LMV422MMX datasheet(8/10 Pages) NSC

8 / 10 page

Application Information

The LMV422 is a dual rail-to-rail output amplifier that can be

switched between two active power modes. The power se-

lect pin (PS) provides a method to optimize the power con-

sumption, bandwidth and short circuit current. When the PS

pin is set to greater than 4.5V (Figure 1a) or left open, the

LMV422 is in Low Power Mode operating at a bandwidth of

27 kHz and consuming only 2 µA of supply current per

channel. Setting the PS pin to less than 0.5V, switches the

LMV422 to Full Power Mode with a bandwidth of 8 MHz and

supply current of 400 uA per channel (Figure 2b).. The PS

pin should not exceed the supply voltage. The active power

modes of the two amplifiers can be set independently.

The LMV422 PS pin has an internal pull up and a logic level

control gate that makes it easy for the PS pin to be controlled

by the output of a logic gate or the output pin of a microcon-

troller. The following figures show the three typical output

configurations for logic gates and microcontrollers.

CAPACITIVE LOAD TOLERANCE

The LMV422 is optimized for maximum bandwidth when

operating at a minimum closed loop gain of +2 or −1, there-

fore, it is not recommended to be configured as a buffer. Like

many other op amps, the LMV422 may oscillate when the

applied load appears capacitive. The threshold of the oscil-

lation varies both with load and circuit gain (see Phase

Margin vs. Gain for various capacitive loads curves). The

load capacitance interacts with the amplifier’s output resis-

tance to create an additional pole. If this pole frequency is

too low, it will degrade the amplifier’s phase margin so that

the amplifier is no longer stable.

Figure 3a and 3b show the addition of a small value resistor

ISO or RX (50

Ω to 100Ω) in series with the op amps output.

Figure 3b shows the addition of a capacitor C

F (5 pF to 10

pF) between the inverting input and the output pin. This

addition capacitor returns the phase margin to a safe value

without interfering with lower frequency circuit operation.

Note that in all cases, the output will ring heavily when the

load capacitance is near the threshold for oscillation.

20109807

Figure 1a Low Power Mode

20109808

Figure 1b Full Power Mode

FIGURE 1.

20109809

Figure 2a

20109810

Figure 2b

20109811

Figure 2c

FIGURE 2.

LMV422MMX Datasheet(PDF) 8 Page - National Semiconductor (TI)

LMV422MMX Datasheet(HTML) 8 Page - National Semiconductor (TI)

Html Pages

1 2 3 4 5 6 7 8 9 10

Datasheet Download

Link URL