SEN-09721 - SparkFun Electronics

Document Number: MPL115A1

Rev. 7, 02/2013

Freescale Semiconductor

Data Sheet: Technical Data

Miniature SPI Digital Barometer

The MPL1 15A1 is an absolute pressure sensor with a digital SPI output targeting

low cost applications. A miniature 5 x 3 x 1.2 mm LGA package is ideally suited

for the space constrained requirements of portable electronic devices. Low

current consumptions of 5 μA during Active mode and 1 μA du ring Shutdown

(Sleep) mode are essential when focusing on low-power applications. The wide

operating temperature range spans from -40°C to +105°C to fit demanding

environment conditions.

The MPL115A1 employs a MEMS pressure sensor with a conditioning IC to

provide accurate pressure measurements from 50 to 115 kPa. An integrated

ADC converts pressure and temperature sensor readings to digitized outputs via

a SPI port. Factory calibration data is stored internally in an on-board ROM.

Utilizing the raw sensor output and calibration data, the host microcontroller

executes a compensation algorithm to render Compensated Absolute Pressure

with ±1 kPa accuracy.

The MPL115A1 pressure sensor’s small form factor, low power capability,

precision, and digital output optimize it for barometric measurement

applications.

Features

• Digitized pressure and temperature information together with programmed

calibration coefficients for host micro use.

• Factory calibrated

• 50 kPa to 115 kPa absolute pressure

• ±1 kPa accuracy

• 2.375V to 5.5V supply

• Integrated ADC

• SPI Interface

• Monotonic pressure and temperature data outputs

• Surface mount RoHS compliant package

Application Examples

• Barometry (portable and desktop)

• Altimeters

• Weather stations

• Hard-disk drives (HDD)

• Industrial equipment

• Health monitoring

• Air control systems

ORDERING INFORMATION

Device Name Package Options Case No. # of Ports Pressure Type Digital

Interface

None Single Dual Gauge Differential Absolute

MPL115A1 Tray 2015 • • SPI

MPL115A1T1 Tape & Reel (1000) 2015 • • SPI

MPL115A1

50 to 115 kPa

Top View

LGA Package

5.0 mm x 3.0 mm x 1.2 mm

Pin Connections

DOUT

DIN

VDD

CAP

SHDN

GND

SCLK

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1 Block Diagram and Pin Descriptions

Figure 1. Block Diagram and Pin Connections

Table 1. Pin Description

Pin Name Function

1VDD VDD Power Supply Connection: VDD range is 2.375V to 5.5V.

2CAP External Capacitor: Output decoupling capacitor for main internal regulator. Connect a 1 μF ceramic capacitor

to ground.

3GND Ground

4SHDN Shutdown: Connect to GND to disable the device. When in shut down the part draws no more than 1 μA supply

current and all communications pins (CS, SCLK, DOUT, DIN) are high impedance. Connect to VDD for normal

operation.

5CS CS: Chip Select line.

6DOUT DOUT: Serial data output

7DIN DIN: Serial data input

8SCLK SPI: Serial Clock Input.

Diff

Amp

Temp

Sensor

MUX

ADC

DIN

GND

VDD

DOUT

Temperature

Pressure

Coefficient

Storage

ADDR

SPI

Interface

SHDN

CAP

SCLK

Diff

Amp

Temp

Sensor

MUX

ADC

DIN

GND

VDD

DOUT

Temperature

Pressure

Coefficient

Storage

ADDR

SPI

Interface

SHDN

CAP

SCLK

VDD

CAP

SHDN

DIN

DOUT

GND

SCLK

μC

1 μF

Microcontroller

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2 Mechanical and Electrical Specifications

2.1 Maximum Rati ngs

Voltage (with respect to GND unless otherw ise noted)

VDD........... ... .............. .............. .............. .............. .............. ......................... ........-0.3 V to +5.5 V

SHDN, SCLK, CS, DIN, DOUT ......................................................................-0.3 V to VDD+0.3 V

Operating Temperature Range..........................................................................-40°C to +105°C

Storage Temperature Range .............................................................................-40°C to +125°C

Overpressure................................................................................................................1000 kPa

2.2 Operating Characteristics

(VDD = 2.375 V to 5.5 V, TA = -40°C to +105°C, unless otherwise noted. Typical values are at VDD = 3.3 V, TA = +25°C.

