Texas Instruments | New-generation ESD-protection devices need no VCC connection | Application notes | Texas Instruments New-generation ESD-protection devices need no VCC connection Application notes

Texas Instruments New-generation ESD-protection devices need no VCC connection Application notes
Interface
Texas Instruments Incorporated
New-generation ESD-protection devices
need no VCC connection
By Roger Liang
High Volume Linear
Introduction
Figure 1. Construction of a diode
As digital and analog ICs grow increasingly sensitive to
electrostatic-discharge (ESD) damage due to their shrinking process nodes, discrete ESD-protection diodes have
n-Type
p-Type
become necessary to guarantee sufficient system-level
Material
Material
ESD protection. In the past, the VCC connection was
added to diodes to reduce their junction capacitance.
With the advent of new diode technology, this is no longer
Anode
Cathode
required. This article explains the VCC connection’s necessity in the past and the advantages of not having to use it
in the present.
ESD is the release of built-up static electricity when two
objects of different electric potential come into contact.
For example, on a dry winter day, up to 20 kV of ESD can
build up simply from packing a printed cuircuit board
diode with the anode grounded and voltage swept across
(PCB) into a foam-lined box. To ensure that electronic
the cathode. While there are many types of diodes made
end equipment is immune to everyday ESD events, disfor different applications, the topic under discussion is
crete diodes with more robust ESD ratings than the stanultrafast-response diodes made for ESD-protection applidard 2-kV human-body model (HBM) are often required.
cations. These diodes can respond to a high ESD voltage
The ESD rating of discrete diodes is directly proportional
very quickly and clamp thousands of volts to just tens of
to the area of the diode’s p-n junction; however, the bigger
volts in a matter of nanoseconds by shunting the ESD
the junction, the larger is the parasitic capacitance. In
current to ground.
order not to compromise a diode’s ESD rating, adding a
There are two contributing factors to a diode’s parasitic
VCC connection is one IC design technique that effectively
capacitance: junction capacitance (due to charge variation
decreases the diode’s parasitic capacitance, but at the risk
in the depletion layer) and diffusion capacitance (due to
of damaging any other device connected to VCC. However,
excess carriers in the quasi-neutral region). Junction capac­
recent improvements in process technologies have allowed
itance dominates in the reverse-biased region, which is the
diode designers to remove the VCC connection
while still guaranteeing a high ESD rating with
Figure 2. Diode IV curve
low capacitance.
Diode characteristics
1.0
0.8
Forward
Bias
0.6
Reverse
Bias
Breakdown
Voltage
0.4
Current (mA)
A diode is the most basic semiconductor
device. It is made from a p-type and an n-type
junction and has two terminals: an anode at the
p-type end and a cathode at the n-type end
(Figure 1). When a large enough voltage is
applied from the cathode to the anode (reverse
biasing), the diode enters its breakdown region
and, in theory, can conduct an infinite amount
of current at zero resistance. A voltage applied
in the other direction (forward biasing) causes
the diode to enter its forward-conducting
region. Figure 2 shows the IV curve of a basic
0.2
0
–0.2
Forward
Voltage
–0.4
–0.6
–0.8
–1.0
–2
–1
0
1
2
3
4
5
6
7
8
9
10
Voltage (V)
23
Analog Applications Journal
1Q, 2014
www.ti.com/aaj
High-Performance Analog Products
Interface
Texas Instruments Incorporated
usual application region for ESD diodes. The junction
capacitance of a diode is characterized by
C j (V ) = A
ND is the donor doping concentration.
φ0 is the built-in voltage of the junction.
VA is the bias voltage applied on the junction.

εSi q  NA N D  
1

,
2  NA + N D   ϕ 0 − VA 
On the application level, the more VA is applied, the
lower the junction capacitance will be (Figure 3). This is
the reason why older diode technology required a VCC bias
in order to adjust VA and bring down the parasitic capacitance. Having a VCC connection also allows a systems engineer to add a large capacitor at the VCC node (Figure 4),
which serves as a charge reservoir to absorb some extra
ESD energy, thus increasing ESD protection incrementally.
with the following definitions:
A is the area of the junction.
εSi is the dielectric constant of silicon.
q is one coulomb charge.
NA is the acceptor doping concentration.
