PM6681A STMicroelectronics, PM6681A Datasheet - Page 22

• Manufacturer Part Number: PM6681A
• Description: Dual synchronous step down controller with adjustable LDO
• Manufacturer: STMicroelectronics

Device description
7.5
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
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.
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
shows inductor current waveforms in PWM and SKIP mode. In order to keep
Inductor current
0
Low side
No audible skip mode
ILOAD
(
SKIP
∼30us
)
=
V
IN
2
−
×
V
L
OUT
×
T
ON
Time
PM6681A