TC1044S Microchip Technology, TC1044S Datasheet - Page 6

• Manufacturer Part Number: TC1044S
• Description: Charge Pump DC-TO-DC Voltage Converter
• Manufacturer: Microchip Technology

TC1044S-12 9/16/96
TC1044S
Combined Negative Voltage Conversion
and Positive Supply Multiplication
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
perform the pump and reservoir functions, respectively, for
the generation of the negative voltage, while capacitors C
and C
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.
Efficient Positive Voltage
Multiplication/Conversion
eration are bidirectional, the charge transfer can be per-
formed backwards as easily as forwards. Figure 10 shows
a TC1044S 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
Figure 9 combines the functions shown in Figures 3 and
Since the switches that allow the charge pumping op-
C 1
4
are pump and reservoir, respectively, for the multi-
+
1
2
3
4
Figure 7. Lowering Oscillator Frequency
TC1044S
Figure 8. Positive Voltage Multiplier
1
2
3
4
TC1044S
8
7
6
5
8
7
6
5
D 1
+
V +
C 1
D 2
+
+
V OUT =
(2 V + ) – (2 V F )
C 2
V
C 2
C OSC
+
V OUT
1
and C
Charge Pump DC-TO-DC Voltage Converter
3
2
6
will bypass the other (D
on), or else the diode and resistor shown dotted in Figure 10
can be used to "force" the internal regulator on.
Voltage Splitting
can also be used to split a higher supply in half, as shown in
Figure 11. The combined load will be evenly shared be-
tween the two sides. Once again, 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
5, +15V can be converted (via +7.5V and –7.5V) to a nominal
–15V, though with rather high series resistance (~250 ).
Negative Voltage Generation for
Display ADCs
a fixed power supply system, the TC7106 will perform
conversions with input signal referenced to power supply
ground.
Negative Supply Generation for 4
Data Acquisition System
supplies. The TC1044S provides an inexpensive –5V source.
(See AN16 and AN17 for TC7135 interface details and
software routines.)
Figure 9. Combined Negative Converter and Positive Multiplier
+
C 1
The same bidirectional characteristics used in Figure 10
The TC7106 is designed to work from a 9V battery. With
The TC7135 is a 4
1
2
3
4
TC1044S
C 2
+
1
and D
8
7
6
5
digit ADC operating from 5V
© 2001 Microchip Technology Inc.
2
V +
in Figure 9 would never turn
D 1
D 2
V OUT =
(2 V + ) – (2 V F )
+
+
Digit
V OUT = –V +
C 3
C 4
DS21348A