The TPSM8A28 and TPSM8A29 devices can be configured to split-rail by using an independent power supply that applies a valid bias on to VCC pin. Connecting a valid VCC bias to the VCC pin overrides the internal LDO, thus saves power loss on that linear regulator and helps to improve overall system level efficiency. 5.0-V rail is the common choice as VCC bias. With a stable VCC bias, the VIN input range under this configuration can be as low as 2.7 V and up to 16 V for both TPSM8A28 and TPSM8A29.

Figure 7-6 shows an example for this split rail configuration.

The VCC external bias current during nominal operation varies with the bias voltage level and also the operating frequency. For example, by setting the device to Skip mode, the VCC pins decreases current draw from the external bias when the frequency decreases under light-load condition. The typical VCC external bias current under FCCM operation is listed in the Electrical Characteristics table to help the user prepare the capacity of the external bias.

Under split rail configuration, VIN, VCC bias, and EN are the signals to enable the part. For start-up sequence, it is recommended that at least one of VIN UVLO rising threshold and EN rising threshold is satisfied later than VCC UVLO rising threshold. A practical start-up sequence example is: VIN applied first, then the external bias applied, and then EN signal goes high.