Building A Portable Charger Without Expensive ASICs Or Bloated PMICs
One of the biggest improvements that can be made to the smartphone user experience is longer battery life. While users may browse on their phones for hours on end, size-limited, internal, non-removable batteries often come up short. Balancing long battery life with size, however, is a tricky problem to solve. As the battery industry struggles to provide higher energy density battery chemistries and technologies, many smartphone users have turned to portable chargers to support their highly active usage habits. This, in turn, creates a great opportunity for low cost, high-efficiency portable chargers.
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Portable chargers are relatively simple devices which comprise a few main components; most commonly Lithium Polymer (LiPo) batteries, a charging circuit, a power distribution switch, a power management IC (PMIC), and a DC-DC boost converter. There are PMIC solutions on the market today which can address these different functions, however many are expensive, power-hungry, and contain many more components and features than are needed for this simple application, leading to a less than ideal solution. Another option is to develop a custom ASIC, however this is only practical in very high volume and often at an exorbitant price, volume commitment, and risk of price hikes in the future.
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Enter Silego Technology's GreenPAK, a Configurable Mixed-signal IC (CMIC) with one-time programmable non-volatile memory (NVM). This incredibly small, flexible chip can be configured just like an ASIC, but allows designers to design and program prototypes in a matter of minutes vs. the weeks needed for true ASICs. It doesn't require a minimum volume commitment or NRE, either. Using Silego's GreenPAK SLG46620V, it is possible to implement a full featured, low-power, universal portable charger control circuit in just 2.0 x 3.0 mm."
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Many smartphone users have the need for prolonged battery life; "“ and employ the use of auxiliary power banks. They allow extended usage 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 get 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 batteries 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).
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Hardware design of portable charger power management circuit 
Figure 1 "“ Functional diagramÂ
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Figure 1 depicts the functional hardware design of an portable charger power management circuit. It is composed of the following segments:
"¢Â     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.Â
"¢Â     Power distribution switch (PDS): It is composed of MOSFETs that are controlled by the PMC unit.Â
"¢Â     LiPo battery "“ For this design, a single cell 3.7V 1000mAh battery is selected as the power bank unit.Â
"¢Â     LiPo charger "“ A controllable DC-DC buck converter design is used as a LiPo charger.
"¢Â     Boost DC-DC Converter "“ boost DC-DC converter is required to boost the LiPo battery
3.7V voltage to 5V required by the smartphone.Â
Power management control (PMC) unit design and implementation:
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.Â
Inputs to PMC are:
"¢Â     Charger present indicator (CHG_IN).
"¢Â     Device power consumption (CUR_SENSE) indicator. This indicator will be implemented using the current sensing method. In case smartphone is drawing current bellow the determined threshold, 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.
"¢Â     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.Â
Outputs from PMC are:
"¢Â     LiPo charger control (LiPO_CHG) "“ this output will send signal to the PDS to route power to the LiPo charger.
"¢Â     Smartphone power control (S_PWR) "“ this output will send signal to the PDS to route power from input to the smartphone.
"¢Â     Boost control (BOOST_CTRL) "“ this output will turn the boost converter on and send signal to the PDS to route power from the boost to the smartphone.
PMC is a digital logics 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 GreenPAK4.
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