A First Look At The MAX77976 Evaluation KitFollow article
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The MAX77976 Evaluation Kit is the latest hardware offering from Maxim Integrated that has been designed to demonstrate the combined capability of single-cell lithium-ion battery management with intelligent USB-C power delivery. The board itself is divided between two ICs with a predominant focus around the MAX77976 battery charging capabilities which complements the MAX77958 USB-C power delivery controller and effectively illustrates the efficiency of the Maxim development environment.
In this article, we will focus a lot on the software to explore the features of the evaluation kit which include the individual functions of the MAX77958 USB-C power delivery controller and the MAX77976 battery charger.
- MAX77976 Evaluation Kit
- Single Cell Lithium-Ion Battery
- T3DSO1104 Digital Storage Oscilloscope
- USB-C Wall adaptor
- Micro-USB cable
MAX77958 Key Features
The MAX77958 is a standalone USB Type-C and power delivery controller that features comprehensive port monitoring and connection provisioning capabilities. The device complies with a range of new and legacy USB protocols that allows it the flexibility to function as both a host and peripheral device.
The device fully supports upstream (UFP) and downstream facing ports (DFP), with bidirectional power delivery and current capacity detection available upon connection. The additional interrupts and status registers enable external monitoring from a standalone MCU but the device can also function as an independent I2C master when connected to matching hardware such as the charge controller.
Maxim has incorporated an impressive range of combined USB power and data functions into the MAX77958 giving it the flexibility to serve as an excellent interface for many USB-C applications.
MAX77976 Key Features
At its core, the MAX77976 is a high-efficiency switch-mode battery charger optimised for single-cell lithium-ion batteries. It features an input voltage range of 3.8v to 19v and fast charging currents of up to 5.5A. The device can automatically adapt its charging characteristics based on battery voltage and size using differential sensing, smart power selection and a high-efficiency buck converter.
The MAX77976 also supports the use of external hardware through a selection of interrupts and status registers that can be accessed through the I2C interface. The additional configuration registers allow the user to set limits on voltage and current while controlling any top-level operating parameters including clock frequency and low-power mode.
The device can also be configured as a reverse boost converter which allows it to power any external equipment with output voltages up to 12v using a single lithium cell. Maxim has really streamlined the design of lithium power systems with this feature, which negates the need for complex multicell battery systems.
Testing and Observations
At a first glance, we can clearly see the MAX77976 Evaluation Kit is intuitively organised into its defining functions on the board, with plenty of space and testing points allocated for an oscilloscope. The Maxim hardware is set up to seamlessly deliver power between the USB-C controller and the battery charger with both devices working together as a potent power solution with a high degree of flexibility.
Connecting USB cables to the board
To evaluate the performance of the kit we first need to establish our testing setup by connecting the battery and USB cables to the board. We can plug the USB-C port into a wall adapter while connecting the USB-micro to our computer, making sure the switch is in the right-hand position. We can then use the GUI provided by Maxim to test any parameters and measure the results using an oscilloscope.
Connect to the board to view the MAX77958 USB-C controller interrupts
We can connect to the kit easily by opening the Maxim GUI and clicking connect in the device menu at the top of the window. The first thing to notice when successfully connected is the interrupts tab that displays a list of event flags triggered on the USB-C port. These events are categorised by type and include changes to connection status and power delivery which is denoted by the circular indicators next to each interrupt.
Viewing the MAX77958 USB-C controller status tab
The status tab helps contextualise these events and delivers a lot more detail about any changes to the user. The USB-C port is being powered by a wall adaptor therefore, we can observe the port operating in sink mode with an input voltage between 4.5 and 5.5. We can also see the orientation of the connector, its data role and a detected 3000mA current capacity, which are all accurately reported.
Viewing the MAX77976 charger interrupts and status flags
The interrupt tab of the battery charger is predictably very similar in appearance to the USB-C tab where we can clearly observe the interrupts and event flags of the device. The battery interrupt is illuminated and the status indicator is zero as we have yet to connect it to the board. These flags will clear when we connect the BATTP and BATTN connection points to the battery terminals.
Evaluation board connected to the battery
Connecting the battery should then update the status flag.
Viewing the MAX77976 charger details tab
With the battery now connected we can check the new status code using the details tab which determines the status as OK. We can also observe the supply voltage from the USB-C port is valid and ready to start charging the battery. However, note the charger is listed as off in the charger details register, which we can change using the configuration registers.
Turn on the battery charger
Attach the oscilloscope probes
Measure the MAX77958 USB-C and MAX77976 charger oscilloscope traces
We can find the smart power selector in the first configuration tab which will allow us to active and modify the operation of the battery charger. The device operates as a buck converter while charging the battery over USB, which can be activated alongside the charger by using the provided drop-down menu. We can then measure the charger converting the 5v USB input to the appropriate charging voltage output.
Note how we can also configure the device as a reverse boost converter to power the USB port from the battery instead.
Viewing the MAX77976 third configuration tab
We can set the current limits of the buck charger and reverse boost converter using the third configuration tab while using the radio button to change the switching frequency of the converter if required.
Viewing the MAX77976 fourth configuration tab
The final configuration tab allows us to set the target voltage of the reverse boost converter when activated. To do this, we need to enable it in OTG mode using the drop-down menu in the first configuration tab. We can then pick the desired voltage using the slider and measure the output using the oscilloscope.
Viewing the MAX77976 reverse boost output and battery input oscilloscope traces
Finally, we can observe the battery charger operating in reverse boost mode which converts the power accumulated by our single-cell lithium battery back into a range of useable voltages. We can now use this operating mode to either power the USB-C port directly as an upstream host or even run 12v industrial or automotive applications using a single lithium cell!
The MAX77976 Evaluation Kit is an impressive platform that demonstrates the combined capability of single-cell lithium-ion battery management with intelligent USB Type-C power delivery. Its capacity to provide bidirectional data and power effectively demonstrates the performance and flexibility of the Maxim hardware range while the intuitive workflow and software GUI significantly streamlines the design process. The MAX77976 device in particular has demonstrated its potential for a broad range of applications and I am keen to see its future use cases in areas of IoT, renewable energy and automotive technologies.