參數(shù)資料
型號(hào): PM6670TR
廠商: STMICROELECTRONICS
元件分類: 穩(wěn)壓器
英文描述: 1.4 A SWITCHING CONTROLLER, QCC24
封裝: 4 X 4 MM, LEAD FREE, VFQFN-24
文件頁數(shù): 20/55頁
文件大小: 849K
代理商: PM6670TR
PM6670
Device description
27/53
7.1.3
Pulse-Skip and No-Audible Pulse-Skip Modes
High efficiency at light load conditions is achieved by PM6670 entering the Pulse-Skip Mode
(if enabled). When one of the two fixed output voltages is set, Pulse-Skip power saving is a
default feature. At light load conditions the zero-crossing comparator truncates the low-side
switch On-Time as soon as the inductor current becomes negative; in this way the
comparator determines the On-Time duration instead of the output ripple (see Figure 33).
Figure 33. Inductor current and output voltage at light load with Pulse-Skip
As a consequence, the output capacitor is left floating and its discharge depends solely on
the current drained from the load. When the output ripple on the pin COMP falls under the
reference, a new shot is triggered and the next cycle begins. The Pulse-Skip mode is
naturally obtained enabling the zero-crossing comparator and automatically takes part in the
C.O.T. algorithm when the inductor current is about half the ripple current amount, i.e.
migrating from continuous conduction mode (C.C.M.) to discontinuous conduction mode
(D.C.M.).
The output current threshold related to the transition between PWM Mode and Pulse-Skip
Mode can be approximately calculated as:
Equation 20
At higher loads, the inductor current never crosses zero and the device works in pure PWM
mode with a switching frequency around the nominal value.
A physiological consequence of Pulse-Skip Mode is a more noisy and asynchronous (than
normal conditions) output, mainly due to very low load. If the Pulse-Skip is not compatible
with the application, the PM6670, when set in adjustable mode-of-operation, allows the user
to choose between forced-PWM and No-Audible Pulse-Skip alternative modes (see 4.1.4 for
details).
VDDQ
Output
Inductor
current
Vreg
TON TOFF
VDDQ
Output
Inductor
current
Vreg
TON TOFF
TIDLE
t
ON
OUT
IN
LOAD
T
L
2
V
)
Skip
2
PWM
(
I
=
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