E-L6920D Datasheet, PDF (6/13 Pages) STMicroelectronics – 1V HIGH EFFICIENCY SYNCRONOUS STEP UP CONVERTER

L6920
Figure 7. PFM mode Condition: V_out = 5V; V_in =1.5V.
Trace1: Vout (50mV~/div) Trace 4: IL (100mA/div)
Time div.: 5µs/div
Figure 9. Heavy load - Inductor current ripples
below I_lim Trace1: V_out (100mV~/div) Trace 4: I_L
(200mA/div) Time div.: 20 µs/div
Figure 8. Heavier load - Train pulses overlapping.
Trace1: V_out (100mV~/div) Trace 4: I_L (200mA/div)
Time div.: 10 µs/div
Figure 10. Heavy load and High ESR. Regulation
falls in continuous mode of operation. Trace1:
V_out (100mV~/div) Trace 4: I_L (200mA/div). Time
div.: 5 µs/div
When Iload is heavier, the pulse trains are overlapped. Figures 7 - 8 show some possible behaviors.
Considering that current in the inductor is limited to 1A, the maximum load current is defined by the following
relationship:
I_{l o a d _lim}
=
--^V----ⁱ--ⁿ---
V_out
⋅
⎛
⎝
I_l
i
m
–T_o
f
f
min
⋅
-^V----^o---^u₂---^t--_â‹-–--_L--^V----ⁱ--ⁿ-_⎠⎞
⋅η
eq. (1)
Where η is the efficiency and I_lim =1A.
Of course, if Iload is greater than Iload_lim the regulation is lost (figure 11).
6/13