ADuM1200/ADuM1201
APPLICATIONS INFORMATION
PCB LAYOUT
The ADuM120x digital isolators require no external interface
circuitry for the logic interfaces. Power supply bypassing is
strongly recommended at the input and output supply pins.
The capacitor value should be between 0.01 μF and 0.1 μF.
The total lead length between both ends of the capacitor and
the input power supply pin should not exceed 20 mm.
See the
for board layout guidelines.
Data Sheet
The ADuM120x are extremely immune to external magnetic
fields. The limitation on the magnetic field immunity of the
ADuM120x is set by the condition in which induced voltage in
the receiving coil of the transformer is sufficiently large enough
to either falsely set or reset the decoder. The following analysis
defines the conditions under which this can occur. The 3 V
operating condition of the ADuM120x 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,
therefore 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)Σ∏r
n2
;
n
= 1, 2, … ,
N
where:
β
is the magnetic flux density (gauss).
N
is the number of turns in the receiving coil.
r
n
is the radius of the nth turn in the receiving coil (cm).
Given the geometry of the receiving coil in the ADuM120x and
an imposed requirement that the induced voltage be 50% at
most of the 0.5 V margin at the decoder, a maximum allowable
magnetic field is calculated, as shown in Figure 13.
100
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 can differ from the propagation delay
to a logic high output.
INPUT (V
Ix
)
50%
t
PLH
OUTPUT (V
Ox
)
t
PHL
50%
04642-012
Figure 12. 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 ADuM120x component.
Propagation delay skew refers to the maximum amount that
the propagation delay differs between multiple ADuM120x
components operating under the same conditions.
MAXIMUM ALLOWABLE MAGNETIC FLUX
DENSITY (kgauss)
10
1
0.1
DC CORRECTNESS AND MAGNETIC FIELD IMMUNITY
Positive and negative logic transitions at the isolator input send
narrow (~1 ns) pulses 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 transi-
tions of more than ~1 μs at the input, 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 internal
pulses for 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 Table 17 and Table 18) by the
watchdog timer circuit.
0.01
10k
100k
1M
10M
MAGNETIC FIELD FREQUENCY (Hz)
100M
Figure 13. Maximum Allowable External Magnetic Flux Density
Rev. I | Page 24 of 28
04642-013
0.001
1k
AD [ ANALOG DEVICES ]
