Layered Isolation
By Mark Cantrell
Creating double insulation barriers with sequential optocouplers is
problematic because the data integrity is poor, and there is no compact
inexpensive way to provide power to the interface between the barriers.
With the advent of high performance digital isolators like iCoupler,® and
integrated power in isoPower® devices, creating high voltage isolation
barriers by layering isolators is now a viable solution.
The recent rapid expansion of new battery and power generation industries
has created demand for interfaces that have high working voltages and
require reinforced insulation. For example, a solar inverter application could
have the following requirements:
• Working voltage of 800 VDC
GND1 1
VDD1 1
16 VISO
GND1 2
15 GNDISO
VIA 3
ADuM6200
VIB 4
RCIN 5
RCSEL 6
15 NC
ADuM2200
14 VDD2
VIA 4
13 VOB
VIB 5
12 VOB
12 NC
NC 6
11 NC
GND1 7
10 NC
10 VE2
GND1 8
VDD1 3
14 VOA
11 VSEL
NC 7
16 GND2
NC 2
9
NC 8
13 VOA
9
GND2
GNDISO
If power must be transferred across both barriers to power an isolated load,
then two isoPower devices can be cascaded as shown below.
• Pollution degree of 2
VDD1 1
• Overvoltage Category III
16 VISO
GND1 2
15 GNDISO
VIA 3
Under IEC 62109-1, for reinforced insulation, this would require:
ADuM6200
VIB 4
RCIN 5
• Impulse to withstand voltage of 6000 VPEAK
VIA 3
13 VOB
VIB 4
11 VSEL
NC 7
• Working voltage of 800 VDC
14 VOA
12 NC
RCSEL 6
10 VE2
GND1 8
VDD1 1
9
GNDISO
16 VISO
GND1 2
15 GNDISO
ADuM6200
RCIN 5
14 VOA
13 VOB
12 NC
RCSEL 6
11 VSEL
NC 7
10 VE2
GND1 8
9
GNDISO
• Reinforced clearance of 8 mm
• Reinforced creepage of 16 mm
This creepage is not possible with the current packaging. However, if
the barrier can be broken into a basic and supplemental barrier, then the
requirement for each barrier is:
• Impulse withstand voltage of 6000 VPEAK
This configuration is compact, but the total power efficiency will be low.
The graph below shows the efficiency of the power sections at the load.
If data is being transferred at rates above 1 Mbps, then the data transfer will
be using part of the available power, and the power consumed by each stage
will have to be calculated in detail. The application, as shown above, draws
about 40 mA from the primary side input to create the entire interface.
• Working voltage of 800 VDC
12
• Basic/supplemental clearance of 5.5 mm
10
EFFICIENCY (%)
• Basic/supplemental creepage of 8 mm
The basic/supplemental insulation creepage, clearance, and impulse
voltage can be met with iCoupler devices in SOIC16W packages.
The following block diagram shows how an isoPower device and a standard high voltage iCoupler device can be cascaded to provide the required
isolation. Care must be taken to determine the overall performance of the
data channels. The propagation delay, pulse width distortion, and channel
matching values will add between the two components. The maximum data
rate will be limited by the slower of the two devices. isoPower devices
provide the power to run the intermediate interfaces. At data rates up to
1 Mbps, the entire barrier will require about 20 mA of power at 5 V. At higher
data rates, additional power will be required.
Share this on: 8
6
4
2
0
0
5
10
15
20
LOAD CURRENT (mA)
25
30
This method was described to solve a problem in a solar inverter application. Under different standards and applications, this method can be applied
to achieve different goals, depending on the details of the particular system
standard. There are many combinations of isoPower devices, digital isolators, and interface devices available to create isolated digital, I2C, and USB
interfaces with and without power to the end load.
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