“Automotive power seats continue to provide greater comfort and convenience. To drive its motor, though, there are some design challenges to address. Multi-channel gate drivers can help solve these challenges by integrating multiple channels into a single chip and providing features such as diagnostics and current-sense amplifiers. The DRV8718-Q1 multi-channel gate driver provides a flexible, compact solution for implementing the latest features in automotive seating.
Unless you’ve ever experienced a spaceship, a car power seat is probably the most complicated seat you’ll ever experience. It has more adjustment options than an airplane seat and is more comfortable than a dental office chair. C car power seats provide luxurious comfort, convenience and safety.
Whether you’re moving the seat up and down, fore and aft, or adjusting the lumbar support, the motor makes it easy. In addition to the advantage of being easy to move, powerful car power seats have other advantages. For example, in-seat features such as fans and heaters can even increase the vehicle’s range by reducing the electrical load on the entire temperature system in the vehicle.
Power Seat Design Trends
Given the multiple options for automotive power seats, manufacturers are looking for ways to drive multiple motors. Designers used to use relays to switch motor power, but relays consisted of multiple tiny mechanical parts with limited rotational speed capabilities. Due to these drawbacks and the fact that relays emit noise each time they switch, they are not suitable for pulse width modulation (PWM) to control motor speed.
Given the various advantages of integrated circuits (ICs), including smaller size, quiet operation, speed control, and reliability, there is now a trend toward replacing electromechanical relays with ICs. With the IC’s fast, quiet switching, PWM can be used for speed control, enabling smooth and synchronized operation of multiple motors.
Relay-driven seats are usually one relay driving only one motor, and the original IC design also followed this pattern. In systems with only a few motors, this complexity is an acceptable drawback. But in a fully functional and complex car seat system, the way the drive circuits for multiple motors are combined can provide significant benefits. This includes a reduced bill of materials and reduced board space through the use of a multi-axis integrated drive design approach.
Multi-Channel Gate Driver Solutions
TI offers multi-motor automotive gate drivers designed for power seats. The half-bridge gate drivers of the DRV8714-Q1 and DRV8718-Q1 have four and eight channels, respectively. They integrate charge pumps, current-sense amplifiers, and logic for multiple loads. A single IC can control up to seven different motors or a combination of motors and heaters, reducing the number of components required for seat modules.
Figure 1 shows the DRV8714-Q1 controlling three motors through a shared half-bridge drive, which can operate any of them individually or in specific combinations simultaneously. You can select the metal-oxide-semiconductor field-effect transistor (MOSFET) that best suits the motor characteristics and adjust the DRV8714-Q1’s registers to optimize performance.
Figure 1: Three-motor seat driven by the DRV8714-Q1 automotive gate driver
With up to eight half-bridge driver channels, the DRV8718-Q1 has the flexibility to use the right number of MOSFETs to drive bidirectional motors, unidirectional motors such as fans, and non-motor loads such as heaters; where each MOSFET is dedicated to Tailored for specific loads.
Figure 2 shows the DRV8718-Q1 controlling four seat motors, a fan, and a heater. The fan (unidirectional rotation) requires only one half-bridge, and the heater requires only one high-side MOSFET, allowing the design to reduce the number of external transistors C, all thanks to the flexibility of the multi-channel gate driver.
Figure 2: DRV8718-Q1 automotive gate driver driving multiple motors, a heater, and a fan
Low drain-source on-resistance MOSFETs can be used to improve thermal performance in high-current applications due to the flexibility to choose each external MOSFET that best suits the respective load. The DRV8718-Q1 series controls the switching slew rate by adjusting the gate current, which is beneficial to improve electromagnetic compatibility. You can also adapt the seat module to various motors by changing the MOSFETs without changing the overall design.
Another advantage of a single chip is that it can significantly reduce the number of signals sent to the microcontroller (MCU). The MCU uses only four pins (using the serial peripheral interface [SPI]), up to eight half-bridges can be controlled from a single DRV8718-Q1, or even more channels in a daisy-chain configuration, as shown in Figure 3. This control includes parameter setting of each half-bridge, independent or coordinated control of the transistors, and diagnostic monitoring.
Figure 3: Controlling 16 half-bridges using a daisy-chain configuration from the MCU to the DRV8718-Q1 automotive gate driver
Unified control reduces the workload of the MCU. With just one command, the MCU can enable all drives; with a single register read, the MCU can tell if any motors are faulty. Subsequent SPI reads can determine the failed channel and details if needed.
Automotive power seats continue to provide greater comfort and convenience. To drive its motor, though, there are some design challenges to address. Multi-channel gate drivers can help solve these challenges by integrating multiple channels into a single chip and providing features such as diagnostics and current-sense amplifiers. The DRV8718-Q1 multi-channel gate driver provides a flexible, compact solution for implementing the latest features in automotive seating.