LP3871 datasheet(13/18 Pages) NSC

13 / 18 page

Application Hints (Continued)

SENSE PIN

In applications where the regulator output is not very close to

the load, LP3874 can provide better remote load regulation

using the SENSE pin. Figure 2 depicts the advantage of the

SENSE option. LP3871 regulates the voltage at the output

pin. Hence, the voltage at the remote load will be the regu-

lator output voltage minus the drop across the trace resis-

tance. For example, in the case of a 3.3V output, if the trace

resistance is 100m

Ω, the voltage at the remote load will be

3.22V with 0.8A of load current, I

LOAD. The LP3874 regulates

the voltage at the sense pin. Connecting the sense pin to the

remote load will provide regulation at the remote load, as

shown in Figure 2. If the sense option pin is not required, the

sense pin must be connected to the V

OUT pin.

SHUTDOWN OPERATION

A CMOS Logic level signal at the shutdown ( SD) pin will

turn-off the regulator. Pin SD must be actively terminated

through a 10k

Ω pull-up resistor for a proper operation. If this

pin is driven from a source that actively pulls high and low

(such as a CMOS rail to rail comparator), the pull-up resistor

is not required. This pin must be tied to Vin if not used.

20063107

FIGURE 1. Error Flag Operation

20063108

FIGURE 2. Improving remote load regulation using LP3874

LP3871 Datasheet(PDF) 13 Page - National Semiconductor (TI)