PM6680ATR datasheet(22/48 Pages) STMICROELECTRONICS

Part #	PM6680ATR

Description	Dual synchronous step-down controller with adjustable output voltages plus LDO

PDF	48 Pages

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Manufacturer	STMICROELECTRONICS [STMicroelectronics]

Direct Link	http://www.st.com

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22 / 48 page

Device description

PM6680A

22/48

7.4

Pulse skip mode

If the SKIP pin is tied to ground, the device works in skip mode.

At light loads a zero-crossing comparator truncates the low-side switch on-time when the

inductor current becomes negative. In this condition the section works in discontinuous

conduction mode. The threshold between continuous and discontinuous conduction mode

is:

Equation 5

For higher loads the inductor current doesn’t cross the zero and the device works in the

same way as in PWM mode and the frequency is fixed to the nominal value.

Figure 31.

PWM and pulse skip mode inductor current

Figure 31 shows inductor current waveforms in PWM and SKIP mode. In order to keep

average inductor current equal to load current, in SKIP mode some switching cycles are

skipped. When the output ripple reaches the regulated voltage Vreg, a new cycle begins.

The off cycle duration and the switching frequency depend on the load condition.

As a result of the control technique, losses are reduced at light loads, improving the system

efficiency.

ILOAD SKIP

()

OUT

–

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PM6680ATR Datasheet(PDF) 22 Page - STMicroelectronics