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LMP91300: Is the LMP91300 a solution to a problem for me?

Scott Mentzer
Prodigy 20 points
Part Number: LMP91300
Other Parts Discussed in Thread: LDC1612, LDC1101

I have an inductive prox switch where I am currently using an Infineon TC 505 IC. It is a 30 mm switch which I am trying to set a range of 30 mm for. I am using a Bourns 3006 trimpot to dial in my sensing range.

The problem I am having is that some units are experiencing a shift in the sensing range - upwards of 10 mm - from 30mm to 40mm. This increase is causing other problems in the application. 

When I get the failed units, i able to 'reset' the switch by readjusting the trim pot but I do not think the trim pot is actually changing.

I am wondering if this 'change' is more a function of the Infineon IC and maybe a different IC may be the answer to my concerns.

I would really like to talk to someone familiar with these Inductive Switch ICs

  • 0
    TI__Genius 13335 points

    Hello Scott,

    Thanks for the post. The LMP91300 may be the correct part, however I have a few questions for you which will help us narrow down the right solution.

    • Just to clarify, you are trying to design a 30mm diameter inductor to achieve a 30mm sensing range? Typically longer sensing ranges (>=100% coil diameter) come with reduced accuracy or looser tolerance on the switching point.
    • Is this a shielded design? Shielded designs can reduce the desired sensing range.
    • Are you able to calibrate each product over temperature (once at cold and once at hot for example)? Take a look at page 33 of the LMP91300 datasheet for more info on temperature effects and compensation techniques. 
    • Is standalone switching functionality required from the IC or are you able to read sensor data and set a switching threshold in software? If so I would recommend our high resolution devices like the LDC1612 which uses I2C or the LDC1101 which uses SPI.

    I would additionally point you to the LDC device selection guide which gives further overview of the different devices and their capabilities: www.ti.com/.../snoa954

    Regards,

    Luke LaPointe

  • 0 in reply to Luke LaPointe
    Prodigy 20 points

    Yes, this is an M30 prox and we are trying to sense 30mm. The Current design construction use s a Infineon TCA 505 BG. I have tried to attached the datasheet. The datasheet is a Siemens datasheet but the device is now sold through Infineon. 

    This IC allows you to set the sensitivity through adjusting the resistance on one of the pins. We use a Bourns 2006 Trimpot to set this resistance. 

    What we are finding is that units are coming back to us from the field with the sensitivity having shifted from 30mm to over 40mm and the hysteresis dramatically increased. We are having a hard time understanding why.

    The speculation is that the something is changing with the IC - thus the inquiry about other IC solutions. Due to the age of this device and that fact it is not an original Infineon device, Product support is almost non-existentSiemens datasheet.pdf. 

    This is a non-shielded device. We are not able to calibrate the device at temperature. We do check all switches at temperature before shipment. 

    I am open other IC solutions and process to calibrate. 

  • 0 in reply to Scott Mentzer
    TI__Genius 13335 points
    Hi Scott,
    These requirements sound like the LMP91300 may be the right fit. I would take a look at the datasheet to get familiar with the part's features including the section on calibrating outlined in Section 7.3.6 of the LMP91300 datasheet. Note that a single room temp calibration will get you very good accuracy but you can get the optimum performance with a cold + hot temp calibration to tune the slope of the look up table (LUT) calibration.
    Additionally, if you are wanting to evaluate the device I've posted detailed information in another thread on how to implement a NPN and PNP style approach, along with an example board to communicate and burn the registers: e2e.ti.com/.../2203467
    Regards,
    Luke LaPointe