Datasheet

Data Sheet ADuM5401/ADuM5402/ADuM5403/ADuM5404
Rev. D | Page 23 of 28
Given the geometry of the receiving coil in the ADuM5401/
ADuM5402/ADuM5403/ADuM5404, and an imposed
requirement that the induced voltage be, at most, 50% of the
0.5 V margin at the decoder, a maximum allowable magnetic
field is calculated as shown in Figure 27.
MAGNETIC FIELD FREQUENCY (Hz)
100
MAXIMUM ALLOWABLE MAGNETIC FLUX
DENSITY (kgauss)
0.001
1M
10
0.01
1k 10k 10M
0.1
1
100M100k
06577-019
Figure 27. Maximum Allowable External Magnetic Flux Density
For example, at a magnetic field frequency of 1 MHz, the maximum
allowable magnetic field of 0.2 kgauss induces a voltage of 0.25 V at
the receiving coil. This voltage is approximately 50% of the sensing
threshold and does not cause a faulty output transition. Similarly, if
such an event occurs during a transmitted pulse (and is of the
worst-case polarity), it reduces the received pulse from >1.0 V to
0.75 V, still well above the 0.5 V sensing threshold of the decoder.
The preceding magnetic flux density values correspond to specific
current magnitudes at given distances from the ADuM5401/
ADuM5402/ADuM5403/ADuM5404 transformers. Figure 28
expresses these allowable current magnitudes as a function of
frequency for selected distances. As shown in Figure 28, the
ADuM5401/ADuM5402/ADuM5403/ADuM5404 are extremely
immune and can be affected only by extremely large currents
operated at high frequency very close to the component. For the
1 MHz example, a 0.5 kA current placed 5 mm away from the
ADuM5401/ADuM5402/ADuM5403/ADuM5404 is required
to affect the operation of the device.
MAGNETIC FIELD FREQUENCY (Hz)
MAXIMUM ALLOWABLE CURRENT (kA)
1k
100
10
1
0.1
0.01
1k 10k 100M100k 1M 10M
DISTANCE = 5mm
DISTANCE = 1m
DISTANCE = 100mm
06577-020
Figure 28. Maximum Allowable Current for Various Current-to-
ADuM5401/ADuM5402/ADuM5403/ADuM5404 Spacings
Note that, at combinations of strong magnetic field and high
frequency, any loops formed by PCB traces can induce error
voltages sufficiently large to trigger the thresholds of succeeding
circuitry. Exercise care in the layout of such traces to avoid this
possibility.
POWER CONSUMPTION
The V
DD1
power supply input provides power to the iCoupler data
channels, as well as to the power converter. For this reason, the
quiescent currents drawn by the data converter and the primary
and secondary input/output channels cannot be determined sepa-
rately. All of these quiescent power demands have been combined
into the I
DD1 (Q)
current, as shown in Figure 29. The total I
DD1
supply
current is the sum of the quiescent operating current; the dynamic
current, I
DD1 (D)
, demanded by the I/O channels; and any external
I
ISO
load.
CONVERTER
PRIMARY
CONVERTER
SECONDARY
PRIMARY
DATA
INPUT/OUTPUT
4-CHANNEL
I
DDP(D)
SECONDARY
DATA
INPUT/OUTPUT
4-CHANNEL
I
ISO(D)
I
ISO
I
DD1(Q)
I
DD1(D)
06577-024
Figure 29. Power Consumption Within the
ADuM5401/ADuM5402/ADuM5403/ADuM5404
Both dynamic input and output current is consumed only
when operating at channel speeds higher than the refresh rate,
f
r
. Each channel has a dynamic current determined by its data
rate. Figure 21 shows the current for a channel in the forward
direction, which means that the input is on the primary side of
the device. Figure 22 shows the current for a channel in the reverse
direction, which means that the input is on the secondary side of
the device. Both figures assume a typical 15 pF load. The following
relationship allows the total I
DD1
current to be calculated:
I
DD1
= (I
ISO
× V
ISO
)/(E × V
DD1
) + Σ I
CHn
; n = 1 to 4 (1)
where:
I
DD1
is the total supply input current.
I
CHn
is the current drawn by a single channel determined from
Figure 21 or Figure 22, depending on channel direction.
I
ISO
is the current drawn by the secondary side external load.
E is the power supply efficiency at 100 mA load from Figure 11
at the V
ISO
and V
DD1
condition of interest.
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