← All case studies
Battery Module · Power Electronics · Mechanical Integration

TWO BOARDS,
ONE CHARGER

A sealed IP65 USB-C battery module, built to drop into a product already in the field.

Li-ion pack design BQ24618 synchronous buck IP65 sealing USB-C sink 0.5mm FFC interconnect Mechanical integration
Exploded view of the battery, charge board, interface board, FFC and extruded housing
Everything in the module: interface board, charge board, 0.5mm flex, the 2P pouch pack, end cap and extruded housing.

The client supplied the cells, and their product already ships. We designed the charge electronics and the sealed enclosure around them. The pack fills the housing, so the charger had to split across two boards.

The two boards laid out with the 0.5mm flat flex cable between them
Two boards. The charge stage carries the BQ24618, inductor and MOSFETs; the interface board carries the USB-C port, button and LEDs. A 0.5mm flex joins them.
The flat flex arcing between the two halves of the housing during assembly
Inside the housing: the pack down one channel, the interface board at the end cap, the flex arcing between the two halves. A rigid connector couldn't take that path.
The two pouch cells seated in the extruded body, the cover held alongside
The 2P, 10.3Ah pack seated in the extruded body. Two-part enclosure: the profile that holds the cells, and the cover that closes it.
The end cap carrying the USB-C port, button and charge-status LEDs, with the pack alongside
The end cap: USB-C port, button and charge-status LEDs. It makes the IP65 seal and mounts the interface board behind it.
Pack specification
Configuration2P polymer lithium ion, 2 × 5150mAh
Nominal voltage3.70V
Rated capacity10300mAh, approximately 38Wh
Charge termination4.20V CV, taper to 0.01C
Discharge cut-off3.00V
Max continuous charge0.5C, 5150mA
Max continuous discharge0.5C, 5150mA
Internal impedance≤100mΩ at 1kHz
ProtectionS8261 protection IC, FS8205A dual MOSFET
Overcharge detection4.28V ±0.025V, 1.2s delay
Over-discharge detection2.40V ±0.05V, 144ms delay
Over-current detection6A to 10A, 10ms delay
Short circuit response≤380µs
Thermistor10k NTC, brought out on the pack connector
Cell size7.0 × 43 × 130mm each
Cycle life300 cycles to 80% of initial capacity at 0.5C
Charge temperature window0 to 45°C
Charge profile
TopologySynchronous buck, 600kHz fixed frequency
InputUSB-C, 5V nominal
Fast charge current2.98A (0.29C)
Input current limit2.52A, dynamic power management
Regulation voltage4.20V
Precharge current503mA below 3.10V
Termination current503mA (0.049C)
Recharge threshold4.10V
Battery overvoltage4.37V
Cycle-by-cycle overcurrent4.76A
Current sensing10mΩ on both input and charge paths
Reverse protectionIdeal diode controller and MOSFET, no series Schottky
Temperature qualificationPack NTC into the controller, hardware enforced
BackupCapacitor-programmed safety timer
Standby current57µA idle, negligible against cell self-discharge
Charge portUSB-C receptacle, IP67 tested, 20,000 mating cycles
Housing sealingDesigned to IP65, gasket-sealed at the end cap

Regulation points are derived from the as-built schematic. Efficiency and charge duration are calculated from the component data rather than measured, and are quoted as design figures pending bench characterisation.

Macro of the board silkscreen reading JVION Engineering
Our silkscreen on the board.

Client-supplied battery in, finished sealed module out.

GOT A PRODUCT
THAT WON'T FIT?
← Back to case studies Follow on LinkedIn ↗