Evaluation Board User Guide UG-403
Rev. 0 | Page 5 of 12
Output Power Connections
An output load can be connected to P7, labeled OUT1, which is the
isolated, regulated 5 V output supply. Connect the return of the
load to P8, labeled ISO_GND, which is the Side 2 ground reference.
Including the current necessary for the ADuM4070 secondary
side (I/O and pulse-width modulation control), this supply can
provide up to 500 mA in the default configuration—a 5 V primary
input supply with a 5 V secondary isolated supply. Figure 4
through Figure 7 show how the efficiency of the power supply
varies with load current, switching frequency, and temperature.
TRANSFORMER SELECTION
The E VA L-ADuM4070EBZ supports multiple transformer
options. In the single-supply configuration, the board is equipped
with a Halo Electronics TGRAD-560V8LF (T2) or a Coilcraft
CR7983-CL (T3) 1CT:2CT turns ratio transformer; the default
is the Coilcraft transformer. The Halo Electronics footprint is in
the middle of the Coilcraft footprint. Figure 4 and Figure 6 show
the efficiency curves when the board operates in single-supply
configuration using a Coilcraft transformer (CR7983-CL) and a
Halo Electronics (TGRAD-560V8LF) transformer, respectively.
SWITCHING FREQUENCY OPTIONS
The resistance connected from the ADuM4070 oscillator control
pin (OC) to ground sets the single-supply switching frequency.
Figure 3 shows the relationship between this resistance and the
converter switching frequency. The EVA L -ADuM4070EBZ can
be configured with 0 Ω, 0603 resistors to set one of four preset
switching frequencies. Table 4 lists the switching frequencies that
can be selected by short- or open-circuiting R12, R13, and R14.
The user can select a different switching frequency by removing
R12 and R13 and then choosing R18 based on Figure 3. The
board is configured for the 500 kHz setting by default. Figure 4 and
Figure 6 show how the switching frequency affects the efficiency of
the supply using a Coilcraft transformer (CR7983-CL) and a Halo
Electronics transformer (TGRAD-560V8LF), respectively. Figure 5
shows how the efficiency curves vary over temperature with a
500 kHz switching frequency.
Table 4. Switching Frequency Selection
R12 R13 R14 R
OC
Switching Frequency (f
SW
)
0 Ω Open Open 300 kΩ 200 kHz
0 Ω Open 0 Ω 75 kΩ 700 kHz
0 Ω 0 Ω 0 Ω 50 kΩ 1 MHz
0
100
200
300
400
500
600
700
800
900
1000
1100
1200
1300
1400
1500
0
50
100
150 200 250 300 350 400 450 500
f
SW
(kHz)
R
OC
(kΩ)
NOTES
1. R
OC
IS A CALCULATED V
ALUE BASED ON THE SELECTION OF
R12, R13, AND R14.
10663-003
Figure 3. Switching Frequency (f
SW
) vs. Oscillator Resistance (R
OC
)
OTHER INPUT AND ISOLATED OUTPUT SUPPLY
OPTIONS
In the single-supply configuration, the board can be set up to
have a 3.3 V secondary isolated supply with a 3.3 V or 5 V primary
input supply. Short-circuiting R10 by soldering a 0 Ω, 0603 resistor
to R9 sets the output supply to 3.3 V. The voltage at the feedback
node (the FB pin of the ADuM4070) should be the desired output
voltage divided to approximately 1.25 V. Having R10 open-circuited
sets the secondary isolated supply to 5 V, and having R10 short-
circuited sets the supply to 3.3 V. See the ADuM4070 data sheet
for more information about setting the secondary isolated output
supply voltage. Figure 7 shows how the efficiency curves change
in single-supply configuration when the board is reconfigured
by open- or short-circuiting R10.
