The device 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 VOUT / VIN.
Equation 2.
where
- IQVIN is the total standby (switching)
current consumed by the operating (switching) buck converter when
unloaded.
- IQ is the current drawn from the
VIN terminal.
- IEN is current drawn by the EN
terminal. Include this current if EN is connected to VIN. Check
ILKG-EN in the Electrical Characteristics for IEN.
- IBIAS is bias current drawn by the
BIAS LDO.
- ηeff is the light-load efficiency of
the buck converter with IQ_VIN removed from the input current of
the buck converter. ηeff = 0.8 is a conservative value that can
be used under normal operating conditions. This can be traced back as the
ISUPPLY in the System Characteristics.