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PNI MicroMag User Manual

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User Manual
SmartSens MicroMag
Magneto-Inductive Sensor Module
Table of Contents
3.1 MODULE CHARACTERISTICS .......................................................................6
3.2 TYPICAL OPERATING CHARACTERISTICS .................................................7
3.3 MECHANICAL DRAWINGS .............................................................................9
3.3.1 MicroMag2 ..........................................................................................9
3.3.2 MicroMag2-on-Carrier Board ........................................................... 11
3.3.3 MicroMag3 ....................................................................................... 12
4.1 PCB ORIENTATION AND OUTPUT POLARITIES ...................................... 13
4.2 PIN/PAD CONNECTIONS ............................................................................ 13
4.3 LINE DESCRIPTIONS .................................................................................. 15
4.3.1 SCLK (SPI Serial Clock) .................................................................. 15
4.3.2 MISO (SPI Master In, Slave Out) ..................................................... 16
4.3.3 MOSI (SPI Master Out, Slave In) ..................................................... 16
4.3.4 SSNOT (SPI Slave Select)............................................................... 16
4.3.5 DRDY (Data Ready) ......................................................................... 16
4.3.6 RESET (Reset) ................................................................................ 17
4.3.7 VDD (DC Voltage Input) ................................................................... 17
4.3.8 COMP (Comparator) ........................................................................ 17
4.3.9 DHST (Clock Output) ....................................................................... 17
4.3.10 VSTBY.............................................................................................. 18
5.1 SPI PORT TIMING ........................................................................................ 19
5.2 COMMAND BYTE ......................................................................................... 21
5.2.1 Axis Select (AS1, AS0) .................................................................... 21
5.2.2 Period Select (PS0, PS1, PS2) ........................................................ 21
5.2.3 Magnetic Oscillator Test (MOT) ....................................................... 22
5.2.4 Oscillator Direction (ODIR)............................................................... 22
5.2.5 High Speed Oscillator Test (DHST) ................................................. 22
5.3 IDLE MODE................................................................................................... 22
5.4 MAKING A MEASUREMENT........................................................................ 23
List of Figures
List of Tables
MicroMag User Manual – March 2010 Page 3 of 23
1 Copyright & Warranty Information
© Copyright PNI Sensor Corporation 2010 All Rights Reserved. Reproduction, adaptation, or translation without prior written permission is prohibited, except as allowed under copyright
laws.
Revised March 2010: for the most recent version visit our website at www.pnicorp.com PNI Sensor Corporation
133 Aviation Blvd, Suite 101 Santa Rosa, CA 95403, USA Tel: (707) 566-2260 Fax: (707) 566-2261
Warranty and Limitation of Liability. PNI Sensor Corporation ("PNI") manufactures its Products from parts and components that are new or equivalent to new in performance. PNI warrants that each Product to be delivered hereunder, if properly used, will, for one year following the date of shipment unless a different warranty time period for such Product is specified: (i) in PNI’s Price List in effect at time of order acceptance; or (ii) on PNI’s web site (www.pnicorp.com) at time of order acceptance, be free from defects in material and workmanship and will operate in accordance with PNI’s published specifications and documentation for the Product in effect at time of order. PNI will make no changes to the specifications or manufacturing processes that affect form, fit, or function of the Product without written notice to the Customer, however, PNI may at any time, without such notice, make minor changes to specifications or manufacturing processes that do not affect the form, fit, or function of the Product. This warranty will be void if the Products’ serial number, or other identification marks have been defaced, damaged, or removed. This warranty does not cover wear and tear due to normal use, or damage to the Product as the result of improper usage, neglect of care, alteration, accident, or unauthorized repair. THE ABOVE WARRANTY IS IN LIEU OF ANY OTHER WARRANTY, WHETHER EXPRESS, IMPLIED, OR STATUTORY, INCLUDING, BUT NOT LIMITED TO, ANY WARRANTY OF MERCHANTABILITY, FITNESS FOR ANY PARTICULAR PURPOSE, OR ANY WARRANTY OTHERWISE ARISING OUT OF ANY PROPOSAL, SPECIFICATION, OR SAMPLE. PNI NEITHER ASSUMES NOR AUTHORIZES ANY PERSON TO ASSUME FOR IT ANY OTHER LIABILITY.
