參數(shù)資料
型號： TCM829
廠商： Microchip Technology Inc.
元件分類： 基準電壓源/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)： 4/9頁
文件大?。?/td> 75K
代理商： TCM829
4
TCM828/829-4 5/22/00
Switched Capacitor
Voltage Converters
TCM828
TCM829
2001 Microchip Technology Inc. DS21488A
Capacitor Selection
In order to maintain the lowest output resistance and
output ripple voltage, it is recommended that low ESR
capacitors be used. Additionally, larger values of C1 will
lower the output resistance and larger values of C2 will
reduce output ripple. (See Equation 1(b)).
Table 1 shows various values of C1 and the correspond-
ing output resistance values @ +25
°
C. It assumes a 0.1
ESR
C1
and 2
R
SW
. Table 2 shows the output voltage ripple
for various values of C2. The V
RIPPLE
values assume 10mA
output load current and 0.1
ESR
C2
.
Table 1. Output Resistance vs. C1 (ESR = 0.1
)
C1(
μ
F)
TCM828 R
OUT
(
)
TCM829 R
OUT
(
)
0.1
1
3.3
10
47
100
850
100
42
25
18
17
302
45
25
19
17
17
Table 2. Output Voltage Ripple vs. C2 (ESR = 0.1
) I
OUT
10mA
C2(
μ
F)
TCM828 V
RIPPLE
(mV)
1
835
3.3
254
10
85
47
20
100
10
TCM829 V
RIPPLE
(mV)
286
88
31
8
5
Input Supply Bypassing
The V
IN
input should be capacitively bypassed to reduce
AC impedance and minimize noise effects due to the switch-
ing internal to the device. The recommended capacitor
depends on the configuration of the TCM828/829.
If the device is loaded from OUT to GND it is recom-
mended that a large value capacitor (at least equal to C1) be
connected from the input to GND. If the device is loaded
from IN to OUT a small (0.1
μ
F) capacitor from IN to OUT is
sufficient.
Voltage Inverter
The most common application for charge pump devices
is the inverter (Figure 3). This application uses two external
capacitors – C1 and C2 (plus a power supply bypass
capacitor, if necessary). The output is equal to V–
voltage drops due to loading. Refer to Table 1 and Table 2
for capacitor selection.
IN
plus any
Cascading Devices
Two or more TCM828/829’s can be cascaded to
increase output voltage (Figure 4). If the output is lightly
loaded, it will be close to (– 2 x V
IN
) but will droop at least by
R
OUT
of the first device multiplied by the I
Q
of the second. It
can be seen that the output resistance rises rapidly for
multiple cascaded devices. For large negative voltage
requirements see the TC682 or TCM680 data sheets.
Paralleling Devices
To reduce the value of R
OUT
, multiple TCM828/829s
can be connected in parallel (Figure 5). The output resis-
tance will be reduced by a factor of N where N is the number
of TCM828/829’s. Each device will require it’s own pump
capacitor (C1), but all devices may share one reservoir
capacitor (C2). However, to preserve ripple performance the
value of C2 should be scaled according to the number of
paralleled TCM828/829’s.
Figure 3.
Test Circuit
C1
C1
C2
5
5
4
3
4
1
2
2
1
3
C2
V
IN
V
OUT
V
OUT =
–
n
V
IN
+
TCM828
TCM829
"1"
TCM828
TCM829
"n"
. . .
. . .
Figure 4.
Cascading TCM828s or TCM829s to Increase Output Voltage
3
2
4
5
1
C3
3.3
μ
F*
C1
3.3
μ
F*
C2
3.3
μ
F*
V
IN
V
OUT
R
L
TCM828
TCM829
C1
–
IN
OUT
C1+
GND
Voltage Inverter
*10
μ
F (TCM828)
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