MAXIM MAXQ314

19-5031; Rev 0; 11/09
TION KIT
EVALUA BLE
IL
AVA A
Single-Phase Power-Measurement
IC with I2C Interface
Features
The MAXQ314 is a dedicated power-measurement IC
that collects and calculates voltage, current, power, and
power factor for a single-phase load. The results can
be retrieved by an external master through the internal
I2C bus. This bus is also used by the external master to
configure the operation of the MAXQ314 and monitor the
status of operations.
S High-Performance, Low-Power DSP Core
S On-Chip Digital Temperature Sensor
S Precision Internal Voltage Reference
S Active Power (W), < ±0.5% Error
S Reactive Power (VAR), < ±0.7% Error
S Apparent Power (VA), < ±0.7% Error
The MAXQ314 performs voltage and current measurements using an integrated ADC that can measure voltage
and current. Other values such as power are calculated
from that data. The MAXQ314 also has an integrated
temperature sensor that provides the die temperature on
demand. The internal current amplifier produces up to
32x gain and the voltage amplifier gain is 1x.
S Power Factor, < ±1% Error
S Voltage RMS, < ±0.2% Error
S Current RMS, < ±0.5% Error
S I2C-Compatible Serial Interface
S Continuous Output of IRMS in Serial or PWM
Applications
Single-Phase AC Power Monitoring
Ordering Information
PART
MAXQ314+
OPERATING VOLTAGE (V)
TEMP RANGE
PIN-PACKAGE
3.0 to 3.6
-40NC to +85NC
20 TQFN-EP*
+Denotes a lead(Pb)-free/RoHS-compliant package.
*EP = Exposed pad.
Block Diagram
MAXQ314
TEMP SENSOR
VP
MUX
PGA
ADC
VN
IL
INTERNAL
REFERENCE
WATCHDOG
TIMER
16-BIT
MAXQ20
RISC CPU
AVDD
AGND
DVDD
DGND
POWER-ON
RESET
(AVDD, DVDD)
I2C
INTERFACE
BUS
SCL
SDA
A0
A1
A2
DSP
SERIAL/PWM
AUX
INTERNAL
8MHz CLOCK
GENERATOR
RST
MAXQ is a registered trademark of Maxim Integrated Products, Inc.
Note: Some revisions of this device may incorporate deviations from published specifications known as errata. Multiple revisions of any device
may be simultaneously available through various sales channels. For information about device errata, go to: www.maxim-ic.com/errata.
________________________________________________________________ Maxim Integrated Products 1
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
MAXQ314
General Description
MAXQ314
Single-Phase Power-Measurement
IC with I2C Interface
TABLE OF CONTENTS
Absolute Maximum Ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Power-Monitoring Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Electrical Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
I2C Electrical Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
I2C Bus Controller Timing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Pin Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Pin Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Detailed Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Clock Source . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Reset Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
External Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Voltage Monitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
I2C Slave Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
I2C Rate and Resets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
I2C Slave Address Generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
I2C Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Data and Control Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Conversion to Physical Units . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
RMS Current Continuous Output (AUX Pin) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Applications Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Grounds and Bypassing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Specific Design Considerations for MAXQ314-Based Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Additional Documentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Development and Technical Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Package Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
2 _______________________________________________________________________________________
Single-Phase Power-Measurement
IC with I2C Interface
Figure 1. Series Resistors (RS) for Protecting Against High-Voltage Spikes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Figure 2. I2C Bus Controller Timing Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Figure 3. Calibration Circuit Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
LIST OF TABLES
Table 1. Slave Address Determination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Table 2. Register Set . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Table 3. DSPCFG Register Detail . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Table 4. Calibration Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
_______________________________________________________________________________________ 3
MAXQ314
LIST OF FIGURES
MAXQ314
Single-Phase Power-Measurement
IC with I2C Interface
ABSOLUTE MAXIMUM RATINGS
Voltage Range on DVDD with
Respect to DGND..............................................-0.3V
Voltage Range on AVDD with
Respect to AGND..............................................-0.3V
Voltage Range on AGND with
Respect to DGND..............................................-0.3V
Voltage Range on AVDD with
Respect to DVDD...............................................-0.3V
to +4.0V
to +4.0V
to +0.3V
to +0.3V
Voltage Range on Any Lead with
Respect to (DGND = AGND)................................-0.3V to +4V
Operating Temperature Range........................... -40NC to +85NC
Storage Temperature Range............................ -65NC to +150NC
Continuous Power Dissipation (TA = +70NC)
20-Pin TQFN (derate 20.8mW/NC above +70NC)........1667mW
ESD Protection (Human Body Model) ................................Q2kV
Soldering Temperature.......................... Refer to the IPC/JEDEC
J-STD-020 Specification.
