UM4401_16 Datasheet, PDF (4/6 Pages) Union Semiconductor, Inc. – 4 Line ESD/EMI Protection for Color LCD Interfaces

UM4401
Applications Information
Device Connection
The UM4401 is comprised of four identical circuits each consisting of a low pass filter for
EMI/RFI suppression and dual TVS diodes for ESD protection. The device is in a 8-pin DFN
package. Electrical connection is made to the 8 pins located at the bottom of the device. A center
tab serves as the ground connection. The device has a flow through design for easy layout. Pin
connections are noted in Figure 1. All path lengths should be kept as short as possible to minimize
the effects of parasitic inductance in the board traces. Recommendations for the ground
connection are given below.
Ground Connection Recommendation
Parasitic inductance present in the board layout will affect the filtering performance of the device.
As frequency increases, the effect of the inductance becomes more dominant. This effect is given
by Equation 1.
Pin
Identification
1-4
Input Lines
5-8
Output Lines
Center Tab
Ground
Equation 1: The Impedance of an Inductor at
Frequency XLF
XLF(L,f ) = 2×л×f ×L
Where:
L= Inductance (H)
f = Frequency (Hz)
Via connections to the ground plane form rectangular wire loops or ground loop inductance as
shown in Figure 2. Ground loop inductance can be reduced by using multiple vias to make the
connection to the ground plane. Bringing the ground plane closer to the signal layer (preferably
the next layer) also reduces ground loop inductance. Multiple vias in the device ground pad will
result in a lower inductive ground loop over two exterior vias. Vias with a diameter d are
separated by a distance y run between layers separated by a distance x. The inductance of the loop
path is given by Equation 2. Thus, decreasing distance x and y will reduce the loop inductance and
result in better high frequency filter characteristics.
Where:
d = Diameter of the wire (in)
x = Length of wire loop (in)
y = Breath of wire loop (in)
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