CS5466 datasheet(13/16 Pages) CIRRUS

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CS5466

Example:

For a given application, assuming a 50 Hz line frequen-

cy and a purely resistive load (unity power factor), the

following configuration is used:

– FREQ2:0 = 3

∴ FREQmax = 2 Hz

– IGAIN1:0 = 2

∴ IGAIN = 100

– VREFIN = VREFOUT = 2.5 V

In this configuration the maximum sine wave that can be

applied is 250 mVp on the voltage channel and 25 mVp

on the current channel. Using the above formula, the

output frequency of E1 or E2 is calculated:

With maximum pure sinusoidal input signals, the fre-

quency of E1 or E2 is half the absolute maximum fre-

quency set with FREQ2:0.

To calculate the frequency of FOUT for the example

above, assume FREQ2 = 0.

5.4

Energy Direction Indicator

The NEG pin indicates the sign of the calculated aver-

age power. If negative average power is detected the

NEG output pin will become active high and will remain

active high until positive average power is detected. The

NEG pin is valid at least 250ns prior to any assertion of

E1 or E2, and FOUT, to indicate the sign of a given en-

ergy output. The NEG pin is updated at a rate of 10 Hz

at MCLK = 4.096 MHz.

5.5

Power-on Reset

Upon powering up, the digital circuitry is held in reset

until the analog voltage reaches 4.0 V. At that time, an

eight XIN clock period delay is enabled to allow the os-

cillator to stabilize. The CS5466 will then initialize. The

device reads the control pins IGAIN1:0, FREQ2:0 and

HPF, and begins performing energy measurements.

5.6

Oscillator Characteristics

XIN and XOUT are the input and output of an inverting

amplifier which can provide oscillation and can be con-

figured as an on-chip oscillator, as shown in Figure 3.

The oscillator circuit is designed to work with a quartz

crystal. To reduce circuit cost, two load capacitors C1

and C2 are integrated in the device, one between XIN

and DGND, one between XOUT and DGND. Lead

lengths should be minimized to reduce stray capaci-

tance. To drive the device from an external clock

source, XOUT should be left unconnected while XIN is

driven by the external circuitry. There is an amplifier be-

tween XIN and the digital section which provides CMOS

level signals. This amplifier works with sinusoidal inputs

so there are no problems with slow edge times.

5.7

Basic Application Circuit

Figure 4 shows the CS5466 configured to measure

power in a single-phase 2-wire system while operating

in a single supply configuration. In this diagram, a shunt

resistor is used to sense the line current and a voltage

divider is used to sense the line voltage. In this type of

shunt resistor configuration, the common-mode level of

the CS5466 must be referenced to the line side of the

power line. This means that the common-mode poten-

tial of the CS5466 will track the high voltage levels, as

well as low voltage levels, with respect to earth ground

potential.

.25Vp * 10 * .025Vp * 100 * 2Hz

2 * 2 *2.5V 2

= 1Hz

FOUT = 2048*(E1+E2) = 2048*(2Hz) = 4096Hz

Oscillator

Circuit

DGND

XIN

XOUT

C1 =

22 pF

C2 =

Figure 3. Oscillator Connection

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