If any Product furnished hereunder fails to conform to the above warranty, Customer’s sole and exclusive remedy and PNI’s sole and exclusive liability will be, at PNI’s option, to repair, replace, or credit Customer’s account with an amount equal to the price paid for any such Product which fails during the applicable warranty period provided that (i) Customer promptly notifies PNI in writing that such Product is defective and furnishes an explanation of the deficiency; (ii) such Product is returned to PNI’s service facility at Customer’s risk and expense; and (iii) PNI is satisfied that claimed deficiencies exist and were not caused by accident, misuse, neglect, alteration, repair, improper installation, or improper testing. If a Product is defective, transportation charges for the return of the Product to Customer within the United States and Canada will be paid by PNI. For all other locations, the warranty excludes all costs of shipping, customs clearance, and other related charges. PNI will have a reasonable time to make repairs or to replace the Product or to credit Customer’s account. PNI warrants any such repaired or replacement Product to be free from defects in material and workmanship on the same terms as the Product originally purchased.
Except for the breach of warranty remedies set forth herein, or for personal injury, PNI shall have no liability for any indirect or speculative damages (including, but not limited to, consequential, incidental, punitive and special damages) relating to the use of or inability to use this Product, whether arising out of contract, negligence, tort, or under any warranty theory, or for infringement of any other party’s intellectual property rights, irrespective of whether PNI had advance notice of the possibility of any such damages, including, but not limited to, loss of use, revenue or profit. In no event shall PNI’s total liability for all claims regarding a Product exceed the price paid for the P roduct. PNI neither assumes nor authorizes any person to assume for it any other liabilities.
Some states and provinces do not allow limitations on how long an implied warranty lasts or the exclusion or limitation of incidental or consequential damages, so the above limitations or exclusions may not apply to you. This warranty gives you specific legal rights and you may have other rights that vary by state or province.
PNI Sensor Corporation DOC# 1015175 r01 MicroMag User Manual – March 2010 Page 4 of 23
2 Introduction
Thank you for purchasing PNI Sensor Corporation’s MicroMag magneto-inductive sensing module. Whether you purchased the MicroMag2 2-axis sensing module or the MicroMag3 3-axis sensing module, we’re sure you’ll be happy with your purchase. If you do have issues with your device, please feel free to contact us.
The MicroMag is an integrated magnetic field sensing module combining PNI’s patented SmartSens magneto-inductive (MI) sensors with the PNI ASIC. Designed primarily to aid in the evaluation and prototyping of PNI’s SmartSens technology, the MicroMag board contains connectors, test points, option solder jumpers and extra support circuits to expedite evaluation. The microprocessor-compatible SPI interface allows easy access to the MicroMag’s measurement parameters and resulting field measurement data.
PNI’s MicroMag benefits include low power consumption, large signal noise immunity under all conditions, and a large dynamic range. Measurements are very stable over temperature and inherently free from offset drift. Also, the MicroMag features software­configurable resolution, sample rate and field measurement range. These advantages make PNI’s MicroMag not only the choice for prototyping high volume SmartSens solutions, but also for lower volume applications that require a complete solution.
For more information on PNI’s magneto-inductive technology please refer to PNI’s Magneto-Inductive Technology Overview (http://www.pnicorp.com/support/articles). For information on the PNI ASIC and Sen-XY & Sen-Z sensors at the core of the MicroMag module, please refer to their respective manuals (http://www.pnicorp.com/support/manuals).
MicroMag User Manual – March 2010 Page 5 of 23
3 Specifications
Parameter
Symbol
Maximum
Units
DC Supply Voltage
VDD
5.25
VDC
Input Pin Voltage
VIN
VDD + 0.3
VDC
Input Pin Current @ 25C
IIN
10 mA
mA
Storage Temperature
T
STRG
+85
C
Parameter
Value
Units
Field Measurement Range1
-1100 to +1100
T
Gain2
31.24
counts/ T
Resolution2 (1/Gain)
0.03
T
Linearity, ± 300 µT
0.6
%
DC Supply Voltage (VDD)
3.0 nominal
2.2 to 5.0 allowable
VDC
Idle Current3
< 0.1
mA rms
Continuous Current3
0.5
mA rms
Sensor Frequency
3,4
175
kHz
Operating Temperature
-20 to +70
C
3.1 Module Characteristics
Table 3-1: Absolute Maximum Ratings
CAUTION:
Stresses beyond those listed in Table 3-1 may cause permanent damage to the device. These are stress ratings only. 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.
