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參數(shù)資料
| 型號： | MAX660 |
| 廠商： | Maxim Integrated Products, Inc. |
| 英文描述： | CMOS Monolithic Voltage Converter |
| 中文描述： | CMOS單片電壓變換器 |
| 文件頁數(shù)： | 5/11頁 |
| 文件大?。?/td> | 259K |
| 代理商： | MAX660 |
Pin Description
Pin
Name
Function
Voltage Inverter
Voltage Doubler
1
FC
Frequency control for internal oscillator:
FC = open, f
OSC
= 10 kHz (typ);
FC = V+, f
OSC
= 80 kHz (typ);
FC has no effect when OSC pin is driven externally.
Connect this pin to the positive terminal of
charge-pump capacitor.
Power supply ground input.
Connect this pin to the negative terminal of
charge-pump capacitor.
Negative voltage output.
Low-voltage operation input. Tie LV to GND when
input voltage is less than 3.5V. Above 3.5V, LV can
be connected to GND or left open. When driving
OSC with an external clock, LV must be connected
to GND.
Oscillator control input. OSC is connected to an
internal 15 pF capacitor. An external capacitor can
be connected to slow the oscillator. Also, an
external clock can be used to drive OSC.
Power supply positive voltage input.
Same as inverter.
2
CAP+
Same as inverter.
3
4
GND
CAP
Power supply positive voltage input.
Same as inverter.
5
6
OUT
LV
Power supply ground input.
LV must be tied to OUT.
7
OSC
Same as inverter except that OSC cannot be driven
by an external clock.
8
V+
Positive voltage output.
Circuit Description
The MAX660 contains four large CMOS switches which are
switched in a sequence to invert the input supply voltage.
Energy transfer and storage are provided by external capaci-
tors. Figure 2 illustrates the voltage conversion scheme.
When S
and S
are closed, C
charges to the supply volt-
age V+. During this time interval switches S
and S
are
open. In the second time interval, S
and S
are open and S
2
and S
are closed, C
is charging C
. After a number of
cycles, the voltage across C
will be pumped to V+. Since
the anode of C
is connected to ground, the output at the
cathode of C
equals (V+) assuming no load on C
, no loss
in the switches, and no ESR in the capacitors. In reality, the
charge transfer efficiency depends on the switching fre-
quency, the on-resistance of the switches, and the ESR of
the capacitors.
Application Information
SIMPLE NEGATIVE VOLTAGE CONVERTER
The main application of MAX660 is to generate a negative
supply voltage. The voltage inverter circuit uses only two ex-
ternal capacitors as shown in the TypicalApplication Circuits.
The range of the input supply voltage is 1.5V to 5.5V. For a
supply voltage less than 3.5V, the LV pin must be connected
to ground to bypass the internal regulator circuitry. This gives
the best performance in low voltage applications. If the sup-
ply voltage is greater than 3.5V, LV may be connected to
ground or left open. The choice of leaving LV open simplifies
the direct substitution of the MAX660 for the LMC7660
Switched Capacitor Voltage Converter.
The output characteristics of this circuit can be approximated
by an ideal voltage source in series with a resistor. The volt-
age source equals (V+). The output resistance R
is a
function of the ON resistance of the internal MOS switches,
the oscillator frequency, and the capacitance and ESR of C
1
and C
2
. A good approximation is:
where R
is the sum of the ON resistance of the internal
MOS switches shown in Figure 2
High value, low ESR capacitors will reduce the output resis-
tance. Instead of increasing the capacitance, the oscillator
frequency can be increased to reduce the 2/(f
x C
) term.
Once this term is trivial compared with R
and ESRs, fur-
ther increasing in oscillator frequency and capacitance will
become ineffective.
The peak-to-peak output voltage ripple is determined by the
oscillator frequency, and the capacitance and ESR of the
output capacitor C
2
:
DS100898-21
FIGURE 2. Voltage Inverting Principle
M
www.national.com
5
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