ADA4800

Rev. A | Page 10 of 16

THEORY OF OPERATION

The ADA4800 is a buffer integrated with an active load. Each

element (the active load and the buffer) operates independently,

as described in the following sections.

Figure 22 illustrates an ADA4800 application configuration for

using this power save feature.

An external resistor connected between the ISF and the

microcontroller GPO pin determines the amount of current

that flows into the input pin. This current can be calculated

by using Equation 1 and Equation 2.

SETTING ACTIVE LOAD CURRENT WITH PIN 6 (ISF)

The ISF pin is used to establish the value of the active current

kΩ

3

V

55

.

1

+

−

=

ISF

ISF

ISF

R

V

I

(1)

SETTING BANDWIDTH WITH PIN 4 (IDRV)

increase. Set the current using Equation 3.

where:

kΩ

28

V

8

.

0

+

−

=

IDRV

IDRV

IDRV

R

V

I

(3)

where:

The active load current (into the IN pin) is directly proportional

(2)

The ADA4800 allows for additional power savings by reducing

the active load current. The active load current can be logically

controlled by connecting the ISF pin to any general-purpose

output (GPO) pin of a system microcontroller through an

external resistor. A GPO logic high enables the flow of the

ISF pin places the ADA4800 into power save mode by shutting

down the active load current.

calculated by Equation 4.

(4)