1. Introduction
Driven by devices such as iphone and ipad, smartphones and tablets have become ubiquitous. Integrated, non-removable batteries in many modern devices have made external power banks a common accessory, and demand for portable backup power has expanded rapidly with the growth of mobile devices.
2. Solution Analysis
2.1 Technical Specifications and Comparison
Typical specifications for power banks intended for phones and tablets are:
- Battery charge and discharge management for lithium cells.
- 5 V output at 500 mA, 1 A, or 2 A.
Battery charge/discharge protection is usually implemented by a protection IC plus an ASIC or MCU. The 5 V/500 mA/1 A/2 A output is achieved by a boost converter from the lithium battery with feedback control. The most critical metric for portable power banks is the boost converter efficiency. Since the boost converter supplies the mobile device, conversion efficiency directly affects usable capacity and thermal behavior. For a 10000 mAh power bank, a boost efficiency difference between 90% and 70% corresponds to about 2000 mAh of usable output. Lower efficiency causes more heating and larger safety risks.
There are two main boost topologies: diode freewheel boost and synchronous boost. The diode freewheel boost is simpler, while synchronous boost is more complex and requires precise timing control. In recent years, many low-cost designs used diode freewheel boost to speed production, but higher-end vendors have shifted to synchronous boost to improve efficiency and thermal performance.
2.2 Synchronous Boost with a Dedicated MCU
A dedicated MCU for power banks, such as the HT45F4M, is widely used for synchronous boost implementations. It offers a compact circuit and high efficiency. Manufacturer specifications include standby current below 10 μA and measured discharge conversion efficiency exceeding 91% (measured at 5 V/700 mA output). Battery protection features include overcurrent, overvoltage, and overtemperature protection.
Compared with a general-purpose MCU, the HT45F4M integrates complementary PWM outputs. The OUTL and OUTH complementary PWM timing controls NMOS and PMOS switching respectively, enabling synchronous boost operation. Evaluations of finished products based on this solution show performance consistent with manufacturer data. Compared with diode freewheel designs, synchronous boost reduces heating of power components under currents above 1 A, resulting in noticeably better thermal and overall performance.
