SLVAFO4 Application note

SLVAFO4 august 2023 TPS61299

2.3 Bypass (TPS61291)

In bypass mode, a separated P-MOS (bypass switch) between the Vin and Vout pins is integrated as Figure 2-5 shows. When the device is disabled (EN=LOW), bypass mode is activated to provide a direct, low impedance connection from the input voltage to output.

Figure 2-5 Bypass During Shutdown

Compared to body diode pass operation and force pass through operation, there is less voltage drop and power loss because the inductor is not in the connecting path. Higher efficiency is obtained when the device shuts down; therefore, the bypass mode is suitable for large current and power loss sensitive applications.

Equation 5.

V_{O U T} = V_{I N} - I_{O U T} \times R_{d s (o n)}

Equation 6.

P_{l o s s} = I_{O U T}^{2} \times R_{d s (o n)}

The TPS61291 integrates bypass mode. Figure 2-6 is the shutdown waveform of TPS61291 (EN is low). The output voltage is discharged to Vin level and there is almost no voltage drop. During shutdown, there is no inductor current across the inductor and high side MOSFET.

Figure 2-6 TPS61291 Shutdown Waveforms