The mobile power supply seems to be very simple, consisting of a single-cell lithium battery, a boost converter (with different battery voltages, and a 5V stable voltage at the output) and a USB port for charging a portable device. Looking closely at a typical mobile power supply, you may find that there are many other subsystems: light-emitting diodes (LEDs) that display battery state, devices that communicate with portable devices on D+/D- lines, or overheating Fault protection mechanism for flow detection. The entire system quickly became complex and many different integrated circuits (ICs) had to work together.
The TI Reference Design for Output Current Sensing and Limiting and Plug-In Detection in Mobile Power (PMP9776) explains how a complete mobile power solution works with all components working together. Figure 1 is a block diagram, and Figure 2 shows a shape factor optimized printed circuit board (PCB). Let's take a look at the various aspects of this reference design in its test report.
Figure 1 : PMP9776 TI Design Mobile Power Block Diagram 
Figure 2: The complete PMP9776 TI Design solution is very small and easily matches the form factor of a mobile power supply
The heart of the mobile power supply is the boost converter, which converts the battery voltage to 5V for portable devices. The reference design uses a highly integrated TPS61236 synchronous boost converter to deliver up to 2.4A to portable devices with over 95% power. This high power ensures that the portable device can receive almost all of the stored electrical energy and minimize the corresponding temperature rise of the mobile power source (due to the power loss of the conversion). The 2.5mm & TImes; 2.5mm integrated circuit achieves a smaller overall form factor, allowing the use of larger capacity batteries. Finally, the TPS61236 also has a constant current (CC) output function, which is especially useful in mobile power sources where the load is trying to draw too much current. The constant current output function keeps operating under safe current conditions and prevents overheating caused by other current limiting measures.
Managing the activity of the mobile power subsystem is critical to maintaining the energy level of the battery, avoiding wasting it on internal functions. The reference design includes an MSP430TM microcontroller (MCU) that acts as a housekeeping MCU to optimize the power consumption of the mobile power supply. When the MCU detects a low load, it shuts down most of the subsystems; in standby mode, the mobile power only consumes 22 mA. To prevent high discharge current from the battery, the MCU will adjust the current limit. When the load current changes, the MCU also makes small adjustments to the output voltage to provide a well-regulated output. Finally, the MCU measures battery voltage and temperature through its integrated analog-to-digital converter (ADC). The MCU then drives the LEDs to display the battery voltage and monitor the temperature to keep the mobile power supply in a safe operating range.
The TPS2514A USB Charging Port Controller works with a wide range of USB charging protocols to mediate D + / D- lines on portable devices to properly detect and charge devices. It is packaged in a small transistor (SOT)-23, which makes the integrated circuit simple and inexpensive, and can accomplish this important task.
In this way, an integrated and complete mobile power supply design can be realized to meet your various needs. Check out the test report for more details, waveforms, and explanations.
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