Power banks can be indispensable on a long flight or during a long meeting if you need to recharge your smartphone’s or tablet’s battery. Having previously charged up your power bank, you efficiently transfer its energy to your portable device to achieve a longer runtime. In order to give your device sufficient energy, the power bank should have a high-capacity battery – on an order of magnitude of your device’s battery. It should also keep nonbattery circuitry to a minimum so that its size is not much bigger than your phone. Finally, the power bank’s efficiency must be very high (over 95%) in order to not waste energy during power transfer and to not get too hot for the user.
Figure 1 shows a typical power-bank power scheme. Since the power source is almost always a single-cell lithium battery and the output voltage is almost always a 5V USB port, the power bank will also need:
- A boost converter to convert the power bank’s battery voltage to USB port levels.
- A load switch to limit the output current to the USB port during faults.
- A detection circuit to notify the system if something is connected to the output USB port.
Figure 1: Typical power-bank power architecture
The TPS61088 is a traditional boost converter that can deliver the 5V output at currents above 5A for very-high-power power banks. As opposed to most other boost converters operating at that power level, the TPS61088 incorporates both power MOSFETs to reduce the total solution size required by half, while still delivering 95% efficiency.
The load switch and detection circuit are extra circuits that will take up space and add losses to the system. Building them into the boost converter, however, reduces both solution size and power loss. Reduced power loss means a lower temperature rise, making higher power densities possible.
Figure 2 shows a power-bank solution using the TPS61235/6 boost converter. The TPS61235/6 has a constant output-current function and output-current monitor pin to fulfill the protection and detection needs in power-bank systems. Incorporating these two functions and using a much smaller 2.5mm-by-2.5mm package allows a maximum output power of 5V at 3A and 95% efficiency.
Figure 2: New power-bank power architecture with the TPS61235/6
What can you do with smaller solution sizes and higher output powers in your power-bank designs?
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