ADuM1510

Data Sheet

Rev. B | Page 8 of 12

APPLICATIONS INFORMATION

PCB LAYOUT

The ADuM1510 digital isolator requires no external interface

circuitry for the logic interfaces. Power supply bypassing is

strongly recommended at the input and output supply pins (see

Figure 9). Bypass capacitors are most conveniently connected

0.1 μF. The total lead length between both ends of the capacitor

and the input power supply pin must not exceed 10 mm. Bypass-

ing between Pin 1 and Pin 8 and between Pin 9 and Pin 16

should also be considered unless the ground pair on each

package side is connected close to the package.

ADuM1510

Figure 9. Recommended PCB Layout

See the AN-1109 Application Note for board layout guidelines.

PROPAGATION DELAY-RELATED PARAMETERS

Propagation delay is a parameter that describes the length of

time it takes for a logic signal to propagate through a component.

The propagation delay to a logic low output can differ from the

propagation delay to a logic high output.

50%

50%

Figure 10. Propagation Delay Parameters

Pulse width distortion is the maximum difference between

these two propagation delay values and is an indication of how

accurately the timing of the input signal is preserved.

Channel-to-channel matching refers to the maximum amount

that the propagation delay differs between channels within a

single ADuM1510 component.

Propagation delay skew refers to the maximum amount that

the propagation delay differs among multiple ADuM1510

components operated under the same conditions.

DC CORRECTNESS AND MAGNETIC FIELD IMMUNITY

Positive and negative logic transitions at the isolator input

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

the decoder. 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 is sent to ensure dc correctness at the output.

If the decoder receives no pulses for more than approximately 5 μs,

the input side is assumed to be unpowered or nonfunctional, in

which case, the isolator output is forced to a default low state by

the watchdog timer circuit (see Table 8).

The limitation on the magnetic field immunity of the device is

set by the condition in which induced voltage in the transformer

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

decoder. The analysis below defines such conditions. In the follow-

ing analysis, the ADuM1510 is examined in a 3 V operating

condition because it represents the most susceptible mode of

operation of all products in its product family.

The pulses at the transformer output have an amplitude greater

than 1.0 V. The decoder has a sensing threshold of approximately

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

where:

β is the magnetic flux density (gauss).

N is the number of turns in the receiving coil.

Given the geometry of the receiving coil in the ADuM1510 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 can be calculated, as shown in Figure 11.

MAGNETIC FIELD FREQUENCY (Hz)

100

0.001

1M

10

0.01

1k

10k

10M

0.1

1

100M

100k

Figure 11. Maximum Allowable External Magnetic Flux Density

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

mum 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), the received pulse is reduced

from >1.0 V to 0.75 V, still well above the 0.5 V sensing threshold

of the decoder.