TC7660SCOA datasheet(9/24 Pages) MICROCHIP

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DS20001467C-page 9

TC7660S

5.0

APPLICATIONS INFORMATION

5.1

Simple Negative Voltage

Converter

Figure 5-1 shows typical connections to provide a

negative 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.

FIGURE 5-1:

Simple Negative Converter.

The output characteristics of the circuit in Figure 5-1

are those of a nearly ideal voltage source in series with

a 70

resistor. Thus, for a load current of -10 mA 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 half of the cycle, the equation is:

EQUATION

5.2

Paralleling Devices

Any number of TC7660S voltage converters may be

paralleled to reduce output resistance (Figure 5-2). The

reservoir capacitor, C2, serves all devices, while each

device requires its own pump capacitor, C1. The resul-

tant output resistance would be approximately:

EQUATION

FIGURE 5-2:

Paralleling Devices Lowers Output Impedance.

FIGURE 5-3:

Increased Output Voltage By Cascading Devices.

V+

TC7660S

VOUT*

10 µF

* VOUT = -V

+ for 1.5V  V+  12V

10 µF

2fC

-----------

3.18



where:

f = 10 kHz and C1 = 10 µF.

OUT

OUT of TC7660S



n number of devices



---------------------------------------------------

“n”

“1”

V+

TC7660S

OUT *

“1”

V+

TC7660S

10 µF

VOUT = -n V+ for 1.5V  V+  12V

“n”

TC7660S

10 µF

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