LMV7275MG National Semiconductor, LMV7275MG Datasheet - Page 12

• Manufacturer Part Number: LMV7275MG
• Description: IC,VOLT COMPARATOR,SINGLE,BICMOS,TSSOP,5PIN,PLASTIC
• Manufacturer: National Semiconductor

Specifications of LMV7275MG

• Rohs Compliant: NO

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Application Notes
CIRCUIT TECHNIQUES FOR AVOIDING OSCILLATIONS
IN COMPARATOR APPLICATIONS
Feedback to almost any pin of a comparator can result in
oscillation. In addition, when the input signal is a slow volt-
age ramp or sine wave, the comparator may also burst into
oscillation near the crossing point. To avoid oscillation or
instability, PCB layout should be engineered thoughtfully.
Several precautions are recommended:
1. Power supply bypassing is critical, and will improve sta-
2. Keep all leads short to reduce stray capacitance and lead
3. It is a good practice to use an unbroken ground plane on
FIGURE 4. Non-Inverting Comparator with Hysteresis
bility and transient response. Resistance and inductance
from power supply wires and board traces increase
power supply line impedance. When supply current
changes, the power supply line will move due to its im-
pedance. Large enough supply line shift will cause the
comparator to mis-operate. To avoid problems, a small
bypass capacitor, such as 0.1uF ceramic, should be
placed immediately adjacent to the supply pins. An addi-
tional 6.8µF or greater tantalum capacitor should be
placed at the point where the power supply for the com-
parator is introduced onto the board. These capacitors
act as an energy reservoir and keep the supply imped-
ance low. In dual supply application, a 0.1µF capacitor is
recommended to be placed across V
inductance. It will also minimize any unwanted coupling
from any high-level signals (such as the output). The
comparators can easily oscillate if the output lead is
inadvertently allowed to capacitively couple to the inputs
via stray capacitance. This shows up only during the
output voltage transition intervals as the comparator
changes states. Try to avoid a long loop which could act
as an inductor (coil).
a printed circuit board to provide all components with a
(Continued)
+
and V
−
pins.
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4. The output trace should be routed away from inputs. The
5. When the signal source is applied through a resistive
6. All pins of any unused comparators should be tied to the
micro SMD LIGHT SENSITIVITY
Exposing the micro SMD device to direct sunlight will cause
mis-operation of the device. Light sources such as Halogen
lamps can also affect electrical performance if brought near
to the device. The wavelengths, which have the most detri-
mental effect, are reds and infrareds.
micro SMD MOUNTING
The micro SMD package requires specific mounting tech-
niques, which are detailed in National Semiconductor Appli-
cation Note AN-1112.
LMV7272 micro SMD to DIP Conversion Board
To facilitate characterization and testing, a micro SMD to DIP
conversion board, LMV7272TLCONV, is available. It is a
2-layer board, with the LMV7272 mounted on the bottom
layer, and a capacitor (C1, between the positive and nega-
tive supplies) added to the top layer.
low inductive ground connection. Make sure ground
paths are low-impedance where heavier currents are
flowing to avoid ground level shift. Preferably there
should be a ground plane under the component.
ground plane should extend between the output and
inputs to act as a guard. This can be achieved by running
a topside ground plane between the output and inputs. A
typical PCB layout is shown in Figure 5.
network to one input of the comparator, it is usually
advantageous to connect the other input with a resistor
with the same value, for both DC and AC consideration.
Input traces should be laid out symmetrically if possible.
negative supply.
FIGURE 5. Typical PCB Layout
LMV7272TLCONV Diagram
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