100mA CHARGE PUMP DC-TO-DC
VOLTAGECONVERTER
TC660
The output characteristics of the circuit in Figure 3 are
those of a nearly ideal voltage source in series with 6.5Ω.
Thus, for a load current of –100mA and a supply voltage of
+5V, the output voltage would be – 4.35V.
Dos and Don'ts
• Do not exceed maximum supply voltages.
• Do not connect the LV terminal to GND for supply
voltages greater than 3.0V.
• Do not short circuit the output to V+ in inverting mode
and for more than 10 sec (a very slow startup!) in
doubler mode.
The dynamic output impedance of the TC660 is due,
primarily, to capacitive reactance of the charge transfer
capacitor (C1). Since this capacitor is connected to the
output for only 1/2 of the cycle, the equation is:
2
XC =
= 0.21Ω,
• When using polarized capacitors in the inverting mode,
the + terminal of C1 must be connected to pin 2 of the
TC660 and the + terminal of C2 must be connected to
GND.
2πf C1
where f = 10 kHz and C1 = 150 µF.
Paralleling Devices
Simple Negative Voltage Converter
Any number of TC660 voltage converters may be paral-
leled to reduce output resistance (Figure 4). The reservoir
capacitor, C2, serves all devices, while each device requires
its own pump capacitor, C1. The resultant output resistance
would be approximately:
Figure 3 shows typical connections to provide a nega-
tive supply where a positive supply is available. A similar
scheme may be employed for supply voltages anywhere in
the operating range of +1.5V to +5.5V, keeping in mind that
pin6(LV)istiedtothesupplynegative(GND)onlyforsupply
voltages below 3.0V.
ROUT (of TC660)
ROUT
=
n (number of devices)
+
V
1
2
3
4
8
7
6
5
V
*
OUT
C
+
1
C
2
150 µF
TC660
150 µF
+
+
+
*
NOTES: 1. V
= –V for 1.5V ≤ V ≤ 5.5V
OUT
Figure 3. Simple Negative Converter
+
V
1
2
3
4
8
7
6
5
1
2
3
4
8
TC660
"1"
R
L
C
7
6
5
1
TC660
C
1
"n"
C
2
+
Figure 4. Paralleling Devices Lowers Output Impedance
4-10
TELCOM SEMICONDUCTOR, INC.
TELCOM [ TELCOM SEMICONDUCTOR, INC ]
