MAXQ3180-RAN+ datasheet(42/48 Pages) MAXIM

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Low-Power, Multifunction, Polyphase AFE

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Table 13. Virtual Register Coefficients

VIRTUAL

INPUT

RESOLUTION IN

METER UNITS

(1 LSB)

OUTPUT

RESOLUTION (1

LSB), DEFINED BY

USER

COEFFICIENT

DEFAULT OUTPUT

RESOLUTION

(1 LSB)

DEFAULT

COEFFICIENT

Power,

0x 801–827

E_res = IFS x

VFS/218

P_res

PWR_FS = 216 x

E_res/P_res

PWR_FS = 0x3539

Voltage,

0x 831–834

Vrms_res = VFS/230

V_res

VOLT_FS = 216 x

V_res/Vrms_res

1μV

VOLT_FS = 0x81F0

Current,

0x 831–834

Irms_res = IFS/230

I_res

AMP_FS = 216 x

I_res/Irms_res

1μA

AMP_FS = 0x17D8

When reading virtual registers, the MAXQ3180 uses the

configurable coefficients TIME_FS, VOLT_FS, AMP_FS,

and PWR_FS to return meaningful data. However, the

user must first configure these coefficients. Table 13

describes how to set the coefficients.

Temperature Measurement

The MAXQ3180 only measures the die temperature

when commanded by the master. To activate tempera-

ture measurement, the master must write one of the

TMPC[1:0] bits in the OPMODE register. When TMPC0

is set to 1, the MAXQ3180 performs a single tempera-

ture conversion by forcing bias currents 1μA and 16μA

through a pair of diode stacks, placing the result in the

RAW_TEMP register and automatically clearing the

TMPC0 bit to 0. When TMPC1 is written to 1, the

MAXQ3180 performs two consecutive temperature con-

versions. The first conversion is the same as previously

stated with 1μA and 16μA bias currents, and the sec-

ond conversion uses reversed 16μA and 1μA bias cur-

rents. The average of the two measurements is placed

in the RAW_TEMP register, and then both TMPC bits

are cleared. Double measurement cancels possible off-

set incidental to single measurement and thus

improves accuracy. The RAW_TEMP register returns

raw ADC sample proportional to absolute temperature.

Conversion to meaningful scale (°F, °C, or °K) should

be done by the master as needed. When finished, the

MAXQ3180 sets the temperature ready flag, TMRD, in

the STATUS1 register. This flag signals an interrupt

request to the master if enabled. The master can then

read the TEMP register and clear the TMRD status flag.

Typical Calibration Procedure

for MAXQ3180

The MAXQ3180 should be calibrated at the user’s fac-

tory and the calibration constants stored in nonvolatile

memory by the host microcontroller. Upon any reset or

loss of power, the host microcontroller must reload the

MAXQ3180 with the calibration constants.

The calibration procedure consists of three passes, one

per each phase A, B, and C. Each pass applies the

same calibration procedure to a single phase, consist-

ing of the following items:

• Current Gain Calibration

• Voltage Gain Calibration

• Power Gain Calibration

• Power Linearity Calibration

• Phase Angle Calibration

Each item requires one or more signals be applied to

the meter’s inputs, then the output to be measured. The

calibration coefficients are then calculated, verified,

and loaded into the MAXQ3180’s RAM registers. The

power linearity calibration and the phase angle calibra-

tion can be performed in any order.

Current Gain Calibration

To perform the current gain calibration, all three phase

voltages 220V should be applied. Only one current sig-

nal of max amplitude (IMAX) is applied to the phase

input being calibrated. From the view of the MAXQ3180

pins, the other current inputs should be grounded or

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