Compact, High‑Efficiency USB Charging for Vehicles: One‑Chip, Multi‑Port Solution

This article presents a single‑chip design that delivers clean 5V to multiple USB ports in a vehicle, while minimizing space, heat, and EMI.

Modern cars feature USB outlets in the head unit, glove box, armrests, and rear seats (see Figure 1). These ports typically connect to the vehicle’s head unit via long captive cables, which can cause Ohmic voltage drop, generate EMI, and overheat the head‑unit charger.

Existing automotive USB solutions often rely on multi‑chip packages, non‑synchronous regulators, or bulky external components. Such designs consume valuable PCB area, dissipate excess heat, and lack spread‑spectrum EMI suppression—making them unsuitable for the growing number of ports in contemporary vehicles.

Ideal One‑Chip Solution

The MAX20037/MAX20038 family integrates a 3.5 A automotive‑grade synchronous buck converter, a USB host‑charger emulator, and robust USB protection switches—all in a 5 mm × 5 mm, 28‑pin TQFN package. Key features include:

• High Efficiency – Synchronous rectification yields peak efficiencies >90% (see Figure 3).
• Low Noise & EMI – Fixed 2.2 MHz PWM with optional spread‑spectrum modulation keeps emissions below regulatory limits.
• Automatic Cable Compensation – A load‑current sense amplifier and configurable feedback adjust VSENSP to cancel voltage drop across captive cables. Adjustments can be made via I²C or external resistors.
• Broad Load Support – Handles USB‑compliant devices (max 30 mA during enumeration, 100 mA/150 mA after enumeration) and non‑compliant loads.
• ESD Protection – MAX20037 offers up to 6 V data‑switch protection with external ESD array; MAX20038 protects up to 18 V internally.

Illustrative Schematic

Figure 2. Car USB 5V adapter schematic

Data lines (HVD‑, HVD+, D‑, D+) handle the USB host‑client handshake before power delivery. The integrated sensing amplifier monitors load current, ensuring a stable 5 V output regardless of cable resistance.

Space & Thermal Advantages

Operating at 2.2 MHz reduces output ripple and allows for smaller external inductor and filter components. The 28‑pin TQFN package occupies less than 25 mm² of board area, freeing valuable space for additional features.

Performance Highlights

Figure 3. MAX20037/MAX20038 efficiency versus load

Typical curves show >90% efficiency across the 3.5 A output range, dramatically reducing heat in the head‑unit and improving system reliability.

Conclusion

By consolidating all necessary functions into a single, high‑current, synchronous‑rectifier IC, the MAX20037/MAX20038 solution addresses the key challenges of adding numerous USB ports to a vehicle: it slashes PCB real estate, eliminates excessive heat, mitigates EMI, and automatically compensates for captive cable losses.

Learn More

Explore the MAX20037/MAX20038 Automotive High‑Current Step‑Down Converters with USB Protection/Host Charger Adapter Emulation for next‑generation in‑vehicle USB infrastructure.

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