Table 3-2: Module Operating Characteristic
Notes:
1) Field Measurement Range is defined as the monotonic region of the output characteristic curve.
2) Period select value of 2048. The Gain and Resolution can be increased by a factor of 2 by
setting the period select to 4095. However, the ASIC counter can overflow if the field is strong
enough to drive the count beyond a signed 16-bit signed integer. Period select set to 2048 is the
highest setting where it is impossible to overflow the counter. In practical magnetometer
PNI Sensor Corporation DOC# 1015175 r01 MicroMag User Manual – March 2010 Page 6 of 23
applications, a sensor gain calibration is optimally performed when the sensor module is in the
host system.
3) VDD = 3.0VDC
4) The sensor frequency is related to the strength of the magnetic field. The specified value is for
when the MicroMag is solely within Earth’s magnetic field.
3.2 Typical Operating Characteristics
Figure 3-1: Temperature Characteristics
MicroMag User Manual – March 2010 Page 7 of 23
Figure 3-2: Linearity vs. Temperature
Figure 3-3: Linearity vs. Temperature, Normalized to Room Temperature
PNI Sensor Corporation DOC# 1015175 r01 MicroMag User Manual – March 2010 Page 8 of 23
3.3 Mechanical Drawings
ALL DIMENSIONS IN MM
3.3.1 MicroMag2
Figure 3-4: MicroMag2 Mechanical Drawing
Figure 3-5: MicroMag2 Suggested SMT Footprint
MicroMag User Manual – March 2010 Page 9 of 23
Item Number
Quantity
Description
1 1 MicroMag2 PCB
2 1 PNI ASIC, MLF package
3 2 SEN-XY
4 1 C1, chip capacitor
5 1 C2, chip capacitor
6 1 R1, chip resistor
7 1 R2, chip resistor
8 1 R3, chip resistor
9 1 R4, chip resistor
10 1 R5, chip resistor
Figure 3-6: MicroMag2 3-D View with Component Call-Out
Table 3-3: MicroMag2 Component Call-Out
PNI Sensor Corporation DOC# 1015175 r01 MicroMag User Manual – March 2010 Page 10 of 23
Item Number
Quantity
Description
1 1 MicroMag2 carrier PCB
2 1 MicroMag2 module
3 2 7-pin header
3.3.2 MicroMag2-on-Carrier Board
Figure 3-7: MicroMag2-on-Carrier Mechanical Drawing
Figure 3-8: MicroMag2-on-Carrier 3-D View
Table 3-4: MicroMag2-on-Carrier Component Call-Out
MicroMag User Manual – March 2010 Page 11 of 23
3.3.3 MicroMag3
Figure 3-9: MicroMag3 Mechanical Drawing
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4 Set-Up & Interface Lines
4.1 PCB Orientation and Output Polarities
Both the MicroMag2-on-Carrier and MicroMag3 have an arrow printed on the PCB indicating the “reference direction” for the module, while the MicroMag2’s reference direction is shown in Figure 3-4. The sensors on the MicroMag modules are arranged in a south-west-down (SWD) coordinate system. The reference direction is parallel to the x-axis sensor, such that when the MicroMag is pointing directly magnetic south (in the absence of any other magnetic field) the x-axis reading of the module will be maximized and the y-axis will be zero. Likewise, when the MicroMag module is pointing directly west the y-axis reading of the module will be maximized and the x-axis reading will be zero. For the MicroMag3, the z-axis reading will depend on the dip angle or inclination at the given location (which is related to latitude). At the geomagnetic equator, where Earth’s magnetic field is horizontal, the z-axis reading will be zero when flat and at its maximum when the module is pointed down such that the top of the module faces magnetic north.
