Tool/software:
LM5156DSSR configured for:
-
Vin = 6.5–35 V
-
Vout = 12 V
-
Iout = 0–2 A
-
fsw = 2.15 MHz
-
Cin = 23 µF @ 13 V
-
Cout = 60 µF @ 12 V
-
Two separate inductors, 3.3 µH (Isat = 15 A)
- Ccomp 12nF, Rcomp 3.9k, Chf 750pF
Issue: at light load (240 mA), the device operates acceptably (see first image below).
However, once Vin exceeds 12 V (Vin > Vout), the output develops a triangular AC component of ~200 mVpp, period 400us, with the amplitude increasing as Vin rises. (second image below)
What could be causing this issue?
Without load, the output exhibits a jagged AC component of ~400 mVpp, period 550ms (0.55s!) which is both unexpected and undesirable.
Beside the above, the device keeps correct Vout 12V.
Please advise, I am puzzled.
Thomas
