NP-SDMC Datasheet, PDF (4/6 Pages) ON Semiconductor – High Current TSPD

NP−SDMC Series
The electrical characteristics of the TSPD help the user to
define the protection threshold for the circuit. During the
open circuit condition the device must remain transparent;
this is defined by the I_DRM. The I_DRM should be as low as
possible. The typical value is less than 5 mA.
The circuit operating voltage and protection voltage must
be understood and considered during circuit design. The
V_(BO) is the guaranteed maximum voltage that the protected
circuit will see, this is also known as the protection voltage.
The V_DRM is the guaranteed maximum voltage that will
keep the TSPD in its normal open circuit state. The TSPD
V_(BO) is typically a 20−30% higher than the V_DRM. Based
on these characteristics it is critical to choose devices which
have a V_DRM higher than the normal circuit operating
voltage, and a V_(BO) which is less than the failure threshold
of the protected equipment circuit. A low on−state voltage
V_t allows the TSPD to conduct large amounts of surge
current (500 A) in a small package size.
Once a transient surge has passed and the operating
voltage and currents have dropped to their normal level the
TSPD changes back to its open circuit state.
Transient Surge
Equipment Failure Threshold
TSPD Protection Voltage
Upper Limit
TSPD Transparent
(open)
TSPD Protection TSPD Transparent
(short)
(open)
Normal System
Operating Voltage
Time
Figure 5. Protection During a Transient Surge
TSPD’s are useful in helping designers meet safety and
regulatory standards in Telecom equipment including
GR−1089−CORE, ITU−K.20, ITU−K.21, ITU−K.45, FCC
Part 68, UL1950, and EN 60950.
ON Semiconductor offers a full range of these products in
the NP series product line.
DEVICE SELECTION
When selecting a TSPD use the following key selection
parameters.
Off−State Voltage V_DRM
Choose a TSPD that has an Off−State Voltage greater than
the normal system operating voltage. The protector should
not operate under these conditions:
Example:
Vbat = 48 Vmax
Vring = 150 Vrms = 150*1.414 = 212 V peak
V_DRM should be greater than the peak value of these two
components:
V_DRM > 212 + 48 = 260 V_DRM
Breakover Voltage V_(BO)
Verify that the TSPD Breakover Voltage is a value less
than the peak voltage rating of the circuit it is protecting.
Example: Relay breakdown voltage, SLIC maximum
voltage, or coupling capacitor maximum rated voltage.
Peak Pulse Current Ipps
Choose a Peak Pulse current value which will exceed the
anticipated surge currents in testing.
Hold Current (I_H)
The Hold Current must be greater than the maximum
system generated current. If it is not then the TSPD will
remain in a shorted condition, even after a transient event
has passed.
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