7

LT1787/LT1787HV

The LT1787 high side current sense amplifier (Figure 1)

provides accurate bidirectional monitoring of current

through a user-selected sense resistor. The sense voltage

is amplified by a fixed gain of 8 and level shifted from the

positive power supply to the ground referenced outputs.

The output signal may be used in a variety of ways to

interface with subsequent signal processing circuitry.

Input and output filtering are easily implemented to elimi-

nate aliasing errors.

Theory of Operation

forced to flow through transistors Q1 and Q2 and are

gives a voltage gain of eight. Positive sense voltages result

ways to interface with subsequent circuitry. Split supply

1787 F 01

1.25k

1.25k

1.25k

1.25k

20k

–

–

+

A1

Q1

Q2

CURRENT MIRROR

+

Figure 1. LT1787 Functional Diagram

and single supply output configurations are shown in the

following sections.

The user may choose to include this current in the moni-

tion polarity.

Selection of External Current Sense Resistor

between power dissipation in the resistor and current

measurement accuracy. The LT1787 makes this decision

less difficult than with competitors’ products. The maxi-

mum sense voltage may be as large as

±500mV to get

maximum resolution, however, high current applications

will not want to suffer this much power dissipation in the

sense resistor. The LT1787’s input offset voltage of 40

µV

gives high resolution for low sense voltages. This wide

operating dynamic range gives the user wide latitude in

tailoring the range and resolution of his supply monitoring

function.