Note that if the MicroMag is used with the PNI CommBoard, the coordinate system is changed in software to be north-east-down (NED).
4.2 Pin/Pad Connections
The pin and pad numbers for the MicroMag modules are identified on their respective mechanical drawings, as given in Section 3.3. The connections to be made the various pins and pads are given below in Table 4-1. The MicroMag2-on-Carrier and MicroMag3 have similar pin-outs, while the pad connections for the MicroMag2 are different and include some additional lines. Descriptions of the functions of the various connections is provided in Section 4.3.
MicroMag User Manual – March 2010 Page 13 of 23
Identifier
MicroMag2-on-
Carrier &
MicroMag3 Pin #
MicroMag2
Pad #
Description
SCLK 1 13
Serial clock input for SPI port, 1 MHz maximum (Rext = 100 kHz)
MISO 2 14
Master In, Slave Out for the SPI port
MOSI 3 1
Master Out, Slave In for the SPI port
SSNOT 4 2
Active low device select for SPI port
DRDY 5 10
Data ready
RESET 6 9
Reset input
GND
7, 14
3, 5, 7
Ground
VDD
12
4, 6
DC supply voltage
COMP
NA
8
Comparator output
DHST
NA
11
High-speed oscillator output.
VSTBY
NA
12
Input protection clamp diode common, connected to VDD
Table 4-1: Pin/Pad Indentifier Table
For reference, a block diagram for the MicroMag2-on-Carrier is given below. This shows the connections for the MicroMag2 as well. The concept also applies to the MicroMag3, although an additional sensor circuit (APZDRV, APZIN..) would be shown.
PNI Sensor Corporation DOC# 1015175 r01 MicroMag User Manual – March 2010 Page 14 of 23
Figure 4-1: MicroMag2-on-Carrier Reference Block Diagram
4.3 Line Descriptions
4.3.1 SCLK (SPI Serial Clock)
The serial clock input is used to synchronize both the data in and out through the MISO and MOSI lines. The serial clock signal is provided by the customer-supplied master device and should be 1 MHz or less. One byte of data is exchanged over eight clock cycles. Data is captured by the master device on the rising edge of SCLK. Data is shifted out and presented to the MicroMag2 on the MOSI pin on the falling edge of SCLK.
MicroMag User Manual – March 2010 Page 15 of 23
4.3.2 MISO (SPI Master In, Slave Out)
An SPI output that sends data from the MicroMag module to the master device. Data is transferred most significant bit first. The MISO line is placed in a high impedance state if the MicroMag is not selected by the master device (SSNOT = 1).
4.3.3 MOSI (SPI Master Out, Slave In)
An SPI input that provides data from the master device to the MicroMag module. Data is transferred most significant bit first. Valid data must be presented at least 100 ns before the rising edge of SCLK, and remain valid for 100 ns after the rising edge. New data may be presented to the MOSI pin after the falling edge of SCLK.
4.3.4 SSNOT (SPI Slave Select)
This signal sets the MicroMag module as the selected slave device on the SPI bus. The SSNOT line must be LOW prior to data transfer in either direction, and must stay LOW during the entire transfer. The SPI bus can be freed up (SSNOT line set HIGH) for communication with another slave device while the MicroMag module is taking a measurement or idle, but only after all communication between the MicroMag and master device is finished. If the host system has no other slave devices, the SSNOT line can be permanently grounded.
4.3.5 DRDY (Data Ready)
It is recommended the DRDY line be used to ensure data is clocked out of the MicroMag only when it is available. DRDY is set low after a RESET. After a command has been received and the data is ready, DRDY will be changed to high.
If it is determined the DRDY line cannot be used due to lack of I/O lines to the host processor, then the times listed in Table 4-2 can be used to set open-loop wait times. The values listed are the maximum delays from the end of the SCLK command until the rise of the DRDY at each period select setting. The maximum delay occurs when the sensor being sampled is in a zero field
PNI Sensor Corporation DOC# 1015175 r01 MicroMag User Manual – March 2010 Page 16 of 23
Period Select
Maximum Delay
32
500 μS
64
1.0 mS
128
2.0 mS
256
4.0 mS
512
7.5 mS
1024
15 mS
2048
35.5 mS
4096
60 mS
Table 4-2: Maximum Delay for DRDY
4.3.6 RESET (Reset)
RESET must be toggled from LOW-HIGH-LOW before sending a measurement command. RESET is usually LOW.