Ref Parameters Symbol Conditions Min Typ Max Units

1 Operating Supply Voltage VDD 2.375 3.3 5.5 V

2 Supply Current IDD Shutdown (SHDN = GND) — — 1 μA

Standby — 3.5 10 μA

Average – at one measurement per second — 5 — μA

Pressure Sensor

3 Range 50 — 115 kPa

4 Resolution —0.15—kPa

5 Accuracy -20ºC to 85ºC — — ±1 kPa

6 Conversion Time

(Start Pressure and Temperature

Conversion)

tc Time between start convert command and

data available in the Pressure and

Temperature registers

—1.63ms

7 Wakeup Time tw Time between leaving Shutdown mode

(SHDN goes high) and communicating with

the device to issue a command or read data.

—35ms

SPI Inputs: SCLK, CS, DIN

8 SCLK Clock Frequency fSCLK (1)

1.Nominal maximum SPI clock frequency.

——8MHz

9 Low Level Input Voltage VIL ——0.3V

DD V

10 High Level Input Voltage VIH 0.7VDD —— V

SPI Outputs: DOUT

11 Low Level Output Voltage VOL1 At 3 mA sink current 0 — 0.4 V

VOL2 At 6 mA sink current 0 — 0.6

12 High Level Output Voltage VOH1 At 3 mA source current VDD – 0.4 V — — V

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3 Overview of Functions/Operation

Figure 2. Sequence Flow Chart

The MPL1 15A interfaces to a host (or system) microcontroller in the user’s application. All communications are via SPI. A typical

usage sequence is as follows:

Initial Power-up

All circuit elements are active. SPI port pins are high impedance and associated registers are cleared. The device then enters

standby mode.

Reading Coefficient Data

The user then typically accesses the part and reads the coefficient data. The main circuits within the slave device are disabled

during read activity. The coefficients are usually stored in the host microcontoller loca l memory but can be re-read at any time.

Reading of the coefficients may be executed only once and the values stored in the host microcontroller. It is not necessary to

read this multiple times because the coefficients within a device are constant and do not change. However, note that the

coefficients will be different from device to device, and cannot be used for another part.

Data Conversion

This is the first step that is performed each time a new pre ssure reading is required which is initiated by th e host sending the

CONVERT command. The main system circuits are activated (wake) in response to the command and after the conversion

completes, the result is placed into the Pressure and Temperature ADC output registers.

The conversion completes with in the maximum conversion time, tc (see Row 6, in the Operating Characteristics Table). The

device then enters standby mode.

Compensated Pressure Reading

After the conversion has been given sufficient time to complete, the host microcontroller reads the result from the ADC output

registers and calculates the Compensated Pressure, a barometric/atmospheric pressure value which is compensated for

changes in temperature and pressure sensor linearity. This is done using the coefficient data from the MPL115A and the raw

sampled pressure and temperature ADC output values, in a compensation equation (detailed later). Note that this is an absolute

pressure measurement with a vacuum as a reference.

From this step the host controller may either wait and then return to the Data Conversion step to obtain the next pressure reading

or it may go to the Shutdown step.

Reading

coeff ic ient dat a

Dat a c onv er s ion

Initial

powerup

Compensated

pres s ur e reading

Shutdown

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Shutdown

For longer periods of inactivity the user may assert the SHDN input by driving this pin low to reduce system power consumption.

This removes power from all internal circuits, including any registers. In the shutdown state, the Pressure and Temperature

registers will be reset, losing any previous ADC output values.

This step is exited by taking the SHDN pin high. Wait for the maximum wakeup time, tw (see Row 7, in the Operating

Characteristics Table), after which another pressure readin g can be taken by transitioning to the data Conversion step.

For values with less than 16 bits, the lower LSBs are zero. For example, c12 is 14 bits and is stored into 2 bytes as follows:

c12 MS byte = c12[13:6] = [c12b13 , c12b12 , c12b11 , c12b10 , c12b9 , c12b8 , c12b7 , c12b6]

c12 LS byte = c12[5: 0] & “00” = [c12b5 , c12b4 , c12b3 , c12b2 , c12b1 , c12b0 , 0 , 0]

3.1 Pressure, Temperature and Coefficient Bit-Width Specifications

The table below specifies the initial coefficient bit-width specifications for the compensation algorithm and the specifications for

Pressure and Temperature ADC values.

