I am trying to us the LM3481MMX to boost 4-12V to 12V/2A. I have used the ti webench to calculate the values of the key parts but I am deviating from that slightly.
At the lower end of the Vin spectrum (~4.5 (USB, 2.5A) - 6.5 (4xAA battery) the boost is failing when I apply a light load (~40mA). Under higher voltages (~9V - ~12V) the boost is handling the load.
Here's a table of the key parts, what Webench recommend, what I am using currently:
Part Webench Current
Cin 470uf 470uF
Cbyp 100nF 100nF
Rivp1 28.7 100k
Rivp2 44.2K 100k
Ccomp1 470nF 470nF
Ccomp2 22nF 22nF
Rcomp 887 887
Cvcc 470nF 1uF
Rfadj 154K 154K
L1 15uH 6.8uH (also tried 15uH)
D1 40V/5A 40/5A
Q1 25V/22A 40V/8A
Rsense 7m 10m
Rfilt 100 100
Cfilt 10p 20pF
Rfb1 1K 10K
Rfb2 8.45K 84.5K
Cout 180uF 180uF
I've attached a picture of a scope showing the failure point when enabling the load. Trace 1 (yellow) shows the output of the boost circuit. Trace 2 is being used to trigger the scope and is the enable signal for the load. The load is a electro-mechanical lock being enabled via a TPS2H160BQPWPRQ1.
Any obvious reasons why the boost is failing within its operating range?
