TC1221ECHTR Datasheet, PDF (8/16 Pages) Microchip Technology – High Frequency Switched Capacitor Voltage Converters with Shutdown in SOT Packages

TC1221/TC1222
4.9 Voltage Doubler/Inverter
Another common application of the TC1221/TC1222 is
shown in Figure 4-6. This circuit performs two functions
in combination. C1 and C2 form the standard inverter
circuit described above. C3 and C4 plus the two diodes
form the voltage doubler circuit. C1 and C3 are the
pump capacitors and C2 and C4 are the reservoir
capacitors. Because both sub-circuits rely on the same
switches if either output is loaded, both will droop
toward GND. Make sure that the total current drawn
from both the outputs does not total more than 40mA.
4.10 Diode Protection for Heavy Loads
When heavy loads require the OUT pin to sink large
currents being delivered by a positive source, diode
protection may be needed. The OUT pin should not be
allowed to be pulled above ground. This is
accomplished by connecting a Schottky diode
(1N5817) as shown in Figure 4-7.
4.11 Layout Considerations
As with any switching power supply circuit, good layout
practice is recommended. Mount components as close
together as possible to minimize stray inductance and
capacitance. Noise leakage into other circuitry can be
minimized with the use of a large ground plane.
FIGURE 4-6:
COMBINED DOUBLER AND INVERTER
V_IN
3
2
C1
+
4
TC1221
TC1222
D1, D2 = 1N4148
D1
6
1
5
Shutdown
Control
+
C3
C2
+
D2
+
C4
V_OUT = -V_IN
V_OUT = (2V_IN) –
(V_FD1) – (V_FD2)
FIGURE 4-7:
HIGH V– LOAD CURRENT
4
GND
TC1221
TC1222
OUT ¹
DS21367B-page 8
 2002 Microchip Technology Inc.