ADUM5200ARWZ2 AD [Analog Devices], ADUM5200ARWZ2 Datasheet - Page 19

• Manufacturer Part Number: ADUM5200ARWZ2
• Description: Dual-Channel Isolators with Integrated DC/DC Converter
• Manufacturer: AD [Analog Devices]

decrease the thermal resistance to the PCB allowing increased
thermal margin it high ambient temperatures.
PROPAGATION DELAY-RELATED PARAMETERS
Propagation delay is a parameter that describes the time it takes
a logic signal to propagate through a component. The propagation
delay to a logic low output may differ from the propagation
delay to a logic high.
Pulse width distortion is the maximum difference between
these two propagation delay values and is an indication of how
accurately the input signal’s timing is preserved.
Channel-to-channel matching refers to the maximum amount
the propagation delay differs between channels within a single
ADuM520x component.
Propagation delay skew refers to the maximum amount the
propagation delay differs between multiple ADuM520x
components operating 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 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
side is assumed to be unpowered or nonfunctional, in which
case the isolator output is forced to a default state (see Error!
Reference source not found.) by the watchdog timer circuit.
The limitation on the ADuM520x’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
ADuM520x 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
where:
INPUT (V
OUTPUT (V
V = (−dβ/dt)
IX
)
OX
)
Figure 18. Propagation Delay Parameters
∑
πr
n
2
t
; n = 1, 2, … , N
PLH
t
PHL
50%
50%
Rev. PrA | Page 19 of 23
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 ADuM520x 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 19.
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
ADuM520x transformers. Figure 20 expresses these allowable
current magnitudes as a function of frequency for selected
distances. As shown, the ADuM520x 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 ADuM520x to affect the component’s operation.
n
is the radius of the n
0.001
0.01
Figure 19. Maximum Allowable External Magnetic Flux Density
100
0.1
10
1
1k
10k
MAGNETIC FIELD FREQUENCY (Hz)
th
turn in the receiving coil (cm).
100k
ADuM5200/5201/5202
1M
10M
100M