The DRV8316 comes with an integrated buck that can support up to 200mA of current and can be used as a 3.3V or a 5V rail in a motor driver system. In some systems, however, the buck may not be needed. If this is the case with your system, how should you disable it? Do you still need to populate the components of the buck if the buck is not being used?
The buck is enabled by default. For the hardware variant (DRV8316T) the buck cannot be disabled, but for the SPI variant of the device (DRV8316R) the buck can be disabled over SPI by writing a 1 to the BUCK_DIS bit in the Control_6 register. Even though the buck can be disabled over SPI, the buck will be operational from the time the device is reset until the MCU disables the buck over SPI. As a result, it is still necessary to populate the buck components on your PCB even if the buck is not being used.
The buck of the DRV8316 can be operated in 2 different modes: inductor mode an resistor mode. Inductor mode is used to support higher buck currents of 40mA or greater, and resistor mode can be used when the buck current is below 40mA. If the buck is not being used in your system then selecting components for resistor mode will allow you to avoid having to place an inductor on your PCB. The image below shows a block diagram of the buck as well as the components needed for operating the buck in resistor mode (see section 8.3.4.2 of the datasheet). RBK is a 22 ohm resistor and CBK is a 22uF 6.3V rated capacitor.
In order to reduce the area and cost of the buck components, you can chose a small package size such as 0603 or 0402 for the 22 ohm RBK resistor and the 22uF CBK capacitor. This can be done because the buck will not need to support any external load current during the period of time when it is on.
