adum6200 Analog Devices, Inc., adum6200 Datasheet - Page 19

• Manufacturer Part Number: adum6200
• Description: Dual-channel, 5 Kv Isolators With Integrated Dc-to-dc Converter Adum6200/adum6201/adum6202
• Manufacturer: Analog Devices, Inc.

With a slow V
voltage is not changing quickly when V
minimum voltage. The current surge is approximately 300 mA
because V
behavior during startup is similar to when the device load is a
short circuit; these values are consistent with the short-circuit
current shown in Figure 12.
When starting the device for V
the current available to the V
The ADuM620x devices may not be able to drive the output to
the regulation point if a current-limiting device clamps the V
voltage during startup. As a result, the ADuM620x devices can
draw large amounts of current at low voltage for extended
periods of time.
The output voltage of the ADuM620x devices exhibits V
overshoot during startup. If this overshoot could potentially
damage components attached to V
such as a Zener diode can be used to clamp the voltage. Typical
behavior is shown in Figure 17 and Figure 18.
EMI CONSIDERATIONS
The dc-to-dc converter section of the ADuM620x devices must
operate at 180 MHz to allow efficient power transfer through the
small transformers. This creates high frequency currents that can
propagate in circuit board ground and power planes, causing
edge emissions and dipole radiation between the primary and
secondary ground planes. Grounded enclosures are recommended
for applications that use these devices. If grounded enclosures
are not possible, follow good RF design practices in the layout
of the PCB. See the
recommendations.
PROPAGATION DELAY 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 output.
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 ADuM620x component.
Propagation delay skew refers to the maximum amount that
the propagation delay differs between multiple ADuM620x
components operating under the same conditions.
INPUT (V
OUTPUT (V
IX
)
OX
DD1
)
is nearly constant at the 2.7 V UVLO voltage. The
DD1
Figure 24. Propagation Delay Parameters
slew rate (in the millisecond range), the input
AN-0971 Application Note
t
PLH
DD1
ISO
power pin to less than 300 mA.
= 5 V operation, do not limit
t
PHL
ISO
, a voltage-limiting device
DD1
reaches the UVLO
50%
for board layout
50%
ISO
Rev. 0 | Page 19 of 24
DD1
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
is sent to ensure dc correctness at the output. If the decoder
receives no internal pulses for more than approximately 5 μs, the
input side is assumed to be unpowered or nonfunctional, and
the isolator output is forced to a default state by the watchdog
timer circuit.
The limitation on the magnetic field immunity of the ADuM620x
is set by the condition in which induced voltage in the receiving
coil of the transformer is sufficiently large to either falsely set or
reset the decoder. The following analysis defines the conditions
under which this may occur. The 3.3 V operating condition of the
ADuM620x is examined because it represents the most suscept-
ible mode of operation.
The pulses at the transformer output have an amplitude greater
than 1.0 V. The decoder has a sensing threshold at 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).
r
N is the total number of turns in the receiving coil.
Given the geometry of the receiving coil in the ADuM620x 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 25.
n
is the radius of the n
V = (−dβ/dt)
0.001
Figure 25. Maximum Allowable External Magnetic Flux Density
0.01
100
0.1
10
1
1k
ADuM6200/ADuM6201/ADuM6202
10k
∑
MAGNETIC FIELD FREQUENCY (Hz)
πr
n
th
2
; n = 1, 2, … , N
turn in the receiving coil (cm).
100k
1M
10M
100M