4.3.7 VDD (DC Voltage Input)
It is recommended the user supply 3.0 VDC on this line, in part because the bias resistor values on the MicroMag module were optimized for 3.0 VDC operation.
However, the MicroMag can be run at other voltages within the specification. While not necessary, if the MicroMag will be run at some other voltage it may be desirable to change the bias resistors for better performance. Refer to the PNI ASIC
User Manual for bias resistor values for other operating voltages. The resistors to be
changed are labeled R1, R2, R3, R4, R6, & R7.
4.3.8 COMP (Comparator)
COMP is only available on the MicroMag2 and it provides the output signal from the comparator component built into the PNI ASIC. This is used for diagnostics.
MicroMag User Manual – March 2010 Page 17 of 23
4.3.9 DHST (Clock Output)
DHST is only available on the MicroMag2 and it outputs the ASIC’s high speed clock, but at half the speed. This is used for diagnostics.
4.3.10 VSTBY
VSTBY is only available on the MicroMag2. (It is wired to VDD on the MicroMag2-on-Carrier and the MicroMag3.) VSTBY provides power to the SPI ports on the PNI ASIC. It should be tied to VDD to prevent current sinking which could be caused when another device is using the SPI bus.
PNI Sensor Corporation DOC# 1015175 r01 MicroMag User Manual – March 2010 Page 18 of 23
5 Operation
A single 8-bit command from the host system configures and initiates a sensor measurement. Only one sensor can be measured at a time. Each magneto-inductive sensor operates in an individual oscillator circuit composed of an external bias resistor along with digital gates and a comparator internal to the PNI ASIC. (See Figure 4-1.)
To make a sensor measurement, a command byte is sent to the MicroMag through the
SPI port specifying the sensor (axis) to be measured and the “Period Select”. The Period
Select defines the number of oscillation cycles (periods) to be measured in both the forward and reverse bias directions. A sensor measurement consists of measuring the time required to complete the host-specified number of oscillation cycles (set by the Period Select) in both the forward and reverse bias directions. The measurement is made with the PNI ASIC’s internal high speed clock, which runs at nominally 2 MHz. The MicroMag returns the difference between the two measurement times represented as a number in a 16-bit 2’s complement format (range: -32768 to 32767), and this number is directly proportional to the strength of the local magnetic field in the direction of the specified axis. Note that the greater the Period Select value, the higher the resolution of the measurement and the longer the sample time.
For a more detailed discussion on the underlying operation of the MicroMag module please refer to the PNI ASIC User Manual (http://www.pnicorp.com/support/manuals) and/or PNI’s Magneto-Inductive Technology Overview (http://www.pnicorp.com/support/articles).
Data flow to and from the MicroMag is through a hardware-handshaking, synchronous serial interface adhering to the SPI bus protocol. Section 4.3 reviews the various interface lines.
5.1 SPI Port Timing
Figure 5-1 graphically shows the timing sequence for the MicroMag. The clock
polarity used with the MicroMag must be normally LOW (cpol = 0).
MicroMag User Manual – March 2010 Page 19 of 23
Figure 5-1: SPI Port Full Timing Sequence
When implementing an SPI port, whether it is a dedicated hardware peripheral port or a software implemented port using general purpose I/O (also known as bit-banging) the timing parameters given in Figure 5-2 must be met to ensure reliable communications. Data is always considered valid while SCLK is HIGH (tDASH = Time, Data After SCLK High). When SCLK is LOW, data is in transition (tDBSH = Time, Data Before SCLK High).The clock set-up and hold times, t
DBSH
and t
must be greater
DASH
than 100 ns.
