TC7129CPL datasheet(10/24 Pages) MICROCHIP

10 / 24 page

TC7129

DS21459B-page 10

4.5

+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

4.6

Connecting to External Logic

External logic can be directly referenced to DGND

(Pin 36), provided that the supply current of the exter-

nal logic does not exceed the sink current of DGND

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

1.2mA. 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

4.7

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 cir-

cuits that can be adjusted to give temperature com-

pensation of about 10mV/°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

µF

–

VIN

TC7660

V+

GND

0.1

µF

0.1

µF

+5V

TC7129

External

Logic

DGND

ILOGIC

TC7129

V-

–

External

Logic

ILOGIC

DGND

V+

TC7129

V-

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