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LM3409HV: Iadj voltage change when LM3409HV is enabled

felipe carvalho
Prodigy 150 points
Part Number: LM3409HV
Other Parts Discussed in Thread: TLV274, LM3409

Hi Irwin,

I have a quick question with regards to the Iadj pin of the LM3409HV. When the IC is disabled (EN=0) I measure 400mV on the Iadj pin, but when I enable it (EN=1) the measurement jumps to just over 800mV.

The voltage is supplied from the output of a TLV274 OP AMP (voltage follower) with an RC circuit (1K + 0.1uF) as in the EVM. I presume that this may be somehow related to the 5uA bias current on Iadj, but I can't see how the voltage measured on the Iadj pin would almost double when the driver is enabled.

Any thoughts?

Regards, 

  • 0
    TI__Mastermind 28655 points

    Hello Felipe,

    What is the TLV274 output set to when enabled and disabled?  If you can measure across the 1 Kohm resistor when it is enabled and disabled.  When disabled the LM3409 goes into low power shutdown.  The external voltage can be sourcing current to the LM3409 internal circuitry.

    Best Regards,