Getting Started with UCC5880-Q1 Without SPI

 The UCC5880-Q1 device is an isolated, highly configurable adjustable slew rate gate driver. One element that makes UCC5880 very useful in high power EV/HEV applications is it’s SPI based device configurability, verification, and diagnostics.

Although the SPI communication provides a lot of flexibility for the system, some applications do not require the complexity of SPI. Customers who are not familiar with SPI may appreciate its benefits, but when getting started with this new driver, may want to do a simple evaluation without spending time and resources developing the software. The UCC5880-Q1 device can support this as it can be used without SPI communication for initial evaluation of the device

Using this functionality, the engineer can evaluate basic driver performance like drive strength, switching losses with power modules, adjustable gate drive, short circuit protection, etc. The user will be able to speed up the evaluation process since there is no requirement to develop any new code or even connect to a computer.

How to configure the SPI pins when not used?

Using the driver without SPI connection requires certain configurations to the SPI pin functions. Leaving input pins floating can cause faults from noise coupling into them. Output pins can be left floating. These changes are listed below.

Table 1: Pin Name and Configuration

How to change the Drive Strength without SPI?

The adjustable drive feature of UC5880-Q1 allows the drive strength to be set to 1 of 3 different drive strengths on the fly. The device has a split output structure: OUTH1, OUTH2, OUTL1, and OUTL2. OUTH1 and OUTL1 have a 15A drive strength, while OUTH2 and OUTL2 have a 5A drive strength. The Output structure is shown in the diagram below.

                                                                                        Figure 1: UCC5880-Q1 Output Structure

This is to control the turn on/off of the FET for different system conditions to optimize the tradeoff between switching energy loss and Drain to Source Overshoot. UCC5880-Q1 has 3 GDx pins (GD0, GD1, GD2) on the low voltage to enable use of this function without the need for SPI. Changing the gate drive strength without SPI is fairly simple. These combinations are listed below and also listed in the datasheet.

Table 2: GDx Pin Truth Table

What are the main challenges when not using SPI?

There are three main challenges when not using the SPI functionality. First is the reconfiguration of the device. SPI allows the user to configure the configuration registers and action register. When not using the SPI, the configurations and actions will be the default programmed values listed in the datasheet.

Second is the live monitoring ability of the device. The device has an internal 10-bit ADC and two analog inputs (AI1 and AI2) which are used to read and monitor useful measurements such as, DC-Link voltage, gate threshold, internal die temp, current sense, etc. The ADC also has DESAT(CS), VCC2, Gate voltage threshold and junction temperature measurement options. Without SPI, the user will have to implement other methods for all of these measurements.

Last but not least is the fault supervision. The UCC5880-Q1 device has 1 status and 2 fault registers with over 30 fault and warning Classifications. Additionally, there are also commanded BIST diagnostics available for the PWM Lane (INP to output), Shoot Through Protection, Gate Voltage Monitoring, Gate Drive Strength Monitoring, DESAT comparator, SC comparator, OC comparator, Clock Monitoring, Configuration CRC, and Digital Comparators. Without SPI it will be challenging to understand what fault has occurred in the system. When a fault occurs, either or both of the nFLT pins will pull low. Holding all the 3 GDx pins high will reset the fault, but there is no way to read exactly what fault has occurred. The best way to address this is to make the sure the default register settings exactly match the requirements of the application and then probe these points to make sure the device is operating as it should. The next section discusses commonly seen faults on our EVM when not using SPI and how to solve them.

What are the common Problems and Fixes?

As said previously, when using the UCC5880-Q1 device without SPI it will be challenging to diagnose the cause of any faults once the nFLT pins pull low. Below are some basic common issues that are easily diagnosable when using the device without the SPI fault reporting. The UCC5880-Q1 EVM provides the easiest solution to evaluate the device with and without SPI. Test points are provided for each signal to diagnose any faults.

Table 3: Common Problems and Fixes

What are the default Settings?

Since the device can only operate with the default configurations, it is important to understand if all the default settings align with the evaluation needs. The default settings are in table 4, 5 and 6. The default configurations are also located in the Datasheet under the Register map section.

Table 4: Configure Registers Default Values

Table 5: Action, Digicomp, ADC, STATUS & FAULT Registers Default Values

Table 6: Control Registers Default Values

Should I use the UCC5880-Q1 in my final design without SPI?

Although the non-SPI functionality of UCC5880-Q1 is a great tool to evaluate the gate driver, it is not recommended to be used for the final design. The fault reporting, monitoring and configurability options are too valuable to not be taken advantage of. The inability to diagnose faults will add many challenges to the system design and make it difficult to even enable the use of some basic safety functions of the final system.

The design of an SPI based software for gate driver control can be intimidating for new users, but TI has a solution to ease the complexity of creating this code with our Complex Device Driver (CDD). the goal of the CDD is to develop a modular, platform independent, configurable SPI interface [support different modes] in complying with the ASPICE process. The CDD is developed on the MCU AM26x platform, to handle SPI Interface, low voltage IO pins (FLT, PWM, Primary ASC, DOUT), diagnostics, FLT monitoring and to read ADC data. The CDD can be integrated to the customer’s different microcontroller AUTOSAR & non AUTOSAR stack using the integration guide and the CDD configuration files. More information can be found in the UCC5880-Q1 product folder.