2001-2012 Microchip Technology Inc. DS21484D-page 5
TC962
3.0 APPLICATIONS INFORMATION
3.1 Theory of Operation
The TC962 is a capacitive pump (sometimes called a
switched capacitor circuit), where four MOSFET
switches control the charge and discharge of a
capacitor.
The functional block diagram shows how the switching
action works. SW1 and SW2 are turned on simultane-
ously, charging C
P
to the supply voltage, V
IN
. This
assumes that the on resistance of the MOSFETs in
series with the capacitor results in a charging time
(3 time constants) that is less than the on time provided
by the oscillator frequency as shown:
3 (R
DS(ON)
C
P
) < C
P
/(0.5 f
OSC
)
In the next cycle, SW1 and SW2 are turned off and after
a very short interval of all switches being off (this
prevents large currents from occurring due to cross
conduction), SW3 and SW4 are turned on. The charge
in C
P
is then transferred to C
R
, but with the polarity
inverted. In this way, a negative voltage is now derived.
An oscillator supplies pulses to a flip-flop that is then
fed to a set of level shifters. These level shifters then
drive each set of switches at one-half the oscillator
frequency.
The oscillator has two pins that control the frequency of
oscillation. Pin 7 can have a capacitor added that is
returned to ground. This will lower the frequency of the
oscillator by adding capacitance to the timing capacitor
internal to the TC962. Grounding pin 6 will turn on a
current source and double the frequency. This will
double the charge current going into the internal
capacitor, as well as any capacitor added to pin 7.
A Zener diode has been added to the TC962 for use as
a reference in building external regulators. This Zener
runs from pin 1 to ground.
3.2 Latch-Up
All CMOS structures contain a parasitic SCR. Care
must be taken to prevent any input from going above or
below the supply rail, or latch-up will occur. The result
of latch-up is an effective short between V
DD
and V
SS
.
Unless the power supply input has a current limit, this
latch-up phenomena will result in damage to the
device. (See AN763, Latch-up Protection for MOSFET
Drivers.)
FIGURE 3-1: Test Circuit
FIGURE 3-2: Typical Applications
TC962
1
2
3
4
8
690
7
5
C
P
+
10 μF
C
OSC
R
L
V
OUT
(–5V)
10 μF
C
R
I
L
I
S
V
(+5V)
+
NC
+
1
2
3
TC962
4
8
7
6
5
C
P2
C
P1
C
R1
10 μF
V
+
+
+
+
10 μF
V
OUT
= –V
+
V
D1
V
D2
V
OUT
=
+
10 μF
Combined Negative Converter and Positive Multiplier
+
C
P
10 μF
+
1
2
3
4
8
7
6
5
10 μF
C
R
+
V
OUT
=
V
2
+
Split V
+
In Half
TC962
Positive Voltage MultiplierLowering Output Resistance by Paralleling Devices
2V –2V
D
TC962
1
2
3
4
8
7
6
5
10 μF
10 μF
V
OUT
=
+
V
D2
V
D1
++
V
+
C
P
C
P
2V –2V
D
C
P1
10 μF
+
C
P2
10 μF
+
TC962
TC962
1
2
3
4
8
7
6
5
1
2
3
4
8
7
6
5
+
V
+
V
OUT
10 μF
C
R
V
+
