Datasheet
5
HIGH FREQUENCY 7660 DC-TO-DC
VOLTAGE CONVERTER
TC7660H
TC7660H-2 10/1/96
© 2001 Microchip Technology Inc. DS21466A
Figure 5. Paralleling Devices Lowers Output Impedance
1
2
3
4
8
7
6
5
TC7660H
V
+
1
2
3
4
8
7
6
5
TC7660H
C
1
R
L
C
2
C
1
"n"
"1"
+
R
L
1
2
3
4
8
7
6
5
TC7660H
+
V
+
+
CMO
S
GATE
1.0 µF
V
OUT
1.0 µF
1 kΩ
V
+
Figure 6. External Clocking
Figure 7. Positive Voltage Multiplier
Positive Voltage Multiplication
The TC7660H may be employed to achieve positive
voltage multiplication using the circuit shown in Figure 7. In
this application, the pump inverter switches of the TC7660H
are used to charge C
1
to a voltage level of V
+
– V
F
(where V
+
is the supply voltage and V
F
is the forward voltage drop of
diode D
1
). On the transfer cycle, the voltage on C
1
plus the
supply voltage (V
+
) is applied through diode D
2
to capacitor
C
2
. The voltage thus created on C
2
becomes (2 V
+
) – (2 V
F
),
or twice the supply voltage minus the combined forward
voltage drops of diodes D
1
and D
2
.
The source impedance of the output (V
OUT
) will depend
on the output current, but for V
+
= 5V and an output current
of 10mA, it will be approximately 60Ω.
Combined Negative Voltage Conversion
and Positive Supply Multiplication
Figure 8 combines the functions shown in Figures 3 and
8 to provide negative voltage conversion and positive volt-
age multiplication simultaneously. This approach would be,
for example, suitable for generating +9V and –5V from an
existing +5V supply. In this instance, capacitors C
1
and C
3
perform the pump and reservoir functions, respectively, for
the generation of the negative voltage, while capacitors C
2
and C
4
are pump and reservoir, respectively, for the multi-
plied positive voltage. There is a penalty in this configuration
which combines both functions, however, 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.
1
2
3
4
8
7
6
5
+
V
+
V
OUT
=
(2 V
+
) – (2 V
F
)
C
1
D
1
+
+
C
3
C
4
V
OUT
=
–(V
+
–V
F
)
C
2
TC7660H
D
2
+
Figure 8. Combined Negative Converter and Positive Multiplier
1
2
3
4
8
7
6
5
V
+
V
OUT
=
(2 V
+
) – (2 V
F
)
+
C
2
D
1
D
2
+
C
1
TC7660H