bq51050b schematics review

Mahmoud,

Table 1 in the bq500212A datasheet shows the LED Modes.  If you followed the EVM on the bq500212A then you used a 42.2k resistor and are in LED control option 1.  In this case, the FOD warning is red blinking and a fault is red on.  

FOD is foreign object detection and is intended to keep metal objects from heating if placed on the transmitter pad during normal operation.  Depending on the receiver configuration, there could be extra metal that is not accounted for.  Additionally, calibration of the receiver is necessary to report its power usage properly.  This would be R4 and R2 in your system.  

C1, C2 and C3 on the receiver schematic are the same values as in the datasheet.  Have you measured your coil inductance and calculated the correct values for C1, C2 and C3?

Have you used your receiver verified on a reference transmitter?  Same question on you transmitter with a standard receiver?  These steps can speed up the debug time.

Regards,

Dick

Hi Dick,

thanks for the reply. during my tests i made sure no metal or foreign objects were close to the coils of the transmitter and the receiver. some times the system works for a while with no faults but most of the times the fault is coming for some reason.Is it normal that the current is fluctuating every second or so?

the first few seconds the system is powered things seem ok looking at the indicators. I havent measured my coils inductance but i remember it is one of the recommended coils in the application note so i assumed the capacitors are ok but i will do the measurement .i should have a reference system very soon . 

I also have a question about the sleep and snooze on the transmitter bq500212A, i asked in another post but maybe you have not seen it so i will describe my problem again: after i assembled the pcbs and started my testing I couldnt see anything happening , then i changed R25( in the application note) to a much smaller value ( application note says 523K ohm) now the 3.3V regulator is on and the system seem to be working ( still needs debugging but it came alive)  but now i believe what i did made the sleep and snooze commands useless , could this also cause a fault? what should i do to have the transmitter work properly ( regarding that resistor specifically).

Thanks again,

Mahmoud

Hello Mahmoud

Regarding you bq500212A Sleep question:

 "I also have a question about the sleep and snooze on the transmitter bq500212A, i asked in another post but maybe you have not seen it so i will describe my problem again: after i assembled the pcbs and started my testing I couldnt see anything happening , then i changed R25( in the application note) to a much smaller value ( application note says 523K ohm) now the 3.3V regulator is on and the system seem to be working ( still needs debugging but it came alive)  but now i believe what i did made the sleep and snooze commands useless , could this also cause a fault? what should i do to have the transmitter work properly ( regarding that resistor specifically)."

I have added an FAQ post that explains how this part of the circuit works, see:

http://e2e.ti.com/support/power_management/wireless_power/f/693/t/372430.aspx

From your description you are describing a problem with the SNOOZE circuit, something is drawing current provided by R25 away from C22.  You can isolate the SLEEP & SNOOZE by removing D2 to help with troubleshooting.

Mahmoud,

The way the transmitter and receiver determine if a foreign object is detected is by comparing the power received by the RX versus the power sent by the TX.  If you are getting fluctuating (which is not normal) then this may be contributing to the issue.

Can you get scope shots of the RECT pin and the OUT pin?  If you can add IOUT, that would be great.

We can discuss temporarily disabling the FOD to see if that points to the problem.

Regards,

Dick

hi Bill,

aftr removing the diode  D2 the circuit is working with R25 set to 523Kohm.

below is a scope shot taken at snooze_cap  followed by a scope shot of the 3.3v regulator output:

these shots were taken without a receiver . i believe this part looks normal,, right?

after the receiver is brought close to the transmitter the 3.3v regulator turns on.

i believe this indicates the snooze circuit is fine?

below is a scope shot of the Tx coil signal with no receiver:

Dick: 

I removed the Fod and Pmod resistors to disable the FOD function but nothing seem to be different.

the charging current is 650 mA but it is not continuous it goes 650 mA for about 2 seconds then it is zero for a short time less than a second  and it keeps going like this again and again ; is the device going to trickle charging mode?

or this is how it works? I have tried different batteries and it is always the same result.

tomorrow i will do some more testing and take scope shots .

thanks,

Mahmoud

Mahmoud,

Were you able to get scope plots of VRECT and VBAT?

Can you measure the frequency during power transfer and when there is no power transfer?

Not, it is not trickle charge mode.  What is the battery voltage?

Have you measured the coil inductance?

Regards,

Dick

Mahmoud

Q1--After removing the diode D2 the circuit is working with R25 set to 523Kohm.

A1---Yes, the Snooze ckt of R25, C22 and Q4 look OK.  But you have to remove D2 to get this ckt to work so you still have a problem around Q7 and Q8 that needs to looked into.

Q2---Below is a scope shot taken at snooze_cap  followed by a scope shot of the 3.3v regulator output:

These shots were taken without a receiver . i believe this part looks normal,, right?