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect device reliability.
POWER-MONITORING SPECIFICATIONS
(VAVDD = VDVDD = 3.0V to 3.6V, TA = +25NC.) (Note 1)
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Active-Power Error
Current input DR 500:1
0.5
%
Reactive-Power Error
Current input DR 500:1
0.7
%
Apparent-Power Error
Current input DR 500:1
0.7
%
Power-Factor Error
Current input DR 500:1
0.1
%
RMS Voltage Error
Current input DR 30:1
0.2
%
RMS Current Error
Current input DR 500:1
0.5
%
ELECTRICAL CHARACTERISTICS
(VAVDD = VDVDD = 3.0V to 3.6V, TA = +25NC, unless otherwise noted.) (Note 2)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
3.6
V
15.0
mA
3.6
V
POWER SUPPLY
Digital Supply Voltage
VDVDD
Supply Current
IDVDD
Analog Supply Voltage
VAVDD
Supply Voltage Power-Fail Trip
Point
UVLO
3.0
IDVDD + IAVDD, fCLK = 8MHz
6.5
3.0
Rising, VDVDD = VAVDD
2.75
Hysteresis
2.8
2.95
100
V
mV
DIGITAL I/O
VIH
2.1
V
Input High Voltage (A0, A1, A2)
VIH2
VDVDD
- 0.3
V
Input Low Voltage (RST)
Input Low Voltage (A0, A1, A2)
VIL
0.8
V
VIL2
0.3
V
Input High Voltage (RST)
4 _______________________________________________________________________________________
Single-Phase Power-Measurement
IC with I2C Interface
(VAVDD = VDVDD = 3.0V to 3.6V, TA = +25NC, unless otherwise noted.) (Note 2)
PARAMETER
SYMBOL
Output Low Voltage (AUX)
VOL
Input Leakage (A0, A1, A2)
IL
Input Capacitance (RST, A0,
A1, A2)
CIN
CONDITIONS
MIN
TYP
IOL = 6mA
MAX
UNITS
+12
FA
0.4
-12
V
10
pF
RST Pullup Resistance
INTERNAL OSCILLATOR
RRST
50
150
200
kI
Oscillator Frequency
fSCLK
7.2
8
8.8
MHz
AFE AND ANALOG-TO-DIGITAL CONVERTER
Voltage Range (VP)
0
1.5
V
Voltage Range (VN)
0
1.5
V
Slow Current Channel (IL)
0
1.5
Input Capacitance Single-Ended
ADC Sampling Rate
Per channel
V
10
pF
5
ksps
INTERNAL VOLTAGE REFERENCE
Reference Accuracy
TA = -40NC to +85NC
1.8
2.07
2.3
V
TEMPERATURE SENSOR
Temperature Accuracy
3
TEP = -40NC to +85NC
NC
I2C ELECTRICAL CHARACTERISTICS
(VAVDD = VDVDD = 3.0V to 3.6V, TA = -40NC to +85NC.) (Note 2)
PARAMETER
Input Low Voltage
SYMBOL
CONDITIONS
MIN
VIL_I2C
Input High Voltage
Input Hysteresis (Schmitt)
Output Logic-Low (Open Drain
or Open Collector)
VIH_I2C
VIHYS_I2C
VOL_I2C
VDVDD > 2V (Note 1)
VDVDD > 2V, 6mA sink current
Input Current on I/O
IIN_I2C
Input voltage from 0.1 x VDVDD to 0.9 x
VDVDD
I/O Capacitance
CIO_I2C
(Note 1)
MAX
UNITS
0.3 x VDVDD
V
0.7 x VDVDD
V
0.05 x VDVDD
V
0
0.4
V
-10
+10
FA
10
pF
