MAXQ3181-RAN+ datasheet(81/84 Pages) MAXIM

81 / 84 page

Low-Power, Active Energy, Polyphase AFE

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Neutral Current

RMS Current, Neutral (I.N) (0x840)

This register reports the RMS current of the neutral current

channel. The units are defined by the AMP_CC setting.

Special Commands

Table 7 shows the read-only virtual registers that acti-

vate special commands when read by the master.

Some commands return dummy values.

Applications 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 MAXQ3181 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

MAXQ3181-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 MAXQ3181 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 MAXQ3181 devices. This can be

accomplished by using a single SPI bus to connect all

NAME

ADDRESS

DESCRIPTION

DATA

LENGTH

(BYTES)

UPD_SFR

0x900

Reading this register copies the mirror registers (R_ADCF, R_ADCRATE,

R_ADCACQ, R_SPICF) into hardware SFR registers. The read returns dummy data.

UPD_MIR

0xA00

Reading this register copies hardware SFR registers into mirror registers (R_ADCF,

R_ADCRATE, R_ADCACQ, R_SPICF). The read returns dummy data.

DSPVER

0xC00

Reading this register returns the DSP firmware version number.

RAWTEMP

0xC01

Reading this register initiates the sampling and averaging of two internal

temperature readings. The result in internal temperature units is read from this

Celsius: T[c] = T[raw] x TempFactor - 273.15

where TempFactor is a value to be determined by calibration. Note that the final

value may be slightly higher than ambient due to internal die heating.

ENTER STOP

0xC02

Reading this register places the device into Stop Mode.

ENTER LOWPM

0xC03

Reading this register places the device into LOWPM Mode.

EXIT LOWPM

0xC04

Reading this register exits LOWPM Mode.

Table 7. Virtual Registers That Activate Special Commands

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