UM8401_16 Datasheet, PDF (4/7 Pages) Union Semiconductor, Inc. – 8 Line ESD/EMI Protection for Color LCD Interfaces

UM8401
Applications Information
Device Connection
The UM8401 is comprised of eight 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 16-pin DFN package.
Electrical connection is made to the 16 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. 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
1-8
Input Lines
9 - 16
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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