L5987 Datasheet, PDF (24/42 Pages) STMicroelectronics – 3 A step-down switching regulator

Application information
L5987 - L5987A
Equation 25
R₃
=
-----------^R----¹----------- ,
4_-----⋅_---B_-----W_{---- – 1}
f_LC
C₃
=
-------------------¹---------------------
2π ⋅ R₃ ⋅ 4 ⋅ BW
The suggested maximum system bandwidth is equals to the switching frequency divided by
3.5 (F_SW/3.5), anyway lower than 100 kHz if the F_SW is set higher than 500 kHz.
For example with V_OUT = 3.3 V, V_IN = 12 V, I_O = 3 A, L = 10 μH, C_OUT = 22 μF, ESR < 1 mΩ,
the type III compensation network is:
R₁ = 4.99kΩ, R₂ = 1.1kΩ, R₃ = 220Ω, R₄ = 3.3kΩ, C₃ = 3.3nF, C₄ = 10nF, C₅ = 180pF
In Figure 12 is shown the module and phase of the open loop gain. The bandwidth is about
71 kHz and the phase margin is 46°.
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