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參數(shù)資料
| 型號(hào)： | MAX860 |
| 廠商： | Maxim Integrated Products, Inc. |
| 英文描述： | 50mA, Frequency-Selectable, Switched-Capacitor Voltage Converters(50mA,高達(dá)250KHz的振蕩頻率,電荷泵電壓轉(zhuǎn)換器) |
| 中文描述： | 50mA、頻率可選的開(kāi)關(guān)電容電壓變換器 |
| 文件頁(yè)數(shù)： | 6/12頁(yè) |
| 文件大?。?/td> | 116K |
| 代理商： | MAX860 |
M
50mA, Frequenc y-S elec table,
S witc hed-Capac itor Voltage Converters
6
_______________________________________________________________________________________
In the doubling configuration, loads connected from the
V
DD
pin to the GND pin are not powered in shutdown
mode. Loads connected from the V
DD
pin to the OUT
pin draw current from the input supply through a path
similar to that of the inverting configuration (described
above).
Frequenc y Control
Charge-pump frequency for both devices can be set to
one of three values. Each device has a unique set of
three available frequencies, as indicated in Table 1.
The oscillator and charge-pump frequencies are the
same (i.e., the charge-pump frequency is not half the
oscillator frequency, as it is on the MAX660, MAX665,
and ICL7660).
*See the Electrical Characteristics for detailed switching-
frequency specifications.
A higher switching frequency minimizes capacitor size
for the same performance and increases the supply
current (Table 2). The lowest fundamental frequency of
the switching noise is equal to the minimum specified
switching frequency (e.g., 3kHz for the MAX860 with
FC open). The spectrum of noise frequencies extends
above this value because of harmonics in the switching
waveform. To get best noise performance, choose the
device and FC connection to select a minimum switch-
ing frequency that lies above your sensitive bandwidth.
Low-Voltage-Operation Input
LV should normally be connected to GND for inverting
operation. To enhance compatibility with the MAX660,
MAX665, and ICL7660, you may float LV if the input volt-
age exceeds 3V. In doubling mode, LV must be connect-
ed to OUT for all input voltages.
__________Applic ations Information
Capac itor S elec tion
The MAX860/MAX861 are tested using 10μF capacitors
for both C1 and C2, although smaller or larger values
can be used (Table 3). Smaller C1 values increase the
output resistance; larger values reduce the output
resistance. Above a certain point, increasing the
capacitance of C1 has a negligible effect (because the
output resistance becomes dominated by the internal
switch resistance and the capacitor ESR). Low-ESR
capacitors provide the lowest output resistance and
ripple voltage. The output resistance of the entire circuit
(inverter or doubler) is approximately:
R
OUT
= R
O
+ 4 x ESR
C1
+ ESR
C2
+ 1 / (f
S
x C1)
where R
O
(the effective resistance of the MAX860/
MAX861’s internal switches) is approximately 8
and f
S
is the switching frequency. R
OUT
is typically 12
when
using capacitors with 0.2
ESR and f
S
, C1, and C2 val-
ues suggested in Table 3. When C1 and C2 are so
large (or the switching frequency is so high) that the
internal switch resistance dominates the output resis-
tance, estimate the output resistance as follows:
R
OUT
= R
O
+ 4 x ESR
C1
+ ESR
C2
A typical design procedure is as follows:
1) Choose C1 and C2 to be the same, for convenience.
2) Select f
S
:
a) If you want to avoid a specific noise frequency,
choose f
S
appropriately.
b) If you want to minimize capacitor cost and size,
choose a high f
S
.
c) If you want to minimize current consumption,
choose a low f
S
.
3) Choose a capacitor based on Table 3, although
higher or lower values can be used to optimize per-
formance. Table 4 lists manufacturers who provide
low-ESR capacitors.
FREQUENCY (kHz)
FC CONNECTION
MAX860
MAX861
FC = V
DD
or open
6
13
FC = GND
50
100
FC = OUT
130
250
ATTRIBUTE
LOWER
FREQUENCY
Larger
Larger
Smaller
HIGHER
FREQUENCY
Smaller
Smaller
Larger
Output Ripple
C1, C2 Values
Supply Current
C1, C2 (μF)
NOMINAL FREQUENCY (kHz)
6
68
13
47
50
10
100
4.7
130
4.7
250
2.2
Table 1. Nominal Switching Frequencies*
Table 2. Switching-Frequency Trade-Offs
Table 3. Suggested Capacitor Values
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