PM6681ATR datasheet(22/47 Pages) STMICROELECTRONICS

22 / 47 page

Device description

PM6681A

22/47

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 33.

PWM and pulse skip mode inductor current

Figure 33

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.

7.5

No-audible skip mode

If SKIP pin is tied to VREF, a no-audible skip mode with a minimum switching frequency of

33 kHz is enabled. At light load condition, If there is not a new switching cycle within a 30

µs

(typ.) period, a no-audible skip mode cycle begins.

Figure 34.

No audible skip mode

OUT

)

SKIP

(

ILOAD

−

Time

Inductor current

No audible skip mode

Low side

∼30us

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