When using LM3405A, my input voltage is "3.8V - 4.2V", and the If and Vf of the loaded LEDs are: 100mA 1.61V, 200mA 1.88V, 300mA 2.14V, 400mA 2.40V. I want to parallel two LEDs, and R1 uses 0.2 ohm to make the output current 1Amax.
Question 1.
Our LEDs' Vf is within the range of 1.6V - 2.4V, not necessarily under full load. Then our LEDs are used in parallel, VOUT = ((n × VF) + VFB) should n also be 1, and Vout is between 1.8 - 2.6. Please confirm if this is so?
Question 2.
① When D2 is connected to Vout, Vboost - Vsw = Vout - VD2 + VD1, approximately 1.8 - 2.6, which may not meet the "Boost to SW voltage is between 2.5V and 5.5V" requirement. As shown in Figure 12.I feel that I cannot use this design reference.
Question 3.
② When D2 is connected to Vin, in this case, Vboost - Vsw = Vin - VD2 + VD1 is approximately 3.8V, which meets "Boost to SW voltage is between 2.5V and 5.5V". Therefore, do I need to use the reference design shown in Figure 23?
Expect your reply ，
best regards.
