The LMR3650x is designed
to have very low input supply current when regulating light loads. This low input
supply current is achieved by powering much of the internal circuitry from the
output. When configured as a fixed output voltage, the VOUT/FB pin 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 3.
where
- IQ_VIN is the total standby (switching) current consumed by the operating (switching) buck converter when unloaded.
- IQ is the current drawn from the
VIN terminal. Check IQ_13p5_Fixed or
IQ_24p0_Fixed in Electrical Characteristics for IQ.
- IEN is current drawn by the EN
terminal. Include this current if EN is connected to VIN. Check
ILKG-EN in Electrical Characteristics for IEN.
- IBIAS is bias current drawn by the
BIAS LDO. Check IB_13p5 or IB_24p0 in Electrical Characteristics for IBIAS.
- 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 System Characteristics.