TC1044S Datasheet, PDF (4/11 Pages) TelCom Semiconductor, Inc – CHARGE PUMP DC-TO-DC VOLTAGE CONVERTER

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 C₁ must be connected to pin 2 of the
TC1044S and the + terminal of C₂ 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.
C1 +
10µF
V+
1
8
2
7
TC1044S
3
6
4
5
VOUT*
C2
+ 10µF
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 (C₁). Since this capacitor is connected to the
output for only 1/2 of the cycle, the equation is:
2
X_C = _{2πf C1} = 3.18Ω,
where f = 10 kHz and C₁ = 10µF.
Paralleling Devices
Any number of TC1044S voltage converters may be
paralleled to reduce output resistance (Figure 4). The reser-
voir capacitor, C₂, serves all devices, while each device
requires its own pump capacitor, C₁. The resultant output
resistance would be approximately:
R_OUT =
R_OUT (of TC1044S)
n (number of devices)
* NOTES:
Figure 3. Simple Negative Converter
V+
1
8
2
7
TC1044S
C1
3
6
4
"1"
5
1
8
2
7
RL
TC1044S
C1
3
6
4
"n"
5
TC1044S-12 9/16/96
Figure 4. Paralleling Devices Lowers Output Impedance
4
+ ^C2
© 2001 Microchip Technology Inc. DS21348A