# ADum5211 Isolator Input Current Question

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 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?

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• Hi Mark,

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

• Hi Mark,

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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