Charge Pump DC-TO-DC Voltage Converter
TC1044S
Dos and Don'ts
• Do not exceed maximum supply voltages.
• Do not connect the LV terminal to GND for supply
voltages greater than 3.5V.
• Do not short circuit the output to V
+
supply for voltages
above 5.5V for extended periods; however, transient
conditions including start-up are okay.
• When using polarized capacitors in the inverting mode,
the + terminal of C
1
must be connected to pin 2 of the
TC1044S 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 70Ω.
Thus, for a load current of –10mA and a supply voltage of
+5V, the output voltage would be – 4.3V.
The dynamic output impedance of the TC1044S 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
=
= 3.18Ω,
2πf C
1
where f = 10 kHz and C
1
= 10µF.
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 +12V, keeping in mind that
pin 6 (LV) is tied to the supply negative (GND) only for supply
voltages below 3.5V.
V+
1
C1
10µF
+
2
TC1044S
3
4
6
5
+
8
7
VOUT
*
C2
10µF
Any number of TC1044S voltage converters may be
paralleled to reduce output resistance (Figure 4). The reser-
voir 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
(of TC1044S)
n (number of devices)
R
OUT
=
*
NOTES:
Figure 3. Simple Negative Converter
V+
1
2
C1
8
7
TC1044S
3
4
"1"
6
5
C1
1
2
8
7
RL
TC1044S
3
4
"n"
6
5
+
C2
Figure 4. Paralleling Devices Lowers Output Impedance
TC1044S-12 9/16/96
4
© 2001 Microchip Technology Inc.
DS21348A
MICROCHIP [ MICROCHIP TECHNOLOGY ]
