5
TC1235
TC1236
TC1237
Inverting Dual (–VIN, –2VIN)
Charge Pump Voltage Converters
with Shutdown
TC1235/6/7-1 3/24/00
2001 Microchip Technology Inc.
DS21371A
Input Supply Bypassing
TheVIN input should be capacitively bypassed to reduce
AC impedance and minimize noise effects due to the switch-
ing internal to the device. It is recommended that a large
value capacitor (at least equal to C1) be connected from VIN
to GND for optimal circuit performance.
Shutdown Input
The TC12351/1236/1237 is enabled when /SHDN is
high, and disabled when /SHDN is low. This input cannot be
allowed to float. (If /SHDN is not required, see the TC1225/
1226/1227 data sheet.) The /SHDN input should be limited
to 0.3V above VIN to avoid significant current flows.
Dual Voltage Inverter
The most common application for the TC1235/1236/
1237 devices is the dual voltage inverter (Figure 2). This
application uses four external capacitors: C1, C2, COUT1,
and COUT2 (NOTE: a power supply bypass capacitor is
recommended). The outputs are equal to – VIN and –2VIN
plus any voltage drops due to loading. Refer to Tables 1a,
1b, 2a, and 2b for capacitor selection guidelines.
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.
TC1235 DEMO Card
The TC1235 DEMO Card is a 2.0” x 2.0” card containing
both a TC1235 and two cascaded TC1219s 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.
Figure 3 is a schematic of the TC1235 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. TC1235 DEMO Card Test Points
TEST POINT
VOLTAGE MEASUREMENT
TP1
VIN [+5V]
TP2
GROUND
TP3
GROUND
TP4
TC1219 U1 OUTPUT [-5V(1)]
TP5
TC1219 U2 OUTPUT [-10V(1)]
TP6
TC1235 STAGE 1 OUTPUT [-5V(2)]
TP7
TC1235 STAGE 2 OUTPUT [-10V(2)]
TP8
EXTERNAL /SHDN INPUT
TP9
TC1219 U1 /SHDN INPUT
TP10
TC1235 U3 /SHDN INPUT
Table 4. TC1235 DEMO Card Jumpers
JUMPER
CURRENT MEASUREMNT
J1
DUAL TC1219 QUIESCENT CURRENT
J2
TC1235 QUIESCENT CURRENT
J3
TC1219 U1 [-5V(1)] LOAD CURRENT
J4
TC1219 U2 [-10V(1)] LOAD CURRENT
J5
TC1235 STAGE 1 [-5V(2)] LOAD CURRENT
J6
TC1235 STAGE 2 [-10V(2)] LOAD CURRENT
J7
TC1219 U1 /SHDN INPUT CURRENT
J8
TC1235 U3 /SHDN INPUT CURRENT
J9
GROUND EXTERNAL /SHDN INPUT
C1
C2
V
IN
C
IN
R
L1
V
OUT1
V
OUT2
R
L2
–V
IN
V
IN
C
OUT1
C
OUT2
–2V
IN
TC1235
TC1236
TC1237
C1–
SHDN
C2–
2
1
9
7
8
10
5
6
4
C1+
C2+
GND
Device
CIN
C1
C2
COUT1
COUT2
TC1235
3.3
F 3.3F
1
F
3.3
F
1
F
TC1236
1
F
1
F 0.33F
1
F
0.33
F
TC1237
0.33
F 0.33F
0.1
F 0.33F
0.1
F