TC7660_02 datasheet(7/18 Pages) MICROCHIP

7 / 18 page

 2002 Microchip Technology Inc.

DS21465B-page 7

TC7660

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 +10V,

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

Ω resistor. Thus, for a load current of -10 mA and

a supply voltage of +5V, the output voltage would be

-4.3V.

5.2

Paralleling Devices

To reduce the value of ROUT, multiple TC7660 voltage

converters can be connected in parallel (Figure 5-2).

The output resistance will be reduced by approximately

a factor of n, where n is the number of devices

connected in parallel.

EQUATION

While each device requires its own pump capacitor

(C1), all devices may share one reservoir capacitor

(C2). To preserve ripple performance, the value of C2

should be scaled according to the number of devices

connected in parallel.

5.3

Cascading Devices

A larger negative multiplication of the initial supply volt-

age can be obtained by cascading multiple TC7660

devices. The output voltage and the output resistance

will both increase by approximately a factor of n, where

n is the number of devices cascaded.

EQUATION

FIGURE 5-2:

Paralleling Devices Lowers Output Impedance.

FIGURE 5-3:

Increased Output Voltage By Cascading Devices.

V+

TC7660

VOUT*

10 µF

* VOUT = -V+ for 1.5V ≤ V+ ≤ 10V

10 µF

ROUT

ROUT of TC7660

()

n number of devices

()

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

VOUT

– V

()

ROUT

× OUT of TC7660

()

“n”

“1”

V+

TC7660

OUT *

“1”

V+

TC7660

10 µF

* VOUT = -n V

+ for 1.5V ≤ V+ ≤ 10V

“n”

TC7660

10 µF

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