TC7129_13 datasheet(10/28 Pages) MICROCHIP

10 / 28 page

TC7129

DS21459E-page 10

 2002-2012 Microchip Technology Inc.

4.2.3

+5V Power Supply

Measurements are made with respect to power supply

ground. COMMON (pin 28) is connected to REF LO

(pin 35). A voltage doubler is needed, since the supply

voltage is less than the 6V minimum needed by the

TC7129. DGND (pin 36) must be isolated from power

supply ground (see Figure 4-3).

Figure 4-3:

Powering the TC7129 From

a +5V Power Supply.

4.3

Connecting to External Logic

External logic can be directly referenced to DGND

(pin 36), provided that the supply current of the external

logic does not exceed the sink current of DGND

(Figure 4-4). A safe value for DGND sink current is

1.2 mA. If the sink current is expected to exceed this

value, a buffer is recommended (see Figure 4-5).

Figure 4-4:

External Logic Referenced

Directly to DGND.

Figure 4-5:

External Logic Referenced

to DGND with Buffer.

4.4

Temperature Compensation

For most applications, VDISP (pin 19) can be connected

directly to DGND (pin 36). For applications with a wide

temperature range, some LCDs require that the drive

levels vary with temperature to maintain good viewing

angle and display contrast. Figure 4-6 shows two

circuits that can be adjusted to give temperature com-

pensation of about 10 mV/°C between V+ (pin 24) and

VDISP. The diode between DGND and VDISP should

have a low turn-on voltage because VDISP cannot

exceed 0.3V below DGND.

V–

V+

DGND

10 µF

–

VIN

TC7660

V+

GND

0.1 µF

+5V

TC7129

External

Logic

DGND

ILOGIC

TC7129

V-

–

External

Logic

ILOGIC

DGND

V+

TC7129

V–

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