SM9235-BCE-S-300-000

SM9233 SMI

Document overview

• PDF pages: 18

Technical content

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DESCRIPTION

The SM923x series are digital, ultra-low pressure sensors offering state-of-the-art MEMS pressure transducer technology and CMOS mixed signal processing technology to produce a digital, fully conditioned, multi-order pressure and temperature compensated sensor in JEDEC standard SOIC-16 package with a dual vertical porting option. It is available in a gauge pressure configuration.

The total accuracy after board mount and system level autozero is less than 1%FS. The excellent warmup behavior and long term stability further assures its expected performance over the life of the part.

Gauge Pressure Sensors

FEATURES

• Pressure ranges: 250 up to 600 Pa Gauge
• Accuracy after Autozero: < 1%FS
• 16 bit I2C Digital interface
• Pressure calibrated and temperature compensated output
• Compensated temperature range: -20 to 85oC

Combining the pressure sensor with a signal-conditioning ASIC in a single package simplifies the use of advanced silicon micro-machined pressure sensors. The pressure sensor can be mounted directly on a standard printed circuit board and a high level, calibrated pressure signal can be acquired from the digital interface. This eliminates the need for additional circuitry, such as a compensation network or microcontroller containing a custom correction algorithm.

The SM9233/SM9235/SM9236 are shipped in sticks or tape & reel.

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1. Absolute Maximum Ratings

All parameters are specified at Vdd = 3.3 V supply voltage at 25oC, unless otherwise noted.

Notes:

a. Tested on a sample basis. b. Clean, dry air compatible with wetted materials. Wetted materials include silicon, glass, RTV (silicone), gold, aluminum, copper, nickel, palladium, epoxy, stainless steel and plastic (mold compound). c. Proof pressure is defined as the maximum pressure to which the device can be taken and still perform within specifications after returning to the operating pressure range. d. Burst pressure is the pressure at which the device suffers catastrophic failure resulting in pressure loss through the device.

1. ESD

3. External Components

\* Not tested in production

4. Calibrated Pressure Ranges

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5. Recommended Operating Conditions

The recommended operating conditions must not be exceeded in order to ensure proper functionality of the device. All parameters specified in the following sections refer to these recommended operating conditions unless stated otherwise.

Notes:

b. Clean, dry air compatible with wetted materials.

6. OPERATING CHARACTERISTICS TABLE

All parameters are specified at Vdd = 3.3 V or 5 V DC supply voltage (as per P/N counter in table 10) at 25oC, unless otherwise noted.

\* Not tested in production

Notes:

e. Supply current given for continuous operation. Device can be set to sleep mode with significantly lower power consumption. Refer to section 11 for details. f. The accuracy specification applies over all operating conditions in dry clean air. This specification includes the combination of linearity, repeatability, and hysteresis errors over pressure, temperature, and 3.3 V supply voltage. g. Based on system level autozero at 25 oC after board mount or solder reflow. h. Based on sample testing during initial product qualification, not tested in production.

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9. Package Reference

SOIC-16 (C) Vertical Package Dimensions

• All dimensions in units of [mm]
• Moisture Sensitivity Level (MSL): Level 3
• Clean, dry air compatible with wetted materials. Wetted materials include : Wetted materials include silicon, glass, RTV (silicone), gold, aluminum, copper, epoxy and mold compound.
• Tolerance on all dimensions ±0.13 mm unless otherwise specified.
• [B] is tube connected to bottom side of sensor die.
• [T] is tube connected to top side of sensor die. Topside pressure is positive pressure. An increase in topside pressure will result in an increase in sensor output
• Bottom plate is stainless steel
• Robust JEDEC SOIC-16 package for automated assembly
• Manufactured according to ISO9001 , ISO14001 and ISO/TS 16949 standards

Lot Number Identification

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13. Functional Description

13.1 Overview

The SM9x3x series is a high precision, factory calibrated Gauge pressure sensor for ultra low pressure measurements. It combines a low pressure MEMS die with a 16 bit ASIC, utilizing DSP for multi dimensional polynomial error correction. The calibrated pressure output data is available via digital data interface (I2C). Status information on the sensor integrity and unique serial number are accessible via this digital interface.