_______________________________________________________________________________________ 5
MAXQ314
ELECTRICAL CHARACTERISTICS (continued)
MAXQ314
Single-Phase Power-Measurement
IC with I2C Interface
I2C BUS CONTROLLER TIMING
(VDVDD = 3.0V to 3.6V, TA = +25NC, unless otherwise noted. Typical values are at VDVDD = 3.3V, TA = +25NC.) (Note 1, Figure 2)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
400
kHz
Serial Clock Frequency
fSCL
Bus Free Time Between a STOP
and a START Condition
tBUF
1.3
Fs
Hold Time (Repeated) START
Condition
tHD:STA
0.6
Fs
Repeated START Condition
Setup Time
tSU:STA
0.6
Fs
STOP Condition Setup Time
tSU:STO
Data Hold Time
tHD:DAT
Data Setup Time
tSU:DAT
120
ns
SCL Clock Low Period
tLOW
1.3
Fs
SCL Clock High Period
tHIGH
0.6
Rise Time of Both SDA and SCL
Signals Receiving
tR_I2C
Fall Time of Both SDA and SCL
Signals Receiving
Fall Time of SDA Transmitting
0.6
Fs
(Note 3)
0.9
Fs
Fs
(Notes 4, 5)
20 +
0.1CB
300
ns
tF_I2C
(Notes 4, 5)
20 +
0.1CB
300
ns
tF_TX
(Notes 4, 5)
20 +
0.1CB
250
ns
Pulse Width of Spike Suppressed
tSP
(Note 6)
50
ns
Capacitive Load for Each Bus
Line
CB
(Note 5)
400
pF
Note 1: Specifications guaranteed, but not production tested.
Note 2: All parameters tested at TA = +25NC. Specifications over temperature are guaranteed by design.
Note 3: A master device must provide a hold time of at least 300ns for the SDA signal (referred to VIL of the SCL signal) to bridge
the undefined region of SCL’s falling edge.
Note 4: ISINK P 6mA. tR_I2C and tF_I2C measured between 0.3 x VDVDD and 0.7 x VDVDD.
Note 5: CB = Total capacitance of one bus line in pF.
Note 6: Guaranteed by design. Input filters on the SDA and SCL pins suppress noise spikes less than 50ns.
6 _______________________________________________________________________________________
Single-Phase Power-Measurement
IC with I2C Interface
MAXQ314
VDVDD
I2C
DEVICE
I2C
DEVICE
RP
MAXQ314
RS
RS
RS
RP
RS
SDA
SCL
Figure 1. Series Resistors (RS) for Protecting Against High-Voltage Spikes
S
SR
P
S
SDA
tBUF
tR_I2C
tF_I2C
tLOW
tSU:DAT
tSU:STA
SCL
tHD:STA
tHD:DAT
tHIGH
tSU:STO
Figure 2. I2C Bus Controller Timing Diagram
_______________________________________________________________________________________ 7
MAXQ314
Single-Phase Power-Measurement
IC with I2C Interface
Pin Configuration
VN
REF
RST
A0
A1
TOP VIEW
15
14
13
12
11
VP 16
10
A2
AVDD 17
9
N.C.
8
SDA
7
SCL
6
N.C.
AGND 18
MAXQ314
IL 19
EP*
2
3
4
5
DVDD
N.C.
AUX
1
DGND
+
N.C.
