ADum5211 Isolator Input Current Question

kornaktech on Apr 30, 2013

I am trying to determine much current the ADuM5211 will draw if it is operating at 1Mbps and also powering an isolated LED at 12mA. Therefore, the isolator power section is supplying about 18mA of isolated current (Idd1=2.7mA and Idd2=2.9mA max at 1Mbps).

The Rev 0 ADuM5210/ADuM5211/ADuM5212 datasheet seems inconsistent.

The maximum current that the device can supply is 30mA.

Output Supply Iiso (MAX) = 30mA

The power supply input current is listed as...

IDDP, No Viso Load IDDP (Q) = 6.8mA to 12mA

IDDP, Full Viso Load IDDP (MAX) = 30mA

That second number seems wrong since the efficiency is listed as...

Efficiency at Iiso (MAX) = 29% (Iiso = 27mA)

Wouldn't the input current draw at full output be...

IDDP (MAX) = 30mA / 29% = 103mA (at Iiso=30mA)

Would IDDP = 18mA / 29% = 62mA (at Iiso=18mA) be a good input current estimate? Or would the efficiency be worse around half load?

Thanks for your help.

0 ADIApproved

on May 1, 2013 5:35 PM over 8 years ago
Hello Kornaktech

Thank you for finding that. You are perfectly correct and your calculation is spot on. It is a typo, 30mA is Iiso max. The number should be the same as in the ADuM5010 data sheet, 104mA typical.

Your Estimate for half load should be pretty good.

I will put a correction in for the data sheet.

Best Regards,

MSCantrell
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0 kornaktech on May 1, 2013 11:32 PM over 8 years ago

Hi Mark,

Thanks for the quick answer.

Best regards,

Scot Kornak
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0 ADIApproved

on May 3, 2013 11:34 PM over 8 years ago
You are welcome
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0 kornaktech on May 12, 2013 3:47 AM over 8 years ago

Hi Mark,

I am testing a ADUM5211CRSZ.

The current with no switching is 34mA, with the device powering only the Vdd1 and Vdd2 sections (nothing significant external).

Vib is High. Via is High.

This is a little higher than the datasheet, even if I use the maximum rather than the typical current figures.

Idd1=2.7mA max, Idd2=2.9mA max

Iddp (Q, No Viso Load) = 12mA max

Only Idd2 is powered by the isolated +5V supply and suffers from the 29% efficiency.

The current I expected was (12 + 2.7+ (2.9/29%) ) = 24.7 mA

What do you think?

Is the current 9mA higher than the max datasheet figures?

Thanks!

Scot
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on May 13, 2013 10:22 PM over 8 years ago
Kornaktech,

That does seem higher than it should be. I would try these things.

1) Disconnect the Viso from the VDD2 pin and verify the quiescent current. drops below 12mA.

2) with Vdd2 disconnected, add a 1.7kohm resistor between Viso and ground, see if the Vddp rises to the expected 25mA range

3) provide power to VDD2 separately and measure the current. Verify that it is less than 2.9mA

If any of these numbers is not as expected, it will point at the thing that needs attention.

Also, remember to tie data inputs to ground or power. A floating input can draw current.

Best regards,

MSCantrell
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