13.2 Global Sensor Parameters

13.2.1 Digital Pressure Transfer Function In general digital output data is available with a word length of 16 bit. The numeric representation is always as 2's complement, which results in a range of:

0 ... +32767 counts (positive range, or 0000h ... 7FFFh) -32768 ... -1 counts (negative range, or 8000h ... FFFFh)

The pressure sensor device is calibrated in the end-of-line production test over the specified Pmin to Pmax pressure range (see Section 4). The output code at Pmin is nominally -26,215 and at Pmax it is nominally 26,214. This allows the sensor to still operate monotically outside its nominal range till the maximum (or minimum) counts are reached. An example for a 250 Gauge SM9233-BCE-S-250-000 is given in the

graph below

Green: Accuracy per specification Red and Blue: Outside specification, but expect monotonic behavior till maximum (or minimum) code is reached

13.2.2 Conversion from counts to pressure The digital output count gives a signed 16 bit value for pressure and to convert the count to a pressure percent reading, p%FS, (in % full scale pressure) the following equation can be used

The equation below converts p%FS to actual calibrated pressure units pp-unit with pmin and pmax as specified in section 4

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13.2.4 Digital Temperature Transfer Function An internal temperature sensor measures the chip temperature. The temperature characteristic is linear and is described by the following equation:

DT = b1 \* TA + b0

The temperature transfer function parameters are as follows:

The typical temperature accuracy at 30 °C is within ± 2 °C.

13.3 Voltage Supply

The device is supplied from pin VDD, typically 3.3 V, but it can operate as high as 5 V. From this supply input several internal voltage regulators are generating stabilized voltage levels for analog and digital circuit sections. The different internal voltages are monitored by power-OK diagnostic circuitry. Also a stabilized voltage for the resistive MEMS pressure sensor is derived from VDD.

The digital data interface allows to set it into Sleep Mode using a specific command (Enter Sleep Mode), which ensures very low consumption (IVDD,SM) of typically less than 10 µA. Of course, in Sleep Mode no pressure data is acquired.

For the I2C command to send the sensor into Sleep Mode see 13.6. To wake-up the sensor to normal operation, the clock input SCL shall be toggled (a rising edge at SCL will wake-up the device).

13.4 Diagnosis Functions

13.4.1 MEMS Sensor Bridge Diagnostics Internal errors of the MEMS pressure sensor are detected and the STATUS registers can be read via the digital I2C interface.

Bridge Diagnostics An integrated bridge diagnostic circuit supervises the resistive pressure sensor to detect any of the faults as follows:

• Sensor faults:
• Short of any of the four bridge resistors of the pressure sensor
• Interruption of any of the four of bridge resistors
• Wiring faults:
• Open connection of any of the bridge supply or signals
• Wrong connection of any sensor bridge terminal to either ground or bridge supply

The MEMS sensor bridge diagnostics are active permanently (true background diagnostics) and in case of an error the bridge check fail event is indicated by setting the bit bc_fail in the internal STATUS register.

Bridge Supply Diagnostics Another diagnostic function checks if the supply to the sensor bridge is in its specified range. Here, in case of a supply error the bit bs_fail in the STATUS register will be set.

13.4.2 Configuration Memory Check The integrity of data stored in the embedded NVM used as the configuration memory (calibration parameters, device configuration, device ID, etc.) is checked at power-up of the component by calculation of a check sum (CRC). If a check sum error is detected no reliable pressure calculation is possible. Therefore, the sensor remains in idle state, i.e. no pressure data transferred to the output registers DSP_T and DSP_S. In this case the bits STATUS.dsp_s_up and dsp_t_up will never be set.

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13.5 I2C Interface

The SM9x3x features an I2C slave interface. This interface provides direct access to registers of the memory of the SM9x3x sensor. An external I2C master (e.g. a microcontroller) can read from and write to memory addresses (registers) of the device using the following commands:

• Random write: Sets a memory address and writes data to consecutive memory addresses of the device starting at the set memory address.
• Random read: Sets a memory address and reads data from consecutive memory addresses of the device starting at the set memory address.
• Read last: Reads data from the device starting at the last memory address set by the master. This facilitates repeated reading of the same memory addresses without transmitting a memory address first.

