tc7662b Microchip Technology Inc., tc7662b Datasheet - Page 6

• Manufacturer Part Number: tc7662b
• Description: Charge Pump Dc-to-dc Voltage Converter
• Manufacturer: Microchip Technology Inc.

TC7662B-8 9/11/96
TC7662B
Positive Voltage Doubling
voltage doubling using the circuit shown in Figure 9. In this
application, the pump inverter switches of the TC7662B are
used to charge C
the supply voltage and V
the supply voltage (V
C
or twice the supply voltage minus the combined forward
voltage drops of diodes D
on the output current, but for V
of 10 mA, it will be approximately 60 .
Combined Negative Voltage Conversion
and Positive Supply Multiplication
and 9 to provide negative voltage conversion and positive
voltage doubling simultaneously. This approach would be,
for example, suitable for generating +9V and –5V from an
existing +5V supply. In this instance, capacitors C
perform the pump and reservoir functions, respectively, for
the generation of the negative voltage, while capacitors C
and C
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.
2
). The voltage thus created on C
C 1
The TC7662B may be employed to achieve positive
The source impedance of the output (V
Figure 10 combines the functions shown in Figures 3
4
are pump and reservoir, respectively, for the doubled
+
1
2
3
4
Figure 8. Lowering Oscillator Frequency
Figure 9. Positive Voltage Multiplier
1
2
3
4
TC7662B
TC7662B
1
to a voltage level of V
+
) applied through diode D
F
8
7
6
5
1
is the forward voltage on C
and D
8
7
6
5
+
D 1
= 5V and an output current
+
V +
2
2
.
becomes (2 V
C 1
D 2
+
– V
+
OUT
+
F
V OUT =
(2 V + ) – (2 V F )
C 2
2
) will depend
(where V
C 2
V +
to capacitor
C OSC
V OUT
+
) – (2 V
1
and C
1
plus
+
F
is
),
3
2
6
Voltage Splitting
split a higher supply in half, as shown in Figure 11. The
combined load will be evenly shared between the two sides
and a high value resistor to the LV pin ensures start-up.
Because the switches share the load in parallel, the output
impedance is much lower than in the standard circuits, and
higher currents can be drawn from the device. By using this
circuit, and then the circuit of Figure 6, +15V can be
converted (via +7.5V and –7.5V) to a nominal –15V, though
with rather high series resistance (~250 ).
Figure 10. Combined Negative Converter and Positive Doubler
V OUT =
R L1
V + –V –
R L2
+
C 1
The bidirectional characteristics can also be used to
2
1
2
3
4
50
F
TC7662B
Figure 11. Splitting a Supply in Half
50 F
+
-
C 2
50
CHARGE PUMP DC-TO-DC
F
+
+
-
+
-
VOLTAGE CONVERTER
8
7
6
5
V +
© 2001 Microchip Technology Inc.
1
2
3
4
TC7662B
D 1
D 2
V OUT =
(2 V + ) – (2 V F )
8
7
6
5
+
+
V OUT =
– (V + – V F )
C 3
C 4
DS21469A
V +
V –