CS5460 datasheet(10/34 Pages) CIRRUS

10 / 34 page

CS5460

DS279PP5

2.2 Performing Measurements

The CS5460 performs measurements of instanta-

neous current, instantaneous voltage, instantaneous

power, energy, RMS current, and RMS voltage.

These measurements are output as 24-bit signed

and unsigned data formats as a percentage of full

scale. The flow of data to perform these calcula-

tions is shown in Figure 5. All of these measure-

ments begin when a start conversion command is

given. The energy and RMS registers are then up-

dated every N conversions (or 1 computation cy-

cle) where N is the content of the Cycle Count

the DRDY bit in the Status and Mask register is set.

The INT pin will also become active if the DRDY

bit is unmasked.

Table 1 provides an example detailing the output

linearity. A computation cycle is derived from the

master

clock

and

its

frequency

(MCLK/K)/(1024*N). Instantaneous calculations

are performed at a 4000 Hz rate where as, IRMS,

VRMS, and energy, are performed at a 1 Hz rate. Al-

so, DRDY is set only after computation cycles are

complete (i.e. there is no indicator flag to indicate

when the instantaneous conversions are read; how-

ever, if the Cycle Count register were set to 1, all

output calculations would be instantaneous and

DRDY would indicate when instantaneous calcula-

tions were finished).

VA+

VD+

CS5460

0.1 µF

100 µF

500 Ω

470 nF

500 Ω

10 Ω

VIN+

VIN-

IIN-

IIN+

PFMON

CPUCLK

XOUT

XIN

Optional

Clock

Source

Serial

Data

Interface

RESET

SDI

SDO

SCLK

INT

EDIR

EOUT

0.1 µF

VREFIN

VREFOUT

DGND

To Service

2.5 MHz to

20 MHz

0.1 µF

L 1

L 2

10 kΩ

5kΩ

VA-

* Refer to Input Current Protection

Figure 4. Typical Connection Diagram (One-Phase 3-Wire)

Energy

Vrms

Irms

Range

1000:1

2:1

500:1

Max Input

See Analog Characteristics

Linearity

(After

Calibration)

0.1% of

reading

0.1% of

reading

0.1% of

reading

Output word

24-bits

Table 1. Specification with MCLK = 4.096 MHz, K = 1,

and N = 4000.

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