Figure 3. TPD4E001 capacitance versus bias voltage
2.1
f = 1 MHz
2.0
1.9
Capacitance (fF)
1.8
1.7
1.6
1.5
1.4
1.3
1.2
1.1
1.0
0
1
2
3
4
5
Bias Voltage (V)
Figure 4. Older diode technology with VCC connection
VCC
Power
Block
ESD Protection
Peripheral
Device 1
Peripheral
Device 2
Hiding
Diode 1
I/O
Zener
Diode
Hiding
Diode 2
GND
GND
Device Under
Protection
24
High-Performance Analog Products
www.ti.com/aaj
1Q, 2014
Analog Applications Journal
Interface
Texas Instruments Incorporated
Figure 5. Discharge path of positive ESD strike
Figure 6. Discharge path of negative ESD strike
Negative ESD
Hiding
Diode 1
Hiding
Diode 1
Positive ESD
I/O
I/O
Zener
Diode
Zener
Diode
Hiding
Diode 2
Hiding
Diode 2
GND
GND
Device Under
Protection
Device Under
Protection
Using high-speed diodes for ESD protection
To design a low-capacitance diode structure with a high
ESD rating, a three-diode approach often is used (see
Figures 5 and 6), for three reasons:
1. A diode can withstand much more current in the
forward-conducting region than in the reversebreakdown region.
2. Hiding Diode 1 with the Zener diode protects against
positive ESD strikes.
3. Hiding Diode 2 protects against negative ESD strikes.
• Moving away from a lateral diode structure to a vertical
diode structure
• Increased unit area ESD performance
• Less NA and ND doping to reach the same forward and
breakdown voltages
These improvements mean a VCC connection is no longer
required to bring down the junction capacitance to support high-speed interfaces. Having no VCC connection gives
the systems engineer the following three advantages.
1. No current leakage into internal power supply
If a higher-voltage input signal is connected to the ESD
Two smaller hiding diodes are connected in series with a
diode I/O with a lower VCC level, signal current could leak
larger Zener diode because the hiding diodes’ smaller
through
Hiding Diode 1 into the VCC and other devices con­
capacitance effectively hides the Zener diode’s large
nected
on
that node (Figure 7). This could damage either
capacitance due to the series structure. During a positive
ESD event, Hiding Diode 1 enters its forwardconducting region. The Zener diode enters its
Figure 7. Leakage path from I/O to VCC
reverse-breakdown region, creating a path for
ESD current to be shunted to ground without
VCC = 3.3 V
entering the device under protection. The size
of the larger Zener diode allows it to withstand
Power
the large amount of current flow in its breakBlock
down region. During a negative ESD event,
Hiding Diode 2 enters its forward-conducting
region and channels ESD energy directly to
5-V Input
Peripheral
Peripheral
ground. During either event, the hiding diodes
Device 1
Device 2
Hiding
can handle the large amount of ESD current
Diode 1
flow because they never break down and enter
I/O
Zener
only the forward-conducting region.
Diode
Advantages of not using a VCC connection
Hiding
Diode 2
Diode-fabrication technology has made great
improvements over the past few years that have
enabled a lower junction capacitance without
sacrificing a high ESD rating. These improvements are:
GND
25
Analog Applications Journal
1Q, 2014
www.ti.com/aaj
High-Performance Analog Products
Interface
Texas Instruments Incorporated
the power supply or any device connected to it.
If VCC is not connected to the ESD diode, there
is no such worry.
Figure 8. Positive ESD strike can damage VCC
VCC
2. No ESD damage to internal power supply
During a positive ESD strike, VCC is along the
ESD current’s discharge path and experiences a
voltage level that is one VF (~0.5 to 0.7 V) drop
below the clamping voltage at the I/O. Although
the power supply is very robust against ESD due
to the shunt capacitor, this raised voltage level
could very likely damage any device powered by
the VCC (Figure 8). Again, if VCC is not connected
to the ESD diode, there is no such worry.
Power
Block
Positive ESD
I/O
3. No external capacitor necessary
ESD-diode process development at Texas
Instruments (TI) is focusing on strengthening
the overall p-n structure so it can withstand
more ESD voltage. With TI’s new generation of
ESD-protection diodes rated as high as 30 kV, an
extra capacitor can improve the overall ESD
rating only marginally. Using one will generally
reach a point of diminishing returns. Not having a capacitor reduces the bill of materials count, saves on cost, and
allows more PCB space for other critical devices.
Examples of TI’s new-generation
ESD-protection devices
TI’s TPD2E2U06 ESD-protection device is a noteworthy
example of the improvements made in diode technology.
