AN5800 Amplified Pressure Product Capabilities APPLICATION NOTE

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1 SM Amplified Pressure Product Capabilities OVERVIEW The SM5800 series pressure product provides a significant advantage to the user due to a number of improvements associated with the technology used in fabricating this part. These advantages include: Integrated amplification Electronic-trim for more precise control of gain and offset Fewer External support components Figure 1a - Standard Thru-Hole Pin Configuration for the SM5800. The following notes are meant as an aid to the user to document some of these improvements. INTRODUCTION The SM5800 series part comes in 2 basic configurations: SM to 3.0 PSI FS part SM to 100 PSI FS part The amplified configuration has some key advantages but these also must be considered in designing the systems into which SM5800 parts are used. For instance, a fairly standard "trick" when using an unamplified part in such absolute applications as barometric measurements is to use a 5 PSIA part. This allows it to operate in the 15 PSIA range with effectively 10 PSI overpressure, in order to get 3X more unamplified output from the part. For the SM5812 part, the part will give no useful output if one runs an SM A at one atmosphere. The output will be stuck at >4.5 volts (but less than 5 volts) until the pressure is reduced to 5 PSIA or less. Likewise, the amplified output requires some thought in the sensor system for differential and gage applications. SMI has provided for three separate configurations for nonabsolute parts. These are: G - Gage Applications where pressure is always positive. One example Figure 1b - Surface-Mount Pin Configuration for the SM5800. would be where duct pressure needs to be monitored. The duct pressure is always positive with respect to the room pressure so the output needs to be one-directional as well. The SM5800 is set to give an output of 0.5 volts for zero and 4.5 volts for full-scale (4 volt span). D - Differential Application where the pressure can be either positive or negative. Measuring respiration where both inhalation and exhalation occur is an example. In this case, because the SM5800 is an amplified device which operates off of a 5 volt supply, a logical choice for the zero is 2.5 volts and the span is then 2 volts. This gives a useable output of 0.5 to 4.5 volts. S - Single-Direction, Differential Application where it is necessary to measure a differential pressure but the pressure never drops below zero. Measuring pressure across a flowrestrictor or orifice is an example. Flow is proportional to the square root of pressure drop across the restrictor. page 1 of 7

2 The SM5800 series part is available in two different pin configurations, one for classical thru-hole printed circuit board applications and one for surface mount applications. These are shown in Figure 1 and the dimensional differences are documented in Figure 2. Note that the only difference between the two are the pins. The ceramic housing, cap and ports are identical between the two configurations. SUPPORT CICUITRY As noted above in the Overview, the addition of amplification at the measurement site has several key advantages. One of those is the required support circuitry. In Figure 3, the required support circuitry for a SM is diagrammed. The SM5800 has been designed to eliminate the need for external components. The SM5800 requires no external components, as opposed to 14 for the SM5651. TRIMMED PERORMANCE One of the key features of the SM5852 is that it is electronically trimmed. As such, the part can be tested and verified before the final trim parameters are programmed. With the conventional laser-trimmed components, the final performance is set by how well the test system can measure millivolt level signals and resistances ranging from less than 50 Ohms to over 5 MegOhm. All of this is done at the end of long test cables and this further makes measurements more uncertain. With the SM5800, the computer acquires the trim data thru the on-board amplifier. This increases resolution and increases overall accuracy. There are several measures on the manufacturability of a part. Yield from a manufacturer's viewpoint is critical but so to is the distribution of parts as manufactured. The tighter the distribution on key parameters, the higher the quality of the part and the lower is the probability that the endcustomer will get a part that will not meet the published specification. A number of measures of performance are generally used to demonstrate process Figure 2a -- Thru-hole (Pin Configuration 3) Version of the SM5800 Series Part Figure 2b -- Surface-Mount (Pin Configuration 5) Version of the SM5800 Series Part page 2 of 7

3 control. One of the most widely used, at this point, is Cpk. This is a measure of process capability. Cpk is defined as: Cpk = min{cpu, CPL} Cp = (USL-LSL) / (6σ short-term ) CPU = (USL- µ) / (3σ short-term ) CPL = (µ -LSL) / (3σ short-term ) Where: µ = Process Mean σ = Process Standard Deviation USL = Upper spec limit LSL = Lower spec limit Table 1 demonstrates the likelihood of a defect based on the Cpk. For a Cpk of 1, statistically, one would expect that 2500 parts per million fall outside the specification limit. At a Cpk of 1.33, the defect rate drops to 67 ppm. To achieve less than 1 ppm defect rate, a Cpk of 1.67 is needed. At a Cpk of 2.0, the likelihood of a defective part drops to 1 part per billion. Table 1 - Cpk vs Defect Rate Comparison Cpk probability of a bad part ppm defect rate in in 15, in 1,500, in 1,700,000, One of the key advantages of the electronic trim associated with the SM5800 series part is the ability to achieve extremely tight tolerances on both the zero and the gain of the part. Three sets of parts were measured from production lots of SM5800 material. The results are presented in Figures 4 to 9. The parts used in this study were the SM D-3-L, the SM D-3-L and the SM A-3-L. A minimum of 150 parts in each lot was tested. A summary of the Cpk for the 3 types is given in Table 2. Figure 3 - Support Circuitry necessary to provide 4 volt amplification of a part. Note that the SM5852 requires no added support components but is the identical size to the SM page 3 of 7

4 Figure 4 -- Cpk Analysis for Zero the SM D. The Zero Limits are +/- 80 mv about a volt target. Figure 5 -- Cpk Analysis for Span the SM D. The Span Limits are +/- 100 mv about a volt target. page 4 of 7

5 Figure 6 -- Cpk Analysis for Zero the SM D. The Zero Limits are +/- 80 mv about a volt target. Figure 7 -- Cpk Analysis for Span the SM D. The Span Limits are +/- 40 mv about a volt target. page 5 of 7

6 Figure 8 -- Cpk Analysis for Zero the SM A. The Zero Limits are +/- 80 mv about a volt target. Figure 9 -- Cpk Analysis for Span the SM A. The Span Limits are +/- 80 mv about a volt target. page 6 of 7

7 Table 2 Summary of Cpk results for 3 different SM5800 Parts at Final test Part Sample Size Cpk - Zero Cpk - Span D D A The results in Table 2 are examples of the process capabilities. The Cpk s achieved here may not be 100% representative of the process, especially with Cpk s over 2. A Cpk of 1.6 is the design target for this device. CONCLUSIONS A number of the features of the SM5800 Series product have been highlighted in this Application Note. Two of the key advantages of the SM5800 product include: A fully amplified product in the same footprint of the non-amplified device, therefore saving both component count and circuit space. Tight Control of Zero and Span during Test, making the part more capable that than the more conventional, unamplified, lasertrimmed parts. Notice: Silicon Microstructures, Inc. reserves the right to make changes to the product contained in this publication. Silicon Microstructures, Inc. assumes no responsibility for the use of any information or circuits described herein, conveys no license under any patent or other right, and makes no representation that the approaches are free of patent infringement. While the information in this publication has been checked, no responsibility, however, is assumed for inaccuracies. Silicon Microstructures, Inc. does not recommend the use of any of its products in life support applications where the failure or malfunction of the product can reasonably be expected to cause failure of a life-support system or to significantly affect its safety or effectiveness. Products are not authorized for use in such applications. page 7 of 7