Several Problem Solving Sharing of BQ25895

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Several Problem Solving Sharing of BQ25895 [Copy link]

The bq25895 is a highly integrated 5A switch-mode battery charge management and system power path management device for single-cell lithium-ion and lithium-polymer batteries, with an I2C serial interface for charging and system settings. However, during use, some problems may occur in the battery charge management design. Here are some typical problems for reference:

Question 1: When BQ25895 is charged at 5V, the charging current can only reach 740mA.

The battery voltage is 3.93V and the charging port input voltage is 5V.

The external resistor limiting ILIM pin is closed. The internal current limit is set to 3.25A maximum and the fast charge current is set to 2A .

Now there are several questions:

1. I inserted the battery first. When inserting the USB charger, the default register parameters were used. When the charger was identified for D+/D-, the charger detected was USB (DCP). However, I measured D- at 2.7V and D+ at 2.0V. According to the instructions, it should have detected a non-standard adapter of 1A.

Charging cannot be performed under the default register parameters. The charging STAT indicator light flashes once and then goes out, and the BATFET is forced to turn off.

2. I set the register REG0D to 0x98, which is 5.0V. It can be charged, but the current is only 740mA. Once REG0D is set to other values, the current drops immediately, or the BATFET is directly turned off, resulting in a charging current of 0. At this time, REG13 (VINDPM Status) is set to 1. What does the VINDPM parameter mean?

Here are the values I set for the registers:

REG00:3F

REG01:05

REG02:6D

REG03:3A

REG04:20

REG05:13

REG06:5E

REG07:8D

REG08:03

REG09:44

REG0A:93

REG0B:76

REG0C:00

REG0D:98

REG0E:52

REG0F:52

REG10:3E

REG11:98

REG12:0B

REG13: BF

REG14:39

Here is my board layout:

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Thank you, is it a problem with the register settings? Check which pin needs to measure the waveform. No matter how I adjust the current, it won't go up.

reply:

BQ25895 has VINDPM. When the power supply is overloaded and the output voltage drops, the BQ25895 charging current decreases and VINDPM adjusts the input voltage.
Your battery voltage is 3.93V, and it enters CV mode at this time, and the current cannot reach the set value.

Thanks for your answer. I tested it again. Now when the current limit is set to 1A, charging will be automatically turned off. When it is set to 900mA, it can charge normally. I looked at the data sheet again and felt that the capacitor and inductor on the SW pin were far apart. The power bank solutions all seemed to be close. I modified the board and tested it these two days.

Reply: It's a problem with your own drawing. The problem can be solved by placing the capacitor and inductor on the SW pin as close to the chip as possible.

Question 2: What is the default behavior of BQ25895 when the I2C pin is left floating? Can it charge or boost the voltage? If so, what are the maximum currents?

What is the default behavior of the BQ25895 when the I2C pin is left floating? Can it charge or boost the voltage? If so, what are the maximum currents?

Reply: You can use the default mode. Please refer to Table 4 of the data sheet for details.
8.2.7.1 Autonomous Charging Cycle

What is the maximum supply current of BOOST by default? Is it 400mA?

Boost mode can only be triggered when the following conditions are met, including the third line writing the OTG register.

Once the register is written, it will enter the host mode from the default mode. For details, please refer to 8.2.5 and 8.3.1

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Question 3: If bq25895 uses TYPEC fast charging input, QC2.0, QC3.0, PD and other fast charging, does it need a fast charging protocol IC? At the same time, can a typec realize input and output functions?

If bq25895 uses TYPEC fast charging input, QC2.0, QC3.0, PD and other fast charging, does it need a fast charging protocol IC? Can a typec realize input and output functions at the same time?

answer:

Protocol IC is not necessarily required, but using IC is the most reliable and economical.
For the same Type-C, theoretically, it can output and input in both directions. However, in actual engineering, only one direction is given.

As long as the BQ25895 conditions are met, no agreement should be required.

What conditions need to be met? How to implement the QC2.0 handshake without a protocol?

Question 4: BQ25895 cannot charge the battery at 4A

Our power adapter outputs 3.6V-6V/3A, 6-9V /2A, 9-12V /1.5A adapters, charging IC uses BQ25895 , for charging 3.4V 4000ma lithium batteries, after all are connected,

The maximum output voltage of the USB interface is 12.2V, and the current for charging the lithium battery is 700mA. After adjusting the register, the current does not reach 1.5A.

Registers read:

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When register 04 is set to 40, the current changes from 0.7A to 0.8A, but does not reach 1.5A. It cannot be charged with a large current. What is the reason?

reply:

BQ25895 charging voltage 12.2, 750mA, battery voltage 3.68V

The resistance of Ilimit is 130 ohms.

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okhxyyo

Great, very detailed write-up, thanks for sharing