Unlike its predecessor, the TPD2E001 does not require a
VCC connection but maintains the same capacitance,
clamps to a lower voltage, and increases the ESD rating
threefold. (See Table 1.) Other similar ESD-protection
devices from TI include the TPD4E1U06, TPD4E1U06,
and TPD4E05U06.
Table 1. Specifications of TPD2E001 versus TPD2E2U06
SPECIFICATIONS
TPD2E001
TPD2E2U06
Recommended
Not required
Contact ESD (kV)
±8
±25
VCC connection
Air ESD (kV)
±15
±30
CIN (pF)*
1.5
1.5
Clamping voltage (V)**
12
9.5
Peripheral
Device 1
Hiding
Diode 1
Peripheral
Device 2
Zener
Diode
Hiding
Diode 2
GND
Conclusion
ESD-protection diodes that don’t require a VCC connection
bring many advantages to the table. No capacitor is needed
on the VCC pin to boost the ESD rating; this reduces component count, simplifies layout, and lowers placement cost.
Having no VCC connection also guarantees no leakage into
the power supply and no ESD damage to any internal
nodes that otherwise would be connected to the power
supply via VCC.
Related Web sites
Interface:
www.ti.com/interface-aaj
www.ti.com/tpd2e001-aaj
www.ti.com/tpd2e2u06-aaj
www.ti.com/tpd4e001-aaj
www.ti.com/tpd4e05u06-aaj
www.ti.com/tpd4e1u06-aaj
For more information about TI’s new-generation ESDprotection devices:
www.ti.com/esd-aaj
Subscribe to the AAJ:
www.ti.com/subscribe-aaj
* Capacitance measured at f = 1 MHz, VBIAS = 2.5 V.
** Clamping voltage measured using TLP curve at 1 A, 100-ns pulse width.
26
High-Performance Analog Products
www.ti.com/aaj
1Q, 2014
Analog Applications Journal
TI Worldwide Technical Support
Internet
TI Semiconductor Product Information Center
Home Page
support.ti.com
TI E2E™ Community Home Page
e2e.ti.com
Product Information Centers
Americas Phone
+1(512) 434-1560
Brazil
Phone
0800-891-2616
Mexico
Phone
0800-670-7544
Fax
Internet/Email
+1(972) 927-6377
support.ti.com/sc/pic/americas.htm
Europe, Middle East, and Africa
Phone
European Free Call
International
Russian Support
00800-ASK-TEXAS
(00800 275 83927)
+49 (0) 8161 80 2121
+7 (4) 95 98 10 701
Note: The European Free Call (Toll Free) number is not active in
all countries. If you have technical difficulty calling the free call
number, please use the international number above.
Fax
Internet
Direct Email
+(49) (0) 8161 80 2045
www.ti.com/asktexas
asktexas@ti.com
Japan
Phone
Fax
Domestic (toll-free number)
0120-92-3326
International
+81-3-3344-5317
Domestic
0120-81-0036
Internet/Email
International
Domestic
support.ti.com/sc/pic/japan.htm
www.tij.co.jp/pic
Asia
Phone
Toll-Free Number
Note: Toll-free numbers may not support
mobile and IP phones.
Australia
1-800-999-084
China
800-820-8682
Hong Kong
800-96-5941
India
000-800-100-8888
Indonesia
001-803-8861-1006
Korea
080-551-2804
Malaysia
1-800-80-3973
New Zealand
0800-446-934
Philippines
1-800-765-7404
Singapore
800-886-1028
Taiwan
0800-006800
Thailand
001-800-886-0010
International
+86-21-23073444
Fax
+86-21-23073686
Email
tiasia@ti.com or ti-china@ti.com
Internet
support.ti.com/sc/pic/asia.htm
Important Notice: The products and services of Texas Instruments
Incorporated and its subsidiaries described herein are sold subject to TI’s
standard terms and conditions of sale. Customers are advised to obtain the
most current and complete information about TI products and services
before placing orders. TI assumes no liability for applications assistance,
customer’s applications or product designs, software performance, or
infringement of patents. The publication of information regarding any other
company’s products or services does not constitute TI’s approval, warranty or
endorsement thereof.
A012014
E2E is a trademark of Texas Instruments. All other trademarks are the property of their
respective owners.
