100mA CHARGE PUMP DC-TO-DC
VOLTAGECONVERTER
TC660
+
V
+
V
+
V
= –V
OUT
1
2
3
4
8
7
6
5
1
2
3
4
8
7
6
5
D
1
V
=
C
3
OUT
+
D
+
D
D
2
(2 V ) – (2 V )
1
TC660
F
TC660
+
+
V
=
+
C
C
C
2
OUT
1
+
2
(2 V ) – (2 V )
F
1
+
+
C
2
C
4
Figure 8. Positive Voltage Doubler
Figure 9 shows an improved way of using the TC660 as
a voltage doubler.
In this circuit, C1 is first charged to VIN and C2 is quickly
brought to within a diode drop of VIN (to prevent substrate
reversal) through D. The optional 200 Ω resistor is only to
limit the brief latchup current.
Onthenexthalf-cycle,VIN isinserieswithC1; C2isthen
charged to 2 VIN. D is now reverse-biased and plays no
further part. For VIN < 3V, R may be necessary to ensure
startup.
Figure 10. Combined Negative Converter and Positive Multiplier
Efficient Positive Voltage
Multiplication/Conversion
Since the switches that allow the charge pumping op-
eration are bidirectional, the charge transfer can be per-
formed backward as easily as forward. Figure 11 shows a
TC660 transforming –5V to +5V. The only problem here is
that the internal clock and switch-drive section will not
operate until some positive voltage has been generated. A
diode and resistor shown dotted in Figure 11 can be used to
"force" the internal regulator on.
200
V
IN
D
V
1
2
3
4
8
7
6
5
OUT
= 2 V
IN
C
–
C
TC660
2
V
= –V
1
OUT
R
1
2
3
4
8
7
6
5
+
R = 0.1 – 1MΩ
Figure 9. Improved Voltage Doubler
150 µF
1 MΩ
+
C
1
TC660
150 µF
Combined Negative Voltage Conversion
and Positive Supply Multiplication
–
V
INPUT
Figure 10 combines the functions shown in Figures 3
and 8 to provide negative voltage conversion and positive
voltage multiplication simultaneously. In this instance, ca-
pacitors C1 and C3 perform the pump and reservoir func-
tions, respectively, for the generation of the negative volt-
age, while capacitors C2 and C4 are pump and reservoir,
respectively, for the multiplied positive voltage. There is a
penalty in this configuration in that the source impedances
of the generated supplies will be somewhat higher due to
the finite impedance of the common charge pump driver at
pin 2 of the device.
Figure 11. Positive Voltage Multiplier
4-12
TELCOM SEMICONDUCTOR, INC.
TELCOM [ TELCOM SEMICONDUCTOR, INC ]
