The EN pin has an internal pullup current source that provides the default condition of the TPS54332 operating when the EN pin floats.

The TPS54332 is disabled when the VIN pin voltage falls below internal VIN UVLO threshold. TI recommends using an external VIN UVLO to add Hysteresis unless VIN is greater than (V_OUT + 2 V). To adjust the VIN UVLO with Hysteresis, use the external circuitry connected to the EN pin as shown in Figure 7-1. After the EN pin voltage exceeds 1.25 V, an additional 3 μA of hysteresis is added. Use Equation 1 and Equation 2 to calculate the resistor values needed for the desired VIN UVLO threshold voltages. The V_START is the input start threshold voltage, the V_STOP is the input stop threshold voltage and the V_EN is the enable threshold voltage of 1.25 V. The V_STOP must always be greater than 3.5 V.

Equation 1. $\mathrm{R}\mathrm{e}\mathrm{n}1=\frac{{\mathrm{V}}_{\mathrm{S}\mathrm{T}\mathrm{A}\mathrm{R}\mathrm{T}}-{\mathrm{V}}_{\mathrm{S}\mathrm{T}\mathrm{O}\mathrm{P}}}{3\mathrm{\mu }\mathrm{A}}$

Equation 2. $\mathrm{R}\mathrm{e}\mathrm{n}2=\frac{{\mathrm{V}}_{\mathrm{E}\mathrm{N}}}{\frac{{\mathrm{V}}_{\mathrm{S}\mathrm{T}\mathrm{A}\mathrm{R}\mathrm{T}}-{\mathrm{V}}_{\mathrm{E}\mathrm{N}}}{\mathrm{R}\mathrm{e}\mathrm{n}1}+1\mathrm{\mu }\mathrm{A}}$

Figure 7-1 Adjustable Input Undervoltage Lockout