N.C. 20
TQFN
(5mm × 5mm)
*EXPOSED PAD.
Pin Description
PIN
NAME
FUNCTION
3
DGND
Digital Ground. AGND and DGND should be connected externally through a single point connection.
4
DVDD
Digital Supply Voltage. Connect AVDD to DVDD externally. Connect a 0.1FF capacitor to DGND.
14
REF
POWER PINS
Buffered Reference Output. Connect this pin to AGND through a 1FF capacitor. No other signals should be
connected to this pin.
17
AVDD
Analog Supply Voltage. Connect AVDD to DVDD externally. Connect a 0.1FF capacitor to AGND.
18
AGND
Analog Ground. AGND and DGND should be connected externally through a single point connection.
—
EP
Exposed Pad. Connect to AGND.
COMMUNICATION AND CONTROL PINS
AUX
RMS Current Continuous Output. This open-drain pin continuously outputs the value of the most recent 16-bit
RMS current measurement. If the SPCFG.PWMOUT bit is set, the value is instead output in PWM format.
7
SCL
I2C Clock Line I/O
8
SDA
I2C Data Line I/O
10
A2
11
A1
12
A0
13
RST
1
Device Selection Address Bits, Input. These bits select the slave address shown in Table 1.
Active-Low Reset Input. The CPU is held in reset when this pin is low. The pin includes pullup current
source and should be driven by an open-drain external source capable of sinking in excess of 4mA.
8 _______________________________________________________________________________________
Single-Phase Power-Measurement
IC with I2C Interface
PIN
NAME
FUNCTION
VOLTAGE AND CURRENT MEASUREMENT PINS
15
VN
Differential Voltage Negative Input
16
VP
Differential Voltage Positive Input
19
IL
Single-Ended Current Input, Low Frequency
NO CONNECTION PINS
2, 5, 6,
9, 20
N.C.
No Connection. Do not connect any signal to this pin.
Detailed Description
The MAXQ314 is a dedicated analog front-end (AFE) that
measures voltage, current, and temperature. The internal
DSP then derives calculated values. It communicates
with a master device using the I2C communication protocol, and continuously executes the following operations:
• S
cans AFE channels and collects raw voltage and
current samples
• Calculates power (real, reactive, apparent)
• R
esponds to register write and read commands from
the master
It is the master device’s responsibility to ensure that all
configuration registers have been set to their correct values in order to achieve the specified accuracy.
Clock Source
An internal oscillator supplies a system clock of approximately 8MHz, varying slightly over temperature and voltage. No external components are needed.
Reset Sources
External Reset
An external reset is generated by driving the RST pin
low for at least 1Fs and remains as long as RST is held
low. Once the external reset has been released, all registers are cleared to their default states, and the device
resumes execution.
Voltage Monitor
The device is held in reset any time the power supply
AVDD drops below the supply voltage power-fail threshold. Once the power supply rises above the supply voltage power-fail level, the device exits reset, and all registers are reset to their defaults and execution resumes.
I2C Slave Operation
The MAXQ314 operates as an I2C slave peripheral and
requires an external I2C master. All communications
between the two are performed over a standard I2C bus,
using commands to read and write values to internal
registers. These registers contain:
• Operating mode settings
• Calibration parameters (supplied by the master)
• R
ead-only registers containing power, current, and
voltage data
During operation, voltage and current measurements are
taken, filtered, and the collected data is processed. The
output results then can be read by the master from readonly registers in parallel with the ongoing measurement
and processing operations.
The device must be initialized by the master with configuration and calibration parameters following every
power-up or reset cycle.
