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參數(shù)資料
| 型號： | TC1240ECHTR |
| 廠商： | Microchip Technology Inc. |
| 英文描述： | Positive Doubling Charge Pumps with Shutdown in a SOT-23 Package |
| 中文描述： | 積極加倍電荷泵與關(guān)機采用SOT - 23封裝 |
| 文件頁數(shù)： | 7/16頁 |
| 文件大小： | 290K |
| 代理商： | TC1240ECHTR |
2003 Microchip Technology Inc.
DS21516C-page 7
TC1240/TC1240A
4.0
DETAILED DESCRIPTION
The TC1240/TC1240A charge pump converter dou-
bles the voltage applied to the V
IN
pin. Conversion con-
sists of a two-phase operation (Figure 4-1). During the
first phase, switches S
2
and S
4
are open and S
1
and S
3
are closed. During this time, C
1
charges to the voltage
on V
IN
and load current is supplied from C
2
. During the
second phase, S
2
and S
4
are closed, while S
1
and S
3
are open.
During this second phase, C
1
is level-shifted upward by
V
IN
volts. This connects C
1
to the reservoir capacitor
C
2
, allowing energy to be delivered to the output as
needed. The actual voltage is slightly lower than 2 x V
IN
since the four switches (S
1
-S
4
) have an on-resistance
and the load drains charge from reservoir capacitor C
2
.
FIGURE 4-1:
Charge Pump Doubler.
Ideal Switched Capacitor
5.0
TYPICAL APPLICATIONS
5.1
Output Voltage Considerations
The TC1240/TC1240A performs voltage doubling but
does not provide regulation. The output voltage will
droop in a linear manner with respect to load current.
The value of this equivalent output resistance is approx-
imately 12
nominal at +25°C and V
IN
= +5.0V for the
TC1240A and 17
nominal at +25°C and V
IN
= +2.8V
for the TC1240. V
OUT
is approximately +10.0V at light
loads for the TC1240A and +5.6V for the TC1240, and
droops according to the equation below:
EQUATION
5.2
Charge Pump Efficiency
The overall power efficiency of the charge pump is
affected by four factors:
1.
Losses from power consumed by the internal
oscillator, switch drive, etc. (which vary with
input voltage, temperature and oscillator
frequency).
I
2
R losses due to the on-resistance of the
MOSFET switches on-board the charge pump.
Charge pump capacitor losses due to effective
series resistance (ESR).
Losses that occur during charge transfer (from
commutation capacitor to the output capacitor)
when a voltage difference between the two
capacitors exist.
2.
3.
4.
Most of the conversion losses are due to factors (2) and
(3) above. These losses are given by Equation 5-1.
EQUATION 5-1:
V
OUT
= 2 x V
IN
C1
C
2
TC1240/TC1240A
V
IN
S
1
S
3
S
4
S
2
OSC
V
IN
VOUT
2
VIN
VDROOP
–
×
=
VDROOP
IOUT
ROUT
×
=
a)
b)
P
LOSS(2,3)
I
OUT
2
R
OUT
×
=
R
OUT
(
F
SW
C
1
)
--------1
8R
SWITCH
4ESR
C1
ESR
C2
+
+
+
=
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