Table 2. Device Memory Map

Address Name Description

0x00 Padc_MSB 10-bit Pressure ADC output value MSB

0x01 Padc_LSB 10-bit Pressure ADC output value LSB

0x02 Tadc_MSB 10-bit Temperature ADC output value MSB

0x03 Tacd_LSB 10-bit Temperature ADC output value LSB

0x04 a0_MSB a0 coefficient MSB

0x05 a0_LSB a0 coefficient LSB

0x06 b1_MSB b1 coefficient MSB

0x07 b1_LSB b1 coefficient LSB

0x08 b2_MSB b2 coefficient MSB

0x09 b2_LSB b2 coefficient LSB

0x0A c12_MSB c12 coefficient MSB

0x0B c12_LSB c12 coefficient LSB

0x0C Reserved* —

0x0D Reserved* —

0x0E Reserved* —

0x0F Reserved* —

0x10 Reserved —

0x11 Reserved —

0x12 CONVERT Start Pressure and Temperature Conversion

*These registers are set to 0x00. These are reserved, and were previously utilized as Coefficient values, c11 and c22, which

were always 0x00.

Pressure, Temperature and Compensation Coefficient Specifications

a0 b1 b2 c12 Padc Tadc

Total Bits 16 16 16 14 10 10

Sign Bits 1 1 1 1 0 0

Integer Bits 12 2 1 0 10 10

Fractional Bits 313 14 13 0 0

dec pt zero pad 0 0 0 9 0 0

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Example Binary Format Definitions:

a0 Signed, Integer Bits = 12, Fractional Bits = 3 : Coeff a0 = S I11 I10 I9 I8 I7 I6 I5 I4 I3 I2 I1 I0 . F2 F1 F0

b1 Signed, Integer Bits = 2, Fractional Bits = 13 : Coeff b1 = S I1 I0 . F12 F11 F10 F9 F8 F7 F6 F5 F4 F3 F2 F1 F0

b2 Signed, Integer Bits = 1, Fractional Bits = 14 : Coeff b2 = S I0 . F13 F12 F11 F10 F9 F8 F7 F6 F5 F4 F3 F2 F1 F0

c12 Signed, Integer Bits = 0, Fractional Bits = 13, dec pt zero pad = 9 : Coeff c12 = S 0 . 000 000 000 F12 F11 F10 F9 F8 F7 F6 F5 F4 F3 F2 F1 F0

Padc Unsigned, Integer Bits = 10 : Padc U = I9 I8 I7 I6 I5 I4 I3 I2 I1 I0

Tadc Unsigned, Integer Bits =10 : Tadc U = I9 I8 I7 I6 I5 I4 I3 I2 I1 I0

NOTE: Negative coefficients are coded in 2’s complement notation.

3.2 Compensation

The 10-bit compensated pressure output, Pcomp, is calculated as follows:

Eqn. 1

Where: Padc is the 10-bit pressure ADC output of the MPL115A

Tadc is the 10-bit temperature ADC output of the MPL115A

a0 is the pressure offset coefficient

b1 is the pressure sensitivity coefficient

b2 is the temper at ure coefficient of of fset (TCO)

c12 is the temperature coefficient of sensitivity (TCS)

Pcomp will produce a value of 0 with an input pressure of 50 kPa and will produce a full-scale value of 1023 with an input pressure

of 115 kPa.

Eqn. 2

3.3 Evaluation Sequence, Arithmetic Circuits

The following is an example of the calculation for Pcomp, the compensated pressure output. Input values are in bold.

c12x2 = c12 * Tadc

a1 = b1 + c12x2

a1x1 = a1 * Padc

y1 = a0 + a1x1

a2x2 = b2 * Tadc

Pcomp = y1 + a2x2

This can be calculated as a succession of Multiply Accumulates (MACs) operations of the form y = a + b * x:

Pcomp a0 b1 c12 Tadc⋅+()Padc b2 Tadc⋅+⋅+=

Pressure (kPa) P=comp 115 50–

1023

---------------------- 50+⋅

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The polynomial can be evaluated (Equation 1) as a sequence of 3 MACs:

Please refer to Freescale application note AN3785 for more detailed notes on implementation.

3.4 SPI Device Read/W rite Operations

All device read/write operations are memory mapped. Device actions e.g. “Start Conversions” are controlled by writing to the

appropriate memory address location. All memory address locations are 6-bit (see Table 2).

