Differences bettween FXTH8715 schematics

[MAPC]

Hello,

I have a customer who is evaluating a FXTH871511 for a new project and is studying the collateral material available on Freescale website. But, he notices there are two different schematics reffering to two different kits:

http://cache.freescale.com/files/sensors/doc/ref_manual/FXTH87EDRM.pdf?fpsp=1&WT_TYPE=Reference%20Ma...

http://cache.freescale.com/files/sensors/development_tools/printed_ciruit_boards_and_schematics/SCH_...

One differs from another. So we are not sure which is the reference design recommended by Freescale. Can anybody clarify this question, please?

Thanks and best regards,

Marco Coelho

Siletec Eletronica

[david_diaz]

Hello Marco,

Basically both documents are referring to the same device, the FXTH87 module evaluation boards (EVB).

The schematic from one of the links mentioned before, is the typical reference demonstrator for FXTH87 at 434 MHz.

The same schematic is shown at Figure 2-2 at the Design Reference Manual along with the bill of materials.

In this case I recommend to use the Design Reference Manual due to it provides all the technical information required to become quickly familiar with the FXTH87 Family Evaluation Tire Pressure Monitoring Sensor (TPMS) devices.

I hope this information will be useful for you.

If I misunderstood your question, feel free to let me know.  I will be glad to help.

Have a great day.

David Diaz.

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[MAPC]

David,

I would like to ask you another question raised by the customer, Probably you may know the answer.

What kind of material is the evaluation kit antenna made of?

Thanks,

Marco Coelho

[david_diaz]

Hello Marco,

I am glad to help.

The metric code represents the surface-mount components dimensions in mm.

For example, a metric 2520 component is 2.5 mm by 2.0 mm which corresponds roughly to 0.10 inches by 0.08 inches (hence, imperial size is 1008).

In this case, the supplier of the coils mentioned is TDK.

You can find more information at the following links:

1. L1 - 110 nH@434 MHz 0402

MLG1005SR11HTD25​

2. L2 - 100 nH@434 MHz 0603

MLG1608BR10JTD25

Please note that they are Freescale recommended preferred products.

Regarding your last question, I want to send you an update:

I am still looking for the Antenna material. I will appreciate your patience.

I hope this information will be useful for you.

If I misunderstood your question, feel free to let me know.  I will be glad to help.

Have a great day.

David Diaz.

[MAPC]

Hello, David

Ok. So the first link is the most recommended schematic, right?

But, If both schematics refer to the same evaluation board, why do they mismatch from each other? If you compare the 434MHz evaluation board schematic from Reference Design Manual to the one at the second link, there are differences between each other. Some components have different values or are placed at different positions.

Are there different versions for this board?

Marco Coelho

[david_diaz]

Hello Marco,

Please accept my apologies for the delay.

The main difference between the schematics mentioned before are the coil values.

The Reference Manual mentions different values for the coils L1 and L3 while the schematic just mentions one value for each coil. 

These different values will affect the frequency operation of the RF circuit.

In order to get the 434 MHz desired, L3 value must be 39nH while L1 must be 110nH or 100nH.

Regarding L1 value, please be aware about the metric code mentioned on Table 2-1 from the Reference Manual.

I hope this information will be useful for you.

If I misunderstood your question, feel free to let me know.  I will be glad to help.

Have a great day.

David Diaz.

[MAPC]

Hi, David

Sorry. Before asking you, I looked up for this information in Evaluation Design Reference Manual, but I haven't found it. Could you please explain me what do those metric codes mean?

Taking the opportunity, did you see my last question regarding the antenna material?

Thank you very much.

Marco Coelho