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參數(shù)資料
| 型號(hào)： | MAX864 |
| 廠商： | Maxim Integrated Products, Inc. |
| 英文描述： | Dual-Output Charge Pump with Shutdown |
| 中文描述： | 雙輸出電荷泵，帶有關(guān)斷 |
| 文件頁數(shù)： | 6/12頁 |
| 文件大?。?/td> | 122K |
| 代理商： | MAX864 |
M
Dual-Output Charge Pump with S hutdown
6
_______________________________________________________________________________________
_______________Detailed Desc ription
The MAX864 requires only four external capacitors to
implement a voltage doubler/inverter. These may be
ceramic or polarized capacitors (electrolytic or tanta-
lum) with values ranging from 0.47μF to 100μF.
Figure 2a illustrates the ideal operation of the positive
voltage doubler. The on-chip oscillator generates a
50% duty-cycle clock signal. During the first half cycle,
switches S2 and S4 open, switches S1 and S3 close,
and capacitor C1 charges to the input voltage (V
IN
).
During the second half cycle, switches S1 and S3
open, switches S2 and S4 close, and capacitor C1 is
level shifted upward by V
IN
volts. Assuming ideal
switches and no load on C3, charge transfers into C3
from C1 such that the voltage on C3 will be 2V
IN
, gen-
erating the positive supply output (V+).
Figure 2b illustrates the ideal operation of the negative
converter. The switches of the negative converter are
out of phase from the positive converter. During the
second half cycle, switches S6 and S8 open, and
switches S5 and S7 close, charging C2 from V+
(pumped up to 2V
IN
by the positive charge pump) to
GND. In the first half of the clock cycle, switches S5
and S7 open, switches S6 and S8 close, and the
charge on capacitor C2 transfers to C4, generating the
negative supply. The eight switches are CMOS power
MOSFETs. Switches S1, S2, S4, and S5 are P-channel
devices, while switches S3, S6, S7, and S8 are N-chan-
nel devices.
Charge-Pump Frequenc y
and Capac itor S elec tion
The MAX864 offers four different charge-pump frequen-
cies. To select a desired frequency, define pins FC0 and
FC1 as shown in Table 1. Lower charge-pump frequen-
cies produce lower average supply currents, while high-
er charge-pump frequencies require smaller capacitors.
Table 1 also lists the recommended charge-pump
capacitor values for each pump frequency. Using val-
ues larger than those recommended will have little
effect on the output current. Using values smaller than
those recommended will reduce the available output
current and increase the output ripple. To cut the out-
put ripple in half, double the values of C3 and C4.
To maintain the lowest output resistance, use capacitors
with low effective series resistance (ESR). At each switch-
ing frequency, the charge-pump output resistance is a
function of C1, C2, C3, and C4’s ESR. Minimizing the
charge-pump capacitors’ ESR minimizes output resis-
tance. Use ceramic capacitors for best results.
Table 1. Frequency Selection
1
2.2
6.8
33
CAPACITORS
C1–C4
(μF)
185
100
33
7
1
1
FREQUENCY
(kHz)
0
1
FC1
1
0
0
0
FC0
IN
a)
b)
S1
S3
C1+
C1
C3
C1-
S2
S4
S5
S6
S7
S8
C2-
GND
V-
R
L
-
R
L
+
C2+
C4
C2
GND
IN
I
L
-
V+
GND
I
L
+
V+
Figure 2. Idealized Voltage Quadrupler: a) Positive Charge Pump; b) Negative Charge Pump
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