The 8-bit command word comprises:

• the most significant bit which is the Read/Write identifier which is '1' for read operations and '0' for write operations.

• the 6-bit address (from Table 2);

• the least significant bit which is not used and is don't care (X).

The device write commands are shown in Table 3.

The actions taken by the part in response to each command are as follows:

Table 3. SPI Write Command

Command Binary HEX(1)

1. The command byte needs to be paired with a 0x00 as part of the SPI exchange to complete the passing of Start

Conversions.

Start Conversions 0010010X 0x24

X = don’t care

Table 4. SPI Write Command Description

Command Action Taken

Start Conversions

Wake main circuits. Start clock. Allow supply stabilization time. Select pressure sensor input.

Apply positive sensor excitation and perform A to D conversion. Select temperature input.

Perform A to D conversion. Load the Pressure and Temperature registers with the result. Shut

down main circuits and clock.

Pcomp a0 b1 c12 Tadc⋅+()Padc b2 Tadc⋅+⋅+=

c12

Tadc

Padc

PComp

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SPI Read operations are performed by sending the required address with a leading Read bit set to ‘1’. SPI operations require

that each byte be addressed individually. All data is transmitted most significant bit first.

3.5 SPI Timing

Table 6 and Figure 3 describe the timing requirements for the SPI system.

Figure 3. SPI Timing Diagram

Table 5. Example SPI Read Commands

Command Binary HEX(1)

1. The command byte needs to be paired with a 0x00 as part of the SPI exchange to complete the passing of stated

command.

Read Pressure MSB 1000000X 0x80

Read Pressure LSB 1000001X 0x82

Read Temperature MSB 1000010X 0x84

Read Temperature LSB 1000011X 0x86

Read Coefficient data byte 1 1000100X 0x88

X = don’t care

Table 6. SPI Timing

Ref Function Symbol Min Max Unit

1Operating Frequency Of— 8 MHz

2SCLK Period tSCLK 125 —ns

3SCLK High time tCLKH 62.5 —ns

4SCLK Low time tCLKL 62.5 —ns

5Enable lead time tSCS 125 —ns

6Enable lag time tHCS 125 —ns

7Data setup time tSET 30 —ns

8Data hold time tHOLD 30 —ns

9Data valid (after SCLK low edge) tDDLY —32 ns

10 Width CS High tWCS 30 —ns

SCLK

DIN

DOUT

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3.6 Example of SPI Reading of Coefficients

These are MPL1 15A1 SPI commands to read coefficients, execute Pressure and T emperature conversions, and to read Pressure

and Tempera tu re data. The sequence of the commands for the interaction is given as an example to operate the MPL115A1.

Utilizing this gathered data, an example of the calculating the Compensated Pressure reading is given in floating point notation.

SPI Commands (simplified for communication)

Command to Write “Convert Pressure and Temperature” = 0x24

Command to Read “Pressure ADC High byte” = 0x80

Command to Read “Pressure ADC Low byte” = 0x82

Command to Read “Temperature ADC High byte” = 0x84

Command to Read “Temperature ADC Low byte” = 0x86

Command to Read “Coefficient data byte 1 High byte” = 0x88

Read Coefficients:

[CS=0], [0x88], [0x00], [0x8A], [0x00] , [0x8C], [0x00], [0x8E], [0x00], [0x90], [0x00], [0x92], [0x00], [0x94], [0x00], [0x96], [0x00],

[0x00], [CS=1]

Start Pressure and Temperatu re Conversion, Read raw Pressure:

[CS=0], [0x24], [0x00], [CS=1], [3 ms Delay]

[CS=0], [0x80] , [0x00], [0x82], [0 x00], [0x84], [0x00,] [0x86], [0x00], [0x0 0], [CS=1]

NOTE: Extra [0x00] at the end of each sequence to output the last data byte on the slave side of the SPI.

