PM6681A STMicroelectronics, PM6681A Datasheet - Page 38

• Manufacturer Part Number: PM6681A
• Description: Dual synchronous step down controller with adjustable LDO
• Manufacturer: STMicroelectronics

Design guidelines
9.7
38/47
Equation 36
Example:
OUT1 = 1.5 V, f
R
eq.28, 29. C = 5.6 nF by Eq.35. Then R = 36 kΩ (eq.36) and R1 = 3 kΩ (eq.37).
Other parts design
●
Figure 41. VIN pin filter
Typical components values are: R = 3.9 Ω and C = 4.7 µF.
●
Figure 42. Inductor current waveforms
ESR
VIN filter. A VIN pin low pass filter is suggested to reduce switching noise. The low pass
filter is shown in the next figure:
VCC filter. A VCC low pass filter helps to reject switching commutations noise:
= 12 mΩ. We choose C
SW
= 290 kHz, L = 2.5 µH, Cout = 330 µF with Rout
INT
= 1 nF by equations 31, 34 and C
R
R
R
1
=
R
C
C
R
×
−
⎛
⎜ ⎜
⎝
C
C
×
×
π
π
1
1
×
×
f
f
Z
Z
⎞
⎟ ⎟
⎠
L
V
V
L
D
D
C
C
O
O
C
C
5
5
filt
≈
= 47 pF, R
12 mΩ. We design
INT
PM6681A
= 1 kΩ by