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參數(shù)資料
| 型號(hào)： | AAT3183 |
| 廠商： | Advanced Analogic Technologies, Inc. |
| 英文描述： | 300mA Inductorless Step-Down Converter |
| 中文描述： | 300mA的電感降壓轉(zhuǎn)換器 |
| 文件頁數(shù)： | 9/16頁 |
| 文件大?。?/td> | 392K |
| 代理商： | AAT3183 |
AAT3183
300mA Inductorless Step-Down Converter
3183.2007.07.1.2
9
Charge Pump Operation
The AAT3183 step-down charge pump is imple-
mented using a fixed 1/2x (gain) converter topolo-
gy. This configuration allows efficient energy trans-
fer with a single ceramic flying capacitor. The
arrangement of the internal switches requires that
the voltage on the flying capacitor is greater than
the output voltage plus the input voltage headroom
to account for a parasitic voltage drop.
Energy is transferred to the flying capacitor and out-
put during alternate ‘charge’ and ‘discharge’ inter-
vals. The amount of energy transferred from the
input voltage source to flying capacitor is proportion-
al to the differential voltage across the flying capaci-
tor (V
DIFF
= V
IN
- V
OUT
) which occurs during the
‘charge’ interval multiplied by the switching frequen-
cy. The step-down charge pump transfers energy to
the output during both the ‘charge’ and ‘discharge’
intervals. Figure 1 illustrates the energy transfer
mechanism during ‘charge’ and ‘discharge’ intervals.
PFM control compensates for changes in the input
voltage and output current by modulating the fre-
quency of switching intervals to maintain the
desired output voltage. The output voltage is
sensed through an internal resistor divider and
compared against a reference voltage by an error
amplifier. As the output voltage decreases, the
voltage at the input to the error amplifier decreas-
es. The error signal increases the effective switch-
ing frequency; providing increased current to the
output current thus maintaining the desired output
voltage. At light loads, the effective switching fre-
quency is greatly reduced which maintains output
regulation while minimizing switching losses.
Operating efficiency (η) is defined as the output
power divided by the input power.
With a constant output current and 1/2x (gain)
operation, the input current is constant regardless
of input voltage. The input current is equal to 50%
[1/2x (gain)] of the output current.
= V
OUT
· I
OUT
)
(V
IN
· I
IN
)
η
= P
IN
P
OUT
η
= (V
OUT
· I
OUT
)
IN
· I
OUT
)
= 2 V
OUT
IN
I
IN
= I
OUT
Figure 1a: Step-Down Charge
Pump “CHARGE” Interval.
Figure 1b: Step-Down Charge
Pump “DISCHARGE” Interval.
V
IN
C
OUT
C
FLY(CHARGE)
V
DIFF
V
OUT
GND
ENERGY
TRANSFER
R
LOAD
I
OUT
V
IN
C
OUT
C
FLY(DISCHARGE)
V
OUT
GND
ENERGY
TRANSFER
R
LOAD
I
OUT
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