Combined doubler and inverter – Rainbow Electronics MAX1681 User Manual
Page 9
Combined Doubler and Inverter
Figure 3 shows a single MAX1680/MAX1681 as an
inverter and a doubler. The maximum output current is
the sum of the loads on the two outputs and is still limit-
ed to 125mA. As the device is loaded, the output volt-
ages move toward ground. In this particular
configuration, connect LV to GND (inverter). The diodes
used in the circuit cause a drop of approximately 0.7V
in the doubler’s output voltage, impacting efficiency.
Compatibility with the MAX660 and
MAX860/MAX861
The MAX1680/MAX1681 can be used in place of the
MAX860/MAX861, except for the SHDN and FSEL pins.
The MAX1680/MAX1681 shut down with a high input
voltage, compared with the MAX860/MAX861. The
MAX1680/MAX1681 have only two frequency choices.
Replacing the MAX660 with the MAX1680/MAX1681
involves a wiring change, as the external oscillator pin
is replaced by the shutdown feature. Table 5 compares
the devices.
MAX1680/MAX1681
125mA, Frequency-Selectable,
Switched-Capacitor Voltage Converters
_______________________________________________________________________________________
9
MAX1681
FSEL
IN
+V
INPUT
CAP+
SHDN
GND
1
µ
F
1
µ
F
LV
CAP-
OUT
GND
MAX1681
"n"
FSEL
IN
CAP+
SHDN
1
µ
F
1
µ
F
1
µ
F
V
OUT
NOTE: USE 4.7
µ
F CAPACITORS FOR MAX1680.
V
OUT
= -V
INPUT
LV
CAP-
OUT
R
OUT
=
R
OUT
OF SINGLE DEVICE
NUMBER OF DEVICES (n)
Figure 2. Paralleling MAX1680/MAX1681s to Increase Output Current
MAX1681
FSEL
IN
+V
INPUT
CAP+
SHDN
GND
1
µ
F
1
µ
F
1
µ
F
1
µ
F
1
µ
F
LV
CAP-
OUT
V
OUT
= -V
INPUT
D1
IN4148
D2
IN4148
V
OUT
= 2V
INPUT
-V
FD1
-V
FD2
NOTE: USE 4.7
µ
F CAPACITORS FOR MAX1680.
Figure 3. Combined Doubler and Inverter