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參數(shù)資料
| 型號： | TCM829ECT |
| 廠商： | Microchip Technology Inc. |
| 元件分類： | 基準(zhǔn)電壓源/電流源 |
| 英文描述： | Switched Capacitor Voltage Converters |
| 中文描述： | 開關(guān)電容電壓轉(zhuǎn)換器 |
| 文件頁數(shù)： | 3/9頁 |
| 文件大小： | 75K |
| 代理商： | TCM829ECT |
3
TCM828/829-4 5/22/00
TCM828
TCM829
Switched Capacitor
Voltage Converters
2001 Microchip Technology Inc. DS21488A
DETAILED DESCRIPTION
The TCM828/829 charge pump converters invert the
voltage applied to the V
IN
pin. Conversion consists of a two-
phase operation (Figure 1). During the first phase, switches
S2 and S4 are open and S1 and S3 are closed. During this
time, C1 charges to the voltage on V
IN
and load current is
supplied from C2. During the second phase, S2 and S4 are
closed, and S1 and S3 are open. This action connects C1
across C2, restoring charge to C2.
APPLICATIONS INFORMATION
Output Voltage Considerations
The TCM828/829 perform voltage conversion but do
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 approximately 25
nominal
at +25
°
C and V
IN
= +5V. V
OUT
is approximately – 5V at light
loads, and droops according to the equation below:
V
DROOP
= I
OUT
x R
OUT
V
OUT
= – (V
IN
– V
DROOP
)
Charge Pump Efficiency
The overall power efficiency of the charge pump is
affected by four factors:
(1) Losses from power consumed by the internal oscil-
lator, switch drive, etc. (which vary with input volt-
age, temperature and oscillator frequency).
(2) I
2
R losses due to the on-resistance of the MOSFET
switches on-board the charge pump.
(3) Charge pump capacitor losses due to effective
series resistance (ESR).
Figure 1. Ideal Switched Capacitor Charge Pump
(4) Losses that occur during charge transfer (from the
commutation capacitor to the output capacitor)
when a voltage difference between the two capaci-
tors exists.
Most of the conversion losses are due to factors (2), (3)
and (4) above. These losses are given by Equation 1.
P
LOSS (2, 3, 4)
= I
OUT2
x R
OUT
I
OUT2
x
[
1
OSC
) C1
+8R
SWITCH
+ 4ESR
C1
+ ESR
C2
]
The 1/(f
OSC
)(C1) term in Equation 1 is the effective
output resistance of an ideal switched capacitor circuit
(Figures 2a, 2b).
The losses in the circuit due to factor (4) above
are also shown in Equation 2. The output voltage ripple is
given by Equation 3.
P
LOSS (4)
=
[
(0.5)(C1)(V
IN2
– V
OUT2
) + (0.5)(C2)(V
RIPPLE2
– 2V
OUT
V
RIPPLE
)
]
x f
OSC
V
RIPPLE
=
I
OUT
OSC
)(C2)
+2(I
OUT
)(ESR
C2
)
Figure 2a. Ideal Switched Capacitor Model
Figure 2b. Equivalent Output Resistance
V
OUT
=
–
(V
IN
)
C1
C2
TCM828/829
IN
S1
S3
S4
S2
V
+
V
OUT
R
L
C1
C2
f
V
+
V
OUT
R
EQUIV
R
EQUIV =
R
L
C2
f x C1
1
Equation 2.
Equation 1.
Equation 3.
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