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TC7660S Datasheet PDF : 8 Pages
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SUPER CHARGE PUMP DC-TO-DC
VOLTAGE CONVERTER
TC7660S
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
TC7660S 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.
V+
C1 +
10µF
1
8
2
7
3 TC7660S 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 TC7660S 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 = 2πf C1 = 3.18Ω,
where f = 10kHz and C1 = 10µF.
Paralleling Devices
Any number of TC7660S 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:
ROUT =
ROUT (of TC7660S)
n (number of devices)
* NOTES:
Figure 3. Simple Negative Converter
V+
1
8
2
7
C1
TC7660S
3
6
4
"1"
5
1
8
2
7
RL
C1
3 TC7660S 6
4
"n"
5
+ C2
Figure 4. Paralleling Devices Lowers Output Impedance
4-72
TELCOM SEMICONDUCTOR, INC.
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