adum3440 Analog Devices, Inc., adum3440 Datasheet - Page 19
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adum3440
Manufacturer Part Number
adum3440
Description
Quad Channel, High Speed Digital Isolators
Manufacturer
Analog Devices, Inc.
Datasheet
1.ADUM3440.pdf
(24 pages)
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The voltage induced across the receiving coil is given by
V = (−dβ/dt)
where:
β is magnetic flux density (gauss).
N is the number of turns in the receiving coil.
r
Given the geometry of the receiving coil in the ADuM344x 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 18.
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 is about 50% of the
sensing threshold and does not cause a faulty output transition.
Similarly, if such an event were to occur during a transmitted
pulse (and was of the worst-case polarity), it would reduce 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
ADuM344x transformers. Figure 19 expresses these allowable
current magnitudes as a function of frequency for selected
distances. As shown, the ADuM344x is 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 noted, one would have to place a 0.5 kA current 5 mm
away from the ADuM344x to affect the component’s operation.
n
is the radius of the n
0.001
0.01
Figure 18. Maximum Allowable External Magnetic Flux Density
100
0.1
10
1
1k
∑
πr
n
10k
2
; n = 1, 2, … , N
MAGNETIC FIELD FREQUENCY (Hz)
th
turn in the receiving coil (cm).
100k
1M
10M
100M
Rev. 0 | Page 19 of 24
Note that at combinations of strong magnetic field and high
frequency, any loops formed by printed circuit board traces
could induce error voltages sufficiently large enough to trigger
the thresholds of succeeding circuitry. Care should be taken in
the layout of such traces to avoid this possibility.
POWER CONSUMPTION
The supply current at a given channel of the ADuM344x
isolator is a function of the supply voltage, the channel’s data
rate, and the channel’s output load.
For each input channel, the supply current is given by
For each output channel, the supply current is given by
where:
I
per channel (mA/Mbps).
C
V
f is the input logic signal frequency (MHz); it is half of the input
data rate expressed in units of Mbps.
f
I
supply currents (mA).
To calculate the total V
currents for each input and output channel corresponding to
V
provide per-channel supply currents as a function of data rate
for an unloaded output condition. Figure 10 provides per-
channel supply current as a function of data rate for a 15 pF
output condition. Figure 11 through Figure 15 provide total
V
ADuM3440/ADuM3441/ADuM3442 channel configurations.
r
DDI (D)
DDI (Q)
L
DDO
is the input stage refresh rate (Mbps).
DD1
DD1
is the output load capacitance (pF).
I
I
I
I
1000
and V
and V
is the output supply voltage (V).
0.01
DDI
DDI
DDO
DDO
, I
, I
100
0.1
10
DDO (D)
DDO (Q)
1
1k
= I
= I
= (I
= I
ADuM3440/ADuM3441/ADuM3442
DISTANCE = 100mm
DD2
DD2
DDI (D)
DDI (Q)
DDO (Q)
DDO (D)
are the input and output dynamic supply currents
are the specified input and output quiescent
for Various Current-to-ADuM344x Spacings
are calculated and totaled. Figure 8 and Figure 9
supply current as a function of data rate for
Figure 19. Maximum Allowable Current
× (2f − f
DISTANCE = 5mm
+ (0.5 × 10
10k
MAGNETIC FIELD FREQUENCY (Hz)
DD1
r
) + I
and V
100k
−3
DDI (Q)
) × C
DD2
L
supply current, the supply
× V
1M
DISTANCE = 1m
DDO
) × (2f − f
10M
r
f ≤ 0.5 f
f > 0.5 f
f ≤ 0.5 f
f > 0.5 f
) + I
100M
DDO (Q)
r
r
r
r