The LMR436x0 is designed to have very low input supply current when regulating light loads. This is achieved by powering much of the internal circuitry from the output. The VOUT/FB pin in the fixed-output voltage variants is the input to the LDO that powers the majority of the control circuits. By connecting the VOUT/FB input pin to the output node of the regulator, a small amount of current is drawn from the output. This current is reduced at the input by the ratio of V_OUT / V_IN as described in Equation 2.

where

• I_QVIN is the total standby (switching) current consumed by the operating (switching) buck converter when unloaded.
• I_Q is the current drawn from the V_IN terminal.
• I_EN is current drawn by the EN terminal. Include this current if EN is connected to VIN. Check I_LKG-EN in Electrical Characteristics for I_EN.
• I_BIAS is bias current drawn by the BIAS LDO.
• η_eff is the light-load efficiency of the buck converter with I_QVIN removed from the input current of the buck converter. η_eff = 0.8 is a conservative value that can be used under normal operating conditions.