Description of problem
I have a problem with a circuit that implements the LTC4015.
The problem occurs when I connect a life power supply or 12V lead-acid battery to the circuit.
The result is the breakdown of the LTC4015.
Functional and testable
When I connect a lab power supply (turned off) to the battery input of the circuit and slowly increase the voltage on the lab power supply, the LTC4015 turns on and opens the OUTFET.
A voltage of 5V can be measured on the INTVCC pin (INTVcc regulator).
Breakdown/failure
When I connect a 12V lead-acid battery to my circuit the LTC4015 breaks. (Case 1)
When I turn on the lab power supply, set the output voltage to 12V and the current limit to 10mA, and then connect it to the circuit, the LTC4015 breaks down, but in a less destructive way. (Case 2)
Test equipment
- Power supply: Rigol DP832A
- DC-load: Siglent SDL1020X-E
Battery specifications
- Manufacturer: MWPower
- Model: MWS 7.2-12
- EAN: 5902135116968
- Voltage: 12V
- Capacity: 7.2Ah
- Internal resistance (charged battery): 36mΩ1
- Max. discharge current: 80A1
LTC4015 after breakdown
After the LTC4015 breaks down the following things can be measure/observed.
- The INTVCC power supply is shorted to ground.
- In the case of (Case 1), a hole can be seen at the bottom right of the chip.
- In the case of (Case 2), no physical damage of the chip can be observed.
Schematic
Some additional information about the schematics that might be useful:
- R30, R31: These are 0Ω shunt resistors to enable/disable the use of the power path from VIN (charger input).
- R10: 100kΩ resistor to use when no NTC is connected.
- C17, C18, C19, C20, C21:
- Manufacturer: Samsung Electro-Mechanics
- Model: CL31A106KBHNNNE
- Capacitance: 10μF (± 10%)
- Voltage rating: 50V
- Dielectric characteristic: X5R
- ESR can be found in image and website of manufacturer2.
- CELLS and CHEMISTRY config:
Pins CELLS2 CELLS1 CELLS0 CHEM1 CHEM0 EQ Config L H Z Z Z L
The following images are the schematics of my circuit design implementing the LTC4015.
Board layout
Some specs of the board and its' layout:
- Layers: 2
- Width/height: 100mm x 80mm
- Board thickness: 1.55mm
- Copper layer thickness: 18 µm
- Base material: FR4IMP
The following images are the top and bottom views of the board layout for my circuit design.
Notes
- On the image of the breakdown of the LTC4015 in chapter "LTC4015 after breakdown", thermocouples with exposed metal tips can be seen. All temperature measurement points were provided with an initial layer of Kapton tape to prevent shorts.
References
[1] Cdn-reichelt.de. 2021. MWS 7,2-12 datasheet. [online] Available at: "cdn-reichelt.de/.../MWS_72-12_DS_EN.pdf" [Accessed 23 July 2021]
[2] Samsungsem.com. 2021. CL31A106KBHNNN specification sheet. [online] Available at: "weblib.samsungsem.com/.../mlcc-ec-data-sheet.do 23 July 2021]
