AN938 Datasheet, PDF (21/33 Pages) STMicroelectronics – The L4973 family is a 3.5 A monolithic DC-DC converter

AN938
Typical application
Co also has to support load transients. An idea of the magnitude of the output voltage drop
during load transients is given below:
Equation 12
ΔV_O
=
-----------------------⁽---^Δ----^I--^O----⁾--²----^â‹---^L----^O-------------------------
2 ⋅ C_O ⋅ (V_inmin ⋅ D_max – V_O)
where ΔI_o is the load current change from 0.5 A to 3.5 A; D_max is the max. duty cycle, 95%;
Vo nominal is 5.1 V; and finally L is 68 µH.
Equation 12, normalized at V_o, is represented in Figure 29 as a function of the minimum
input voltage.
These curves are represented for different output capacitors 2x150 µF, 2x220 µF, 2x330 µF
all KY, 35 V.
Figure 29. Output drop (%) vs minimum input voltage
8
7
6
5
4
3
2
1
0
10
15
20
25
30
35
40
45
Vin
Cout = 2 x 15 0uF
Cout = 2 x 22 0uF
Cout = 2 x 33 0uF
AM03511v1
3.6
Compensation network
The complete control loop block diagram is shown in Figure 30. The error amplifier basic
characteristics are:
● gm = 2.5 mS
● Ro = 1.2 MΩ
● Avo = 60 dB
● Isource/sink = 300 µA.
Doc ID 5410 Rev 10
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