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.

I_{Q_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, I_Q, and either its FB pin for fixed versions or BIAS pin for adjustable versions, I_B. Since BIAS or FB is connected to the circuit’s output, the power consumed is converted from input power with an effective efficiency, η_eff, 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:

Equation 1.

where

• I_{Q_VIN} is the current consumed by the Buck converter utilizing the LM53600-Q1 or LM53601-Q1 while unloaded.
• I_Q is the current drawn by the LM53600-Q1 or LM53601-Q1 from its VIN terminal. See I_Q in section 7.6.
• I_EN is current drawn by the LM53600-Q1 or LM53601-Q1 from its EN terminal. Include this current if EN is connected to VIN. See I_EN in section 7.6. Note that this current drops to a very low value if connected to a voltage less than 5 V.
• I_B is bias/feedback current drawn by the LM53600-Q1 or LM53601-Q1 while the Buck converter utilizing it is unloaded. See I_B in section 7.6.
• I_div is the current drawn by the feedback voltage divider used to set output voltage for adjustable devices. This current is zero for fixed output voltage devices.
• η_eff is the light load efficiency of the Buck converter with I_{Q_VIN} removed from the Buck converter’s input current. 0.8 is a conservative value that can be used under normal operating conditions

Note that the EN pin consumes a few microamperes when tied to high; see I_EN. Add I_EN to I_Q as shown in the above equation if EN is tied to V_IN. 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.