LM8207MT/NOPB National Semiconductor, LM8207MT/NOPB Datasheet - Page 14

• Manufacturer Part Number: LM8207MT/NOPB
• Description: IC BUFFER+VCOM+VREF 18CH 48TSSOP
• Manufacturer: National Semiconductor

Specifications of LM8207MT/NOPB

• Applications: TFT-LCD Panels: Gamma Buffer, VCOM Driver
• Output Type: Rail-to-Rail
• Number Of Circuits: 18
• -3db Bandwidth: 2MHz
• Slew Rate: 1 V/µs
• Current - Supply: 6.5mA
• Current - Output / Channel: 50mA
• Voltage - Supply, Single/dual (±): 6 V ~ 16 V
• Mounting Type: Surface Mount
• Package / Case: 48-TFSOP (0.240", 6.10mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: *LM8207MT; *LM8207MT/NOPB; LM8207MT

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Application Section
GAMMA BUFFERS
This section gives an overview for the applications of the
gamma buffers and also defines the gamma correction
curve. Specifications for the buffers are derived from their
operation range. Also included are the formulas for the real-
ization of the gamma correction curve using external resis-
tors. An overview is given for the gamma voltage accuracy,
using the LM8207 in combination with external resistors.
As discussed in the section entitled “Principle Operation of a
TFT-LCD,” the basic function of the gamma buffers is to
make the gamma correction curve independent of the be-
havior of the column driver. Writing data to each subsequent
pixel will cause load variations. The gamma buffers have a
low impedance output and can handle these variations with-
out changing the gamma correction curve. A typical gamma
correction curve is given in Figure 8.
FIGURE 7. Voltage Reference Headroom vs. Load
FIGURE 8. Typical Gamma Correction Curve
Current
(Continued)
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Each buffer covers a part of the correction curve and, there-
fore, has its own specifications. All buffers require that the
output should recover quickly from disturbances caused by
the switching of the column driver. The gamma voltage level
of each buffer (VGMA1…VGMA18) depends on its position
for the levels decrease sequentially. To best utilize the
LM8207, each buffer is optimized for its position in the
gamma correction curve.
• Gamma Buffers 1-2
• Gamma Buffers 3-16
• Gamma Buffers 17-18
Example:
A typical application using the LM8207 is given in Figure 9.
The
(VGMA1...VGMA18) is defined in Table 1. The Voltage Ref-
erence supplies the 14.4V to the resistor network. The cal-
culations for the resistor values and for setting the Voltage
Reference are shown in the section “Voltage Reference.”
Operating voltage range: V
operating voltage, only negative transitions at the output
are possible. Positive transitions will exceed the supply
voltage V
bias the resistive load of the column driver having an
open collector structure. To meet the operating voltage
range, these outputs need a resistive load connected to a
lower potential sourcing an output current of at least
1 mA.
Operating voltage range: V
the operating range, both positive and negative transi-
tions at the outputs are possible.
Operating voltage range: V
operating voltage, only positive transitions at the output
are possible. Negative transitions will exceed the nega-
tive supply voltage V
current from the resistive load of the column driver having
an open collector structure. To meet the operating volt-
age range, these outputs need a resistive load connected
to a higher potential sinking an output current of at least
1 mA
corresponding
DD
. These buffers are able to source current to
SS
. These buffers are able to sink
gamma
DD
DD
DD
– 1V to V
to V
- 2 to V
SS
correction
+2V. Due to the
SS
SS
. Due to the
+ 1V. Due to
curve