Evaluation Board User Guide
UG-197
Rev. 0 | Page 7 of 16
DOUBLE SUPPLY
The second power supply implemented with the ADuM3471 on
this evaluation board is a double supply. This circuit, which is
shown in Figure 10, is located on the top half of the board. The
ADuM347x data sheet also discusses the ADuM347x in this
configuration. Figure 17 shows the schematic.
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010
Figure 10. Double Supply
In its default configuration, the double supply provides a
regulated 15 V output and an unregulated 7.5 V output, which
are isolated from the 5 V primary input supply. The double
supply is capable of delivering up to 140 mA to external loads.
The isolated data channels on Side 2 load the secondary isolated
supply and reduce the total available current. See the ADuM347x
data sheet electrical characteristics for specifications on output
supply current to determine how much current the Side 2 I/O
lines require at a given data rate. It can be reconfigured as 12 V
(regulated) and 6 V (unregulated) secondary isolated supplies
or as positive and negative supplies. See the Other Secondary
Isolated Supply Configurations section for more details.
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011
SIDE 1 TERMINAL
SIDE 2 TERMINAL
Figure 11. Double Supply Terminals
TERMINALS
The double supply has terminal blocks on Side 1 (the primary/
power supply input side) and Side 2 (the secondary/power
supply output side). A 4.3 mm isolation barrier separates Side 1
and Side 2. Figure 11 shows these terminals. Although the board
is populated with the ADuM3471, it is designed to accommo-
date the entire ADuM347x family. Therefore, the silkscreen
shows I/Ox to denote the four
i
Coupler data channels. J4 is a 0.1
inch (2.54 mm) 6x1 header, and J6 is a 0.1 inch 7x1 header. J5
has pads for an optional SMA connector (not populated)
terminated into 50 Ω. Table 3 summarizes the functions of the
terminal connections. They are described in detail in the Input
Power Connections, Output Power Connections, and Data I/O
Connection sections.
Input Power Connections
C5 V to Pin 1 of J4, l5V IN. Connect the
supply negative to Pin 6, labeled GND (GND3 in the schematic).
These are the only off-board connections required for the
double supply to function.
+5V IN supplies V
DD1
and V
DDA
to U2, the double supply
ADuM3471. V
DD1
is the ADuM3471 transformer driver supply,
and V
DDA
is its primary supply voltage (see the ADuM347x data
sheet for additional information about these pin functions).
V
DD1
/V
DDA
is bypassed by a 47 µF ceramic capacitor, labeled
C13, and a 0.1 µF local bypass capacitor located close to the
ADuM3471 (C18). R17, R18, C30, and C31 are provided for an
optional and unpopulated snubber, which can be used to reduce
radiated emissions.
Output Power Connections
An output load can be connected to Pin 1 of J6, labeled VISO2
in the schematic and +15/12V in the silkscreen, which is the
isolated, regulated 15 V output supply. Connect the return of
the load to Pin 7 of J6. It is labeled GND ISO on the silkscreen
and GND4 in the schematic.
Side 2 is powered by the secondary isolated 15 V supply. The
ADuM3471 internal low-dropout regulator converts this
voltage to 5 V. The regulated 5 V supply powers the ADuM3471
secondary side. Therefore, the ADuM3471 V
REG
pin is 15 V, and
the V
DD2
pin is 5 V. The 15 V supply connects to Pin 1 of J6. The
7.5 V supply connects to Pin 2 of J6, which is l7.5V/6V
on the silkscreen and VISO1 on the schematic. The Side 2
ground reference is tied to Pin 7 of J6. Note that the single and
double supplies do not share grounds, though they have the
same names on the silkscreen. The two supplies are isolated
from each other with an over 15 mm gap. See the ADuM347x
data sheet for an explanation of the double supply theory of
operation. Figure 12 through Figure 15 shows efficiency curves
for the double supply with the +15/+12 V isolated output supply
connected to V
REG
.
Powering V
REG
from the Unregulated 7.5 V
V
REG
can be powered by the unregulated 7.5 V supply, which
results in higher efficiency. However, when the 15 V supply is
unloaded, the unregulated 7.5 V supply is approximately 3 V,
which is not high enough to power the ADuM3471 secondary
side. This causes the double supply to run open loop, leaving
the 15 V supply unregulated. Because the secondary side of the
ADuM3471 is not sufficiently powered, its data channels are
inoperable. Using 15 V for V
REG
ensures that the secondary side
of the ADuM3471 powers up under light load conditions. Move
the 0 Ω 0805 from R19 to R20 to power Side 2 from the 7.5 V
supply.
