The TPS25772-Q1 has a fixed V_IN(UVLO) with rising and falling thresholds between 5 and 5.5 V, refer to Buck-Boost Regulator for exact values. The falling threshold, V_{IN(UVLO_F)}, disables the device when the battery voltage is too low for continued operation. To establish a turn on voltage higher than V_{IN(UVLO_R)}, connect a resistor divider from the IN supply voltage to the EN/UVLO pin. When V_EN/UVLO > V_EN(OPER), nominally 1.25 V, the device exits low power shutdown and begins to startup.

In this example a V_IN turn on voltage of approximately 6.5 V is required. Use the equations and examples below to determine the required resistor values.

• Choose standard value R_ENB = 22 kΩ.
• Calculate R_ENT
  Equation 3. ${\mathrm{R}}_{\mathrm{E}\mathrm{N}\mathrm{T}}=\left(\frac{{\mathrm{V}}_{\mathrm{O}\mathrm{N}}}{{\mathrm{V}}_{\mathrm{E}\mathrm{N}\left(\mathrm{O}\mathrm{P}\mathrm{E}\mathrm{R}\right)}}-1\right)\times {\mathrm{R}}_{\mathrm{E}\mathrm{N}\mathrm{B}}$
  Equation 4. ${\mathrm{R}}_{\mathrm{E}\mathrm{N}\mathrm{T}}=\left(\frac{6.5\mathrm{ }\mathrm{V}}{1.25\mathrm{ }\mathrm{V}}-1\right)\times 22\mathrm{ }\mathrm{k}\mathrm{\Omega }=92.4\mathrm{ }\mathrm{k}\mathrm{\Omega }$

• Select a standard value of 91 kΩ.
• Using 22 kΩ and 91 kΩ. Rearranging Equation 3 results in
  Equation 5. ${\mathrm{V}}_{\mathrm{O}\mathrm{N}}=\left(\frac{{\mathrm{R}}_{\mathrm{E}\mathrm{N}\mathrm{T}}}{{\mathrm{R}}_{\mathrm{E}\mathrm{N}\mathrm{B}}}+1\right)\times {\mathrm{V}}_{\mathrm{E}\mathrm{N}\left(\mathrm{O}\mathrm{P}\mathrm{E}\mathrm{R}\right)}$
  Equation 6. ${\mathrm{V}}_{\mathrm{O}\mathrm{N}}=\left(\frac{91\mathrm{ }\mathrm{k}\mathrm{\Omega }}{22\mathrm{ }\mathrm{k}\mathrm{\Omega }}+1\right)\times 1.25\mathrm{ }\mathrm{V}=6.42\mathrm{ }\mathrm{V}$
• Calculate V_OFF
  Equation 7. ${\mathrm{V}}_{\mathrm{O}\mathrm{F}\mathrm{F}}=\left(1-\frac{{\mathrm{V}}_{\mathrm{E}\mathrm{N}\left(\mathrm{H}\mathrm{Y}\mathrm{S}\right)}}{{\mathrm{V}}_{\mathrm{E}\mathrm{N}\left(\mathrm{O}\mathrm{P}\mathrm{E}\mathrm{R}\right)}}\right)\times {\mathrm{V}}_{\mathrm{O}\mathrm{N}}$
  Equation 8. ${\mathrm{V}}_{\mathrm{O}\mathrm{F}\mathrm{F}}=\left(1-\frac{0.1\mathrm{ }\mathrm{V}}{1.25\mathrm{ }\mathrm{V}}\right)\times 6.42\mathrm{ }\mathrm{V}=5.91\mathrm{ }\mathrm{V}$
• Lastly, confirm the selected resistors do not trigger the EN/UVLO pin MAX clamp voltage. Assuming 36 V as a maximum V_IN transient.
  Equation 9. ${\mathrm{V}}_{\mathrm{E}\mathrm{N}/\mathrm{U}\mathrm{V}\mathrm{L}\mathrm{O}\left(\mathrm{M}\mathrm{A}\mathrm{X}\right)}=\left(\frac{{\mathrm{V}}_{\mathrm{I}\mathrm{N}\left(\mathrm{M}\mathrm{A}\mathrm{X}\right)}\times {\mathrm{R}}_{\mathrm{E}\mathrm{N}\mathrm{B}}}{{\mathrm{R}}_{\mathrm{E}\mathrm{N}\mathrm{T}}+{\mathrm{R}}_{\mathrm{E}\mathrm{N}\mathrm{B}}}\right)$
  Equation 10. ${\mathrm{V}}_{\mathrm{E}\mathrm{N}/\mathrm{U}\mathrm{V}\mathrm{L}\mathrm{O}\left(\mathrm{M}\mathrm{A}\mathrm{X}\right)}=\left(\frac{36\mathrm{ }\mathrm{V}\times 22\mathrm{ }\mathrm{k}\mathrm{\Omega }}{22\mathrm{ }\mathrm{k}\mathrm{\Omega }+91\mathrm{ }\mathrm{k}\mathrm{\Omega }}\right)=7\mathrm{ }\mathrm{V}$

• The result, 7 V, is less than the EN/UVLO pin maximum clamp voltage.