TC1240A Datasheet, PDF (10/16 Pages) Microchip Technology – Positive Doubling Charge Pumps with Shutdown in a SOT-23 Package

TC1240/TC1240A
5.7 Cascading Devices
Two or more TC1240/TC1240As can be cascaded to
increase output voltage (Figure 5-4). If the output is
lightly loaded, it will be close to ((n + 1) x V_IN), but will
droop at least by R_OUT of the first device multiplied by
the I_Q of the second. It can be seen that the output
resistance rises rapidly for multiple cascaded devices.
For the case of the two-stage ‘tripler’, output resistance
can be approximated as R_OUT = 2 x R_OUT1 + R_OUT2,
where R_OUT1 is the output resistance of the first stage
and R_OUT2 is the output resistance of the second stage.
5.8 Paralleling Devices
To reduce the value of R_OUT, multiple TC1240/
TC1240As can be connected in parallel (Figure 5-5).
The output resistance will be reduced by a factor of N,
where N is the number of TC1240/TC1240As. Each
device will require its own pump capacitor (C1x), but all
devices may share one reservoir capacitor (C2).
However, to preserve ripple performance, the value of
C2 should be scaled according to the number of
paralled TC1240/TC1240As, respectively.
5.9 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.
FIGURE 5-4:
+
C_1A
V_IN
6 _C+
V_IN ¹
TC1240
TC1240A
2 _GND
3 _{C- "1" OUT} 5
4 _SHDN
+
6 _C+
V_IN ¹
+ C_{1B TC1240}
TC1240A
2 _GND
3
4
C- "n"
SHDN
OUT
5
+
C_2A
V_OUT
C_2B
V_OUT = (n + 1)V_IN
Cascading Multiple Devices To Increase Output Voltage.
R_OUT =
R_OUT OF SINGLE DEVICE
NUMBER OF DEVICES
V_IN ^{. . .}
V_IN
FIGURE 5-5:
C_{1A +}
Shutdown
Control
3
TC1240
2 _TC1240A
6
"1"
4 _SHDN
1
C_1B
5
1
3
TC1240
2 _TC1240A
+
6
4
"n"
SHDN
5
...
+
V_OUT = 2 x V_IN
V_OUT
C₂
Paralleling Multiple Devices To Reduce Output Resistance.
DS21516C-page 10
 2003 Microchip Technology Inc.