All reads/writes must start at word aligned addresses (i.e. LSB of memory address equals 0) and read/write an even number of bytes.

I2C Interface Timing Diagram:

13.5.1 I2C Command Format The SM9x3x-Sensor uses a standard 7-bit I2C slave address field. The LSB of the slave address specifies the frame type used to perform read and write operations. For LSB = 0 the protocol is compatible to standard I2C EEPROMs, for LSB = 1 the protocol is extended by a CRC protection. Thus, each device occupies two I2C addresses: even addresses are for standard EEPROM compatible protocols and odd addresses are for CRC protected protocols. Unprotected and CRC protected frames can be interleaved.

The two different frame types - standard EEPROM (without CRC) or CRC protected - are shown in the next two figures.

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I2C Read / Write Commands - Standard EEPROM compatible protocol:

I2C Read / Write Commands - CRC protected protocol:

The memory address field sets the byte address of the first memory location to be read from or written to. Only 16-bit-word aligned reads/writes are supported, i.e. the LSB of memory address has to be zero always. The read/write data is transferred MSB first, low byte before high byte. The length field (bits[7:4]) required for CRC protected frames specifies the number of data bytes to be transferred decremented by one, i.e. a value of 0001b corresponds to two bytes. All frames must transfer an even number of bytes. The maximum length for CRC protected read/write frames is 16/4 bytes. For unprotected frames the length is unlimited.

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The CRC4 and CRC8 for redundancy check are computed in the same bit and byte order as the transmission over the bus. The polynomials employed are:

• CRC4: polynomial 0x03; initialization value: 0x0F
• CRC8: polynomial 0xD5; initialization value: 0xFF

If a CRC errors occurs, then the event bit com_crc_error in the STATUS register will be set.

13.5.2 I2C Command Examples For all examples below the 7-bit device slave address used is 0x6C for unprotected commands, and 0x6D for CRC protected commands, respectively.

The command sequence following describes an unprotected Read command (without CRC) of 3 subsequent 16-bit words starting at memory address 0x2E to read the corrected IC temperature, corrected pressure signal, and (synchronized) status bits of the sensor.

Random Read:

The following sequence writes one 16-bit word to address 0x22. This will copy 0x6C32 into the command register CMD to move the component to Sleep Mode.

Random Write:

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13.6 Register Descriptions

Register Read or Write are performed via the digital communication interface. After power-up of the IC all registers except STATUS and CMD are write protected.

Command register:

Temperature register:

Pressure register:

The registers DSP_T and DSP_S contain invalid data after power-up until the first temperature and pressure values have been measured by the device and transferred to these registers. In case a NVM CRC error occurred, the DSP_T and DSP_S registers would never be updated. Thus, after power up it is necessary to wait until the STATUS.dsp_s_up and dsp_t_up bits have been set at least once before using the temperature or pressure data. It is not sufficient to wait just for a fixed time delay.

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Status register - synchronized:

The bits STATUS_SYNC[15:5,0] are identical to the bits STATUS[15:5,0]. The bits STATUS_SYNC[4:3] are copied from the STATUS register when the corresponding DSP registers are read. First reading the DSP registers and then STATUS_SYNC ensures that both values are consistent to each other. The synchronized status STATUS_SYNC register can be used to continuously poll the pressure, temperature and status of the device with a single read command by reading three 16 bit words starting at address 0x2E. By evaluating STATUS_SYNC.dsp_t_up and STATUS_SYNC.dsp_s_up it can be determined if the values in DSP_T and DSP_S acquired during the same read contain recently updated

temperature or pressure values.

Status register:

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1)

• "Event" type flags remain set until cleared by writing '1' to the respective bit position in STATUS register (not STATUS_SYNC). Writing 0xFFFF to the STATUS register will clear all event bits.
• "Status" type flag represents a condition of a hardware module of the IC and persists until the condition has disappeared.

Serial Number register 0:

Serial Number register 1:

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