ADUM3223 AD [Analog Devices], ADUM3223 Datasheet - Page 16

• Manufacturer Part Number: ADUM3223
• Description: Isolated Precision Half-Bridge Driver
• Manufacturer: AD [Analog Devices]

ADuM3223/ADuM4223
In Figure 5, the
for a 12 V output are shown for a C
amount of ringing of the output in Figure 5 with C
R
where less than 1 is desired for good damping.
Output ringing can be reduced by adding a series gate resistance
to dampen the response. For applications of less than 1 nF load,
it is recommended to add a series gate resistor of about 2 Ω
to 5 Ω.
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 of more than 1 µs at the input, 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 for more than about
3 µs, the input side is assumed to be unpowered or nonfunc-
tional, in which case, the isolator output is forced to a default
low state by the watchdog timer circuit. In addition, the outputs
are in a low default state while the power is coming up before
the UVLO threshold is crossed.
The
fields. The limitation on the
field immunity 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 following analysis defines
the conditions under which this can occur. The 3 V operating
condition of the
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
where:
β is the magnetic flux density (gauss).
N is the number of turns in the receiving coil.
r
Given the geometry of the receiving coil in the ADuM3223/
ADuM4223
voltage is, at most, 50% of the 0.5 V margin at the decoder, a
maximum allowable magnetic field is calculated, as shown in
Figure 22.
n
SW
is the radius of the nth turn in the receiving coil (cm).
of 1.1 Ω, R
ADuM3223/ADuM4223
V = (−dβ/dt) ∑π r
Q
=
(
R
SW
and an imposed requirement that the induced
GATE
+
ADuM3223/ADuM4223
1
ADuM3223/ADuM4223
R
GATE
of 0 Ω, and a calculated Q factor of 0.75,
n
)
2
, n = 1, 2, ... , N
×
L
ADuM3223/ADuM4223
C
TRACE
is immune to external magnetic
GS
GS
of 2 nF. Note the small
output waveforms
is examined because
GS
of 2 nF,
magnetic
Rev. 0| Page 16 of 20
For example, at a magnetic field frequency of 1 MHz, the maxi-
mum allowable magnetic field of 0.08 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. Simi-
larly, if such an event were to occur during a transmitted pulse
(and had 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 thresh-
old of the decoder.
The preceding magnetic flux density values correspond to
specific current magnitudes at given distances away from the
ADuM3223/ADuM4223
these allowable current magnitudes as a function of frequency
for selected distances. As shown, the
are immune and only can be affected by extremely large currents
operated at a high frequency and very close to the component.
For the 1 MHz example, a 0.2 kA current must be placed 5 mm
away from the
component’s operation.
0.001
0.01
Figure 22. Maximum Allowable External Magnetic Flux Density
0.01
100
100
0.1
0.1
10
1k
10
1
1
1k
1k
Figure 23. Maximum Allowable Current for Various
DISTANCE = 100mm
Current-to-ADuM3223/ADuM4223
ADuM3223/ADuM4223
DISTANCE = 5mm
10k
10k
MAGNETIC FIELD FREQUENCY (Hz)
MAGNETIC FIELD FREQUENCY (Hz)
transformers. Figure 23 expresses
100k
100k
DISTANCE = 1m
ADuM3223/ADuM4223
1M
1M
to affect the
Spacings
10M
10M
Data Sheet
100M
100M