BUF04701 datasheet(15/30 Pages) TI2

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InputDataHEX0

DD1

SS1

GMA1

GMA2

GMA3

GMA4

GMA5

GMA6

GMA7

GMA8

GMA9

GMA10

=10V

R =2k

COM

100

1000

LoadCapacitance,C (pF)

BUF07703

BUF06703

BUF05703

www.ti.com

SBOS269C – MARCH 2003 – REVISED APRIL 2010

INPUT VOLTAGE RANGE GAMMA BUFFERS

Connect buffer 1 to the gamma voltage closest to

VDD, and buffers 2 and 3 to the sequential voltages.

Figure 36 shows a typical gamma correction curve

Buffer

should

connected

the

gamma

with 10 gamma correction reference points (GMA1

correction voltage closest to GND (or the negative

through GMA10). As can be seen from this curve, the

rail), buffers 4 and 5 to the sequential higher

voltage requirements for each buffer varies greatly.

voltages.

The swing capability of the input stages of the various

buffers in the BUFxx703 is carefully matched to the

COMMON BUFFER (VCOM)

application. Using the example of the BUF07703 with

six gamma correction channels, buffers 1 to 3 have

The common buffer output of the BUF07703 and

input stages that include VDD, but will only swing

BUF05703 has a greater output drive capability than

within 1V to GND. Buffers 1 through 5 have only a

the gamma correction buffers, to meet the heavier

single NMOS input stage. Buffers 4 through 6 have

current demands of driving the common node of the

only a single PMOS input stage. The input range of

LCD panel. It was also designed to drive heavier

the PMOS input stage includes GND.

capacitive loads and still remain stable, as shown in

Figure 37.

Figure 36. Gamma Correction Curve

Figure 37. Phase Shift vs Load Capacitance

OUTPUT VOLTAGE SWING GAMMA

CAPACITIVE LOAD DRIVE

BUFFERS

The BUFxx703 has been designed to be able to

The output stages have been designed to match the

sink/source DC currents in excess of 10mA. Its output

characteristic of the input stage. Once again using

stage has been designed to deliver output current

the example of the BUF07703 means that the output

transients with little disturbance of the output voltage.

stage of buffer 1 swings very close to VDD, typically

However, there are times when very fast current

VCC − 100mV at 5mA; its ability to swing to GND is

pulses are required. Therefore, in LCD source-driver

limited. Buffers 2 and 3 have smaller output stages

buffer applications, it is quite normal for capacitors to

with slightly larger output resistances, as they will not

be placed at the outputs of the reference buffers.

have to swing as close to the positive rail as buffer 1.

These are to improve the transient load regulation.

Buffers 4 through 6 swing closer to GND than VDD.

These will typically vary from 100pF and more. The

Buffer 6 is designed to swing very close to GND,

BUFxx703 gamma buffers were designed to drive

typically GND + 100mV at a 5mA load current. See

capacitances in excess of 100pF and retain effective

the Typical Characteristics for more details. This

phase margins above 50°, as shown in Figure 38.

approach significantly reduces the silicon area and

cost of the whole solution. However, due to this

architecture, the correct buffer needs to be connected

to the correct gamma correction voltage.

Product Folder Link(s): BUF07703 BUF06703 BUF05703

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