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Waterproofing marine equipment - 07 - Receiver Design Considerations

ForcisConnect

This weeks post will be about my receiver board design. I already published the schematic a few weeks ago, as I wanted to make it available as soon as possible, just in case someone else could use it. But now I want to elaborate a little bit on the decisions I had to make for the receiver.

 

I have very closely based my design on the evaluation board receiver. There are different reasons for it: The first is to start with design that is known to work. This will help troubleshoot problems while assembling and testing these first units. The second reason is the required tuning of the resonant capacitors. In order to properly do it we have to measure the coils inductance at 100kHz and 1Vrms to then calculate with these values the capacitors. I don’t have a LCR meter, and the ones with these characteristics are quite expensive. So it’s best to stay close to the EVM values and coils, at least at first.

 

My goal is to achieve a waterproof enclosure. Because of it there will be no external power adaptor. In this way we reduce the necessary openings in the enclosure to none. All the corresponding circuitry from the evaluation board has been removed.

 

The temperature NTC resistor values were also taken from the bq51013B datasheet. A low temperature threshold of -10ºC on the low side and a value of 100 ºC on the high side seemed reasonable.

 

Another important adjustment is the current limit of the chip. I want to be able to get the maximum current of 1.0A out, so the corresponding resistor has been set to 75Ohm.

 

The chip also has different operating modes that can be selected by pulling high or low the EN1 and EN2 pins. The following table from the data sheet summarizes the possible combinations. In our case both are tied to ground. 

image

 

 

So now I have a wireless power receiver. But for my waterproofing application I need not only a power receiver, but also a way to store the energy. This will be done with a Lipo battery. As mentioned by mcb1 these batteries are quite sensitive to overvoltage and wrong charging. Therefore I need a Lipo battery charger.  The bq51050B has essentially the same pins as the 51013B (the only difference is that OUT is called BAT and EN1 is called TERM, all the other pins are the same) and additional components, but includes a Li-Ion charger in the IC. This chip just seems perfect for my application. After having a look at the evaluation board for the bq51050B and noticing that it’s essentially the same as the one of the bq51013B I decided to make a PCB that could be used with both ICs. In this way I won’t need to order separate PCBs, which will save me some money, and the additional board area will be small. Depending on which IC gets mounted, some components will be left unpopulated, while others may be substituted with 0 Ohm resistors.

 

The only components I had to add to make the board compatible with both IC were two resistors between TERM (EN1 at the bq51013B) and GND. These will determine when charging will be completed. I selected a value of 2400 Ohm, which means loading will finish when current gets below 10% of the maximal value, in my case 1A.

 

I have also added a couple of 0 Ohm resistors in series with  FOD, ILIM, TERM and RECT resistors (R8,R9,R10,R12) in order to be able to add a second one in case I needed to change the resistor values to non standard ones afterwards. I got this suggestion at the TI Wireless Power Forum. (http://e2e.ti.com/support/power_management/wireless_power/f/693/t/333462.aspx)

 

I now finally have a complete receiver design!

 

Here is the BOM

 

Qty

Value

Device

Package

Parts

Description

Farnell Code

1

 

LED0603

0603

LED1

LEDs

1465991

2

  1. 0.01uF

CAP

0603

C5, C6

Capacitor

1817916

3

  1. 0.1uF

CAP

0603

C14, C16, C17

Capacitor

2146610

2

  1. 0.47uF

CAP

0603

C3, C4

Capacitor

2354077

1

  1. 1.0uF

CAP

0805

C15

Capacitor

1833815

1

  1. 1.5k

RESISTOR

0402

R3

Resistor

2072645

1

100pF

CAP

0603

C7

Capacitor

1344349

1

10k NTC

RESISTOR

0402

R7

Resistor

9528067

2

10uF

CAP

1206

C12, C13

Capacitor

2394272

1

1800pF

CAP

0603

C8

Capacitor

1865530

1

196

RESISTOR

0402

R1

Resistor

1802961

1

20k

RESISTOR

0402

R4

Resistor

2072753

2

22nF

CAP

0603

C1, C2

Capacitor

1301890

1

  1. 4.22k

RESISTOR

0402

R5

Resistor

2350371

1

47nF

CAP

0603

C9

Capacitor

2070428

1

  1. 66.5k

RESISTOR

0402

R6

Resistor

2073198

2

68nF

CAP

0603

C10, C11

Capacitor

1414650

1

75

RESISTOR

0402

R2

Resistor

2073246

1

AC Coil

LONGPADS

LONGPADS

JP1

 

2114372

1

BQ51013

BQ51013B

QFN-N20

U1

 

 

1

Vout

LONGPADS

LONGPADS

JP2

Header 2

 

4

0

RESISTOR

0402

R8, R9, R10, R12

Resistor

2072513

1

  1. 2.4k

RESISTOR

0402

R11

Resistor

1358052

 

The schematic:

 

image

And PCB layout:

 

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As always: Comments and suggestions are welcome. Once I send the design to the fab it will be too late!

 

EDIT: I have updated the files. I have corrected some smaller issues I noticed while assembling the first units

Attachments:
WirelessReveiver_v0.2.zip
Parents

  • Eduardo

    Well done.

    Strangely the TI datasheet doesn't seem to worry about a particular layout, so I guess the resonant capacitors placement doesn't affect the overall frequency because the coil inductance is so high.

     

    It's really good to see the TI forum support you received.

     

    TI also have an excellent free sample service, and I now wish I had noticed the bq51050B when I sent away for mine. (element14 don't stock the IC on it's own)

    They have the ability to also do 5v charging, so could be a very useful device to have around.

     

    I had some boards done recently through Hackvana. I'm very happy with the result.

     

    Thanks for sharing

    Mark

  • in reply to mcb1

    Hi Mike, Suggestion on Hackvana will have a go. I have finalised a project with any CAD software so this will be a good challenge for me. Nice Job Eduardo.

Comment Children
  • in reply to waelect

    Hi Mike

    It's Mark

     

    Be sure to check his DRC and CAM file for the boards.

    The DRC will not tell you if the font is too small and for mine the 5mil was a little thin ... it printed okay but the wider was much better looking.

     

    When you run the CAM job (to turn the board into the various layers) be sure to watch for the warnings

      imageimage

    Just hit Yes

     

    I see he currently has a 5 day delay, but some problems if you ship via DHL.

    https://docs.google.com/document/d/1p6FH25ltGpzJQ5_8fbflDukqEKghiEcpuhJpngth2Is/edit?pli=1

     

    The other thing is the factory place a unique number on the board.

    This has been increased in size and on mine they cleverly placed it under the IC.

    If you're concerned Mitch offers this


    Q: Will my design get modified?

     

    A: A manufacturing code is added to the board to make sure the right board goes to the right person.  If for some reason you’d rather the numbers go on a particular layer (maybe you want to keep the code out of a certain area, or to have it put in a certain area), please tell me in your order email.  Note, it isn’t guaranteed, this information might be ignored.

     

     

    If you’d like to specify where to put the manufacturing code, here’s how to do it:

     

     

    • Include another layer in your .zip file, separate to the other layers.
    • Call this layer “mfgcode.gto” (for the code on the top) or “mfgcode.gbo” (for the code on the bottom).
    • Use your CAD package to add this text to that layer:  XxXxXxXxXxXx(That’s 12 Xs).  There should be nothing else in that layer.
    • Make the text at least 0.8mm (30mil) high, and use a stroke width (aperture size) for the text of at least 0.15mm (6mil).

     

    Which I thought was pretty good.

     

     

    Good luck

    Mark