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参数资料
| 型号： | SRDA3.3-4 |
| 元件分类： | 参考电压二极管 |
| 英文描述： | 500 W, UNIDIRECTIONAL, SILICON, TVS DIODE, MS-012AA |
| 封装： | SOP-8 |
| 文件页数： | 11/13页 |
| 文件大小： | 272K |
| 代理商： | SRDA3.3-4 |
7
2006 Semtech Corp.
www.semtech.com
PROTECTION PRODUCTS
SRDA3.3-4 through SRDA12-4
Applications Information (continued)
the current will be directed through the integrated TVS
diode to ground. The total clamping voltage seen by
the protected IC due to this path will be:
V
C
= V
F(RailClamp)
+ V
TVS
This is given in the data sheet as the rated clamping
voltage of the device. For an SRDA05-4 the typical
clamping voltage is <16V at I
PP
=30A. The diodes
internal to the RailClamp are low capacitance, fast
switching devices that are rated to handle high tran-
sient currents and maintain excellent forward voltage
characteristics.
Using the RailClamp does not negate the need for good
board layout. All other inductive paths must be consid-
ered. The connection between the positive supply and
the SRDA and from the ground plane to the SRDA
must be kept as short as possible. The path between
the SRDA and the protected line must also be mini-
mized. The protected lines should be routed directly to
the SRDA. Placement of the SRDA on the PC board is
also critical for effective ESD protection. The device
should be placed as close as possible to the input
connector. The reason for this is twofold. First,
inductance resists change in current flow. If a signifi-
cant inductance exists between the connector and the
TVS, the ESD current will be directed elsewhere (lower
resistance path) in the system. Second, the effects of
radiated emissions and transient coupling can cause
upset to other areas of the board even if there is no
direct path to the connector. By placing the TVS close
to the connector it will divert the ESD current immedi-
ately and absorb the ESD energy before it can be
coupled into nearby traces.
(Reference Semtech application note SI99-01 for
further information on board layout)
technology, the SRDA3.3-4 can effectively operate at
3.3V while maintaining excellent electrical characteris-
tics.
The IV characteristic curve of the EPD device is shown
in Figure 4. The device represents a high impedance
to the circuit up to the working voltage (V
RWM). During a
transient event, the device will begin to conduct as it is
biased in the reverse direction. When the punch-
through voltage (V
PT) is exceeded, the device enters a
low impedance state, diverting the transient current
away from the protected circuit. When the device is
conducting current, it will exhibit a slight “snap-back” or
negative resistance characteristic due to its structure.
This must be considered when connecting the device
to a power supply rail. To return to a non-conducting
state, the current through the device must fall below
the snap-back current (approximately < 50mA) to allow
it to travel back through the negative resistance
region. If this is a concern, a 10k
current limiting
resistor can be placed between the supply rail and the
positive reference pins (2 and 3) to prevent device
latch-up.
RailClamp is a registered trademark of Semtech corporation
IPP
I
SB
IPT
I
R
VRWM
V
PT VC
VBRR
I
BRR
SB
Figure 4 - EPD TVS IV Characteristic Curve
SRDA3.3-4 EPD TVS Characteristics
The internal TVS of the SRDA3.3-4 is constructed using
Semtech’s proprietary EPD technology. The structure
of the EPD TVS is vastly different from the traditional
pn-junction devices that are internal to the SRDA05-4
and SRDA12-4 devices. At voltages below 5V, high
leakage current and junction capacitance render
conventional avalanche technology impractical for
most applications. However, by utilizing the EPD
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