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Part Number: BQ25700A
We had questions related to the use of the chip bq25700a. The schematic is shown in Figure 1, in an enlarged format in Figures 2-4.
The parameters we used shown in Figures 5-7. The Figures 8-12 show the data from Battery Management Studio v1.3.80 and indication of an external power source.
We encountered the following problems:
1) With using the charger we hear a significant noise, which becomes quieter or louder depending on the position of the device and charging current.
2) We suppose to use the device for charging with a current of 3 A. However, even at a current of 2 A, a significant heating of the chip and transistor VT11 is observed. Within 5 minutes of our temperature of 100 ºC.
3) If the resistor R27 is set to 20 mΩ instead of 10 mΩ, input current is not adjusted correctly. The board consumes twice less current than is set in the 0x3F register. Setting the resistor parameter in the 0x30 register does not result. This problem is illustrated in Figures 8-9. With installing a resistor of 10 mΩ problems are not observed.
4) Charge and input currents from ADC in Battery Management Studio are not true. With using 20 mΩ input resistor the input current shows correctly, but when using 10 mΩ this does not happen, but the charging current is still incorrect. This problem is shown in Figures 10-12. At the same time, the charger correctly regulates the current (with 10 mΩ resistors), but the data in the Battery Management Studio is not shown correctly.
Please comment on this situation and give appropriate recommendations regarding the using the chip.
Thanking in advance.
Figure 1 – Schematic
Battery Charger Solutions
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In reply to ezhao:
In reply to Joel Hernandez II:
Correcton of this mistake has not given result. Chip and MOSFET are heating yet.
Using of 20 mOhm resistor still leads to wrong ADC data and incorrect input current regulation.
Also, board is working quietly and correctly in buck-mode, but not in boost-mode.
In reply to user4962001:
Can you provide a waveform of the SYS voltage. BAT voltage, BAT current, and either VBUS input voltage or input current when in both buck and boost mode.
I want to see if your design is unstable.
Charge Current 2A, Input Current 3.25A. Input Voltage: boost mode – 12 V; buck mode – 18V.
IADPT(4 green) VSYS (3 purple) IBAT (1 yellow) VBUS (2 blue)
10 mOhm RAC, Boost:
10 mOhm RAC, Buck:
20 mOhm RAC, Boost:
20 mOhm RAC, Buck
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