Other Secondary Isolated Supply Configurations; Schematic - Analog Devices EVAL-ADuM3070EBZ User Manual

UG-402
OTHER SECONDARY ISOLATED SUPPLY
CONFIGURATIONS
The double supply can be configured for 12 V regulated and 6 V
unregulated secondary isolated supplies by short-circuiting R17
with a 0 Ω resistor for R18. The regulated supply voltage is set
by the fraction of it that is fed back to the
voltage divider comprising R16, R17, R32, and R18. The voltage
at the feedback pin is 1.25 V. With R18 open-circuited, the
ADuM3070 feedback voltage is approximately 1.25 V if VISO2
is 15 V. When R18 is short-circuited, the feedback voltage is
approximately 1.25 V if VISO2 is 12 V (see the
sheet for more details on setting the secondary isolated output
supply voltage). Figure 15 shows the efficiency curves for both
output settings at 500 kHz with the 1:5 Coilcraft transformer.
Positive and Negative Outputs
The double supply can be set up as a positive and negative ±15 V
supply by changing the transformer to a turns ratio 1CT:5CT
transformer (see the ADuM3070
on these transformers). Other changes begin with removing the
0 Ω resistors from R24 and R22 and inserting them into R23 and
R21. Short-circuiting R23 instead of R24 makes the 7.5 V/6 V P7

SCHEMATIC

ADuM3070 via the
ADuM3070 data
data sheet for more information
Figure 17. Double Supply Schematic
Rev. 0 | Page 8 of 12
Evaluation Board User Guide
become the −15 V supply. Short-circuiting R21 instead of R22
connects the transformer center tap to the ground plane instead
of the node where L3, C12, and C13 are connected. Figure 16
shows which resistors should be short-circuited and open-
circuited for the double supply or positive and negative supply
configurations. Note that the negative supply is unregulated.
The positive and negative supplies can be set for ±12 V instead
of ±15 V by short-circuiting R18.
Whereas the 15 V output can be regulated, the same problems
with regulation can happen as described in the Powering V
from the Unregulated 7.5 V Supply section. In addition, the
−15 V supply can vary over a wide range because it is unregulated
and influenced by the changes that happen on the 15 V output.
DOUBLE SUPPLY
Figure 16. Double Supply Configuration with 0 Ω Resistors (Red)
REG
POSITIVE AND NEGATIVE SUPPLY