ADuM3154ARSZ datasheet(20/22 Pages) AD

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ADuM3154

Data Sheet

For example, at a magnetic field frequency of 1 MHz, the

maximum allowable magnetic field of 0.5 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.

If such an event occurs, with the worst-case polarity, during a

transmitted pulse, it reduces the received pulse from >1.0 V to

0.75 V, which is 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 away from the

ADuM3154 transformers. Figure 16 expresses these allowable

current magnitudes as a function of frequency for selected

distances. The ADuM3154 is insensitive to external fields. Only

extremely large, high frequency currents very close to the

component are potentially a concern. For the 1 MHz example

noted, a user would have to place a 1.2 kA current 5 mm away

from the ADuM3154 to affect component operation.

MAGNETIC FIELD FREQUENCY (Hz)

1000

100

0.1

0.01

10k

100M

100k

10M

DISTANCE = 5mm

DISTANCE = 1m

DISTANCE = 100mm

Figure 16. Maximum Allowable Current for

Various Current to ADuM3154 Spacings

At combinations of a strong magnetic field and high frequency,

any loops formed by the PCB traces may induce sufficiently

large error voltages to trigger the thresholds of succeeding

circuitry. Take care to avoid PCB structures that form loops.

POWER CONSUMPTION

The supply current at a given channel of the ADuM3154

isolator is a function of the supply voltage, the data rate of the

channel, the output load of the channel, and whether it is a high

or low speed channel.

The low speed channels draw a constant quiescent current

caused by the internal ping-pong datapath. The operating

frequency is low enough that the capacitive losses caused by

the recommended capacitive load are negligible compared to

the quiescent current. The explicit calculation for the data rate

is eliminated for simplicity, and the quiescent current for each

side of the isolator due to the low speed channels can be found

in Table 3, Table 5, Table 7, and Table 9 for the particular operating

voltages.

These quiescent currents add to the high speed current as is

shown in the following equations for the total current for each

side of the isolator. Dynamic currents are taken from Table 3

and Table 5 for the respective voltages.

For Side 1, the supply current is given by

(

)

(

)

(

)

(

)

DD1(Q)

DD1

L(MI)

DDO(D)

MCLK

DDI(D)

DD1

−3

MSS

For Side 2, the supply current is given by

(

)

(

)

(

)

(

)

(

)

(

)

(

)

(

)

(

)

(Q)

L(SSx)

DDO(D)

SSx

L(SI)

DDO(D)

L(SCLK)

DDO(D)

SCLK

DDI(D)

−

where:

IDDI(D), IDDO(D) are the input and output dynamic supply currents

per channel (mA/Mbps).

fX is the logic signal data rate for the specified channel (Mbps).

CL(x) is the load capacitance of the specified output (pF).

VDDx is the supply voltage of the side being evaluated (V).

IDD1(Q), IDD2(Q) are the specified Side 1 and Side 2 quiescent

supply currents (mA).

Figure 4 and Figure 7 show the supply current per channel as a

function of data rate for an input and unloaded output. Figure 5

and Figure 8 show the total IDD1 and IDD2 supply currents as a

function of data rate for ADuM3154 channel configurations with

all high speed channels running at the same speed and the low

speed channels at idle.

INSULATION LIFETIME

All insulation structures eventually break down when subjected

to voltage stress over a sufficiently long period. The rate of

insulation degradation is dependent on the characteristics of the

voltage waveform applied across the insulation, as well as the

materials and material interfaces.

Two types of insulation degradation are of primary interest:

breakdown along surfaces exposed to the air and insulation

wear out. Surface breakdown is the phenomenon of surface

tracking and the primary determinant of surface creepage

requirements in system level standards. Insulation wear out is

the phenomenon where charge injection or displacement

currents inside the insulation material cause long-term

insulation degradation.

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