LM2702MT-ADJ/NOPB National Semiconductor, LM2702MT-ADJ/NOPB Datasheet - Page 19

• Manufacturer Part Number: LM2702MT-ADJ/NOPB
• Description: IC MODULE PANEL TFT DISP 16TSSOP
• Manufacturer: National Semiconductor

Specifications of LM2702MT-ADJ/NOPB

• Applications: LCD Display
• Current - Supply: 2.6mA
• Voltage - Supply: 2.2 V ~ 12 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 16-TSSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: *LM2702MT-ADJ; *LM2702MT-ADJ/NOPB; LM2702MT-ADJ

Operation
Vcom AND Gamma COMPENSATION
The architecture used for the amplifiers in the LM2702 re-
quires external compensation on the output. Depending on
the equivalent capacitive load of the TFT-LCD panel, exter-
nal components at the amplifier outputs may or may not be
necessary. If the capacitance presented by the load is equal
to or greater than 5nF no external components are needed
as the TFT-LCD panel will act as compensation itself. Dis-
tributed resistive and capacitive loads enhance stability and
increase performance of the amplifiers. If the capacitance
presented by the load is less than 5nF external components
will be required as the load itself will not ensure stability. No
external compensation in this case will lead to oscillation of
the amplifier and an increase in power consumption. A single
5nF or greater capacitor on the output will ensure a stable
amplifier with no oscillations. For applications requiring a
higher slew rate, a good choice for compensation is to add a
50Ω (R
C
This allows for driving zero to infinite capacitance loads with
no oscillations, minimal overshoot, and a higher slew rate
than using a large capacitor. The high phase margin created
by the external compensation will guarantee stability and
good performance for all conditions.
For noise sensitive applications greater output capacitance
may be desired. When the power supply for the amplifiers
(AV
the output ripple of the regulator will produce ripple at the
output of the amplifiers.
GAMMA
IN
) is connected to the output of the switching regulator,
COM
) capacitor from the output of the amplifier to ground.
or R
GAMMA
(Continued)
) in series with a 1nF (C
FIGURE 3. Multi-Layer Layout
COM
or
19
LAYOUT CONSIDERATIONS
The LM2702 uses a single ground connection, GND. The
feedback, softstart, delay, and compensation networks
should be connected directly to a dedicated analog ground
plane and this ground plane must connect to the GND pin, as
shown in Figure 3. If no analog ground plane is available
then the ground connections of the feedback, softstart, de-
lay, and compensation networks must tie directly to the GND
pin, as show in Figure 4. Connecting these networks to the
PGND plane can inject noise into the system and effect
performance.
The input bypass capacitor C
IC. This will reduce copper trace resistance which effects
input voltage ripple of the IC. For additional input voltage
filtering, a 100nF bypass capacitor can be placed in parallel
with C
noise to ground. The output capacitor, C
placed close to the IC. Any copper trace connections for the
C
directly effects output voltage ripple and efficiency. The feed-
back network, resistors R1 and R2, should be kept close to
the FB pin, and away from the inductor, to minimize copper
trace connections that can inject noise into the system.
Trace connections made to the inductor and schottky diode
should be minimized to reduce power dissipation and in-
crease overall efficiency.
OUT
capacitor can increase the series resistance, which
IN
, close to the V
IN
pin, to shunt any high frequency
IN
must be placed close to the
20051152
OUT
, should also be
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