Transformer Selection; Switching Frequency Options - Analog Devices EVAL-ADuM3070EBZ User Manual

Evaluation Board User Guide

TRANSFORMER SELECTION

The EVAL-ADuM3070EBZ
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
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
sets the double supply switching frequency. Figure 4 shows the
relationship between this resistance and the converter switching
frequency. The EVAL-ADuM3070EBZ
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
Open Open 300 kΩ
0 Ω Open 100 kΩ
Open 0 Ω 75 kΩ
0 Ω 0 Ω 50 kΩ
90
80
70
60
50
40
30
20
10
0
0 10 20 30 40 50
LOAD CURRENT (mA)
Figure 12. 5 V In to 15 V Out Efficiency with the 1:3 Coilcraft Transformer at
Various Switching Frequencies
supports multiple transformer
data sheet for a details on
ADuM3070 OC pin to ground
can be configured with
Switching Frequency
200 kHz
500 kHz
700 kHz
1 MHz
f
= 1MHz
SW
f
= 700kHz
SW
f
= 500kHz
SW
f
= 200kHz
SW
60 70 80 90 100 110 120 130 140
90
80
70
60
50
40
30
20
10
0
0 10
Figure 13. 5 V In to 15 V Out Efficiency with the 1:3 Coilcraft Transformer at
90
80
70
60
50
40
30
20
10
0
0 10
Figure 14. 5 V In to 15 V Out Efficiency with the 1:3 Halo Transformer at
80
70
60
50
40
30
20
10
0
0 5
Figure 15. Double Supply Efficiency with the 1:5 Coilcraft Transformer for
Rev. 0 | Page 7 of 12
20 30 40 50 60 70 80 90 100 110 120 130
LOAD CURRENT (mA)
500 kHz and Various Temperatures
20 30 40 50 60 70 80 90 100 110 120 130
LOAD CURRENT (mA)
Various Switching Frequencies
5V IN TO 12V OUT
5V IN TO 15V OUT
10 15 20 25 30 35 40 45 50
LOAD CURRENT (mA)
Different Output Options at 500 kHz
UG-402
T = –40°C
A
T = +25°C
A
T = +105°C
A
140
T = –40°C
A
T = +25°C
A
T = +105°C
A
140
55 60 65 70