The MAXM17537 has two internal low-dropout (LDO) regulators that power VCC. During power-up, when the EN/UVLO pin voltage is above the true shutdown voltage (0.8V), then the VCC is powered from INLDO. When VCC voltage is above the VCC UVLO threshold and EXTVCC voltage is greater than 4.7V (typ), the VCC is powered from EXTVCC LDO. Only one of the two LDOs is in operation at a time depending on the voltage level present at EXTVCC. Powering VCC from EXTVCC increases efficiency at higher input voltages. EXTVCC voltage should not exceed 24V