Normal Operation

Transition Region

Low Dropout Mode

Dropout

reduce dropout

Forced

off-time

Forced

off-time

Regulation

Point

Extended

increased to

LM5088, LM5088-Q1

www.ti.com

SNVS600H – DECEMBER 2008 – REVISED MARCH 2013

Figure 18. Dropout Voltage Reduction using Dynamic Frequency Control

Frequency Dithering (LM5088-1 Only)

Electro-Magnetic Interference (EMI) emissions are fundamentally associated with switch-mode power supplies

due to sharp voltage transitions, diode reverse recovery currents and the ringing of parasitic L-C circuits. These

emissions will conduct back to the power source or radiate into the environment and potentially interfering with

nearby electronic systems. System designers typically use a combination of shielding, filtering and layout

techniques to reduce the EMI emissions sufficiently to satisfy EMI emission standards established by regulatory

bodies. In a typical fixed frequency switching converter, narrowband emissions typically peak at the switching

frequency with the successive harmonics having less energy. Dithering the oscillator frequency spreads the EMI

energy over a range of frequencies, thus reducing the peak levels. Dithering can also reduce the system cost by

reducing the size and quantity of EMI filtering components.

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