How I can get max current in BQ24296MEVM-655?

Hello Jose,

Your register setup seems correct. Since you are using the EVM, have you tried changing the potentiometer on ILIM to ~145 Ohms? That should set the Input current limit to ~3A.

Do you have any load on SYS during your testing or just the battery charging?

Hello Fernando,

I have set the potentiometer at max of current that it permit, I have measured it and its measure is 1 Ohms.

While I am battery charging I had not connected load on SYS, I just was battery charging. 

Why if I setted the potentiometer to 1 Ohms, I did not get 3 Amps of charge in battery?

Thanks for your answers Fernando.

Hello again Fernando,

I set the potentiometer to 145 Ohms approximately, and I get at current of 1,3 Amps. Just like before I am only charging the battery.

How can I do to get 3 Amps of load?

Thanks in Advance

Hello Jose,

The input current limit is actually the lower between the ILIM setting and the I2C setting. I see you are setting the I2C register to 3A, but you have your watchdog enabled to 160sec. Could you verify if the input current limit is being reset to a different value than 3A due to watchdog timer expiration? 

Is your device reporting and DPM condition in the status registers?

Hello Fernando,

When the watchdog expires it stays the same value in the register. Moreover, I put to 0 reg01[6] to avoid throw a new fault. In this way I am sure that reg00 will have the same value that at begining.

By other hand, register reg 08, the bit 4 it is a 0, i.e. not have input DPM.

The registers have the following values (all in hex):

REG08: A4

REG09: 00

REG0A: 20

Thanks again Fernando.

Hello Jose,

Thanks for the information.

Are you charging with a real battery or are you using a battery emulator/bipolar power supply? If using a real battery, what is the capacity of it? 

If a real battery is being used, I would like to rule out that what's happening is the cell is receiving 3A momentarily and reaching constant voltage quickly and the charge current begins to taper below 3A.

If using a battery emulator, I would like to verify if there is a significant amount of impedance along the charge path (perhaps from the wires). If the voltage drop across the wire is too large, the voltage at the BAT pin might be near constant voltage while you are still observing a "normal" voltage on the emulator side. 

Also, can you please verify your power supply is not limiting the current somehow?

Thank you.

Hi Fernando,

I'm Tomás Mateo, the PI of a R&D project at the University of Huelva, Spain for which we bought the BQ24296MEVM-655 board. We plan to buy more several units for our project but as you know we're having serious problems to start up. In order to resume the working conditions, these are the followings:

We're using a Velleman LABPS3005D power source (up to 30V, 5A) to power the BQ24296MEVM-655 board through J1 (VBUS, GND). In addition, we're using a Li-Po battery (9000 mAh, 3.7V) of one cell through J4 (BAT, GND). We're using a resistor (2.7 Ohm, 10W) for simulating the load system through J3 (SYS, GND).

Regarding the battery, we tried to charge it from 2.8V to 4.13V and observed the pre-charge, fast charging and charge termination stages with no problem. When observing the current, it took 128 mA for the pre-charge. However, during the fast charging it never reached more than 1.5A.

Pin /CE is short to GND in JP7 to enable the charging process. PSEL pin is short to GND through JP1 (D+/PSEL, LOW) because we don't use an USB source. The value for REG00[2:0] is [111] and ILIM is set to 131 Ohm through the variable resistor on the board. The watchdog is reset before 160s through the GUI of the Battery Management Studio (bqStudio). We measured ILIM between TP14 and GND in a range between 131-500 Ohm although in section "2.3.1 Current Settings" of the user's guide (BQ24296MEMV-655.pdf) the ohmeter should be pointed between TP9 and GND (I think it could be a typo error).

If possible, we can talk by phone/skype (maybe in spanish) for a quick understanding. Thanks for your support.

Waiting to hear from you soon.

