AN938 Datasheet, PDF (10/33 Pages) STMicroelectronics – The L4973 family is a 3.5 A monolithic DC-DC converter

Power supply, UVLO and voltage reference
AN938
In this condition, because of the fixed blanking time, the output current is given by:
Equation 5
I_max
=
--------------------------^[--^V----^C----^C-----^â‹---^T----^B----^â‹---^F----^S----^W------–----^V----^f---^â‹---⁽---¹----–-----^T----^B-----^â‹---^F---^S----^W-----⁾--^]--------------------------
[R_O + (R_D + R_L)(1 – T_B ⋅ F_SW) + (R_dson + R_L)T_B ⋅ F_SW]
where R_o is the load resistance and V_f is the diode forward voltage. R_D and R_L are the
series resistance of, respectively, the freewheeling diode and the choke.
Typical output characteristics are given in Figure 9 and 10. In Figure 10, the pulse-by-pulse
protection is effective in limiting the output current.
In Figure 9 the pulse-by-pulse protection is no longer effective in limiting the current due to
the minimum T_on fixed by the blanking time T_B, and the hiccup protection intervenes
because the output peak current reaches the relative threshold.
Figure 11. Schematic of internal current limiting
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Figure 12. Output current and soft-start voltage
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4.5A
10/33
Doc ID 5410 Rev 10
AM03494v1