Data Center Software Series: Current/Voltage Monitor

The Data Center Software is Total Phase’s free bus monitoring software that allows users to interface with Total Phase protocol analyzers supporting I2C, SPI, USB, CAN, and eSPI protocols. These analyzers include the Beagle I2C/SPI Protocol Analyzer, the line of Beagle USB Protocol Analyzers, the USB Power Delivery Analyzer, the Komodo CAN Duo Interface, and the Promira Serial Platform with the eSPI Analysis Application.

What is the Current/Voltage Monitor?

The Current/Voltage Monitor within the Data Center Software offers a convenient way for users to correlate USB data traffic with power events, including monitoring and tracking USB VBUS current and voltage drawn from the bus by the target device. This feature is available for the Beagle USB 480 Power Protocol Analyzer – Standard and Ultimate Editions and the USB Power Delivery Analyzer.

Viewing the Current/Voltage Monitor

There are two ways to view the Current/Voltage Monitor:

  1. Click “View” in the top menu and then select “Current/Voltage Monitor”.
  2. Click the icon located at the top of the software.

Once the Current/Voltage is displayed, users can easily move the graph within the interface per the user’s preferences.

Current/Voltage Monitor with the Beagle USB 480 Power Protocol Analyzer

The Beagle USB 480 Power Protocol Analyzer captures and monitors USB 2.0 traffic in real time and has the ability to monitor current and voltage measurements on VBUS. The Current/Voltage Monitor provides a real-time visualization of the VBUS voltage and current measurements compared to the time lapsed of the data capture. The red trace displays the voltage measurement in volts (V) and the blue trace displays the current measurement in milliamps (mA).

In this example, we can see a sample capture from a mass storage device:

Current/Voltage Monitor Current/Voltage Monitor View of a sample capture from a mass storage device.

The Current/Voltage Monitor corresponds directly to the data captured in the Transaction Window. Users can use the plot cursor feature within the graph to click on a set of coordinates which will directly correlate that point with a specific data transaction. This also works vice versa; users can click on any data transaction in the window and locate this exact point in the graph. The vertical green dash marker within the graph corresponds to the selection in the Transaction Window. Having these capabilities allows users to easily pinpoint any irregularities in VBUS measurements and their sources.

Measurement Characteristics

For the Beagle USB 480 Power Protocol Analyzer - Standard and Ultimate Editions, the USB-A and USB-B capture inputs are rated for 1A continuous current and 0 to 24V. Although the analyzer can be configured to trigger on a current level from -3A to 3A, the continuous current should not exceed 1A. The voltage trigger level can be configured from 0 to 24V.

VBUS Trigger

The Beagle USB 480 Power Protocol Analyzer - Ultimate Edition also supports advanced triggering on VBUS current or voltage, allowing users to assert external outputs or trigger the capture when the specified threshold is matched. This threshold is specified on the Device Settings dialog:

VBUS Trigger Settings VBUS Trigger Settings

Only a single threshold, either voltage or current, is supported. The threshold can be included in any state of the Complex Matching state machine and each state can vary the edge(s) of the threshold it detects.

VBUS Event Trigger VBUS Trigger in the Event Configuration dialog

For a rising edge trigger, the specified threshold must be at or lower than the initial condition. If this is not the case, a multi-state trigger can be used. The first state is to set a falling edge trigger, followed by a rising edge trigger both at the desired threshold.

VBUS Complex Matching and Triggering states Complex Matching with VBUS Triggers

 

Current/Voltage Monitor with the USB Power Delivery Analyzer

The USB Power Delivery Analyzer provides insight into Power Delivery (PD) negotiations between USB Type-C sources and sinks. It can capture current and voltage on VBUS and VCONN, as well as the voltage of CC1 and CC2 lines. The Current/Voltage Monitor displays a real-time visualization of the current (mA) and voltage (V) measurements compared to the time elapsed in the data capture (m:ss). The red trace displays the VBUS voltage, the blue trace displays VBUS current, the orange and purple traces display VCONN voltage and current respectively, and the green trace displays CC1 voltage while brown trace displays CC2 voltage.

Like the Current/Voltage Monitor when used with the Beagle USB 480 Power Protocol Analyzer, the graph coordinates are directly correlated to the data transactions in the Transaction Window. Users can select a point on the graph to correlate to a specific data transaction or users can select a data transaction of interest and locate this point on the graph. The vertical green dash marker corresponds to the selection in the Transaction Window.

In this example, we can see a sample capture taken between an LG Type-C monitor and a Chromebook Pixel. The green dash shows the selection in the Transaction Window is the Accept before a PR_Swap.

Power Delivery Current/Voltage Monitor Current/Voltage Monitor View of a sample capture taken between an LG Type-C monitor and a Chromebook Pixel.

Measurement Characteristics

The USB Power Delivery Analyzer is rated for 3A continuous and up to 20V on VBUS.

A measurement is taken on each of the 6 channels, once approximately every 8 milliseconds, in a sequential (round-robin) fashion. The previous channel values are held in the graph until the next valid measurement.

Functions of the Current/Voltage Monitor View

The Current/Voltage Monitor View for both the Beagle USB 480 Power Protocol Analyzer and USB Power Delivery Analyzer offers multiple tools to assist with common operations:

  • Basic Navigation:Left mouse button pans and right mouse button zooms the view. Scroll Wheel zooms the time axis.
  • Individual Axis Pan and Zoom:The Shift Key and the Control Key (Command Key on the Mac) restrict pan and zoom operations to the current and voltage axis respectively. Alternatively, users can use the Set Pan/Zoom Axis tool for the same effect.
  • Scroll Scroll tool in Current/Voltage Monitor: When selected, the view will continuously scroll and track the latest current/voltage readings from the analyzer.
  • Export Export tool in Current/Voltage Monitor: Export to CSV. Current/voltage measurement data are also saved in binary .tdc files with File | Save.
  • Reset Zoom Reset Zoom Tool in Current/Voltage Monitor: Reset axes to their default ranges.
  • Show All Show All Tool in Current/Voltage Monitor: Rescale axes to display all the captured measurements.
  • Find Record Find Record Tool in Current/Voltage Monitor: Activate cursor for finding the record in the Transaction Window by clicking in the Current/Voltage Monitor View.
  • Set Pan/Zoom Axis Set Pan/Zoom Axis Tool in Current/Voltage Monitor: Restrict pan/zoom to the selected axis.
  • Transaction Window Selection Tracking: The Current/Voltage Monitor View renders a vertical green dash marker at the time point of the selected record in the Transaction Window. Note that unlike the Transaction Window, the Current/Voltage Monitor View only displays data from a single session. The Transaction Window thus serves as the primary interface for switching sessions in the Current/Voltage Monitor View.
  • Channel Enable/Disable:The bottom row of the Monitor shows all available channels. Clicking on a channel will toggle it between Enabled and Disabled. This is a convenient way to filter the display if you're only interested in a specific item.

Conclusion

The Current/Voltage Monitor in the Data Center Software provides insight into power measurements within your embedded system and its correlation to the captured USB/USB Power Delivery data. This graph helps users to easily visualize the fluctuations in current and voltage measurements and determine the origins of power-related bugs. For more information on this feature and the tools that support it, please email sales@totalphase.com.