Figure 5-2: SPI Port Timing Parameters
PNI Sensor Corporation DOC# 1015175 r01 MicroMag User Manual – March 2010 Page 20 of 23
Position
7 6 5 4 3 2 1
0
BIT Name
DHST
PS2
PS1
PS0
ODIR
MOT
AS1
AS0
RESET
0 0 0 0 0 0 0
0
Axis Measured
AS1
AS0
X axis 0 0
X axis 0 1
Y axis 1 0
Z axis (MicroMag3)
1
1
5.2 Command Byte
The operation of the MicroMag is controlled by the data received into the SPI port on the command byte. The command byte syntax is as follows:
Table 5-1: Command Byte
5.2.1 Axis Select (AS1, AS0)
The Axis Select bits establish which sensor is to be measured, as given below
Table 5-2: Axis Select
5.2.2 Period Select (PS0, PS1, PS2)
The Period Select bits establish how many oscillations are to occur for the
measurement. The greater the Period Select, the greater the resolution and the
longer the measurement time. Note that with a Period Select of “4096”, the counter
buffer may overflow.
MicroMag User Manual – March 2010 Page 21 of 23
Period Select
PS2
PS1
PS0
32
0 0 0
64
0 0 1
128
0 1 0
256
0 1 1
512
1 0 0
1024
1 0 1
2048
1 1 0
4096
1 1 1
Table 5-3: Period Select
5.2.3 Magnetic Oscillator Test (MOT)
When set HIGH, MOT causes the magnetic oscillator circuit (selected by AS0 and AS1 in the directions selected by ODIR) to run continuously until the MicroMag is RESET.
5.2.4 Oscillator Direction (ODIR)
ODIR determines the magnetic oscillator direction if MOT is set to 1. It has no effect on direction when the MOT bit is set to zero. This is used for debug purposes only, and will not be set in normal operation.
5.2.5 High Speed Oscillator Test (DHST)
When high, the internal high speed clock is set to drive the DHST pad at ½ the clock speed. When low, the DHST pad is set to DVDD. This is used for debug purposes only, and will not be set in normal operation.
5.3 Idle Mode
The MicroMag incorporates an idle mode to reduce power consumption, in which it
automatically goes to sleep when it is not exchanging data or taking a measurement. However, it does not necessarily initialize in the idle mode at power-up. To ensure the MicroMag will be in idle mode after being turned on, it is necessary to cycle the system through one measurement operation.
PNI Sensor Corporation DOC# 1015175 r01 MicroMag User Manual – March 2010 Page 22 of 23
5.4 Making a Measurement
To make a sensor measurement, a command byte is sent to the MicroMag through
the SPI port specifying the sensor (axis) to be measured and the “Period Select”. The
Period Select defines the number of oscillation cycles (periods) to be measured in both the forward and reverse bias directions. A sensor measurement consists of measuring the time required to complete the host-specified number of oscillation cycles (set by the Period Select) in both the forward and reverse bias directions. The measurement is made with the PNI ASIC’s internal high speed clock, which runs at nominally 2 MHz. The MicroMag returns the difference between the two measurement times represented as a number in a 16-bit 2’s complement format (range: -32768 to 32767), and this number is directly proportional to the strength of the local magnetic field in the direction of the specified axis. Note that the greater the Period Select value, the higher the resolution of the measurement and the longer the sample time.
The sequence and timing are discussed in Section 5.1 and the command byte
syntax is discussed in Section 5.2.
The steps to make a sensor measurement are as follows:
1. SSNOT pin is set LOW. (This enables communication with the master device.)
2. RESET pin is set HIGH, then LOW. This will reset the PNI ASIC. It is necessary
to reset the MicroMag before each measurement.
3. A command word is clocked into the MicroMag on the MOSI pin. Once 8 bits
have clocked in, the MicroMag will execute the command (take a measurement).
4. A measurement consists of forward biasing the sensor and making a period
count; then reverse biasing the sensor and counting again; and then taking the
difference between the two directions.
5. At the end of the measurement, the DRDY line is set HIGH, indicating data is
ready. The data is clocked out on the MISO pin with the next 16 clock cycles. If another measurement is to be made, start at Step 2. The next command can be
sent after resetting. In this case, SSNOT should be kept LOW. If the MicroMag will not immediately be used again and there are other devices on the SPI bus, set SSNOT to HIGH to free up the SPI bus.
MicroMag User Manual – March 2010 Page 23 of 23
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