_______________________________________________________________________________________ 9
MAXQ314
Pin Description (continued)
MAXQ314
Single-Phase Power-Measurement
IC with I2C Interface
I2C Rate and Resets
The I2C bus is dedicated to communications with the
master device. The master device initiates all communications. During an I2C transfer, data is transmitted and
received over the serial data line (SDA) with respect to
a serial shift clock (SCL). I2C transfers always start with
Table 1. Slave Address Determination
A2
A1
A0
SLAVE ADDRESS :7
L
L
L
60h (1100 000b)
L
L
Z
61h (1100 001b)
L
L
H
62h (1100 010b)
L
Z
L
63h (1100 011b)
L
Z
Z
64h (1100 100b)
L
Z
H
65h (1100 101b)
L
H
L
66h (1100 110b)
L
H
Z
67h (1100 111b)
L
H
H
68h (1101 000b)
Z
L
L
69h (1101 001b)
Z
L
Z
6Ah (1101 010b)
Z
L
H
6Bh (1101 011b)
Z
Z
L
6Ch (1101 100b)
Z
Z
Z
6Dh (1101 101b)
Z
Z
H
6Eh (1101 110b)
Z
H
L
6Fh (1101 111b)
Z
H
Z
70h (1110 000b)
Z
H
H
71h (1110 001b)
H
L
L
72h (1110 010b)
H
L
Z
73h (1110 011b)
H
L
H
74h (1110 100b)
H
Z
L
75h (1110 101b)
H
Z
Z
76h (1110 110b)
H
Z
H
77h (1110 111b)
H
H
L
78h (1111 000b)
H
H
Z
79h (1111 001b)
H
H
H
7Ah (1111 010b)
the most significant bit and end with the least significant
bit. All I2C transfers are 8 bits in length, followed by an
ACK/NACK bit.
The clock rate used for the I2C interface is determined
by the bus master, but can be at most 400kHz. The
MAXQ314 can hold the SCL line low while processing
commands to delay reception of further data. For frequencies at or below 100kHz, the delay can be transparent, but at 400kHz delays can be noticeable.
A timeout provision resets the I2C controller if a low level
is detected on the SCL pin for a period of 30ms. The I2C
controller returns to its default state, and the SDA and
SCL pins go their idle state.
I2C Slave Address Generation
The A2, A1, and A0 pins are latched following every
reset and used to construct the 7-bit slave address as
shown in Table 1. The pin states are represented by L for
logic 0, H for logic 1, and Z for high impedance.
I2C Protocol
The I2C protocol supports bus timeout and optionally
packet-error checking. When packet-error checking is
enabled by setting the PECEN bit (DSPCFG.3) to 1, a
packet-error code (PEC) byte is appended at the end
of each transaction. The byte is calculated as CRC-8
checksum, calculated over the entire message including
the address and read/write bit. The polynomial used is
x8 + x2 + x + 1 (the CRC-8-ATM HEC algorithm, initialized to zero).
Commands are read and write, the command code byte
being an address of a register to read/write. Data length
is 2 bytes for most registers, both read and write; 3 bytes
for power (P, Q, S, PAVG), VRMS, and IRMS read commands. The MAXQ314 could be unable to report data
like power, IRMS, VRMS, etc., immediately if the read
command is received while the requested data is being
calculated. In such a case, the clock line is held low
until the calculation completes or a bus timeout occurs.
The firmware does not support ARA address or address
broadcast features.
10 �������������������������������������������������������������������������������������
Single-Phase Power-Measurement
IC with I2C Interface
surement values taken by the device. All the read/write
registers are calculation coefficients set by the master.
The only exceptions are the DSPCFG register, which
configures operating features of the device, and the
ADC_AZ register, which resets the internal ADC when it
is written to.
