The DRV81008-Q1 is supplied by two supply voltages:

• V_M (analog supply voltage used also for the logic)

• V_DD (digital supply voltage)

The V_M supply line is connected to a battery feed and used, in combination with V_DD supply, for the driving circuitry of the power stages. In situations where V_M voltage drops below V_DD voltage (for example during cranking events down to 3 V), an increased current consumption may be observed at VDD pin. V_M and V_DD supply voltages have an undervoltage detection circuit.

• An undervoltage on both V_M and V_DD supply voltages prevents the activation of the power stages and any SPI communication (the SPI registers are reset)

• An undervoltage on V_DD supply prevents any SPI communication. SPI read/write registers are reset to default values.

• An undervoltage on V_M supply forces the DRV81008-Q1 to drain all needed current for the low-side switches and for the logic from V_DD supply.

Figure 7-3 shows a basic concept drawing of the interaction between supply pins V_M and V_DD, the output stage drivers and SDO supply line.

Figure 7-3 Internal Power Supply Architecture

When 3 V ≤ V_M ≤ V_DD - V_MDIFF, DRV81008-Q1 operates in Cranking Operative Range (COR). In this condition, the current consumption from VDD pin increases while it decreases from VM pin. Total current consumption remains within the specified limits.

Figure 7-4 shows the voltage levels at VM pin where the device goes in and out of COR. During the transition to and from COR, I_VM and I_VDD change between values defined for normal operation and for COR operation. The sum of both current remains within limits specified in Section 6.5.

Figure 7-4 Cranking Operative Range

When V_{M_UVLO} ≤ V_M ≤ V_{M_OP}, it may be not possible to switch ON a channel that was previously OFF. All channels that are already ON keep their state unless they are switched OFF via SPI or via IN pins. An overview of channel behavior according to different V_M and V_DD supply voltages is shown in Table 7-2, Table 7-3 and Table 7-4 (the tables are valid after a successful power-up).