Other Parts Discussed in Thread: LM3409
(if the system wokrs, there must be a link somewhere to a related question.... )
I ran into the same issue: The LM3409 draws current from the IADJ pin when EN is low. This current is much larger than the 5 uA that it sources from the pin when operating normally. In my case there are multiple LM3409 chips on one PCB They share a common, adjustable IADJ voltage.
Referring to the datasheet, you expect that the voltage source that drives this will need to sink about 5 uA per LM3409. However, when the PWM dimming hits "0" on one or more channels, the disabled chip will draw much more than 5 uA from the voltage source.
I think that mentioning: "when disabled, the LM3409 will draw typically xxx uA from the iadj pin" in the specifications section of the datasheet would have helped me and others not to fall for this pitfall.