;

C

L

R

S

C

S

500 pF

330

Ω

6800 pF

680 pF

270

Ω

8200 pF

1000 pF

220

Ω

.015 µF

20123156

FIGURE 1. Snubber Network to Improve Phase Margin

20123160

FIGURE 2. 1000 pF and no Snubber

20123161

FIGURE 3. 1000 pF with Snubber

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