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參數(shù)資料
| 型號： | AMS682EP |
| 廠商： | Advanced Monolithic Systems, Inc. |
| 英文描述： | INVERTING VOLTAGE DOUBLER |
| 中文描述： | 反向電壓倍增 |
| 文件頁數(shù)： | 4/7頁 |
| 文件大?。?/td> | 62K |
| 代理商： | AMS682EP |
Advanced Monolithic Systems, Inc.
6680B Sierra Lane, Dublin, CA 94568 Phone (925) 556-9090 Fax (925) 556-9140
AMS682
APPLICATIONS
(Continued)
Capacitor Selection
The output resistance of the AMS682 is determined in part by
the ESR of the capacitors used. An expression for R
OUT
is
derived as shown below:
R
OUT
= 2( R
SW1
+R
SW2
+ESR
C1
+ R
SW3
+R
SW4
+ESR
C2
)
+2(R
SW1
+R
SW2
+ESR
C1
+ R
SW3
+R
SW4
+ESR
C2
)
+1/ (f
PUMP
X C1) +1/ (f
PUMP
X C2) + ESR
C3
Assuming all switch resistances are approximately equal:
R
OUT
= 16 R
SW
+ 4ESR
C1
+ 4ESR
C2
+ ESR
C3
+1/ (f
PUMP
X C1) +1/ (f
PUMP
X C2)
R
OUT
is typically 140
at +25
°
C with VIN =+5V and 3.3
μ
F
low ESR capacitors. The fixed term (16RSW) is about 80-
90
. Increasing or decreasing values of C1 and C2 will affect
efficiency by changing R
OUT
.
Table 1 shows R
OUT
for various values of C1 and C2 (assume
0.5
ESR). C1 must be rated at 6VDC or greater while C2
and C3 must be rated at 12VDC or greater.
Output voltage ripple is affected by C3. Typically the larger
the value of C3 the less the ripple for a given load current.
The formula for p-p V
RIPPLE
is :
V
RIPPLE
= [1/[2(f
PUMP
X C3)]+2(ESR
C3
)] (I
OUT
)
For a 10
μ
F (0.5
ESR), f
PUMP
= 10kHz and I
OUT
=10mA the
peak -to-peak ripple voltage at the output will be less than
60mV. In most applications (I
OUT
≤
10mA) a 10-20
μ
F
capacitor and 1-5
μ
F pump capacitors will be sufficient. Table
2 shows V
RIPPLE
for different values of C3 (assume 1
ESR).
Paralleling devices
Paralleling multiple AMS682 reduces the output resistance of
the converter. The effective output resistance is the output
resistance of one device divided by the number of devices.
Figure 5 illustrates how each device requires separate pump
capacitors C
1
and C
2
, but all can share a single reservoir
capacitor.
-5V Regulated Supply From A Single 3V Battery
Figure 6 shows a -5V power supply using one 3V battery.
The AMS682 provides -6V at V
-OUT
, which is regulated to -5V
by the negative LDO. The AMS682 input can vary from 3V to
5.5V without affecting regulation significantly. A voltage
detector is connected to the battery to detect undervoltage.
This unit is set to detect at 2.7V. With higher input voltage,
more current can be drawn from the outputs of the AMS682.
With 5V at V
IN
, 10mA can be drawn from the regulated
output. Assuming 150
source resistance for the converter,
with I
L
=10mA, the charge pump will drop 1.5V.
Table 1. R
OUT
vs. C1, C2
C1, C2 (
μ
F)
0.05
0.10
0.47
1.00
3.30
5.00
10.00
22.00
100.00
Table 2. V
RIPPLE
Peak-to-Peak vs. C3 (I
OUT
=10mA)
C3(
μ
F)
0.50
1.00
3.30
5.00
10.00
22.00
100.00
R
OUT
(
)
4085
2084
510
285
145
125
105
94
87
V
RIPPLE
(mV)
1020
520
172
120
70
43
25
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