MAX9665ETP+ Maxim Integrated, MAX9665ETP+ Datasheet - Page 10

• Manufacturer Part Number: MAX9665ETP+
• Description: LCD Gamma Buffers 6/8/10-Channel 10-Bit Nonvolatile Programmable Gamma and VCOM Reference Voltages
• Manufacturer: Maxim Integrated

6/8/10-Channel, 10-Bit, Nonvolatile Programmable
Gamma and VCOM Reference Voltages
The MAX9665/MAX9666/MAX9667 are a family of multi-
channel, programmable reference voltages. Each
channel has a 10-bit DAC to create the reference volt-
age. One channel has an operational amplifier that fol-
lows the DAC while all other channels have a buffer
after the DAC. The user can program the DAC codes
into on-chip nonvolatile memory, which is called multi-
ple-time programmable (MTP) memory since data can
be written into it up to 300 times.
The MAX9665/MAX9666/MAX9667 provide the gamma,
VCOM, and level shifter reference voltages in a LCD
panel. A single chip can potentially replace a discrete
digital variable resistor (DVR), VCOM amplifier, gamma
buffers, high-voltage linear regulator, and resistor
strings. The high-voltage linear regulator can be elimi-
nated because the DAC contains a lowpass filter that
reduces horizontal line frequency noise by 40dB. Power
sequencing is well-controlled since a single chip gener-
ates all the various reference voltages needed for the
LCD panel.
Each part has an I
the MTP memory and the I
ty with legacy flicker adjustment production equipment,
these devices include a single-wire interface that is
compatible with the MAX1512.
With the MTP memory and the I
devices enable automatic gamma and flicker calibra-
tion on a panel-by-panel basis on the production line.
Contact your Maxim representative for more details.
The reference input, REF, accepts a DC voltage
between ground (GND) and the analog supply voltage
(AVDD). The voltage at REF sets the full-scale output of
the DACs. Determine the output voltage using the fol-
lowing equations:
where CODE is the numeric value of the DAC’s binary
input code and N is the bits of resolution. For the
MAX9665 family, N = 10 and CODE ranges from 0 to
1023.
Note that even if REF is less than AVDD, the DAC can
never output REF because the maximum value of
CODE is always one LSB less than the reference. For
example, if REF = 16V and CODE = 1023, then the out-
put voltage is:
10
______________________________________________________________________________________
10-Bit Digital-to-Analog Converters
V
V
OUT
OUT
2
C interface for programming both
= (V
= (16V x 1023)/2
= 15.98438V
Detailed Description
REF
2
C registers. For compatibili-
x CODE)/2
2
C interface, these
10
N
There are two types of DAC output buffers: 5mA and
10mA. The 5mA buffer is guaranteed to source or sink
5mA of DC current within 0.2V of the supplies, and the
10mA buffer does the same with 10mA. The 10mA
buffers should be attached to the ends of the resistor
ladders that set the transfer function of the source dri-
ver (look at the connections from OUT0, OUT4, OUT5,
and OUT9 on the typical operating circuit of the
MAX9667). The 5mA buffers should be attached to the
middle tap points of the resistor ladder because those
places require less current than the ends (see the con-
nections from OUT1, OUT2, OUT7, and OUT8 on the
typical operating circuit of the MAX9667).
If the 10mA buffers cannot provide enough current to
drive the ends of the resistor ladders, attach an addi-
tional resistor from the nearest supply. For example, at
the very top of the resistor ladder, attach an additional
resistor to AVDD. At the very bottom of the resistor lad-
der, attach an additional resistor to GND. The
MAX9665/MAX9666/MAX9667 greatly diminish any
noise from the AVDD supply through the discrete resis-
tor because the high-frequency noise from REF has
been attenuated, and the buffers have excellent AC
PSRR. See Figure 1.
The source drivers can kick back a great deal of cur-
rent to the buffer outputs during a horizontal line
change or a polarity switch. The 5mA DAC output
buffers can source/sink 200mA of peak transient cur-
rent, and the 10mA DAC output buffers can source/sink
400mA of peak transient current to reduce the recovery
time of the output voltages when critical levels and pat-
terns are displayed.
The operational amplifier attached to the bottom DAC
holds the VCOM voltage stable while providing the abil-
ity to source and sink 400mA into the backplane of a
TFT-LCD panel. The operational amplifier can directly
drive the capacitive load of the TFT-LCD backplane
without the need for a series resistor in most cases. The
VCOM amplifier has current limiting on its output to pro-
tect its bond wires.
The output (VCOM) and negative input (FB) of the oper-
ational amplifier are typically connected together in a
unity-gain configuration. If higher output current is
required, add an npn emitter follower and a pnp emitter
follower in the feedback loop.
If a higher, closed-loop gain is desired, add feedback
resistors as shown in Figure 2.
VCOM Amplifier
Gamma Buffers