MAXQ3180-RAN+ datasheet(46/48 Pages) MAXIM

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c) Calculate pair of coordinates (x1,y1):

x1 = (ln(I1_raw/216) - 6.0625)/16

y1 = (-PAerr1) x 216

3) Repeat the phase angle error measurement

across the range.

Repeat steps 2a to 2c using other input currents

across the range. It is recommended to spread

input current points uniformly in logarithmic scale,

resulting in a set of point coordinates:

(x1,y1), (x2,y2), . . . (xN,yN)

The number of points N is not limited.

4) Calculate the coefficients (PA_n) of best fit polyno-

mial curve.

The calculation recipe depends on the order of

polynomial.

a) For zero-order curve (requires at least one

point):

PA_0 = average(y1,y2, . . . yN)

PA_1 = PA_2 = PA_3 = 0

5) For first-order curve (requires at least two points):

PA_1 = {

∑ (xi-x_avg)(yi-y_avg)}/{∑ (xi-x_avg)2}

PA_0 = y_avg - PA_1 x x_avg

PA_2 = PA_3 = 0

where x_avg = average (x1,x2, . . . xN),

y_avg = average (y1,y2, . . . yN)

These two cases cover the majority of practical situa-

tions. For higher order curves, the formulas are more

complex, and the calculations can be performed using

built-in functions of Microsoft Excel® or MATLAB® from

The MathWorks, Inc.

Note that all intermediate calculations should be per-

formed with double precision, the last result rounded to

the nearest integer. Also note that PA_n are 16-bit

signed coefficients. If the calculated value exceeds 16

bits, the phase angle cannot be calibrated. In this case,

assign the largest possible value, i.e., 0x7FFF for posi-

tive overflow or 0x8000 for negative overflow.

Application Information

Grounds and Bypassing

Careful PCB layout significantly minimizes noise on the

analog inputs, resulting in less noise on the digital I/O

that could cause improper operation. The use of multi-

layer boards is essential to allow the use of dedicated

power planes. The area under any digital components

should be a continuous ground plane if possible. Keep

any bypass capacitor leads short for best noise rejec-

tion and place the capacitors as close to the leads of

the devices as possible.

The MAXQ3180 must have separate ground areas for

the analog (AGND) and digital (DGND) portions, con-

nected together at a single point.

CMOS design guidelines for any semiconductor require

that no pin be taken above DVDD or below DGND.

Violation of this guideline can result in a hard failure

(damage to the silicon inside the device) or a soft fail-

ure (unintentional modification of memory contents).

Voltage spikes above or below the device’s absolute

maximum ratings can potentially cause a devastating

IC latchup.

Microcontrollers commonly experience negative volt-

age spikes through either their power pins or general-

purpose I/O pins. Negative voltage spikes on power

pins are especially problematic as they directly couple

to the internal power buses. Devices such as keypads

can conduct electrostatic discharges directly into the

microcontroller and seriously damage the device.

System designers must protect components against

these transients that can corrupt system memory.

Specific Design Considerations for

MAXQ3180-Based Systems

To reduce the possibility of coupling noise into the

microcontroller, the system should be designed with a

crystal or oscillator in a metal case that is grounded to

the digital plane. Doing so reduces the susceptibility of

the design to fast transient noise.

Because the MAXQ3180 is designed for use in systems

where high voltages are present, care must be taken to

route all signal paths, both analog and digital, as far

away as possible from the high-voltage components.

It is possible to construct more elaborate metering

designs using multiple MAXQ3180 devices. This can be

accomplished by using a single SPI bus to connect all

the MAXQ3180 devices together but using separate

slave select lines to individually select each MAXQ3180.

Additional Documentation

Designers must ensure they have the latest MAXQ3180

errata documents. Errata sheets contain deviations

from published specifications. A MAXQ3180 errata

sheet for any specific device revision is available at

www.maxim-ic.com/errata.

Low-Power, Multifunction, Polyphase AFE

______________________________________________________________________________________

Microsoft Excel is a registered trademark of Microsoft Corp.

MATLAB is a registered trademark of The MathWorks, Inc.

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