# 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?

Parents
• 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

• 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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