Recommendation for a boost charger setup with high efficiency

Hi Jeff,

I was able to get the BQ25616EVM module and play with it for the last couple of days to evalulate all of the functions related to my application.

I could confirm that the charge efficiency to my li-ion battery is as described from the datasheet (87%)

However, I ran into a few issues and I couldn't find a solution and hopefully you could help me.

The module is connected to a power supply with voltage and current limit to be 5.2V and 3A, respectively, via the VAC and GND (J1). I connect J5 to a li-ion battery. The schematic is the same as figure 1 in the user guide. I turned the potentiometers R22 and R12 all the way counter clock wise to get maximum I_LIM and I_CHG. I observed the current drawn from the power supply and I saw that it only delivers 122 mA for a observed period of 1 hour.

The STAT Led D6 blinks very fast  (maybe 10 Hz) when the battery is not connected, and remains on when the battery is connected

The LED D7 is steadyly on, which indicates power is good. 

I don't know what caused the charger to deliver such a low current to the battery. And I am also curious about a related information that is not presented in the datasheet: what is the duration of precharge time (Figure 9-5).

Thank you for your support.

Khoi

Hi Khoi,

Can you please provide the battery voltage, battery current, input voltage, and input current when this is happening? Is there a system load at the time? Can you capture a waveform of the SW node, battery current, battery voltage, and STAT voltage?

Regards,

Mike Emanuel

BQ25616EVM_Test.pdf

Dear Mike,

I have attached a 4 page images of the test results here. For current and voltage measurement of the VAC and BAT, I used INA260 chips provided by Pololu and confirmed that they work appropriately. For the waveform, I used digilent analog discovery 3.

The efficiency seems to hover around 78% at 3.5V battery voltage, which is lower than my expectation. And it went to 87% when bat voltage is 3.8V. Also, the charger was not able to deliver more than 250 mA, which is quite low, and finally, you could see the frequency switching of STAT when the battery is not connected.

What I also noticed is that adjusting R22 and R12 in any direction did not change the current at all. I was not able to find information discussing this in the EVM userguide

Thank you very much for your supports.

Khoi Ly

Hi Michael,

Thank you for your reply.  This explained the behavior of the blinking frequency of the STAT pin. I do not have system load so It seems that our data are quite in the same range. I also did not use kelvin test points for VBUS and VBAT. I used INA260 module from Adafruit for the test.

I have a follow-up question. In what condition that I can achieve higher current to my battery? What is the cause for current to be only about 300 mA. I thought that we should be able to get higher current thanks to the power supply that can provide upto 10A. I was not able to make a different in current output when I adjusted both the R12 and R22 all the way.

Thank you,

Khoi Ly

Hi Khoi,

Someone will get back to you by next Tuesday. 

Regards,

Mike Emanuel

Hi Khoi,

The charge maximum input current and charge current is 3A when you can set by lower R12 and R22 to zero. What are the voltages at the IC VBUS pin (TP7) and BAT (TP15) when you can only get 300mA of charge current?  

Regards,

Jeff

Hi Jeff, 

So I measured the resistor of R12 and R22 and they are both very close to 0 Ohm so they are good. I realized that the INA260 chips from adafruit has quite a lot of resistance so the voltage measurement is incorrect.

I removed them and connected the power supply directly to the BQ25616EVM and the battery without any INA260. I measured the voltage VBUS with my multimeter: without the battery connected, the VBUS  reads the set voltage from PSU, which is 5.4V, but when I connect the battery in, the VBUS value is 4.3V and almost fixed regardless of voltage from the PSU (I tried 5V to 6.5V)

Without the INA260, the current now is 550 mA, which is significantly better than before. VBAT is currently 3.913V. 

Is this result considered good for the EVM? I am still confused about VBUS being constant even it's connected directly to the power supply unit (PSU).

Thank you,

Khoi Ly

Hi Khoi,

VBUS=4.3V means the charger is in VINDPM and is regulating the input voltage to 4.3V by limiting the charger's input current.

Are you certain that the input supply is set higher than 3A?  Is there something resistive, like DMM or thin cable, connecting the input supply to VBUS to cause a 5V-4.3V = 700mV voltage drop?

Regards,

Jeff

Hi Jeff,

The wiring is indeed the culprit in my test. I shortened all of the wires and were able to get 1.2A of current from the psu to the battery. Thank you very much!

Hi TI Supports,

I have a related question about the schematics of the combined TPS61027 and the BQ25616 for charging, I appreciate if you could help me take a look for obvious errors in a few short day. It's almost put together.

Thank you very much,

Khoi Ly