BQ51050B: How to improve the wireless distance

Hello Vincenzo
I did not see the schematic can you resend?
What tuning are you using with the Wurth 760308103202, C1 and C2 from data sheet section 9.2.1.2.1?

The L Value of this coil is low, some others to consider:
1.) Wurth 760308201, 10uH 37mm square
2.) Vishay IWAS4832FFEB9R7J50, 9.7uH 48mm X 32mm
3.) Wurth 760308103202, 12uH 48mm X 32mm

Sorry, here the schematic.

For C1 and C2 I have used exactly the values indicated in the schematic.

About the coil I cannot use bigger coil because of the small dimension of my device. I can accept the rectangular shape of 29mm x 15mm (760 308 103 206) as indicated in your bill of material

Hello

Check the voltage at RECT during start up, to start voltage at this pin needs to be greater than 2.7V to start (UVLO).  After starting it can tune the TX to a higher operating point.

Tuning the coil may help, value of C16, C17 and C20 could be increase. 

4762.bqTESLA FAQ--Start up.pdf

Thank you Bill.

I have measured the voltage on RECT pin at the start up and I confirm that it is 5V. I have modified the capacitors value of C16, C17 and C20 from 68nF to 366nF (step around 47nF) without any improvement.

What I noticed is that if I connect the Pin2 of Coil (J5) to GND, the distance between my RX coil and TX Qi transmitter improve to 4/5 mm as my requested. Do you know why? 

1) Do you have any other suggestions?

2) Becasue of I want to use a 300mAh LiPo battery capacity, can you indicate the correct value of R12, R14 and R15?

Best regards

Vincenzo

Hello, do you have any answers about my two questions?

Best regards

Vincenzo

Hello
1.) connect the Pin2 of Coil (J5) to GND, the distance between my RX coil and TX Qi transmitter improve to 4/5 mm.. Do you know why? ---Bill J - No not clear why this is help helping your circuit. Can you tell if the voltage is higher at the RECT pin or has the depth of modulation of comm packets increased? Trying to understand what parameter changes to increase the coil to coil distance.
2.) Because of I want to use a 300mAh LiPo battery capacity, can you indicate the correct value of R12, R14 and R15? --- Bill J - This is FOD calibration and are determined by running the procedure with a special FOD TX to determine loss. Current values are OK to start with.

Hello Bill. Following you can find some graphs

Here the voltage on VRECT. As you can notice there is not enough energy to start with the charger

When I connect the pin 2 of the coil to GND I can measure this trend on VRECT (CH1) and between pin 1 and pin 2 of the coil (CH2). In this way there is communication between TX and RX and my battery is charging

I have tested again the VRECT without the PIN2 of the coil to GND and following you can notice the increment in voltage of VRECT when I connect the pin2 of the coil to GND

----NORMAL (VRECT with pin2 of the coil NOT to GND)

----INCREMENT in voltage (VRECT with pin2 of the coil TO GND)

I hope they can help you to understand

About the charging current I need to recharge the LiPo at 160mA and not at 500mA to avoid to damage it. Can you indicate the correct value of R12, R14 and R15 or this device is not able to recharge battery with current around 160mA?

Best regards

Vincenzo

Hi Vincenzo
Regarding setting of the ILIM / FOD pins for a charge current of 160mA.
The total value for R14 and R15 needs to be 2k ohms, recommend using 1k each resistor. R24 can be 20k. This will be a value to start test with, final value will be set during FOD calibration.
Also termination at currents below 30mA may not be accurate and recommend setting the termination at 20% or 4.8k ohms value for R12.

Hi Vincenzo
The first scope capture of RECT shows a 100mS pulse every 600mS, amplitude is less than 2V. As you pointed out this is below UVLO, the RX will not start.
The 2ed scope capture that shows a start up with coil pin 2 connected to ground. I think this configuration is acting as a voltage double and increasing RECT voltage above UVLO.
The 3ed scope capture (normal) looks like the voltage is increasing enough for the RX to reply. But communications is poor and when TX decodes the signal an error is detected. TX shuts down then restarts. Time between packets is about 40mS, typical time for a restart after decode error.
The 4th scope capture looks like the RX reply but no start up.

Grounding of coil pin 2 has not been evaluated and I do not recommend this approach.
Increasing RX coil inductance will increase the voltage at RECT from the digital ping and should start at increased distance.

Thank you Bill.

About the coil you told me that I need to increase the inductance. What do you think about the TDK model WR222230-26M8-G? It is a round coil with L = 27uH in comparison to Wurth coil of 7.5uH (27uH at 100kHz 1.10ohm at 25°C) This is the maximum size I can accept for my device. But returning to your specifications, you indicated that the Wurth coil 760308103206 can be used. Really it is not totally correct as this only works if I am 1mm from the TX coil (see your bill of material)

Hello
The above TDK coil is a good one, the additional L should improve coil to coil distance.

Regarding TIDA-00669 use of the Wurth 760308103206 I will review the design and update the report or BOM.