MEMS-G1
MULTIFUNCTION METROLOGY DEVICE WITH UART OUTPUT
FEATURES
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Single phase power measurement on a chip.
Compatible with a variety of current sensor technologies.
Simple one-wire UART interface.
Compact 8-pin package.
Low power consumption.
Simple integration into new and existing designs.
APPLICATIONS
The Sentec Micro Energy Monitoring Solution (MEMS) type G1 has been specifically designed to reduce the size, part
count and complexity of integrating power measurement into an appliance or creating stand-alone appliance-level
energy monitoring products, including smart plugs, clamps and leads.
It combines a single-phase active power and frequency measurement engine with a one-wire UART interface, in a
compact MSOP package. No software is required to set up the device and measurements are sent out on the TX pin
in an easy-to-parse format.
The MEMS-G1 is part of a wider range of metrology devices developed by Sentec. The range of Micromonitor devices
covers all aspects of energy monitoring and a variety of communication interfaces, with the same key features of low
cost, reduced part count and ease of implementation. For more information about the Micromonitor family, contact
Sentec on mm@sentec.co.uk
© 2014-15 Sentec Ltd
14874DOC13 R3.01
February 2015
CONFIDENTIAL
For more information please contact
mm@sentec.co.uk +44 1223 303800
www.sentec.co.uk
MEMS-G1
MULTIFUNCTION METROLOGY DEVICE WITH UART OUTPUT
FUNCTIONAL BLOCK DIAGRAM
VDD
Current
ADC
ISENSE
HPF
÷
Ref
ADC
×
x‾
×
Acc W
W Cal
Voltage
ADC
VSENSE
HPF
÷
Frequency
Watts
Acc W
Metrology
Registers
UART
Interface
DITHER
VSS
NC
TX
NC
PIN FUNCTION DESCRIPTIONS AND RATINGS
Pin
Mnemonic
Description
1
VDD
Positive supply voltage. 3.3V with respect to VSS.
2
NC
Not connected.
3
TX
UART TX digital output. VOL Max = 0.6V, VOH Min = VDD – 0.7V.
4
NC
Not connected.
5
DITHER
DC bias generator with dynamic range enhancement.
6
ISENSE
Current signal analogue input. The input range is from VSS to VSS + 2V.
7
VSENSE
Voltage signal analogue input. The input range is from VSS to VSS + 2V.
8
VSS
Ground. Reference point for analogue inputs and digital output.
TYPICAL APPLICATION BLOCK DIAGRAM
© 2014-15 Sentec Ltd
CONFIDENTIAL
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MEMS-G1
MULTIFUNCTION METROLOGY DEVICE WITH UART OUTPUT
TYPICAL MEASUREMENT PERFORMANCE
LOW POWER PERFORMANCE
8.0
Power Error (W)
6.0
4.0
2.0
0.0
-2.0
1
10
100
-4.0
-6.0
-8.0
Reference Power (W)
HIGH POWER PERFORMANCE
8%
6%
% Power Error
4%
2%
0%
-2%
100
1000
-4%
-6%
-8%
Reference Power (W)
These graphs illustrate the typical power measurement performance of the MEMS-G1. At low powers (<100W) the
power measurement is within ±2W and at high powers (>100W) the power measurement is within ±2%. The
frequency measurement is within ±2%. The graphs were recorded under the following test conditions:
© 2014-15 Sentec Ltd
Reference circuit
Implementing example voltage and current input circuits described
in this datasheet.
VDD
3.3V
Voltage
230VAC
Power factor
1.0
Frequency
50Hz
Temperature
25°C
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MEMS-G1
MULTIFUNCTION METROLOGY DEVICE WITH UART OUTPUT
SPECIFICATIONS
The Sentec MEMS-G1 is manufactured by Microchip Technology Incorporated.
Footprint*
MSOP-8
Packaging
Tape and reel
Power consumption
Typ 1mA @ 3.3V
Operating temperature**
0°C TA+70°C
*See www.microchip.com/packaging for package dimensions and recommended land pattern.
**The accuracy of the metrology is not guaranteed over the whole temperature range.
ABSOLUTE MAXIMUM RATINGS (†)
Voltage on VDD with respect to VSS
-0.3V to +4.0V
Voltage on all other pins with respect to VSS
-0.3V to (VDD + 0.3V)
Ambient temperature under bias
-40°C to +85°C
Storage temperature
-65°C to +150°C
† Stresses above those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. This is
a stress rating only and functional operation of the device at those or any other conditions above those indicated in
the operation listings of this specification is not implied. Exposure above maximum rating conditions for extended
periods may affect device reliability.
DESIGN GUIDELINES
The MEMS-G1 is designed to require a minimum number of supporting components. The following notes outline
some useful approaches and important considerations when designing for the device. However, Sentec is not liable for
customer circuit design, and customers are entirely responsible for their products and applications that incorporate
this device.
