# ADuM4070 with high input voltage and 3.3V 1A output

Document created by analog-archivist on Feb 23, 2016Last modified by analog-archivist on Feb 23, 2016
Version 3Show Document

### Q

1.
I have already used the AduM3070, as isolated Power supply of 2W. Now I would
use this chip to make an isolated power supply of 3.5W-4W, as I need to solve
space. Do you have any application ready, or can you address me on the right
solution ?
Here are the data:
Vin=18..36VDC
Vout=3.3V/1A

2.
I forgot to add: we need isolation rating of 6KV peak.

3.
I designed my DC-DC application and I want you to review
"DC-DC_3V31A_test.pdf". My colleague helps me with EFDB type (5W is OK)
transformer. I ask you only to verify the input stage, as I would enter with
18..36VDC. And also I have doubts on input current on X1/X2 of the ADuM4070.

### A

1.
The best I have is a schematic and data for a high voltage input with the
Voltage.pptx"). You would need to use a transformer, inductor and Schottky
diodes for 1A output.

2.
ADuM4070 can fulfill 6kV peak according to VDE V 0884-10. Table 7 from
datasheet shows that the isolation rating (1-minute test) is 5kV rms. Table 8
from datasheet : the maximum transient isolation voltage is 6kV peak.

3.
The input current for 18V low line should be under 300mA for 60 – 70%
efficiency and 3.3W output. That assumes the losses are not too great in the
transformer, inductor and Schottky diodes. For a conservative 30% duty cycle on
the input with 300mA input current the peak current would be 1A for a square
wave input current. But, the input current will have ripple which depends on
the inductance of the primary windings, if you have 60 - 100uH inductance per
winding, 0.6usec for 30% duty cycle at 500kHz switching frequency, Iripple =
V/L*dt = 16V/60uH*0.6us = 0.16A, which adds a 0.08A to the 1A for a 1.08A peak
current. You don't want the peak primary current to be close to the 1.25A
current limit. Therefore it is important that you have enough inductance in the
primary windings or you will hit the current limit for high Vin.