Texas Instruments | Does BAV99 Really Protect My System from ESD? | Application notes | Texas Instruments Does BAV99 Really Protect My System from ESD? Application notes

Texas Instruments Does BAV99 Really Protect My System from ESD? Application notes
Application Report
SLVA898 – September 2017
Does BAV99 Really Protect My System from ESD?
Cameron Phillips
ABSTRACT
This document provides in-depth analysis of one of the most widely used devices for electrostatic
discharge (ESD) protection, the BAV99, while also comparing these results to that of ICs designed
particularly for ESD event protection. This application note describes the use case of the BAV99 and its
limitations.
1
2
3
4
5
6
7
Contents
Introduction ...................................................................................................................
BAV99 Overview .............................................................................................................
BAV99 Transient Event Reaction ..........................................................................................
Fail-Safe Limitations of BAV99.............................................................................................
Form Factor ..................................................................................................................
Summary ......................................................................................................................
References ...................................................................................................................
2
2
3
5
5
6
6
List of Figures
1
BAV99 Internal Top Down View ........................................................................................... 2
2
BAV99 I-V Curve (Multiple VCCs)
3
BAV99 Insertion Loss ....................................................................................................... 3
4
IEC 61000-4-2 ESD Waveform ............................................................................................ 4
5
BAV99 During ESD Event .................................................................................................. 4
6
TPD1E05U06 Functional Block Diagram ................................................................................. 4
7
Typical BAV99 Setup........................................................................................................ 5
8
SOT23 Package vs DPY and DPL Package ............................................................................. 6
..........................................................................................
3
List of Tables
1
ESD Protection Suggestion Devices ...................................................................................... 6
SLVA898 – September 2017
Submit Documentation Feedback
Does BAV99 Really Protect My System from ESD?
Copyright © 2017, Texas Instruments Incorporated
1
Introduction
1
www.ti.com
Introduction
In most, if not all, electronic devices developed today, there is a risk of electro-static discharge or ESD at
interfaces with metal contacts. For many companies, protection against these risks are not seen as highpriority concerns; therefore, many engineers may not invest time thinking about devices they can use to
mitigate the risk, but rather follow poor ESD-protection methods. The BAV99 device has been around for
quite a long time and people have found creative ways to implement it in ESD areas. Although not
described in the data sheet as an ESD protection device, there are many instances in which this device is
selected for its very low cost and simplicity. It is important to know the actual functionality and limitations
of the device to make sure that the ESD protection is being handled properly. The ensuing sections
describe the BAV99 functionality, its response to a transient event, its limitation in fail-safe mode, and its
size drawbacks all in comparison to Texas Instrument devices specifically designed for ESD protection.
2
BAV99 Overview
The BAV99 device is a 3-pin steering diode that has small forward voltage, large breakdown voltage, and
low capacitance. The device consists of stacking two diodes by connecting the cathode of one to the
anode of another and provides pins to the cathode, anode, and in between the two diodes. Figure 1
shows an internal top-view diagram of the device.
3
1
2
Figure 1. BAV99 Internal Top Down View
The typical use case is to have the center tap, pin 3, connected to an input/output (I/O) digital line with the
top pin cathode, pin 2, connected to some supply (VCC) and the bottom anode, pin 1, connected to ground
(GND). The BAV99 is essentially one half of the structure of TI's unidirectional devices, as is discussed in
Section 3.
2.1
Device Characterization
The following section outlines the characterization testing for the BAV99. These results show the behavior
of the internal diodes (I-V Curve) as well as the insertion loss. Designers should pay attention to this
important information when selecting an ESD protection device.
Figure 2 shows the I-V curve of the BAV99. Note that this device is just two diodes with a forward bias of
0.7 V; therefore, if a bias, VCC, is applied to the cathode (pin 2) this I-V curve will shift to
VCC + 0.7 V, as shown in Figure 2.
2
Does BAV99 Really Protect My System from ESD?