Off-line power supply
The typical power consumption of the device is 1mA @ 3.3V. This low power consumption allows the use of the
device with a low-cost line drop (capacitive or resistive) power supply. The on-chip voltage reference is calibrated
from VDD six seconds after power up; it is important that the supply voltage is stable and accurate by this time. The
supply voltage must be accurate to 3.3V ± 1% in order to match the accuracy of the chip. Because the voltage
reference is used for measurement of current and voltage, a 1% error in VDD will lead to a 2% error in power.
Signal conditioning
The voltage and current signal inputs should be biased to a DC level of VSS + 1V and cannot go above outside the input
range of VSS to VSS + 2V at any time for correct operation of the device. It is recommended that the dither output
from the MEMS-G1 is used to create the bias for the current input as it improves the dynamic range of the
measurement – see Example Current Input Circuit. The device expects analogue inputs proportional to voltage and
current. The current channel front end circuitry must contain an integrator for operation with dI/dt Rogowski current
sensors.
The input sensitivities are as follows:
Pin
Channel
Sensitivity
VSENSE
Voltage
2.5mV/V
ISENSE
Current
40mV/A
© 2014-15 Sentec Ltd
CONFIDENTIAL
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MEMS-G1
MULTIFUNCTION METROLOGY DEVICE WITH UART OUTPUT
Example Voltage Input Circuit
This design uses R10 and R11 to bias the voltage channel input around ~1V and the resistance ratio of the input chain
gives the required voltage channel input signal of 2.5mV/V. The stability and initial accuracy of measurements is
dependent on the tolerances of selected components.
Example Current Input Circuit
This design uses a 2mΩ shunt for the current sensor and an op-amp stage with a differential gain of x20 to give the
required current channel input signal of 40mV/A. For reference circuits using different current sensors (CT, Rogowski,
other values of shunt etc) please contact Sentec.
For both example input circuits the resistor tolerances are ≤1%.
© 2014-15 Sentec Ltd
CONFIDENTIAL
Page 5 of 7
MEMS-G1
MULTIFUNCTION METROLOGY DEVICE WITH UART OUTPUT
One-wire UART interface
No software or programming is required to set up the device in its default configuration. The following string is
transmitted out of the TX pin every 5 seconds:
pXXXXfXXXX↵↓
p
Power in W units (16bit signed number) as hexadecimal ASCII
f
Frequency in 0.1Hz units (16bit unsigned number) as hexadecimal ASCII
↵
Carriage return (CR – value 0x0D)
↓
Line feed (LF – value 0x0A)
Example string:
p0064f01F4↵↓
p
100W
f
50.0Hz
One-wire UART settings
Baud
38400
Data bits
8
Parity
None
Stop bits
1
Flow control
None
ORDERING INFORMATION
The Sentec MEMS-G1 may be available for sale by Microchip Technology Incorporated or its affiliates, subject to
Microchip’s terms and conditions of sale.
Sentec part number
Microchip catalog number
Footprint
Packaging
Package Marking
MOQ
MEMS-G1-eJ
PIC12LF1572T-I/MS024
MSOP-8
Tape and reel
Line 1: MSG1eJ
10,000
Line 2: Date code
Smaller quantities for prototyping and early stage manufacturing setup can be obtained directly from Sentec. Contact
mm@sentec.co.uk for more details.
DOCUMENT REVISION
© 2014-15 Sentec Ltd
Release
Comments
R1.00
Initial release
R2.00
Update to device specification
R3.00
Update to device specification
R3.01
Production release
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MEMS-G1
MULTIFUNCTION METROLOGY DEVICE WITH UART OUTPUT
TERMS OF USE
Information contained in this publication regarding device applications and the like is provided only for your
convenience and may be superseded by updates. It is your responsibility to ensure that your application meets with
your specifications. SENTEC LTD MAKES NO REPRESENTATIONS OR WARRANTIES OF ANY KIND WHETHER
EXPRESS OR IMPLIED, WRITTEN OR ORAL, STATUTORY OR OTHERWISE, RELATED TO THE INFORMATION,
INCLUDING BUT NOT LIMITED TO ITS CONDITION, QUALITY, PERFORMANCE, MERCHANTABILITY OR
FITNESS FOR PURPOSE. Sentec Ltd disclaims all liability arising from this information and its use. Use of Sentec Ltd
devices in life support and/or safety applications is entirely at the buyer’s risk, and the buyer agrees to defend,
indemnify and hold harmless Sentec Ltd from any and all damages, claims, suits, or expenses resulting from such use.
No licenses are conveyed, implicitly or otherwise, under any Sentec Ltd intellectual property rights.
© 2014-15 Sentec Ltd
CONFIDENTIAL
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