A2—The Snooze time looks like about 300mS which is a little short, double check R25 and C22 value.Snooze_cap is only used to tell the bq500212 it was in a short Snooze off time about 500mS, if it had been in a longer Sleep time the voltage would have been lower.  Check C11, you should see a higher voltage.  Charge pulse is only getting to 300mV and then voltage is only 50mV.

After the receiver is brought close to the transmitter the 3.3v regulator turns on.I believe this indicates the snooze circuit is fine?

BJ---With no RX present the TX will use Snooze to reduce standby power, cycle on / off to check for an RX.  No RX you will see 3.3V cycle on / off.  With RX you will see 3.3V on

Bill: 

thanks for your reply . I will look into the problem around Q7 and Q8  and let you know. I noticed that the snooze time was 300 ms too and i will check the capacitor ratings again.

Dick:

thanks for your replies and help.

I havent measured the inductance of the coils yet but I am using:

a-  6.3 uH coil from Wurth on the Tx :http://www.farnell.com/datasheets/1736770.pdf

b- 10 uH coil from Wurth on Rx: http://www.farnell.com/datasheets/1736774.pdf

 I will try to take scope shots tomorrow .

i have  a quick question  about something i read in another thread  ( i cant find the link) the person who posted it mentioned that after soldering the thermal pad to ground his system worked fine . my question is: is the thermal pad connected internally? my Tx thermal pad is not soldered to ground ( for some reason there's solder mask on the pad ) would this cause an issue?

Best,

Mahmoud

Hi Dick,

This morning i did a little experiment. I connected a small lamp in parallel with the battery on the receiver output then moved the receiver close to the transmitter, once the power transfer started i removed the battery completely from the circuit  the lamp stayed on drawing a current about 190 mA. after some time i also did it with 2 lamps and the receiver was delivering a constant current of about 380 mA  .

shouldnt the receiver disconnect when the load voltage is removed?

Hi Dick,

today i noticed that when i power the transmitter from a battery not a power supply, the output current is more stable .

I managed to charge my first battery but it's been over 12 hrs  , the charging was supposed to be ended at 78 mA( Rilim= 270 ohms), right now the charging current is less than 50 mA and still charging.

i started charging another battery( that i discharged completely( the voltage was 3.18v : maybe i over discharged it). when i first moved the receiver over the transmitter the current was going up to 650 mA then going to zero for few minutes, then it started to go between 650mA and 580 mA for few minutes, now the current is more stable and is going between 480mA and 460 mA; it seems that with time the charging current becomes less but more constant( withing 10 minutes from the start of charging) . is this a closer situation to the way it should be acting?

I would like to know if you can help me achieve a higher charging current ( i have attached links to the coils am using in an earlier post), my goal is 1A charging current. 

below are the specs of the battery :

thanks,

Mahmoud

Mahmoud,

Have you used a current probe to investigate the current into the transmitter.  Based on your comment about the battery, I am concerned that the transmitter supply is going into current limit.  What is the current limit of the input supply?  

Based on your value of 1.69k on RTERM, the charge current should terminate at:

%ILIM = RTERM / KTERM = 1690 / 240 = 7%  (range of 6% to 8.4%).  

IILIM = KILIM / RILIM = 300 / (270+187) = 656mA

Termination current is between 39mA and 55mA.  Below 50mA is not unexpected.

The battery spec shows charging time approximately 10 hours at 1A.  The time you are seeing is reasonable for the current you're using.

I have not used this battery, but I generally see very stable currents produced by the bq51050B.

Any IOUT plots would be helpful as well.

Regards,

Dick

Hi Dick,

I read in one of the documents that omitting FOD_Cal resistor results in the default FOD_cal value; may i know the default value for the bq500212A?

so far i have two major problems with my charger:

1- the snooze/sleep circuit ( I had to omit the diode to isolate them so the circuit worked)

       - the snooze function works fine except for the time between pulses. I have used the same values used in the EVM but I am getting a 300mS (instead of 400 mS)between each consecutive pulses, which i dont understand why.

2- FOD AND PMOD problem 

when the resistors values were set as in the evm schematics , the charger was indicating a fault right after the receiver was moved over.

after omitting the PMOD and FOD resistors the charger would start charging but the charging current isnt constant ( is goes between 680mA-580mA) the input current to the transmitter  was about 380mA at 12V.

the power source was a 12v100Ah  battery( so i dont think current limit is an issue here).

i also noticed another thing that when the current goes down below 300 mA it would remain constant .

I hope you could help me with these issues .

Thanks,

Mahmoud

Hi Mahmoud

The bq500212A is a 5V input device but you are saying you are running the unit from a 12V 100Ah battery.  How are you converting the battery voltage to a regulated 5V?

But you should be able to operate from a 5V power supply or 5V AC to DC adapter with output current of 2A.  

Hi Bill, 

the 12 v are fed into a buck regulator (LM22676 from TI) which has a fixed 5v output and capable of providing up to 3A of current ( which should be more than enough for the charger).

Thanks,

Mahmoud