TC1225 Datasheet, PDF (5/10 Pages) Microchip Technology – Inverting Dual (-VIN, -2VIN) Charge Pump Voltage Converters

Inverting Dual (–V_IN, –2V_IN)
Charge Pump Voltage Converters
TC1225
TC1226
TC1227
Dual Voltage Inverter
The most common application for the TC1225/1226/
1227 devices is the dual voltage inverter (Figure 2). This
application uses four external capacitors: C1, C2, C_OUT1,
and C_OUT2 (NOTE: a power supply bypass capacitor is
recommended). The outputs are equal to – V_IN and –2VIN
plus any voltage drops due to loading. Refer to Tables 1a,
1b, 2a, and 2b for capacitor selection guidelines.
Device
TC1225
TC1226
TC1227
C_IN
C1
3.3µF 3.3µF
1µF 1µF
0.33µF 0.33µF
C2
1µF
0.33µF
0.1µF
C_OUT1
3.3µF
1µF
0.33µF
C_OUT2
1µF
0.33µF
0.1µF
V_IN
C_IN
6
C1
7 _C1+
V_IN
–V_IN ⁸
1 _{C1– TC1225}
C_OUT1
R_L1
2 _C2+
TC1226
TC1227
C2
4
–2V_IN
3 _C2–
GND
C_OUT2
R_L2
5
V_OUT1
V_OUT2
Figure 3 is a schematic of the TC1225 DEMO Card, and
Figure 4 shows the assembly drawing and artwork for the
board. Table 3 lists the voltages that are monitored by the
test points and Table 4 lists the currents that can be
measured using the jumpers.
Table 3. TC1225 DEMO Card Test Points
TEST POINT VOLTAGE MEASUREMENT
TP1
VIN [+5V]
TP2
GROUND
TP3
GROUND
TP4
TCM828 U1 OUTPUT [-5V(1)]
TP5
TCM828 U2 OUTPUT [-10V(1)]
TP6
TC1225 STAGE 1 OUTPUT [-5V(2)]
TP7
TC1225 STAGE 2 OUTPUT [-10V(2)]
Table 4. TC1225 DEMO Card Jumpers
JUMPER
CURRENT MEASUREMNT
J1
DUAL TCM828 QUIESCENT CURRENT
J2
TC1225 QUIESCENT CURRENT
J3
TCM828 U1 [-5V(1)] LOAD CURRENT
J4
TCM828 U2 [-10V(1)] LOAD CURRENT
J5
TC1225 STAGE 1 [-5V(2)] LOAD CURRENT
J6
TC1225 STAGE 2 [-10V(2)] LOAD CURRENT
Figure 2. Dual Voltage Inverter Test Circuit
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. Also use a large ground plane to minimize
noise leakage into other circuitry.
TC1225 DEMO CARD
The TC1225 DEMO Card is a 2.0” x 2.0” card containing
both a TC1225 and two cascaded TCM828s that allow the
user to compare the operation of each approach for gener-
ating a –1X and –2X function. Each circuit is fully assembled
with the required external capacitors along with variable
load resistors that allow the user to vary the output load
current of each stage. For convenience, several test points
and jumpers are available for measuring various voltages
and currents on the demo board.
© 2001 Microchip Technology Inc. DS21369A
5
TC1225/6/7-1 3/24/00