Preliminary Technical Data

ADuM4160

directly from the 3.3V supply.

Figure 5, shows how a typical application is connected if the

upstream side of the coupler was getting power directly from

the USB bus and the downstream side was receiving 3.3V from

the peripheral power supply.

PC BOARD LAYOUT

The ADuM4160 digital isolator requires no external interface

circuitry for the logic interfaces. For full speed operation the

D+ and D- line on each side of the device require a 24Ω

series termination resistor. These resistors are not required for

low speed applications. Power supply bypassing is required at

the input and output supply pins (Figure 5). Install bypass

capacitor value should have a minimum value of 0.1 μF and low

ESR. The total lead length between both ends of the capacitor

and the power supply pin should not exceed 10 mm . Bypassing

between Pin 2 and Pin 8 and between Pin 9 and Pin 15 should

also be considered, unless the ground pair on each package side

is connected close to the package.

Figure 5. Recommended Printed Circuit Board Layout

In applications involving high common-mode transients, care

should be taken to ensure that board coupling across the isolation

barrier is minimized. Furthermore, the board layout should be

designed such that any coupling that does occur equally affects

all pins on a given component side. Failure to ensure this could

cause voltage differentials between pins exceeding the device’s

Absolute Maximum Ratings, thereby leading to latch-up or

0.001

1k

10k

100k

10M

100M

1M

MAGNETIC FIELD FREQUENCY (Hz)

Figure 6. 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

10

1

0.1

0.01

voltage of 0.25 V at the receiving coil. This is about 50% of the

side is assumed to be unpowered or nonfunctional, in which

case the isolator output is forced to a default state (see Table 10)

by the watchdog timer circuit.

The limitation on the ADuM4160’s magnetic field immunity is

set by the condition in which induced voltage in the transformer’s

receiving coil is sufficiently large to either falsely set or reset the

decoder. The following analysis defines the conditions under

which this may occur. The 3 V operating condition of the

ADuM4160 is examined because it represents the most

susceptible mode of operation.

The pulses at the transformer output have an amplitude greater

than 1.0 V. The decoder has a sensing threshold at about 0.5 V, thus

establishing a 0.5 V margin in which induced voltages can be

tolerated. 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.

Given the geometry of the receiving coil in the ADuM4160 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 6.

100

permanent damage.

sensing threshold and does not cause a faulty output transition.

DC CORRECTNESS AND MAGNETIC FIELD

IMMUNITY

Positive and negative logic transitions at the isolator input

cause narrow (~1 ns) pulses to be sent to the decoder via the

transformer. The decoder is bistable and is, therefore, either set

or reset by the pulses, indicating input logic transitions. In the

absence of logic transitions at the input for more than ~1 μs, a

periodic set of refresh pulses indicative of the correct input state

are sent to ensure dc correctness at the output. If the decoder

receives no internal pulses of more than about 5 μs, the input

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

ADuM4160 transformers. Figure 7 expresses these allowable

current magnitudes as a function of frequency for selected

distances. As shown, the ADuM4160 is extremely immune and

can be affected only by extremely large currents operated at

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