Amphenol NPI-19 I2C Digital Pressure Sensor User Guide
- June 15, 2024
- Amphenol
Table of Contents
NPI-19 I2C Digital Pressure Sensor
Application Guide 
Advanced Sensors
Dec 2022
General Description
The NPI I2C digital pressure sensors combines Amphenol Advanced Sensors’ SenStable® silicon fusion bonded pressure die technology with packaged electronics to provide highly stable, amplified and calibrated pressure measurement.
Output Characteristics
2.1 Pressure Output Options
The NPI-19 I2C product is available in a range of pressure ratings, pressure
configurations. The nominal output ranges for standard product ranges are
detailed in Tables 1 and 2 below.
Table 1: Available Pressure Output Ranges for Standard Products
| Device series | Units | Absolute / Gauge | Excitation |
|---|---|---|---|
| NPI-19 I2C | Counts | 1638 | 14745 |
Table 2: Output Transfer Function
| Pressure | % Output | Decimal Counts | Hexadecimal Counts |
|---|---|---|---|
| Pmin | 10 | 1638 | 0x0666 |
| Pmid | 50 | 8192 | 0x2000 |
| Pmax | 90 | 14746 | 0x399A |
2.2 Pressure Output Characteristics
All NPI-19 digital pressure sensors are factory calibrated to give a defined
linear change in output over a specified range of pressures. Outside this
range, the output varies with pressure but with unspecified accuracy.
Pressure can be calculated from the sensor output using the
following formula: 
where
P = calculated pressure
Out = measured sensor output
2.3 Pressure Accuracy
The measurement accuracy of calibrated NPI-19 Digital pressure sensor is
defined in terms of percentage of full scale (FS) over a specified compensated
temperature range. Standard parts are specified to be ±1.0%. This accuracy
figure is a total error band and includes all errors due to offset, span,
linearity and temperature, as illustrated in Figure 2 below.
Digital Output (I2C)
3.1 General
NPI pressure sensor provides digital output data using the industry standard
I2C protocol. Bit rates up to 400 kHz are supported, compatible with the
Standard-mode (Sm) and Fast-mode (Fm) standards. Devices are supplied with a
slave address of 0x28 as standard.
3.2 Block Diagram
3.3 I2 C Timing
Table 3: I2 C Timing Parameters
| Parameter | Symbol | Min | Max | Units |
|---|---|---|---|---|
| SCL clock frequency | fSCL | 100 | 400 | kHz |
| Start condition hold time relative to SCL edge | tHDSTA | 0.1 | μs | |
| Minimum SCL clock low width* | tLOW | 0.6 | μs | |
| Minimum SCL clock high width* | tHIGH | 0.6 | μs | |
| Start condition setup time relative to SCL edge | tSUSTA | 0.1 | μs | |
| Data hold time on SDA relative to SCL edge | tHDDAT | 0 | μs | |
| Data setup time on SDA relative to SCL edge | tSUDAT | 0.1 | μs | |
| Stop condition setup time on SCL | tSUSTO | 0.1 | μs | |
| Bus free time between stop and start condition | tBUS | 2 | μs |
-
Combined low and high widths must equal or exceed minimum SCL period.
Two conditions can cause communication errors:- Sending a start-stop condition without any transitions on the SCL line (no clock pulses in between) creates a communication error for the following communication, even if the next start condition is correct and the clock pulse is applied.
- Restart condition – a falling SDA edge during data transmission when the SCL line is still high will cause the next communication to fail.
In both situations, an additional start condition should be sent to restore
communication.
3.4 Data Read Operations
To read data from the NPI-19 digital sensor, the I 2 C master device sends 8
bits — the 7 bit slave address (0x28 for standard devices) and the 8th bit = 1
to designate a read request. The NPI-19 digital sensor then sends acknowledge
(ACK) to indicate success.
The NPI-19 digital sensor has three I2 C read commands:
Read_DF2: Pressure (2 bytes)
Read_DF3: Pressure (2 bytes) +
Temperature (1 byte) Read_DF4:
Pressure (2 bytes) + Temperature (2 bytes)
The number of data bytes returned by the NPI-19 digital sensor is determined
by when the 2 IC master device sends the NACK and stop conditions as shown in
Figure 5 below.
| Start Condition
---|---
| Device Slave Address (example: Bit 5)
| Data Bit(example: Bit 2)
| Read/Write Bit (example: Read=1)
| Acknowledge (ACK)
| No Acknowledge (NACK)
| Stop Condition
| Status Bit
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