AN3357
Application note
HSP061-8M16 high speed line protection on HDMI 1.4 link
Introduction
This Application note presents the HSP061-8M16 and its capability to protect HDMI 1.3 and
HDMI 1.4 TMDS lines.
The HDMI interface is provided for transmitting digital television audiovisual signals from
DVD players, set-top- boxes and other source to television sets and other video displays.
HSP061-8M16 has been developed to be compliant with:
■
HDMI version 1.4 standard knowing the key point is the capability to transfer data with a
maximum rate of 3.4 Gbps per channel without distortion. This leads the HSP061-8M16
to have a large bandwidth, to pass fast voltage slope and to keep the 100
Ω
line
impedance, HSP061-8M16 is used on the TMDS line.
IEC 61000-4-2 level 4 (15 kV contact discharge)
■
April 2011
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Location for HSP061-8M16
AN3357
1
Location for HSP061-8M16
Many PCB parasitic elements may degrade the overall ESD performance of a system. The
recommendations below are aimed at optimizing ESD protection device placement and the
PCB layout to reach the best ESD performance possible.
The layout shown in
Figure 1
may induce parasitic inductances responsible for artificial
overvoltages directly applied on the IC to be protected.
Figure 1.
Non-optimized location for
HSP061-8M16
Figure 2.
Significant overvoltages due
to non-optimal location of
HSP061-8M16
1
2
3
4
5
6
7
16
16
15
14
V
G
N
D
13
12
11
10
9
IC to
protect
L
di
dt
V
IC
IC to
protect
=
8
ESD surge is 15 kV with 1 ns
rise time, this leads to 71 A/ ns
Via to GND
Via to
GND
GND layer
Via to
GND
A very simple calculation shows that for a 15 kV ESD contact surge according to
IEC61000-4-2, the overvoltage due to parasitic inductances may be really significant, as
shown in
Figure 2.
This test is done with a contact discharge as the air discharge waveform
is not defined in the IEC 61000-4-2 specification. Assuming that each inductance value is 5
nH (corresponds to metal track 5 mm long):
di
= 71 A/ns
dt
then the overvoltage seen by the IC is:
V
IC
= V + L·
di
dt
V
IC
= V + 355 V
This parasitic inductance must be reduced as much as possible by shortening the ground
path return to the GND via.
To avoid ESD propagation on the PCB, the ESD protection must be placed as close as
possible to the ESD source with the layout given in the datasheet.
The layout given in the datasheet reduces parasitic inductance. It is important to connect the
connector on one side of the HSP and the transceiver on the other side. The GND via on
both sides must be used.
As ESD stress can be propagated on both sides of the cable, a protection device on each
end of the cable is required.
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AN3357
Figure 3.
Protection location on HDMI equipment
Location for HSP061-8M16
Protection
Protection
Tx
Wire
Rx
Board
Receptacle
(connector)
Source device (i.e., DVD)
Plug
Board
Receptacle
(connector)
Cable assembly
Sink device (Display)
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HSP061-8M16 topology
AN3357
2
HSP061-8M16 topology
HSP061-8M16 is packaged in µQFN-16L (3.3 mm x 1.5 mm) to protect eight high speed
lines (see
Figure 4).
This package keeps the 100
Ω
differential impedance on HDMI
(Figure
5).
The device is rated V
BR
min = 6 V @ 1 mA with a low typical leakage current of
0.1 nA @ 25 °C.
Figure 4.
HSP061-8M16 topology
Out 1 Out 2 Out 3 Out 4 Out 5 Out 6 Out 7 Out 8
16
15
14
13
12
11
10
9
GND
on
Tab
7
In 7
1
2
3
4
5
In 1
In 2
In 3
In 4
In 5
In 6
6
In 8
Figure 5.
HSP061-8M16 PCB footprint
400 µm
16
15
14
13
12
10
11
8
GND
Via to
GND
Via to
GND
1
2
3
4
5
6
7
F o o t p r in t p a d
P C B tra c k s
For further information refer to the product datasheet for HSP061-8M16.
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AN3357
Characteristics related to HDMI 1.4
3
Characteristics related to HDMI 1.4
Protection bandwidth must be large enough to be transparent when a high bit rate is
transferred on the line. The equation below give the relationship between lines, pixels, color
depth and bit rate per channel:
⎛
Color_depth
⎞
10
Lane data rate = (H_total_pixels) × (V_total_lines) ×
⎜
⎜
× (Frame_rate) × 8
⎝
⎠
3
Table 1.
Sample characteristics
Frame
rate (Hz)
Color
depth
(bits)
24
30
HDMI
data rate
(Gbps)
4.46
5.57
6.68
8.91
Lane
data rate
(Gbps)
1.49
1.86
2.23
2.97
Horizontal Vertical
CEA video
Video format total pixel total lines
code
per line
per frame
16
1920 x 1080p
2200
1125
60
36
48
Considering the protection device is equivalent to an RC circuit, the relationship between
the required cut-off frequency (f
c
) and lane data rate is:
f
cmin
= 0.875 × (lane data rate)
For instance, with a 3.4 Gbps data rate:
f
cmin 3.4 Gbps
= 0.875 × 3.4 Gbps = 2.98 GHz
Figure 6
shows the cut-off frequency of the HSP061-8M16 is 6.3 GHz which is high enough
to manage HDMI signals at 3.4 Gbps.
Figure 6.
S21 attenuation measurement
0
-1
-2
-3
-4
-5
-6
-7
F (Hz)
-8
10MHz
30MHz
100MHz 300MHz
1GHz
3GHz
db
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