A dual coil relay only require two low-side drivers if the center tap is connected to VM. The body diodes of the unused FETs act as freewheeling diodes, so additional freewheeling diodes are not needed when driving a dual-coil relay with the DRV8251. The PWM interface can be used to control the dual-coil relay. The following figures show the schematic and timing diagram for driving dual-coil relays.

Figure 9-11 Schematic of dual-coil relay driven by the OUTx H-bridge

Figure 9-12 Timing diagram for driving a dual-coil relay with PWM interface

Table 9-4 shows the logic table for the PWM interface. The descriptions in this table reflect how the input and output states drive the dual coil relay. When Coil1 is driven (OUT1 voltage is at GND), The voltage at OUT2 will go to VM. Because the center tap of the relay is also at VM, no current flows through Coil2. The same is true when Coil2 is driven; Coil1 shorts to VM. The body diodes of the high-side FETs act as freewheeling diodes, so extra external diodes are not needed. Figure 9-15 shows oscilloscope traces for this application.