CS5460A
performed on each individual power meter, during
final calibration/test of the meter.
Referring to Figure 20, the addition of capacitors
C1 and C2 can help to further attenuate these
high-frequency power surges, which can greatly
decrease the chances that the CS5460A will be
damaged. Typical values for C1 and C2 may be on
the order of 10 pF, although the exact value is re-
lated to the reactive and resistive properties of the
voltage and current sensor devices. In addition, di-
odes D1 - D4 can help to quickly clamp a high volt-
age surge voltage presented across the
voltage/current inputs, before such a surge can
damage the CS5460A. An example of a suitable
diode part number for this application is BAV199,
which has the ability to turn on very quickly (very
small turn-on time). A fuse could potentially serve
this purpose as well (not shown). R3 and R4 can
provide protection on the “-” sides of the two input
pairs. Set R3 = R1 and R4 = R5. Finally, placing
50 Ω resistors in series with the VA+ and VD+ pins
is another technique that has sometimes proven to
be effective in protecting the CS5460A from such
high-level, high-frequency voltage/current surges.
However, these 50 Ω resistors may not be neces-
sary if the protection on the analog input channels
is sufficient, and this is not the most attractive so-
3.14 Protection Against High-Voltage
and/or High-Current Surges
In many power distribution systems, it is very likely
that the power lines will occasionally carry brief but
large transient spikes of voltage/current. Two com-
mon sources of such high-energy disturbances are
1) a surge in the line during a lightning storm, or 2)
a surge that is caused when a very inductive or ca-
pacitive load on the power line is suddenly turned
on (“inductive kick”). In these situations, the input
protection resistors and corresponding input filter
capacitors (discussed in the previous sections)
may not be sufficient to protect the CS5460A from
such high-frequency voltage/current surges. The
surges may still be strong enough to cause perma-
nent damage to the CS5460A. Because of this, the
designer should consider adding certain additional
components within the voltage/current channel in-
put circuitry, which can help to protect the
CS5460A from being permanently damaged by the
surges.
Ω
Ω
5 k
10 k
N
L
Ω
Ω
Ω
10
500
500
0.1 µF
120 Vrms
0.1 µF
470 nF
To reduce
EMI susceptibility
For Input Surge
Protection
100 µF
5.1 Volt
50
50
14
VA+
3
VD+
+5 V
CS5460A
8
MODE
NC
17
2
PFMON
CPUCLK
XOUT
9
VIN+
R2
R1
NC
L1
D1
C3
C5
1
D2
4.069 MHz
C4
10
R3
C1
24
20 k 20 k
10 k 10 k
47 k 47 k
VIN-
IIN-
XIN
INT
L2
L3
1 k
1 k
15
19
R4
7
D4
SDO
C6
C8
D3
C7
23
RSHUNT
R5
SCLK
C2
+5 V
6
CS
16
5
IIN+
SDI
+5 V
L4
20
RESET
EDIR
12
11
22
21
VREFIN
VREFOUT
EOUT
To Service
1 k
VA-
13
DGND
4
SCLK
SDO
CS
0.1 µF
1 k
R
L
INT
SDI
Input protection for single-ended input configurations, using resistive
divider and current shunt resistor.
1 k
1 k
RST
Note that the digital interface is isolated using opto-isolators.
GND
Figure 20. Input Protection for Single-Ended Input Configurations
37
CIRRUS [ CIRRUS LOGIC ]