All transactions consist of the master writing to or reading from data, configuration, or control registers. Each
register has an 8-bit address. There are several categories of internal registers; read-only registers return mea-
READ WORD
S
ADDR:7
W
A
CMD:8
A
SR
ADDR:7
R
A
D0:8
A
D1:8
N
P
W
A
CMD:8
A
SR
ADDR:7
R
A
D0:8
A
D1:8
A
D2:8
W
A
CMD:8
A
D1:8
A
P
READ LONG
S
ADDR:7
N
P
WRITE WORD
S
ADDR:7
D0:8
A
READ WORD WITH PEC
S
ADDR:7
W
A
CMD:8
A
SR
ADDR:7
R
A
D0:8
A
D1:8
A
A
SR
ADDR:7
R
A
D0:8
A
D1:8
A
D1:8
A
PEC:8
N
P
READ LONG WITH PEC
S
ADDR:7
W
A
CMD:8
D2:8
A
PEC:8
N
P
WRITE WORD WITH PEC
S
ADDR:7
W
A
CMD:8
A
D0:8
A
PEC:8
A
P
A = ACKNOWLEDGE (ACK) BIT
ADDR:7 = 7-BIT DEVICE ADDRESS; MUST MATCH THE ADDRESS SELECTED BY A[2:0]
CMD:8 = REGISTER/COMMAND SELECTED IN TABLE 2
D0:8 = 8-BIT DATA; MULTIBYTE COMMANDS CAN REQUIRE D0, D1, D2, ETC.
PEC:8 = 8-BIT PEC DATA
N = NEGATIVE ACKNOWLEDGE (NACK) BIT
P = STOP BIT
S = START BIT
SR = REPEATED START BIT
W = WRITE BIT
______________________________________________________________________________________ 11
MAXQ314
Data and Control Registers
MAXQ314
Single-Phase Power-Measurement
IC with I2C Interface
Table 2. Register Set
NAME
DESCRIPTION
ACCESS
BITS
CMD CODE
0100 0010b (0x42)
P
Active power
R
23:0
Q
Reactive power
R
23:0
0011 0010b (0x32)
S
Apparent power
R
23:0
0011 1010b (0x3A)
PAVG
Average power
R
23:0
0101 1010b (0x5A)
VRMS
RMS-voltage
R
23:0
0100 1010b (0x4A)
IRMS
RMS-current
R
23:0
0101 0010b (0x52)
Power factor; LSB = 2-16
R
23:0
0011 1100b (0x3C)
Temperature sample
R
15:0
0000 0111b (0x07)
PF
RAWTEMP
Phase-angle compensation coefficient
R/W
15:0
0010 0100b (0x24)
I_GAIN
PA
Current gain coefficient
R/W
15:0
0010 1011b (0x2B)
V_GAIN
Voltage gain coefficient
R/W
15:0
0010 1010b (0x2A)
DSPCFG
DSP configuration
R/W
15:0
0010 0010b (0x22)
Lowpass filter compensation
R/W
15:0
0010 0011b (0x23)
SUMCNT
LPFC
Number of sampling frames per DSP cycle
R/W
15:0
0011 0100b (0x34)
ADC_AZ
ADC autozero operation. The master issues this command only
when it is initializing the MAXQ314. Any value written to this
register initiates a reset of the ADC, which takes approximately
1.5ms to complete.
W
7:0
0000 1111b (0x0F)
P_OFFS
Offset added to the P register
R/W
15:0
84
P_GAIN
Gain added to the P register
R/W
15:0
8c
Correction factor for IRMS calculation
R/W
15:0
B2
Voltage-dependent gain correction factor for IRMS calculation
R/W
15:0
ba
Offset for IRMS calculation
R/W
15:0
ac
Voltage-dependent offset for IRMS calculation
R/W
15:0
ac
IK
IGV
I_OFFS
I_OV
12 �������������������������������������������������������������������������������������
Single-Phase Power-Measurement
IC with I2C Interface
BIT
NAME
0
DISIL
1
RESERVED
Must be set to 1
2
RESERVED
Must be set to 0
3
PECEN
4
AVGP
5
AVGRD
6
PWMOUT
7
DISPGA
8
ILPGA
9
ACMODE
10:11
RESERVED
12:15
RESET_STATUS
DESCRIPTION
1 = disable IL measurements
0 = enable IL measurements (default)
1 = PEC enabled for I2C transmission
0 = PEC disabled for I2C transmission (default)
1 = Begin accumulating PAVG
0 = Stop accumulating PAVG (default)
1 = PAVG calculation complete
0 = PAVG calculation in progress, following AVGP 1 R 0
(This bit is automatically cleared the next time the master sets AVGP to 1.)
