Other Input And Isolated Output Supply Options - Analog Devices EVAL-ADuM3070EBZ User Manual

UG-402
The user can select a different switching frequency by removing
R10 and R11 and then choosing R1 based on Figure 4. The
board is configured for the 500 kHz setting by default. Figure 5
and Figure 7 show how the switching frequency affects the
supply's efficiency with either transformer installed. Figure 6
shows how the efficiency curve varies over temperature with a
500 kHz switching frequency.
Table 2. Switching Frequency Selection
R10 R11 R
OC
Open Open 300 kΩ
0 Ω Open 100 kΩ
Open 0 Ω 75 kΩ
0 Ω 0 Ω 50 kΩ
1500
1400
1300
1200
1100
1000
900
800
700
600
500
400
300
200
100
0
0 50 100 150 200
Figure 4. Switching Frequency vs. R
OTHER INPUT AND ISOLATED OUTPUT SUPPLY
OPTIONS
The single supply can be configured to have a 3.3 V secondary
isolated supply with a 3.3 V or 5 V primary input supply. Short-
circuiting R4 by soldering a 0 Ω, 0805 resistor to R9 sets the
output supply for 3.3 V. The voltage at the feedback node (the
FB pin of the ADuM3070) should be the desired output voltage
divided to approximately 1.25 V. Having R9 open-circuited sets
the secondary isolated supply to 5 V, and having it short-circuited
sets the supply to 3.3 V. See the
details on setting the secondary isolated output supply voltage.
Figure 8 shows how the single supply efficiency curve changes
when it is reconfigured for either of these supply options.
Switching Frequency
200 kHz
500 kHz
700 kHz
1 MHz
250 300 350 400 450 500
R (Ω)
OC
Resistance
OC
ADuM3070 data sheet for more
90
80
70
60
50
40
30
20
10
0
0 50
Figure 5. 5 V In to 5 V Out Efficiency with 1:2 Coilcraft Transformer at Various
90
80
70
60
50
40
30
20
10
0
0 50
Figure 6. 5 V In to 5 V Out Efficiency with 1:2 Coilcraft Transformer at 500 kHz
90
80
70
60
50
40
30
20
10
0
0 50
Figure 7. 5 V In to 5 V Out Efficiency with 1:2 Halo Transformer at Various
Rev. 0 | Page 4 of 12
Evaluation Board User Guide
100 150 200 250 300 350
LOAD CURRENT (mA)
Switching Frequencies
100 150 200 250 300 350
LOAD CURRENT (mA)
over Temperature
100 150 200 250 300 350
LOAD CURRENT (mA)
Switching Frequencies
f
= 1MHz
SW
f
= 700kHz
SW
f
= 500kHz
SW
f
= 200kHz
SW
400 450 500
T = –40°C
A
T = +25°C
A
T = +105°C
A
400 450 500
f
= 1MHz
SW
f
= 700kHz
SW
f
= 500kHz
SW
f
= 200kHz
SW
400 450 500