TC1235 Datasheet, PDF (5/10 Pages) Microchip Technology – Inverting Dual (-VIN, -2VIN) Charge Pump Voltage Converters with Shutdown

Inverting Dual (–V_IN, –2V_IN)
Charge Pump Voltage Converters
with Shutdown
TC1235
TC1236
TC1237
Input Supply Bypassing
Layout Considerations
TheV_IN 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 V_IN
to GND for optimal circuit performance.
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.
Shutdown Input
TC1235 DEMO Card
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 V_IN 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, 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
TC1235
TC1236
TC1237
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
78
C1
9 _C1+
V_IN SHDN
–V_IN ¹⁰
1 _{C1– TC1235}
C_OUT1
R_L1
2 _C2+
TC1236
TC1237
C2
5
–2V_IN
4 _C2–
GND
C_OUT2
R_L2
6
V_OUT1
V_OUT2
Figure 2. Dual Voltage Inverter Test Circuit
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
TP2
TP3
TP4
TP5
TP6
TP7
TP8
TP9
TP10
VIN [+5V]
GROUND
GROUND
TC1219 U1 OUTPUT [-5V(1)]
TC1219 U2 OUTPUT [-10V(1)]
TC1235 STAGE 1 OUTPUT [-5V(2)]
TC1235 STAGE 2 OUTPUT [-10V(2)]
EXTERNAL /SHDN INPUT
TC1219 U1 /SHDN INPUT
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
© 2001 Microchip Technology Inc. DS21371A
5
TC1235/6/7-1 3/24/00