1 = AUX pin outputs in PWM format
0 = AUX pin outputs in digital format (default)
1 = Disable gain switching
0 = Enable gain switching (recommended, default)
1 = PGA for IL = x4 (default)
0 = PGA for IL = x1
1 = AC mode
0 = DC mode (default)
—
Reset Status Indicator. These bits allow the master to determine if the MAXQ314 has performed a reset since the last time these bits were cleared. When these bits are 1111, the
MAXQ314 has performed a reset. After the bits have been read, the master must write 0000
to these bits to clear the reset indicator. Writing to and reading from these bits does not
affect processor operation or cause a reset; they are only status bits.
______________________________________________________________________________________ 13
MAXQ314
Table 3. DSPCFG Register Detail
MAXQ314
Single-Phase Power-Measurement
IC with I2C Interface
Calibration
Four parameters can be calibrated to optimize system
performance.
Conversion to Physical Units
The output registers are in “meter” units, and need to be
scaled with the input circuits to yield meaningful physical
values. Two conversion coefficients are needed: the voltage transducer ratio (VTR) and the current transducer
ratio (ITR), each specifying the ratio between the input
and output of the corresponding transducer. The VTR
represents the input voltage that would produce a 1V
signal on the VP or VN pin. The ITR represents the input
current that would produce a 1V signal on the IL pin.
For example, if the voltage-sensing circuit consists of a
749kI and 1kI resistor-divider, then VTR = 750(V/V).
If the current-sensing circuit is a 20mI shunt, then 50A
current would produce 1V signal on the IL pin, so ITR =
50(A/V).
The following equations convert “meter” units into physical units:
Voltage (V) = VRMS x VTR x VREF/224
Current (A) = IRMS x ITR x VREF/224
Active Power (kW) = P x VTR x ITR x VREF x VREF/
(103 x 224)
Reactive Power (kVAR) = Q x VTR x ITR x VREF x VREF/
(103 x 224)
Apparent Power (kVA) = S x VTR x ITR x VREF x VREF/
(103 x 224)
where VREF is the reference voltage on the REF pin in
volts.
The current RMS correction is:
IRMS = I_OFFS + I_OV x VRMS + [(I_GAIN +IGV x
VRMS)IMU + IK/IMU]
where IMU is the current measured in meter units before
correction.
Voltage RMS correction is:
VRMS = V_GAIN x VMU
LINE
where VMU is the voltage measured in meter units before
correction.
749kΩ
Active power correction is:
VP
LOAD
P = V_GAIN x I_GAIN x P_GAIN x (P_OFFS + PMU)
1kΩ
MAXQ314
IL
20mΩ
NEUTRAL
where PMU is the active power measured in meter units
before correction.
Apparent power is computer from the corrected voltage
and current:
S = VRMS x IRMS
AGND
Reactive power is computer from corrected S and P:
Q = S2 − P2
Figure 3. Calibration Circuit Example
Table 4. Calibration Parameters
REGISTER
DESCRIPTION
V_GAIN
Voltage Gain Factor. This factor affects the voltage RMS output and power output. The VRMS output is scaled
by (1 + V_GAIN/216). V_GAIN is a signed integer and defaults to 0x0000h.
I_GAIN
Current Gain Factor. This factor affects the current RMS output and power output. The IRMS output is scaled by
(1 + I_GAIN/216). I_GAIN is a signed integer and defaults to 0x0000h.