Copyright © 2017, Texas Instruments Incorporated
SLVA898 – September 2017
Submit Documentation Feedback
BAV99 Transient Event Reaction
www.ti.com
1 mA
Current (mA)
0.5 mA
-0.5 mA
VCC = 1.8V
VCC = 3.3V
VCC = 5.0V
-1 mA
-10
-8
-6
-4
-2
0
2
Voltage (V)
4
6
8
10
D001
Figure 2. BAV99 I-V Curve (Multiple VCCs)
The BAV99 device is also tested with respect to insertion loss and –3-dB bandwidth. This parameter is
important because it is a limiting factor regarding the bandwidth of a system. The –3-dB bandwidth of the
device is determined by . the total capacitance present in the BAV99 device. This is important because
signals that are higher frequency than the –3-dB point will experience a significant amount of loss and
should not be put through the device.
Figure 3. BAV99 Insertion Loss
3
BAV99 Transient Event Reaction
Since this device is just two diodes stacked on top of each other, it is natural to wonder how this device
could be used for something like ESD or surge. The key to the BAV99 is that it does not have to take
much of the transient events. The IEC 61000-4-2 is the international ESD standard that models an ESD
event to look like Figure 4. When that is applied to the I/O (pin 3) of BAV99 with pin 1 connected to GND
and pin 2 connected to VCC, the diode from I/O to VCC becomes forward biased and "steers" the current to
the VCC plane shown in Figure 5.
SLVA898 – September 2017
Submit Documentation Feedback
Does BAV99 Really Protect My System from ESD?
Copyright © 2017, Texas Instruments Incorporated
3
BAV99 Transient Event Reaction
www.ti.com
IPEAK
30
Current (A)
90% IPEAK
20
10
800 ps 90/10 rise time
10% IPEAK
0
0
20
40
60
Time (ns)
80
100
Figure 4. IEC 61000-4-2 ESD Waveform
VCC
IEC
Current
BAV99
Figure 5. BAV99 During ESD Event
This means that the BAV99 itself is not providing the ESD protection, but rather whatever capacitor or
clamps on VCC provide the ESD protection. Therefore, without some sort of clamping circuit on the VCC rail,
this ESD pulse could break whatever is providing the rail.
In comparison, all TI ESD devices, such as the TPD1E05U06 shown in Figure 6, have an internal clamp
so that when an ESD event occurs, the pulse is clamped by the internal clamping diode and the current is
dispersed through the ground plane.
I/O
GND
Figure 6. TPD1E05U06 Functional Block Diagram
4
Does BAV99 Really Protect My System from ESD?
Copyright © 2017, Texas Instruments Incorporated
SLVA898 – September 2017
Submit Documentation Feedback
Fail-Safe Limitations of BAV99
www.ti.com
Another transient event the BAV99 is subject to is surge. This transient event is characterized by IEC
61000-4-5 which outlines a pulse with a rise time of 1.2 µs and decays to 50% at 50 µs for the voltage
waveform. This pulse is much longer than the ESD pulse and therefore will have much more energy. As
with the ESD pulse, the BAV99 does not actually protect what is connected to the center tap, but rather
steers this transient event through the forward diode to the power plane it is connected to, forcing some
other protection device to take the brunt of the energy. Just as with the ESD event, the BAV99 is limited
by the power dissipated through its diodes. If the ESD strike or surge event is too high, instead of steering
the transient pulse away, the internal diodes will break and cause either an open or a short on that diode
path.
NOTE: The BAV99 is not the protection device for any transient event such as ESD or surge.
When the BAV99 is placed in a system, the passing level of IEC 61000-4-2 or IEC 61000-4-5 will be
almost exclusively dependent on what is connected to the rail to which the BAV99 is connected. The only
role that the BAV99 plays is if it becomes too hot from thermal dissipation, the diode could be broken. The
BAV99 is not specified to pass any level of IEC 61000 since it has to be part of a bigger system to be
tested.
4
Fail-Safe Limitations of BAV99
In modern end equipment it is not uncommon to have multiple different power supplies even for the same
voltage node. For this reason, it is reasonable to assume that sometimes what is on the I/O pin of BAV99
might not be derived from the same VCC as connected to BAV99. This setup is shown in Figure 7.
VCCA
VCCB
BAV99
Sensor
ADC
OUT
Figure 7. Typical BAV99 Setup
This means that VCCA were ever to lose power (0 V) when VCCB was still active and the sensor was
outputting, the BAV99 would be forward biased from pin 3 to pin 2. Current is then flowing into the VCCA
rail which could damage that power supply during a power supply sequence event.
