CS5466

DS659F1

13

5.3.5

E1 and E2 Frequency Calculation

The pulse output frequency of E1 and E2 is directly pro-

portional to the active power calculated from the input

signals. To calculate the output frequency on E1 and

E2, use the following transfer function:

Example:

For a given application, assume a 50 Hz line frequency

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

lowing configuration is used:

– FREQ[2:0] = 3

– IGAIN[1:0] = 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 equa-

tion, the output frequency of energy pulse 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 FREQ[2:0].

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 active

power. If negative active power is detected, the NEG

output pin will become active-high and will remain ac-

tive-high until positive active 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 IGAIN[1:0], FREQ[2:0]

and HPF, and begins performing energy measure-

ments.

5.6

Oscillator Characteristics

XIN and XOUT are the input and output of an inverting

amplifier which can be configured as an on-chip oscilla-

tor, as shown in Figure 3. The oscillator circuit is de-

signed 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 and the other

between XOUT and DGND. Lead lengths to/from the

crystal 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 sinusoi-

dal inputs so there are no problems with slow edge

times.

VIN = rms voltage across VIN+ and VIN- [V]

IIN = rms voltage across IIN+ and IIN- [V]

IGAIN = Current channel gain selection (10, 50, 100, 150)

PF = Power Factor

VREFIN = Voltage at VREFIN pin [V]

FREQE1,E2

VIN 10

×

IIN

×

IGAIN

×

PF

×

FREQmax

×

VREFIN

2

------------------------------------------------------------------------------------------------------------------

=

0.25Vp 10

×

0.025Vp

×

100

×

1

×

2Hz

×

22

×

2.5V

2

×

---------------------------------------------------------------------------------------------------------

1Hz

=

FOUT

2048

E1 E2

+

()

×

2048 2Hz

×

4096Hz

==

=

Oscillator

Circuit

DGND

XIN

XOUT

C1

C1 =

22 pF

C2

C2 =

Figure 3. Oscillator Connection