BQ25703A: Using bq25703a as only battery charging station(there is not system output, etc.)

Hey Nedd,

1) The charger requires the external PMOS BATFET. As you quoted, this is due to the regulation of VSYS during charge disabled to VSRN + 160mV. Because the VSRN and VSYS are essentially shorted through the 10mOhm sense resistor, the control loop continues to inject current to the output until VSYS reaches its OVP threshold.

2) You can remove this FET. This is in the EVM for customers to validate the functionality of the battery presence detection.

3) Please pull this pin to ground if your are not using OTG mode. Don't leave it no connect.

4) The IADPT pin resistor is absolutely required for proper converter control. Please size this as listed in Table 3 of the datasheet. This gives the converter the information required about the inductor value.

5) That is also not needed. You may use any other rail available to you but please consider the absolute maximum voltage ratings of the pins you will place a pull-up resistor on.

6) You can use either 120kOhm (upper) and 100kOhm (lower) for a 2S configuration or 42kOhm (upper) and 100kOhm (lower) resistance value for 4S configuration. However, this can be any value you like as long as you adhere to the voltage percentage listed in Table 1 of the datasheet.


Regards,
Joel H

Hi,

Please let me know.

1) Thank you. Can I remove capacitors from system output? What is your advice? Is BAT output need capacitors like SYSTEM output?

2) Thank you.

3) Ok, thank you. I will pull down this pin to GND by 100ohm or 0ohm? What is your advice?

4) Thank you.

5) Thank you. I'm plannig to use REGN pin by voltage divider for 3.3V output, is it okey? Which one is better, VDDA or REGN for that? (I will use 3.3V for supply to SCL, SDA, CHRG_OK, etc. )

In addition I'm not sure voltage level of REGN output(6V or 6.5V ?).Could you please provide me information about REGN output?

6) Thank you, it's okey right now.

IN ADDITION:

7) About Input Current Limit (ILIM_HIZ):

I would like to set 4A or 3A as input current limit and I know for 4A input current limit Vılım_hız pin should be 2.6V and  for 3A input current limit Vılım_hız pin should be 2.2V.

When I'm checking the EVM I have seen 383k and 220k resistors for ILIM_HIZ pin. Input current limit(Idpm) shown as 6A in the schematic of EVM.

Vilim_hiz= 1V + 40 x Idpm x RAC

Vilim_hiz= 1V + 40 x 6A x 0.01ohm

Vilim_hiz= 3.4V

It's looking good BUT when I'm not sure about voltage divider. Vilim_hiz = VDDA x [ (220k) / (220k+383k) ]  . VDDA should be 9.32V . Is it possible?

Could you please suggest me values of voltage divider resistors. I'm not sure because of VDDA as I mentioned above.

8) I'm not sure about PROCHOT? Is it important for my system? What do you advice for that?

9) Can I send my schematic file by e-mail to you for checking?

Thank you.

Hey Need,

1) The converter absolutely needs capacitors on both SYS and BAT. They are needed on SYS for proper buck converter operation and they are needed on BAT for the LDO mode of charging to be stable as well.

3) Either way works. You can tie it directly to an analog ground net/trace without the need for a resistor.

5) I thought a little more about this one. VDDA is the same voltage as REGN. The datasheet dictates that this must be connected to REGN through a 10 Ohm resistor. Effectively, you get the same pin. I believe you may need an external LDO to drive your pullup rails. The issue with the REGN voltage is it's range across input voltage. The internal REGN LDO operates in dropout at lower input voltages, causing it swing lower than 6V, while at higher voltage 6V is the maximum. If your voltage divider can tolerate this range (from 3.8V from 5VIN to 6V) than you may do so, but you are better off using an external device to create this rail from SYS or BAT.

7) I'm not exactly sure where you selected 6A from the EVM schematic, but based on the typical VDDA voltage (as connected to REGN, when the LDO is not in dropout) is 6V. Running through the calculations shows that the ILIM_HIZ voltage is approximately 2.18V. This yields a typical current limit of ~3A. For your applications, you are correct that either 2.2 or 2.6V on ILIM_HIZ will yield either 3A or 4A, respectively. Your resistor divider should reflect this if you intend to use the external ILIM feature. Also note that this can be disabled in registers and you may opt to only use the register setting for IINDPM. If you do decide to use the external, you may also opt to use the same external LDO I've suggested for (5).

8) nPROCHOT is useful for your system only if you would like the charger to report a critical overloading issue across different programmable threshold so you may throttle back current. If your system will pull whatever current it likes (up to the current limit), you can ignore this pin. It was designed for Intel processors as a way to force the processor to throttle back on processes and reduce power consumption.

9) That is fine. I will send you a private email.


Regards,
Joel H

Hi Joel,

Firstly, Thank you for your attention.

1) I will NOT(never) use SYSTEM Output so that I thought I don't need a lot of capacitors for SYSTEM output. Maybe I can use 2 capacitors between Q2 and Q3 . What do you thinking about that? Is it necessary?

9) I have send e-mail to you.

Thank you.

Best Regards,

Hey Nedd,

I have not received an email from you.


Regards,
Joel H