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Battery Management - Chargers Forum
Battery Charger minimum Input Voltage
I'm new here in this forum, hope you can help on my little problem.
I'm designing a 3 cells Li-ion/Poly battery charger, and I come across with this part number: bq24610.
It have a reference design, but I would like to know if I have a 3 cells in series, what would be the minimum Input voltage of the adaptor?
The set charging current is at 500mA.
Is a 15V/1.5A Adaptor is enough for the battery charger.
Hope to hear your constructive reply.
Thanks and Best Regards,
3 cells Li-ion in series will give you 12.6V, thus 15V input should be enough.
Thank you for your confirmation.
I have another question on the maximum charge current. We want to limit the charge current to 0.5A.
On the datasheet there is a table for the recommended combination of Inductor, capacitor and Rsense.
Based on that table, the minimum defined charge current is 2A.
Is there a formula for selecting that inductor and capacitor? And also the formula in selecting the Iset1 and Iset2.
Hope you can help me on this one.
These basic design info are described in the datasheet such the ISET1, ISET2, output cap, inductor…etc.
I strongly recommend that you consider using the bq24170 or bq24133 instead of the bq24610. The bq24170 and bq24133 have integrated FETs which will significantly reduce your design time and minimize the possibility of layout issues. I also recommend you use the EVM layout if possible. You can use the 1A referrence design values for your 0.5A design. I am curious about your application and what drives your maximum charge current of 0.5A
Thank you for your recommendation. This is good for our requirement.
Our system is consuming 1A at maximum and we only planning to use 15V / 2A Power Adaptor, and we don't want to drive the Power Adaptor to maximum limit that is why we want to limit the charging current maximum at 0.5A only.
Based on the bq24170 or bq24133 datasheet, 1A reference design is only available, do you have 0.5A reference design especially for the specifying the output Inductor, and output capacitor.
Hope to hear from you the soonest.
For reducing the current, one can adjust the sense resistor as per the data sheet.
For the inductor, go to digikey and search for a shielded inductor.
A good one to use is: CDRH74-100MC, 10uH, 1.84A
this is 3 times the inductance, so you can use 1/3 the capacitance.
Also note that the bq24170 has input current DPM which means that you can dynamically reduce the charging current to keep the charging + system current below your desired value. You can still use the 2A design, even for a 0.5A charge current. I would suggest that you evaluate the EVM to help understand IC functionality and how it will work in your system.
Is this a typo error?
I look deeper on the reference schematic and I'm little confuse why it is NMOS is use in controlling the Input Voltage?
Does the circuit will oscillate?
Let say, during charging there is an adaptor which is rated at 15V.
What is the output voltage of ACDRV to make the two Q1 and Q2 "ON"?
At the initial state the Q1 and Q2 source pin is zero volt it will conduct once there is a voltage at the gate pin (VGS is satisfied). Once it conducting the voltage seen at the source of the FET is 15V, this time the minimum required VGS to turn on both the FET is not satisfied. The FET will basically turn "OFF" and return to initial state and the cycle will repeat. AND this cause OSCILLATION which is not good for EMI response.
Is there a way to use PMOS instead?
bq2417x IC have recommended input voltage of 4.5V to 17V. The schematic you pasted above is correct. You must us N-ch FETs. It works well and there are no oscillations. bq24170 IC is powered from the AVCC pin, not the PVCC pin. PVCC pin is the power path. I would recommend that you get an EVM and perform lab testing to ensure the IC meets your needs. That will allow you to "exercise" the IC to get a good feel for how it works.
I recommend we close this post out and put any additional questions in a separate post so we can keep each post very specific to a single function or question about a single IC.
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