LTC1041

5

1041fa

APPLICATIO S I FOR ATIO

source during the controller’s active time is critical in

determining errors caused by the input charging current.

For source resistances less than 10k

and no error is caused by the charging current.

For source resistances greater than 10k

charge, causing voltage errors. To minimize these errors,

another error term. Each time the input switches cycle

discharged. The average input current due to this is

Because the input current is directly proportional to the

differential input voltage, the LTC1041 can be said to have

Sampling Frequency). This finite input resistance causes

The input voltage error caused by both of these effects is

reduced to 1Hz, the voltage error from the input

impedance effects is reduced to 136

µV.

Figure 2. Equivalent Input Circuit

LTC1041 • AI01

S1

S2

(

≈ 33pF)

LTC1041 DIFFERENTIAL INPUT

+

–

Input Voltage Range

The input switches of the LTC1041 are capable of

the input voltage range includes both supply rails. This is

a further benefit of the sampling input structure.

Error Specifications

The only measurable errors on the LTC1041 are the

deviations from “ideal” of the upper and lower switching

levels (Figure 1b). From a control standpoint, the error in

the SET POINT and deadband is critical. These errors may

SET POINT error

V

SET POINT

deadband error

V

U

U

≡

+









≡

()

V

V

DELTA

L

L

2

2

–

–– •

The specified error limits (see electrical characteristics)

include error due to offset, power supply variation, gain,

time and temperature.

It is often desirable to use the LTC1041 with resistive

networks such as bridges and voltage dividers. The power

consumed by these resistive networks can far exceed that

of the LTC1041 itself.

At low sample rates the LTC1041 spends most of its time

≈ 80µs)

and to a high impedance (open circuit) when internal

power is switched off.

voltage is not precisely controlled when driving a load

In spite of this, high precision can be achieved in two ways:

(1) driving ratiometric networks and (2) driving fast set-

tling references.

In ratiometric networks all the inputs are proportional to

does not affect accuracy.