Hello Fernando I forward the following message:

Hi Fernando, 

I'm Tomás Mateo, the PI of a R&D project at the University of Huelva, Spain for which we bought the BQ24296MEVM-655 board. We plan to buy more several units for our project but as you know we're having serious problems to start up. In order to resume the working conditions, these are the followings:

We're using a Velleman LABPS3005D power source (up to 30V, 5A) to power the BQ24296MEVM-655 board through J1 (VBUS, GND). In addition, we're using a Li-Po battery (9000 mAh, 3.7V) of one cell through J4 (BAT, GND). We're using a resistor (2.7 Ohm, 10W) for simulating the load system through J3 (SYS, GND).

Regarding the battery, we tried to charge it from 2.8V to 4.13V and observed the pre-charge, fast charging and charge termination stages with no problem. When observing the current, it took 128 mA for the pre-charge. However, during the fast charging it never reached more than 1.5A.

Pin /CE is short to GND in JP7 to enable the charging process. PSEL pin is short to GND through JP1 (D+/PSEL, LOW) because we don't use an USB source. The value for REG00[2:0] is [111] and ILIM is set to 131 Ohm through the variable resistor on the board. The watchdog is reset before 160s through the GUI of the Battery Management Studio (bqStudio). We measured ILIM between TP14 and GND in a range between 131-500 Ohm although in section "2.3.1 Current Settings" of the user's guide (BQ24296MEMV-655.pdf) the ohmeter should be pointed between TP9 and GND (I think it could be a typo error).

When varying the potenciometer, we set ILIM to the minimum value of 500 mA, so it seems that this lower limit works fine (not for the upper limit of 3A). Do you recommed to manually short ILIM at TP14 directly to ground??

If possible, we can talk by phone/skype (maybe in spanish) for a quick understanding. Thanks for your support.

Waiting to hear from you soon.

Hello Jose,

I've sent you a private message to communicate offline, but I suspect the following is happening:

Jose Manuel Lozano Dominguez said:

We're using a resistor (2.7 Ohm, 10W) for simulating the load system

Your device configuration seems correct. Since you are using a 5V/3A input and your MINSYS voltage is 3.5V, meaning your system voltage with range from 3.5V to 4.2V. When you enter fast charging around VBAT=3V, the system load is going to be ~1.3A. 

Your fast charge setting is 3A. However, there is always a ~1.3A load on system present due to the 2.7Ohms load. The bq24296M is a power-path device, meaning that the system is prioritized over charging. The device will decrease charge current to maintain the system current without overloading the adapter. If you take the measured charging current of ~1.5A plus the ~1.3A system load, you will get  2.8A which after taking into consideration the efficiency loss, seems about right for a 5V/3A adapter.

Could you repeat the charge cycle, same settings but without the 2.7 Ohms load and verify the charge current?

Hello Fernando,

you are right, if I connect to charger a  2.8 Ohms resistor and a battery. But in the case that I use this configuration, power supply give current max of 2.2 A (not approximately 3A). 

By other hand, I connect to charger only a battery (capacity 9Ah), on this occasion power supply give current max of 1,5 A when battery is in fast charging. Never I have achieved 3A of charge in fast charging mode although only I connect battery, battery have a 9Ah of capacity and 1C.

When varying the potenciometer, we set ILIM to the minimum value of 500 mA, so it seems that this lower limit works fine (not for the upper limit of 3A). Do you recommed to manually short ILIM at TP14 directly to ground?

Waiting to hear from you soon. Thanks again.

I rewrite to talk about my problem. I have done some test, I tried to get the maximum current form the charger. I have achieved as maximum current 2,8A, to get it I put a battery of 9Ah (1C, a lipo cell) connected to BAT and a 2 Ohms resistance connected to SYS. If I only connect the resistance I get as maximum 2,1A, and if I only connect the battery I get as maximum 1,7A aproximately.

I have prevented the charger from activating VINDPM and the value of REG00[6:3] is 0000 (bin). The value of REG00 is 0x07 (hex).
Also, I have modified some registers, the new configuration is the next (hex):
Reg00: 0x07
Reg01: 0x1B
Reg02: 0x9C
Reg03: 0x11
Reg04: 0xAE
Reg05: 0x88
Reg06: 0x73
Reg07: 0x4B

I would like to know why if the charger is able to supply ~3A using battery and SYS, it is not able to charge the battery to 3A when there is nothing in SYS.

Thanks in advance