or

-11 k:

0.07

0.07

LPV531

SNOSAK5B – MARCH 2006 – REVISED MARCH 2013

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(5)

For the characterized power modes these equations lead to the minimum values in Table 2 below.

Table 2. Minimum Values for Characterized Power Modes

1

Ω

9 µA

3 mA

770

Ω

100 k

Ω

0.9 µA

300 µA

7.8 k

Ω

1 M

Ω

99 nA

55 µA

70.8 k

Ω

The smallest load resistor that the LPV531 can drive when in low power mode is 70.8 k

Ω, as shown in Table 2.

When driving smaller loads, such as the 10 k

Ω load resistor used in the Electrical Characteristics tables

specification, the output swing in the low power mode is limited. If the application requires a 10 k

Ω load then it is

not recommended to use the LPV531 in low power mode.

traces as possible.

Typical Application

AC COUPLED CIRCUITS

The programmable power mode makes the LPV531 ideal for AC coupled circuits where the circuit needs to be

kept active to maintain a quiescent charge on the coupling capacitors with minimal power consumption.

by I/O ports of a microcontroller. The advantage of the low power active mode for AC coupled amplifiers is the

elimination of the time needed to re-establish a quiescent operating point when the amplifier is switched to full

power mode.

When an amplifier without a low power active mode is used in low power applications, there are two ways to

minimize power consumption. The first method turns off the amplifier by switching off power to the op amp using

a transistor switch. The second method uses an amplifier with a shutdown pin. Both of these methods have the

when in the shutdown state. When the amplifier is turned on again, the quiescent DC voltages must reestablish

themselves. During this time, the amplifier’s output is not usable because the output signal is a mixture of the

amplified input signal and the charging voltage on the coupling capacitors. The settling time can range from a

several milliseconds to several seconds depending on the resistor and capacitor values.

When the LPV531 is placed into the low power mode, the power consumption is minimal but the amplifier is

active to maintain the quiescent DC voltage on the coupling capacitors. The transition back to the operational

high power mode is fast, within a few hundred nanoseconds. The active low power mode of the LPV531

separates two critical aspects of a low power AC amplifier design. The values of the gain resistors, bias resistors,

and coupling capacitors can be chosen independently of the turn-on and stabilization time.

16

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