LT2940CMS datasheet(12/24 Pages) LINER

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LT2940

2940f

APPLICATIONS INFORMATION

the full-scale output current of ±200μA, the achievable

full-scale power is:

IN FS

()

•

04 2

(10)

In some applications the PMON output is converted to a

voltage by a load resistor:

VPMON = IPMON • RPMON

(11)

The complete end-to-end scaling is then given by:

VPMON = PIN • KPMON • kV • kI • RPMON

(12)

The current monitor output current at IMON is found by

combining Equations 4 and 8a:

IIMON = IIN • GIMON • kI

(13)

The output current may be positive (sourcing) or negative

(sinking) depending on the signs of IIN and kI. Provided

that the magnitude of VI does not exceed 200mV, at the

full-scale output current of ±200μA the achievable full-

scale input current is:

IN FS

()

(14)

If IMON current is converted to a voltage by a load resis-

tor, then:

VIMON = IIMON • RIMON

(15)

and the ﬁnal end-to-end scaling is given by:

VIMON = IIN • GIMON • kI • RIMON

(16)

Accuracy

The principal accuracies of the power and current monitor

outputs are characterized as absolute percentages of full-

scale output currents, using the nominal values of scaling

parameters. The total error of the IPMON output, EPMON, is

typically ±2%, and is deﬁned as:

µA

PMON

− 500

200

100

•(

•

)

•%

(17)

Contributors to the power output accuracy such as the scal-

ing (KPMON), the output offset (IPMON(OS)), and the voltage

and current sense input offsets (VV(OSP) and VI(OSP)), are

separately speciﬁed at key conditions and may be totaled

using the root sum-of-squares (RSS) method.

The total error of the IIMON output, EIMON, is typically

±1.5%, and is deﬁned as:

IMON

− 1000

200

100

•

•%

(18)

Contributors to the current output accuracy such as the

scaling (GIMON) and the current sense input offset (VI(OSI))

are separately speciﬁed at key conditions. Here again, use

the RSS method of totaling errors.

Figure 3. Basic Power Sensing Application Showing Derivation of kV and kI

LT2940

PIN = VIN • IIN

2940 F03

11 10

PMON

LOAD

V +

V –

I +

I –

IMON

kV =

VI = IIN • RSENSE

kI = RSENSE

VV = VIN •

R1 + R2

VIN

RSENSE

IIN

RIMON

VIMON

IIMON

RPMON

VPMON

IPMON

–

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