5
Form Factor
The most obvious drawback of the BAV99 is its size. The big purpose of having ESD devices are that they
should be invisible in normal application and should not impede the normal operation of the circuit it is
trying to protect. While having the BAV99 on a schematic may make it look inconspicuous, when trying to
layout all components it can be extremely frustrating to place because of how big it is. The BAV99 for the
most part is in the SOT23 package pictured below with dimensions and only a one channel device. In
comparison the TPD1E04U04 is in the DPL (0201) and DPY (0402) package that provides a space
savings of 3.17 mm2 because it only requires two pins for one channel protection.
SLVA898 – September 2017
Submit Documentation Feedback
Does BAV99 Really Protect My System from ESD?
Copyright © 2017, Texas Instruments Incorporated
5
Summary
www.ti.com
2.90
1.0
3.77 mm2
0.6
1.30
0.6 mm
2
0.6
0.3
2
0.18 mm
DPY
SOT-23
DPL
Figure 8. SOT23 Package vs DPY and DPL Package
6
Summary
In conclusion, the BAV99 is two diodes stacked on top of each other with a pin in between. This device is
useful in applications where current needs to be steered away from the middle pin. However, it is
extremely important to recognize that the BAV99 itself does not actually provide the protection from
transients such as electrostatic discharge or surge events. Therefore, it is difficult to be sure that your
system is protected against certain levels of the standard because the BAV99 or the device somewhere
else that is actually taking all of this current could break without knowing where the problem stems from.
Also in fail-safe applications, where the driving signal is powered off another rail than the receiving end,
the receiving end rail could be damaged since the top diode would steer the current to that supply. Finally
the form factor of the BAV99 is so large for one channel applications when compared to TI's portfolio of
ESD protection that it can become a pain for board layout. As it can be seen the BAV99 device itself is not
providing protection, therefore a more complete solution with fixed protection limits would be to use Texas
Instruments selection of discrete ESD diodes. Suggestions for Texas Instrument devices that can replace
the BAV99 by providing robust protection against ESD events is found in Table 1
Table 1. ESD Protection Suggestion Devices
Parameter
ESD401
TPD1E05U06
TPD1E04U04
TPD1E10B06
IEC 61000-4-2 Contact Rating
±24 kV
±12 kV
±16 kV
±30 kV
±15 kV
Breakdown Voltage
–7.5 V and 7.5 V
–0.7 V and 6.5 V
–0.7 V and 6.2 V
–7.8 V and 8.4 V
–8.25 V and 7.25 V
Clamping Voltage (TLP)
7
24 V at
16 A
10 V at 1 A
14 V at 5 A
5.3 V at 1 A
8.9 V at 16 A
8 V at 1 A
12.5 V at 5
A
8V
13.5 V
Line Capacitance
0.77 pF
0.42 pF
0.5 pF
12 pF
6 pF
Dynamic Resistance
0.7 Ω
0.8 Ω
0.25 Ω
0.32 Ω
0.55 Ω
Surge Clamping Voltage
14.8 V at 4.5 A
16 V at 2.5 A
15 V at 3 A
15.82 V at 6.75 A
14.7 V at 4.45 A
Surge Max Power
67 W
40 W
19 W
106 W
65 W
Package Size
1.0 mm × 0.6 mm
1.0 mm × 0.6 mm
1.0 mm × 0.6 mm
0.6 mm × 1.00 mm
0.6 mm × 0.3 mm
References
•
•
•
•
•
6
11 V at 1 A
TPD1E6B06
ESD401 product folder
TPD1E05U05 product folder
TPD1E04U04 product folder
TPD1E10B06 product folder
TPD1E6B06 product folder
Does BAV99 Really Protect My System from ESD?
Copyright © 2017, Texas Instruments Incorporated
SLVA898 – September 2017
Submit Documentation Feedback
IMPORTANT NOTICE FOR TI DESIGN INFORMATION AND RESOURCES
Texas Instruments Incorporated (‘TI”) technical, application or other design advice, services or information, including, but not limited to,
reference designs and materials relating to evaluation modules, (collectively, “TI Resources”) are intended to assist designers who are
developing applications that incorporate TI products; by downloading, accessing or using any particular TI Resource in any way, you
(individually or, if you are acting on behalf of a company, your company) agree to use it solely for this purpose and subject to the terms of
this Notice.