© 2014 Texas Instruments Incorporated
SLYT561
IMPORTANT NOTICE
Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, enhancements, improvements and other
changes to its semiconductor products and services per JESD46, latest issue, and to discontinue any product or service per JESD48, latest
issue. Buyers should obtain the latest relevant information before placing orders and should verify that such information is current and
complete. All semiconductor products (also referred to herein as “components”) are sold subject to TI’s terms and conditions of sale
supplied at the time of order acknowledgment.
TI warrants performance of its components to the specifications applicable at the time of sale, in accordance with the warranty in TI’s terms
and conditions of sale of semiconductor products. Testing and other quality control techniques are used to the extent TI deems necessary
to support this warranty. Except where mandated by applicable law, testing of all parameters of each component is not necessarily
performed.
TI assumes no liability for applications assistance or the design of Buyers’ products. Buyers are responsible for their products and
applications using TI components. To minimize the risks associated with Buyers’ products and applications, Buyers should provide
adequate design and operating safeguards.
TI does not warrant or represent that any license, either express or implied, is granted under any patent right, copyright, mask work right, or
other intellectual property right relating to any combination, machine, or process in which TI components or services are used. Information
published by TI regarding third-party products or services does not constitute a license to use such products or services or a warranty or
endorsement thereof. Use of such information 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.
Reproduction of significant portions of TI information in TI data books or data sheets is permissible only if reproduction is without alteration
and is accompanied by all associated warranties, conditions, limitations, and notices. TI is not responsible or liable for such altered
documentation. Information of third parties may be subject to additional restrictions.
Resale of TI components or services with statements different from or beyond the parameters stated by TI for that component or service
voids all express and any implied warranties for the associated TI component or service and is an unfair and deceptive business practice.
TI is not responsible or liable for any such statements.
Buyer acknowledges and agrees that it is solely responsible for compliance with all legal, regulatory and safety-related requirements
concerning its products, and any use of TI components in its applications, notwithstanding any applications-related information or support
that may be provided by TI. Buyer represents and agrees that it has all the necessary expertise to create and implement safeguards which
anticipate dangerous consequences of failures, monitor failures and their consequences, lessen the likelihood of failures that might cause
harm and take appropriate remedial actions. Buyer will fully indemnify TI and its representatives against any damages arising out of the use
of any TI components in safety-critical applications.
In some cases, TI components may be promoted specifically to facilitate safety-related applications. With such components, TI’s goal is to
help enable customers to design and create their own end-product solutions that meet applicable functional safety standards and
requirements. Nonetheless, such components are subject to these terms.
No TI components are authorized for use in FDA Class III (or similar life-critical medical equipment) unless authorized officers of the parties
have executed a special agreement specifically governing such use.
Only those TI components which TI has specifically designated as military grade or “enhanced plastic” are designed and intended for use in
military/aerospace applications or environments. Buyer acknowledges and agrees that any military or aerospace use of TI components
which have not been so designated is solely at the Buyer's risk, and that Buyer is solely responsible for compliance with all legal and
regulatory requirements in connection with such use.
TI has specifically designated certain components as meeting ISO/TS16949 requirements, mainly for automotive use. In any case of use of
non-designated products, TI will not be responsible for any failure to meet ISO/TS16949.
Products
Applications
Audio
www.ti.com/audio
Automotive and Transportation
www.ti.com/automotive
Amplifiers
amplifier.ti.com
Communications and Telecom
www.ti.com/communications
Data Converters
dataconverter.ti.com
Computers and Peripherals
www.ti.com/computers
DLP® Products
www.dlp.com
Consumer Electronics
www.ti.com/consumer-apps
DSP
dsp.ti.com
Energy and Lighting
www.ti.com/energy
Clocks and Timers
www.ti.com/clocks
Industrial
www.ti.com/industrial
Interface
interface.ti.com
Medical
www.ti.com/medical
Logic
logic.ti.com
Security
www.ti.com/security
Power Mgmt
power.ti.com
Space, Avionics and Defense
www.ti.com/space-avionics-defense
Microcontrollers
microcontroller.ti.com
Video and Imaging
www.ti.com/video
RFID
www.ti-rfid.com
OMAP Applications Processors
www.ti.com/omap
TI E2E Community
e2e.ti.com
Wireless Connectivity
www.ti.com/wirelessconnectivity
Mailing Address: Texas Instruments, Post Office Box 655303, Dallas, Texas 75265
Copyright © 2014, 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

Related manuals

Download PDF

advertising