Figure 4. SPI Read Coefficient Datagram

a0 coefficient MSB =0x41

a0 coefficient LSB =0xDF a0 coefficient =0x41DF =2107.875

b1 coefficient MSB =0xB0

b1 coefficient LSB =0x28 b1 coefficient =0xB028 =-2.49512

b2 coefficient MSB =0xBE

b2 coefficient LSB =0xAD b2 coefficient =0xBEAD = -1.02069

c12 coeffici ent MSB =0x38

c12 coefficient LSB =0xCC c12 coefficient =0x38CC =0.00086665

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Figure 5. SPI Start Conversion Datagram

Command to S tart Pressure and Temperature Conversion, 0x24

Figure 6. SPI Read Results Datagram

3.7 Example of Pressure Compensated Calculation in Floating-point Notation

Pressure Compensation:

Pressure MSB =0x67

Pressure LSB =0xC0 Pressure =0x67C0 =0110 0111 11 00 0000

=415 ADC counts

Temperature MSB =0x80

Temperature LSB =0x40 Temperature =0x8040 =1000 0000 01 00 0000

=513 ADC counts

a0 coefficient =2107.875

b1 coefficient =-2.49512

b2 coefficient =-1.02069

c12 coefficient =0.00086665

Pressure =415 ADC counts

Temperature =513 ADC counts

Pcomp a0 b1 c12 Tadc⋅+()Padc b2 Tadc⋅+⋅+=

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Using the evaluation sequen ce shown in Section 3.3:

4 Solder Recommendations

1. Use SAC solder alloy (i.e., Sn-Ag-Cu) with a melting point of about 217°C. It is recommended to use SAC305

(i.e., Sn-3.0 wt.% Ag-0.5 wt.% Cu).

2. Reflow

• Ramp up rate: 2 to 3°C/s.

• Preheat flat (soak): 110 to 130s.

• Reflow peak temperature: 250°C to 260°C (depends on exact SAC alloy composition).

• Time above 217°C: 40 to 90s (depends on board type, thermal mass of the board/quantities in the reflow).

• Ramp down: 5 to 6°C/s.

• Using an ine rt reflow environment (with O2 level about 5 to 15 ppm).

NOTE: The stress level and signal offset of the device also depends on the board type, board core material, board thickness

and metal finishing of the board.

c12x2 = c12 * Tadc = 0.00086665 * 513 = 0.44459

a1 = b1 + c12x2 = -2.49512 + 0.44459 = -2.05052

a1x1 = a1 * Padc = -2.05052 * 415 = -850.96785

y1 = a0 + a1x1 = 2107.875 + (-850.96785) = 1256.90715

a2x2 = b2 * Tadc = -1.02069 * 513 = -523.61444

PComp = y1 + a2x2 = 1256.90715 + (-523.61444) = 733.29270

Pressure (kPa) P=comp 115 50–

1023

---------------------- 50+⋅

733.29=115 50–

1023

---------------------- 50+⋅

96.59kPa=

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5 Handling Recommendations

It is recommended to handle the MPL115A pressure sensor with a vacuum pick and place tool. Sharp objects utilized to move

the MPL115A pressure sensor increase the possibility of damage via a foreign object/tool into the small exposed port.

The sensor die is sensitive to light exposure. Direct light exposure through the port hole can lead to varied accuracy of pressure

measurement. Avoid such exposure to the port during normal operation.

6 Soldering/Landing Pad Information

The LGA package is compliant with the RoHS standard. It is recommended to use a no-clean solder paste to reduce cleaning

exposure to high pressure and chemical agents that can damage or reduce life span of the Pressure sensing element.

Figure 7. MPL115A1 Recommended PCB Lan din g Pattern

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7 Tape and Reel Specifications

Figure 8. LGA (3 by 5) Embossed Carrier Tape Dimensions

Figure 9. Device Orientation in Chip Carrier

(I) Measured from centerline of sprocket hole to

centerline of pocket.

(II) Cumulative tolerance of 10 sprocket holes is

±0.20.

(III) Measured from centerline of sprocket hole to

centerline of pocket.

(IV) Other material available.

Dimensions are in millimeters.

Ao 3.35 ± 0.10

Bo 5.35 ± 0.10

Ko 1.20 ± 0.10

F 5.50 ± 0.1 0

P1 8.00 ± 0.10

W 12.00 ± 0.10

Pin 1 Index Area

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PACKAGE DIMENSIONS

CASE 2015-02

ISSUE A

LGA PACKAGE

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Table 4. Revision History

Revision

number Revision

date Description of changes

7 02/2013 • Change d Example Binary format definitions b1 signed from 7 to 13, added F11 to Coeff b1, b2

and c12 on page 6.

• Removed MPL115A1T2 from ordering table.

Document Number: MPL115A1

Rev. 7

02/2013

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