Introduction

Many smartphone users have the need for prolonged battery life and employ the use of auxiliary power banks. These allow extended use of their smartphones by up to 6 times (depending on the capacity of the power bank). Power banks are usually mounted on back of the smartphone and they are connected via a charging connector (lightning or USB). For enhanced user experience, they are allowed to be charged using the same smartphone charger and the user doesn’t have to worry about charging it separately. Circuit design of these devices include LiPo battery power bank, charging circuit for the power bank, the power distribution switch, power management control and the DC-DC boost converter (used to provide the phone with the required voltage (5V).

Figure 1 depicts the functional hardware design of an auxiliary smartphone battery power management circuit. It is composed of the following segments:

Figure 1. Functional diagram

• Power management control (PMC) unit – this is the main logic unit of the device. It decides whether to route power to the smartphone or to the additional power bank. It decides when to turn the boost DC-DC converter on, in order to stop the internal battery power to smartphone.
• Power distribution switch (PDS): It is composed of MOSFETs that are controlled by the PMC unit.
• LiPo battery – For this design, a single cell 3.7V 1000mAh battery is selected as the power bank unit.
• LiPo charger – A controllable DC-DC buck converter design is used as a LiPo charger.
• Boost DC-DC Converter – boost DC-DC converter is required to boost the LiPo battery 3.7V voltage to 5V required by the smartphone.

The complete design file created in the GreenPAK Designer software, can be found here.

1. Power management control (PMC) unit design and implementation

The power management control (PMC) unit uses inputs from the rest of the device to make power routing decisions. PMC controls the PDS and the DC-DC boost converter.

Inputs to PMC are:

• Charger present indicator (CHG_IN).
• Device power consumption (CUR_SENSE) indicator. This indicator will be implemented using the current sensing method. In case the smartphone is drawing current below the determined threshold, the PMC will route power from the input to LiPo charger as well, so that the power bank can be charged. If the current is above the determined threshold, power from the input will be routed to the smartphone only.
• Power bank voltage indicator (VBAT). This indicator is used so that PMC can determine whether to turn the DC-DC boost converter on (to step up voltage from the power bank and provide it to smartphone) or not.

Outputs from PMC are:

• LiPo charger control (LiPO_CHG) – this output will send signal to the PDS to route power to the LiPo charger.
• Smartphone power control (S_PWR) – this output will send signal to the PDS to route power from input to the smartphone.
• Boost control (BOOST_CTRL) – this output will turn the boost converter on and send a signal to the PDS to route power from the boost to the smartphone.

PMC is a digital logic circuit with 3 inputs and 3 outputs. This can be easily implemented using LUT tables. Three 3-bit LUT tables are used for implementation of PMC using GreenPAK™ IC.

Figure 2 shows the functional table for the PMC input and outputs.

Figure 2. LUT Tables

Each output is implemented using one 3bit GreenPAK LUT unit. Inputs from the pins are routed to each LUT table.

Figure 3 explains the implementation of the PMC using GreenPAK.

Figure 3. LUT tables implementation using GreenPAK

2. Power distribution switch design and implementation

The power distribution switch is controlled by the PMC outputs LIPO_CHG, S_PWR, BOOST_CTRL.

Figure 4 depicts block schematics of the PDS. Control signals are provided by the PMC. PDS provides sensor signals...