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LM2903 Datasheet(PDF) 8 Page - 3PEAK INC.

Part No. LM2903
Description  36V Low Power Dual/Quad Differential Comparators
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Maker  3PEAK [3PEAK INC.]
Homepage  http://www.3peakic.com/
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LM2903 Datasheet(HTML) 8 Page - 3PEAK INC.

 
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8
LM2903/LM2901
36V Low Power Dual/Quad Differential Comparators
Rev. B
www.3peakic.com.cn
current to flow, which is greater than the LM2903/LM2901
’s input bias current at +27°C (±6pA, typical). It is
recommended to use multi-layer PCB layout and route the comparator
’s -IN and +IN signal under the PCB
surface.
The effective way to reduce surface leakage is to use a guard ring around sensitive pins (or traces). The guard
ring is biased at the same voltage as the sensitive pin. An example of this type of layout is shown in Figure 5 for
Inverting configuration application.
1. For Non-Inverting Configuration:
a) Connect the non-inverting pin (VIN+) to the input with a wire that does not touch the PCB surface.
b) Connect the guard ring to the inverting input pin (VIN
–). This biases the guard ring to the same reference as the
comparator.
2. For Inverting Configuration:
a) Connect the guard ring to the non-inverting input pin (VIN+). This biases the guard ring to the same reference voltage as
the comparator (e.g., VDD/2 or ground).
b) Connect the inverting pin (VIN
–) to the input with a wire that does not touch the PCB surface.
VIN+
VIN-
+VS
Guard Ring
Figure 5. Example Guard Ring Layout for Inverting Comparator
Ground Sensing and Rail to Rail Output
The LM2903/2901 family implements a rail-to-rail topology that is capable of swinging to within 10mV of either rail.
Since the inputs can go 300mV beyond either rail, the comparator
can easily perform ‘true ground’ sensing.
The maximum output current is a function of total supply voltage. As the supply voltage of the comparator
increases, the output current capability also increases. Attention must be paid to keep the junction temperature of
the IC below 150°C when the output is in continuous short-circuit condition. The output of the amplifier has
reverse-biased ESD diodes connected to each supply. The output should not be forced more than 0.5V beyond
either supply, otherwise current will flow through these diodes.
ESD
The LM2903/2901 family has reverse-biased ESD protection diodes on all inputs and output. Input and output
pins cannot be biased more than 300mV beyond either supply rail.
Power Supply Layout and Bypass
The LM2903/2901 family
’s power supply pin should have a local bypass capacitor (i.e., 0.01μF to 0.1μF) within
2mm
for good high frequency performance. It can also use a bulk capacitor (i.e., 1μF or larger) within 100mm to
provide large, slow currents. This bulk capacitor can be shared with other analog parts.
Good ground layout improves performance by decreasing the amount of stray capacitance and noise at the
comparator
’s inputs and outputs. To decrease stray capacitance, minimize PCB lengths and resistor leads, and
place external components as close to the comparator
’ pins as possible.
Proper Board Layout
The LM2903/2901 family is a series of fast-switching, high-speed comparator and requires high-speed layout
considerations. For best results, the following layout guidelines should be followed:
1. Use a printed circuit board (PCB) with a good, unbroken low-inductance ground plane.
2. Place a decoupling capacitor (0.1
μF ceramic, surface-mount capacitor) as close as possible to supply.
3. On the inputs and the output, keep lead lengths as short as possible to avoid unwanted parasitic feedback
around the comparator. Keep inputs away from the output.


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