Only at an input voltage >12V PWM occurs and the charging current appears (0.14A input current). Otherwise, there are no signals. The charge status and error are read at <12 volts as well as at >12 volts at the input: nCHG = 0, nFLT = 1.
I need Vfloat = 4.0-4.2V, batery voltage which I try to charge V=3.5V. Vin=6-8.4V (two LiPo cells), Vout=4V (single cell LiFePO4).
May be only LTC4121-4.2 can work with <12Vin? But I need Adj Vfloat.
What should I do to start PWM on low voltage with LTC4121EUD?
PS. When Vin < 12V Vfloat avg = 2.74V, voltage ripple with a frequency of 1/280 ms, Vp-p=2.7-2.8V looks like a saw.
Unlike the LTC4121 chip, the 4.2V fixed voltage IC (LTC4121-4.2) works well at low voltage. Only the FB resistor divider for the new chip was removed, BATSNS connected to BAT.
Good morning, we also have had similar issue.
LTC4121 do not charge battery if input voltage was greater than 10V, our inductor is 68uH and charging current is 220mA for a single LiFePo4 battery.
We have solved by inserting a 10 ohm resistor in series with boost capacitor and changed this from 22nF to 100nF. Our layout is 2 layers PCB with standard thickness 1.6mm.
Of course this IC remains strongly sensitive to layout and shows some silicon issues.
Using a 2-layer board for any switch mode supply is unlikely to yield performance or pass EMI. Thats just a fundamental of DCDC design and I have seen this many many times causing bad results.