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BQ24780S: can not charge

Part Number: BQ24780S

Hi Sir,

When the system power load increases, the Charger IC cannot be charged
The conditions are as follows
Adapter: 19V, 7.89A

when Rac seting 0.01Ohm and on Rac voltage as below:
1. At 40% system loading, 37.8mV, the battery can be charged 0.5A
2. At 60% system loading, 45mV, the battery can be charged 0.5A
3. At 100% system loading, 58.1mV, the battery cannot be charged

there any errors in the setting of the attached theschematic? Is the schematic correct? please kindly let us learn from you and suggestion to us.

MG4U_DVT_DC BOARD_0518-1430.pdf

  • Hi, Tommy,

    There is an input current register 0x3F, its default value is 4.096A. From schematic, the ILIM pin is limit to 3.05A. You may run into input current limit, thus limiting your charge current. 

    Datasheet 7.6.11, "The total input current, from a wall cube or other DC source, is the sum of the system supply current and the
    current required by the charger. When the input current exceeds the set input current limit, the bq24780S device
    decreases the charge current to provide priority to system load. As the system current rises, the available charge
    current drops linearly to 0."

  • Hi Tiger:

    I am ESVS James Liu

    The schematic is my company project

    The BQ24780S register setting

    0x12H      8108

    0x3BH      C210

    0x38H      0384

    0x37H      1A40

    0x3CH      4A54

    0x3DH     8120

    0x3AH      0020

    0x14H      0200

    0x15H      41A0

    0x39H      2600

    0x3FH      1E80   7808mA

    The Rac is 58.1mV , So input current is 5.81A < 7.8A

    Can you help me?

  • Hi, James,

    Please check your battery voltage as well. Does this happen at fully-charged battery or low-charged battery? If fully-charged, the charge current may terminate when max charge voltage is reached. 

  • Hi Tiger:

    I confirm that the battery is not fully charged. 

  • Could you get 3A charge current when the system load is zero?  or  Could you measure the SRN voltage and report back?

  • Hi Tiger:

    3A charge current, Rsr=31.1mV, the charger current=3.11A.

  • It looks like a test setup issue. Please refine your test setup and use adequate wire gauge for high current test.