2. Switched Discrete Power Modes

In this typical application, the LPV531 can operate at two (or

more) power modes in order to fulfill the demands of the

design. One of the modes is used to save power. It is a low

power mode which is set by using a large resistor. The

others are the higher power modes which are set by one or

more smaller resistors. The larger resistor that sets the low

power mode can be permanently connected while the

smaller resistor(s) can be switched in parallel to set the high

power mode(s). This configuration allows the designer to get

the required performance from the LPV531 when needed.

The switches shown in Figure 3 can be easily implemented

with an open drain I/O port of an ASIC or any other simple

pull down switch.

3. DAC Controlled Power Modes

For voltage controlled filter applications, where control of the

gain bandwidth is essential, a DAC and a resistive voltage

divider can be used. In this application the current drawn

from the I

output range is divided to match the V

has the range of 0-110 mV.

The output of the resistive voltage divider should have an

impedance that is small compared to the value of R

allow a linear control of the power level. Therefore, R

EXT2

needs to have a value in the order of R

and

R

mode operation, these resistor values will divide the maxi-

mum voltage of V

DETERMINING THE R

To determine the value of R

supply current or bandwidth, the following equations can be

used:

or

For the power modes characterized in this datasheet, these

formulas lead to the values in Table 1. These values deviate

slightly from the typical values presented in the electrical

characteristic tables. The values in Table 1 are calculated

using approximated linear equations while the values in the

Electrical Characteristics table are the result of characteriza-

tion measurement procedures.

TABLE 1. Values for Characterized

Power Modes

R

EXT

I

SEL

Supply Current

Gain Bandwidth

Product

1

Ω

9 µA

400 µA

4.6 MHz

100 k

Ω

0.9 µA

40 µA

460 kHz

1M

Ω

99 nA

5.3 µA

60 kHz

To calculate the R

a minimum output current at all times and over all tempera-

tures, use the following equations:

If the output has to be kept at V

tance, the required R

equations:

20132363

FIGURE 3. Power Modes Set by Resistors and

Switches

20132364

FIGURE 4. DAC Controlled Power Mode Configurations

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