PA
LPFC
Phase-Angle Compensation
Lowpass Filter Coefficient. This factor affects the lowpass filtering. It can be left unchanged for typical configurations. It is defined as:
LPFC ~ G x fC x tFR x 216, where fC is the corner frequency
Default value ~ 3.14 x 1.82 (Hz) x 200 x E - 6 (s) x 216 = 75 = 0x004B
14 �������������������������������������������������������������������������������������
Single-Phase Power-Measurement
IC with I2C Interface
SYNC
1
1
0
8
7
6
5
4
3
2
1
0
SAMPLE DATA
0
D D D D D D D D D D D D D D D D
19 18 17 16 15 14 13 12 11 10 9
FRAME GAP
L
L
L
L
RMS Current Continuous Output
(AUX Pin)
The AUX pin can be configured to output a 16-bit RMS
current value. Bit time is 2000 system clocks, or a typical
data rate of 4kbps. The bit format is pulse-width modulation, in which each bit cell is divided into four time slices.
At the first time slice, the data line switches from a zero
state to a one state. Then, if the bit to be transmitted is a
zero, the data line switches back to zero after one time
slice. If the bit to be transmitted is a one, the data line
switches back to zero after three time slices.
A data frame consists of one complete 20-bit sample
word and a frame delimiter. The frame delimiter consists
of the data line idling in a low state for nominally four bit
times (tBIT).
The receiver detects the first rising edge of the sync
field and synchronizes on the 1100 pattern. The receiver
should be synchronized by the time the first data bit is
available. After 16 data bits, the data line becomes idle
for four tBIT periods, after which the next synchronization
bit begins.
The AUX pin can output continuous PWM as well by
setting the PWMOUT (DSPCFG.6) bit. The PWM output
period is 65,535 system clocks, or 8.19ms.
Applications Information
Grounds and Bypassing
Careful PCB layout significantly minimizes system-level
digital noise that could interact with the microcontroller
or peripheral components. The use of multilayer 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 rejection and place
the capacitors as close to the leads of the devices as
possible.
CMOS design guidelines for any semiconductor require
that no pin be taken above supply voltage or below
ground. Violation of this guideline can result in a hard
SYNC
1
1
0
8
7
6
5
4
3
2
1
0
SAMPLE DATA
0
D D D D D D D D D D D D D D D D
FRAME GAP
L
L
L
L
failure (damage to the silicon inside the device) or a soft
failure (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 voltage spikes through either their power pins or generalpurpose 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
MAXQ314-Based Systems
To reduce the possibility of coupling noise into the
microcontroller, the systems that use an external crystal
should be designed with a crystal 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 MAXQ314 is used 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 MAXQ314 devices. This can be accomplished by
using a single I2C bus, but with a different slave address
for each device.
Additional Documentation
Designers must have the following documents to fully use
all the features of this device. This data sheet contains
pin descriptions, feature overviews, and electrical specifications. Errata sheets contain deviations from published
specifications.
• M
AXQ314 data sheet, which contains electrical/timing
specifications and pin descriptions
• M
AXQ314 revision-specific errata sheet
(www.maxim-ic.com/errata)
______________________________________________________________________________________ 15
MAXQ314
19 18 17 16 15 14 13 12 11 10 9
MAXQ314
Single-Phase Power-Measurement
IC with I2C Interface
Development and Technical
Support
Maxim offers the MAXQ314 evaluation kit (EV kit) as an
aid in developing and prototyping applications based
on the MAXQ314. The EV kit is a reference design from
which a developer can begin designing their own system. The EV kit data sheet contains a schematic of the
board that can be reviewed by engineers who want to
perform a preliminary investigation of the device uses
before purchasing the EV kit.
Package Information
For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. Note that
a “+”, “#”, or “-” in the package code indicates RoHS
status only. Package drawings may show a different suffix character, but the drawing pertains to the package
regardless of RoHS status.
PACKAGE TYPE
PACKAGE CODE
DOCUMENT NO.
20 TQFN-EP
T2055+4
21-0140
Technical support is available at https://support.maximic.com/micro.
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied.
Maxim reserves the right to change the circuitry and specifications without notice at any time.
16
© 2009
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products, Inc.