CAPZero
For MOV placement that is not directly across the X Capacitor1 (for
example MOVPOS2 in Figure 3) the 1000 V CAPZero devices can be
used up to a surge specification of 1.5 kV. For differential surge
voltage specifications of >1.5 kV it is recommended that the MOV is
Pin Functional Description
The pin configuration of Figure 2 ensures that the width of the SO-8
package is used to provide creepage and clearance distance of over
4 mm.
always placed in the location shown in Figure 3 as MOVPOS1
.
Although electrical connections are only made to pins 2, 3, 6 and 7, it
is recommended that pins 1-4 and pins 5-8 are coupled together on
the PCB – see Applications Section.
It is always recommended that the peak voltage between terminals
D1 and D2 of CAPZero is measured during surge tests in the final
system. Measurements of peak voltage across CAPZero during surge
tests should be made with oscilloscope probes having appropriate
voltage rating and using an isolated supply to the oscilloscope to
avoid ground currents influencing measurement results. When
making such measurements, it is recommended that 50 V engineer-
ing margin is allowed below the breakdown voltage specification (for
example 950 V with the 1000 V CAPZero).
D Package (SO-8)
8
7
6
5
1
2
NC
D1
NC
D2
If the measured peak Drain voltage exceeds 950 V, an external 1 kV
ceramic capacitor can be placed between D1 and D2 terminals to
attenuate the voltage applied between the CAPZero terminals during
surge. Please refer to the Application Note AN-48 for the details.
This optional external capacitor placement is shown as CEXT in Figure
3. It should be noted that use of an external capacitor in this way will
increase power consumption slightly due to the CEXT charge/discharge
currents flowing in R1 and R2 while AC is connected.
3
4
D2
D1
NC
NC
PI-5608-060810
PCB Layout and External Resistor Selection
Figure 4 shows a typical PCB layout configuration for CAPZero. The
external resistors in this case are divided into two separate surface
mount resistors to distribute loss under fault conditions – for example
where a short-circuit exists between CAPZero terminals D1 and D2.
R1 and R2 values are selected according to Table 1.
Figure 2. Pin Configuration.
Key Application Considerations
Breakdown Voltage Selection
Figure 3 illustrates possible system configurations influencing the
choice of CAPZero breakdown voltage. The system configuration
variables include the placement of the system MOV and X capacitor(s)
as well as the differential surge voltage specifications of the
application.
Under a fault condition where CAPZero terminals D1 and D2 are
shorted together, each resistor will dissipate a power that can be
calculated from the applied AC voltage and the R1 and R2 values. For
example in an application using CAP004 or CAP014, R1=R2=390 kW.
If CAPZero is shorted out at 265 VAC R1 and R2 will each dissipate
45 mW.
As shown in Table 1, each device in the CAPZero family has a 825 V
or 1000 V option. For applications where the system MOV is placed
in position 1 (MOVPOS1 in Figure 3), the 825 V option will typically
provide adequate voltage withstand for surge requirements up to 3 kV
or more. The 1 kV CAPZero would be recommended for higher surge
requirements or if additional voltage margin is required.
Resistors R1 and R2 should also be rated for 50% of the system input
voltage again to allow for the short-circuitry of CAPZero D1 to D2 pins
during single point fault testing.
R1
D1
MOVPOS1
MOVPOS2
Other EMI
Filter
Components
CEXT
AC
X Capacitor1
X Capacitor2
D2
CAPZero
R2
PI-6600-110711
Figure 3. Placement Options of MOV and CEXT
.
2
Rev. H 03/18
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