DIY Lithium Battery Charger & Booster

Batteries power our world, but managing them efficiently requires smart circuits. In this project, I designed a compact lithium battery charger with a 5V boost converter, combining a TI BQ24075 charger IC and a Diodes Inc. PAM2401 boost IC into a tiny 24mm × 34mm PCB.

But the journey wasn’t smooth! A hidden schematic mistake turned my board into a toaster before I fixed it. In this Instructable, I’ll walk you through:

✔ Circuit design & PCB layout

✔ Assembly & soldering tips

✔ The debugging nightmare (and how I fixed it!)

✔ Final testing & performance

Let’s dive in!

Electronics Components

1. IC1: BQ24075 (LiPo Charger)
2. IC2: PAM2401 (Boost Converter)
3. L1: 2.2µH Inductor (2A saturation current)
4. D1: Schottky Diode (SS34)
5. USB-C Connector (SMD, 16-pin)
6. JST 2.0mm Connectors (Battery + Output)
7. LEDs (Power/Charge Status)

Tools & Materials

1. PCB Fabrication: JLCPCB (Purple solder mask!)
2. Soldering:
3. Stencil
4. Solder Paste (Low-Temp)
5. Hotplate
6. Precision Tweezers
7. Debugging:
8. Oscilloscope
9. Multimeter
10. Microscope
11. Design Software: Altium Designer

The Two Key ICs

1. BQ24075 Charger IC
2. Why? Handles all lithium battery charging logic
3. Key Feature: Built-in thermal regulation (no cooked batteries!)
4. Setup: Identical to my previous project (USB-C in, 500mA default)
5. PAM2401 Boost Converter
6. Why? Converts low battery voltage 0.9V–4.2V battery voltage to a stable 5V/500mA output
7. Key Specs: 1MHz switching, needs 2.2µH inductor (I used a 2A-rated one)
8. Gotcha: LX pin requires careful PCB routing

Schematic Tips

1. Isolate power paths! My mistake: Accidentally connecting charger/booster outputs (more in Step 4).
2. Add reverse protection (Schottky diode on USB input).

Critical Design Choices

1. Size: 24mm × 34mm (fits behind a battery)
2. Ground Plane: Full copper pour under power components
3. Component Placement:Inductor <5mm from PAM2401 (reduces noise)
4. USB-C port on left edge for easy access

🛠️ Design Tools Used

1. Schematic Capture: Altium Designer
2. Component Sourcing: Selected JLCPCB-compatible parts for easy assembly

⚠️ Pro Tip: Run a Design Rule Check (DRC) before ordering PCBs!

📁 Design Files:

1. Full Schematic PDF
2. Altium 365 Project

After getting the Circuit very well designed, I generated its related GERBER files and uploaded them to JLCPCB website to order these Purple color PCBs.

Soldering Steps

🛠️ Tools Needed:

1. Stencil + solder paste (I used Chip Quik TS391LT)
2. Hotplate (or reflow oven)
3. Precision tweezers (for 0402 components)

1. Apply solder paste using a stencil.

2. Place components with the aid of tweezers in this order:

1. Start with the small parts (Capacitors, resistors)
2. PAM2401/BQ24075 ICs
3. Inductor and passives
4. USB-C connector (check alignment!)

3. Reflow on a hotplate (220°C for 90 sec).

🔍 Check: Inspect joints under a microscope, look for bridged pins or cold solder.

After getting the circuit very well assembled, I moved to do some tests targeting a 5V output voltage from a Lithium 3.7V battery so the needed result should be a boosted stable voltage coming from this circuit:

❌The Problem

1. Booster output stuck at 3V instead of 5V
2. Inductor overheating
3. LX pin showing glitchy pulses (scope capture below)

Symptoms & Fixes

Inductor overheating ---> Output short ---> Check LX pin with scope

3V output (not 5V) ---> Booster disabled ---> Verify EN pin voltage

Erratic LX pulses Feedback ---> loop broken ---> Measure FB pin (0.6V?)

1. Root Cause:
2. My schematic accidentally connected the charger and booster outputs!

✔️The Fix

1. Cut the conflicting trace between ICs.
2. Verified clean 5V output afterward.
3. Check the output Pulses signal from the booster LX pin to the inductor

I then updated the Design files and fixed the GERBER as well :)

Performance Metrics

1. Efficiency: 92% at 500mA load
2. Output Stability: ±50mV ripple
3. Charging Current: 500mA (adjustable via resistor)

✅ Success! Now it charges batteries and delivers 5V reliably.