Texas Instruments | Flat-Clamp TVS Layout in SMA/SMB Footprints | Application notes | Texas Instruments Flat-Clamp TVS Layout in SMA/SMB Footprints Application notes

Texas Instruments Flat-Clamp TVS Layout in SMA/SMB Footprints Application notes
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Flat-Clamp TVS Layout in SMA/SMB Footprints
Alec Forbes
For systems in need of transient IEC 61000-4-5 surge
protection, TI’s new Flat-Clamp family of TVS devices
offers flatter voltage clamping, improved reliability, and
lower leakage currents in a much smaller package
than industry standard solutions, leading to more
efficient and effective input protection design. For
more information on the Flat-Clamp family
implementation and advantages, please see the FlatClamp surge protection technology for efficient system
protection white paper.
that there is no overlap in solder pads. The examples
below show layout compatibility with the SMA
package, however the SMB package is very similar
with slightly taller pads that not should not affect the
design.
While TI’s much smaller device package is critical in
many space constrained applications, for applications
where space is not a factor it can be inconvenient that
the Flat-Clamp devices do not share a footprint with
industry standard SMA/SMB surge diode package
footprints.
Figure 2. Recommended Footprint
Table 1. Stencil Dimensions
Figure 1. Package Size Comparison
For designers that want to use a common input stage
for multiple designs, there is an advantage to being
able to share a package footprint. A shared footprint
enables a designer to use the same layout when
switching between designs that require the precise
Flat-Clamp voltage regulation and designs that are
able to accept the poor voltage regulation of standard
TVS diodes.
With creative use of board layout, it is possible to
create a PCB footprint that can be used during
production for both the unidirectional Flat-Clamp
diodes 2x2 mm standard outline no-leads (SON)
package and the conventional SMA/SMB package.
This can be done because the large separation
between the leads on the SMA/SMB package enables
the entire SON package to sit in between the leads, so
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Dimension
Millimeters (Mils) Nominal
A
2.7 (106)
B
2.1 (83)
C
1.27 (50)
D
1.01 (40)
E
0.4572 (18)
F
1.6 (63)
G
0.25 (10)
H
0.14 (53)
During layout placement, superimpose both footprints
with the SON package fitting between the SMA/SMB
pins. Short the IN and GND pins of both packages
respectively with a copper pour and then use solder
mask openings for the individual pins. Figure 3 shows
the solder mask openings in green and the copper
planes that electrically short the pins in red. Keeping
the solder mask openings separate is important to
prevent assembly problems during reflow. The
recommended SMA/SMB footprint will vary based on
vendor, however the package is standardized and will
allow for the layout shown in Figure 3. The landing
pads above will allow for reliable manufacturing for
SMA/SMB packages regardless of recommended
manufacturer footprint.
Flat-Clamp TVS Layout in SMA/SMB Footprints Alec Forbes
Copyright © 2018, Texas Instruments Incorporated
1
www.ti.com
This layout allows engineers to improve their design
flexibility by having one layout for multiple TVS
footprints, removing any challenge of TI’s uniquely
small footprint. For designers that do not always need
the small size of the 2x2 mm SON package, this
strategy can save costs and time by enabling a
common front end layout with multiple protection
options.
Figure 3. Layout Example
To ease the transition towards a new footprint, TI also
offers a Flat-Clamp adapter board kit that easily
enables evaluation of the Flat-Clamp devices in an
existing SMA/SMB footprint, however the kit is
intended for evaluation only and not for production.
In addition, because the solder mask openings for the
SMA/SMB and SON footprints are electrically shorted,
if the SMA/SMB pins incidentally create a short there
will not be any problems.
Figures 4 and 5 show the Flat-clamp and standard
SMA respectively on the combined footprint
Figure 4. Flat-Clamp SON Package Populated
Figure 7. Flat-Clamp Evaluation Kit
Table 2. Device Recommendations
Figure 5. SMA Device Populated
Figure 6 shows a side view of the SMA device
populated, showing that the pins of SMA package do
not contact the solder mask of the SON footprint.
ILEAK (nA)
IPP (A, 8/20
µs)
38
19
43
32.5
1.7
43
27.7
3.2
40
18
22.8
0.5
40
TVS1400
14
18.4
2
40
TVS0500
5
9.2
0.07
35
Device
VRWM (V)
TVS3300
33
TVS2700
27
TVS2200
22
TVS1800
VCLAMP (V)
Related Documentation
Flat-Clamp surge protection technology for
efficient system protection
TVS Surge Protection in High-Temperature
Environments
TVS0500-3300EVM Adapter Board
Figure 6. Package Footprint Comparison
2
Flat-Clamp TVS Layout in SMA/SMB Footprints Alec Forbes
Copyright © 2018, Texas Instruments Incorporated
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