Datasheet

TC1044S-12 9/16/96
TC1044S
Charge Pump DC-TO-DC Voltage Converter
4
© 2001 Microchip Technology Inc. DS21348A
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:
Paralleling Devices
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:
2
2πf C
1
X
C
= = 3.18Ω,
where f = 10 kHz and C
1
= 10µF.
Figure 4. Paralleling Devices Lowers Output Impedance
1
2
3
4
8
7
6
5
TC1044S
V
+
1
2
3
4
8
7
6
5
TC1044S
C
1
R
L
C
2
C
1
"n"
"1"
+
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.
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.
1
2
3
4
8
7
6
5
TC1044S
10µF
+
V
+
10µF
+
V
OUT
*
NOTES:*
C
1
C
2
Figure 3. Simple Negative Converter
R
OUT
(of TC1044S)
n (number of devices)
R
OUT
=