Analog Devices EVAL-ADuM3070EBZ, Руководство пользователя

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Evaluation Board User Guide UG-402
Rev. 0 | Page 7 of 12
TRANSFORMER SELECTION
The EVAL-ADuM3070EBZ supports multiple transformer
options. The double supply is equipped with a Halo TGSAD-
290V6LF (T3) or a Coilcraft JA4650-BL (T4) 1:3 turns ratio
transformer. The Coilcraft footprint is directly to the left of the
Halo footprint (see the
ADuM3070 data sheet for a details on
transformer selection with the ADuM3070 ). Figure 12 and
Figure 14 show the supply’s efficiency with a Coilcraft and a
Halo transformer, respectively, at different switching frequencies.
SWITCHING FREQUENCY OPTIONS
The resistor connected from the ADuM3070 OC pin to ground
sets the double supply switching frequency. Figure 4 shows the
relationship between this resistance and the converter switching
frequency. The
EVAL-ADuM3070EBZ can be configured with
0 Ω, 0805 resistors to four different preset switching frequen-
cies. Short-circuiting R26 sets R28 (300 kΩ) and R29 (150 kΩ)
in parallel, and short-circuiting R27 sets R28 and R30 (100 kΩ)
in parallel. Table 4 lists the switching frequencies that can be
selected by short- or open-circuiting R26 and R27. The user can
select a different switching frequency by removing R26 and R27
and then choosing R28 based on Figure 4. The board is config-
ured for the 500 kHz setting by default. Figure 12 and Figure 14
show how the switching frequency affects the efficiency with
either transformer installed. Figure 13 shows how temperature
affects efficiency.
Table 4. Switching Frequency Selection
R26 R27 R
OC
Switching Frequency
Open Open 300 kΩ 200 kHz
0 Ω Open 100 kΩ 500 kHz
Open 0 Ω 75 kΩ 700 kHz
0 Ω 0 Ω 50 kΩ 1 MHz
90
80
70
60
50
40
30
20
10
0
0 140
E
FF
IC
IE
NC
Y
(%
)
LOAD CURRENT (mA)
10 20 30 40 50 60 70 80 90 100 110 120 130
f
SW
= 1MHz
f
SW
= 700kHz
f
SW
= 500kHz
f
SW
= 200kHz
10653-
012
Figure 12. 5 V In to 15 V Out Efficiency with the 1:3 Coilcraft Transformer at
Various Switching Frequencies
90
80
70
60
50
40
30
20
10
0
0 140
E
FF
IC
IE
NC
Y
(%
)
LOAD CURRENT (mA)
10 20 30 40 50 60 70 80 90 100 110 120 130
T
A
= –40°C
T
A
= +25°C
T
A
= +105°C
10653-
013
Figure 13. 5 V In to 15 V Out Efficiency with the 1:3 Coilcraft Transformer at
500 kHz and Various Temperatures
90
80
70
60
50
40
30
20
10
0
0 140
E
FF
IC
IE
NC
Y
(%
)
LOAD CURRENT (mA)
10 20 30 40 50 60 70 80 90 100 110 120 130
T
A
= –40°C
T
A
= +25°C
T
A
= +105°C
10653-
014
Figure 14. 5 V In to 15 V Out Efficiency with the 1:3 Halo Transformer at
Various Switching Frequencies
80
0
0 70
E
FF
IC
IE
NC
Y
(%
)
LOAD CURRENT (mA)
10
20
30
40
50
60
70
5 10 15 20 25 30 35 40 45 50 55 60 65
5V IN TO 12V OUT
5V IN TO 15V OUT
10653-
015
Figure 15. Double Supply Efficiency with the 1:5 Coilcraft Transformer for
Different Output Options at 500 kHz