100mA CHARGE PUMP DC-TO-DC
VOLTAGE CONVERTER
TC660
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.
• When using polarized capacitors in the inverting mode,
the + terminal of C
1
must be connected to pin 2 of the
TC660 and the + terminal of C
2
must be connected to
GND.
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.
The dynamic output impedance of the TC660 is due,
primarily, to capacitive reactance of the charge transfer
capacitor (C
1
). Since this capacitor is connected to the
output for only 1/2 of the cycle, the equation is:
2
X
C
=
= 0.21Ω,
2πf C
1
where f = 10 kHz and C
1
= 150
µF.
Paralleling Devices
Simple Negative Voltage Converter
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
pin 6 (LV) is tied to the supply negative (GND) only for supply
voltages below 3.0V.
V
1
C1
150 µF
+
2
3
4
8
7
VOUT
*
C2
150 µF
+
Any number of TC660 voltage converters may be paral-
leled to reduce output resistance (Figure 4). The reservoir
capacitor, C
2
, serves all devices, while each device requires
its own pump capacitor, C
1
. The resultant output resistance
would be approximately:
R
OUT
=
R
OUT
(of TC660)
n (number of devices)
TC660
6
5
+
*
NOTES:
1. VOUT = –V+ for 1.5V
≤
V+
≤
5.5V
Figure 3. Simple Negative Converter
V+
1
2
C1
3
4
8
7
1
2
C1
3
4
8
7
RL
TC660
"1"
6
5
TC660
"n"
6
5
+
C2
Figure 4. Paralleling Devices Lowers Output Impedance
4-10
TELCOM SEMICONDUCTOR, INC.
TELCOM [ TELCOM SEMICONDUCTOR, INC ]