TI’s provision of TI Resources does not expand or otherwise alter TI’s applicable published warranties or warranty disclaimers for TI
products, and no additional obligations or liabilities arise from TI providing such TI Resources. TI reserves the right to make corrections,
enhancements, improvements and other changes to its TI Resources.
You understand and agree that you remain responsible for using your independent analysis, evaluation and judgment in designing your
applications and that you have full and exclusive responsibility to assure the safety of your applications and compliance of your applications
(and of all TI products used in or for your applications) with all applicable regulations, laws and other applicable requirements. You
represent that, with respect to your applications, you have all the necessary expertise to create and implement safeguards that (1)
anticipate dangerous consequences of failures, (2) monitor failures and their consequences, and (3) lessen the likelihood of failures that
might cause harm and take appropriate actions. You agree that prior to using or distributing any applications that include TI products, you
will thoroughly test such applications and the functionality of such TI products as used in such applications. TI has not conducted any
testing other than that specifically described in the published documentation for a particular TI Resource.
You are authorized to use, copy and modify any individual TI Resource only in connection with the development of applications that include
the TI product(s) identified in such TI Resource. NO OTHER LICENSE, EXPRESS OR IMPLIED, BY ESTOPPEL OR OTHERWISE TO
ANY OTHER TI INTELLECTUAL PROPERTY RIGHT, AND NO LICENSE TO ANY TECHNOLOGY OR INTELLECTUAL PROPERTY
RIGHT OF TI OR ANY THIRD PARTY IS GRANTED HEREIN, including but not limited to any patent right, copyright, mask work right, or
other intellectual property right relating to any combination, machine, or process in which TI products or services are used. Information
regarding or referencing third-party products or services does not constitute a license to use such products or services, or a warranty or
endorsement thereof. Use of TI Resources may require a license from a third party under the patents or other intellectual property of the
third party, or a license from TI under the patents or other intellectual property of TI.
TI RESOURCES ARE PROVIDED “AS IS” AND WITH ALL FAULTS. TI DISCLAIMS ALL OTHER WARRANTIES OR
REPRESENTATIONS, EXPRESS OR IMPLIED, REGARDING TI RESOURCES OR USE THEREOF, INCLUDING BUT NOT LIMITED TO
ACCURACY OR COMPLETENESS, TITLE, ANY EPIDEMIC FAILURE WARRANTY AND ANY IMPLIED WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, AND NON-INFRINGEMENT OF ANY THIRD PARTY INTELLECTUAL
PROPERTY RIGHTS.
TI SHALL NOT BE LIABLE FOR AND SHALL NOT DEFEND OR INDEMNIFY YOU AGAINST ANY CLAIM, INCLUDING BUT NOT
LIMITED TO ANY INFRINGEMENT CLAIM THAT RELATES TO OR IS BASED ON ANY COMBINATION OF PRODUCTS EVEN IF
DESCRIBED IN TI RESOURCES OR OTHERWISE. IN NO EVENT SHALL TI BE LIABLE FOR ANY ACTUAL, DIRECT, SPECIAL,
COLLATERAL, INDIRECT, PUNITIVE, INCIDENTAL, CONSEQUENTIAL OR EXEMPLARY DAMAGES IN CONNECTION WITH OR
ARISING OUT OF TI RESOURCES OR USE THEREOF, AND REGARDLESS OF WHETHER TI HAS BEEN ADVISED OF THE
POSSIBILITY OF SUCH DAMAGES.
You agree to fully indemnify TI and its representatives against any damages, costs, losses, and/or liabilities arising out of your noncompliance with the terms and provisions of this Notice.
This Notice applies to TI Resources. Additional terms apply to the use and purchase of certain types of materials, TI products and services.
These include; without limitation, TI’s standard terms for semiconductor products http://www.ti.com/sc/docs/stdterms.htm), evaluation
modules, and samples (http://www.ti.com/sc/docs/sampterms.htm).
Mailing Address: Texas Instruments, Post Office Box 655303, Dallas, Texas 75265
Copyright © 2017, Texas Instruments Incorporated
Was this manual useful for you? yes no
Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Download PDF

advertising