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TC7660 Datasheet PDF : 9 Pages
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CHARGE PUMP DC-TO-DC
VOLTAGE CONVERTER
TC7660
+
10µF
1
8
2
7
3 TC7660 6
4
5
V+
1 kΩ
V+
CMOS
GATE
VOUT
10µF
+
+
C1
Figure 6. External Clocking
1
8
2
7
3 TC7660 6
4
5
V+
COSC
VOUT
+ C2
Figure 7. Lowering Oscillator Frequency
Positive Voltage Multiplication
The TC7660 may be employed to achieve positive
voltage multiplication using the circuit shown in Figure 8. In
this application, the pump inverter switches of the TC7660
are used to charge C1 to a voltage level of V+– VF (where V+
is the supply voltage and VF is the forward voltage drop of
diode D1). On the transfer cycle, the voltage on C1 plus the
supply voltage (V+) is applied through diode D2 to capacitor
C2. The voltage thus created on C2 becomes (2 V+) – (2 VF),
or twice the supply voltage minus the combined forward
voltage drops of diodes D1 and D2.
The source impedance of the output (VOUT) will depend
on the output current, but for V+ = 5V and an output current
of 10 mA, it will be approximately 60Ω.
1
8
2
7
3 TC7660 6
4
5
V+
D1
VOUT =
D2
(2 V+) – (2 VF)
+
C1
+
C2
Combined Negative Voltage Conversion
and Positive Supply Multiplication
Figure 9 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 C1 and C3
perform the pump and reservoir functions, respectively, for
the generation of the negative voltage, while capacitors C2
and C4 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.
V+
1
8
2
7
3 TC7660 6
+
4
C1
5
+
C2
VOUT =
– (V+– VF)
D1
+ C3
D2
V(2OVU+T)
=
–
(2
VF)
+
C4
Figure 9. 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 backwards as easily as forwards. Figure 10 shows
a TC7660 transforming –5V to +5V (or +5V to +10V, etc.).
The only problem here is that the internal clock and switch-
drive section will not operate until some positive voltage has
been generated. An initial inefficient pump, as shown in
Figure 9, could be used to start this circuit up, after which it
will bypass the other (D1 and D2 in Figure 9 would never turn
on), or else the diode and resistor shown dotted in Figure 10
can be used to "force" the internal regulator on.
4-58
Figure 8. Positive Voltage Multiplier
TELCOM SEMICONDUCTOR, INC.
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