If SYNC/MODE is held low for a period greater than a few microseconds, the LM53600-Q1 and LM53601-Q1 devices will enable automatic power saving light load operation and diode emulation. In this mode, if peak current needed to regulate output voltage drops below a selected value, the clock of the LM53600-Q1 or LM53601-Q1 device slows to maintain regulation. The gain of this clock slowing circuit is low to maintain stability. Output voltage with no load is approximately 1% higher than with a load high enough to allow full frequency operation.
IQ_VIN is the current consumed by a converter utilizing a LM53600-Q1 or LM53601-Q1 device while regulating without a load. While operating without a load, the LM53600-Q1 or LM53601-Q1 is only powering itself. The LM53600-Q1 and LM53601-Q1 device draws power from two sources, its VIN pin, IQ, and either its FB pin for fixed versions or BIAS pin for adjustable versions, IB. Since BIAS or FB is connected to the circuit’s output, the power consumed is converted from input power with an effective efficiency, ηeff, of ~80%. Here, effective efficiency is the added input power needed when lightly loading the converter of the LM53600-Q1 and LM53601-Q1 devices is divided by the corresponding additional load. This allows unloaded current to be calculated as follows:
Note that the EN pin consumes a few microamperes when tied to high; see IEN. Add IEN to IQ as shown in the above equation if EN is tied to VIN. If EN is tied to a voltage less than 5 V, virtually no current is consumed allowing EN to be used as a UVL once a voltage divider is added.