PM6681A STMicroelectronics, PM6681A Datasheet - Page 31

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

PM6681A
9.3
Equation 15
If hard saturation inductors are used, the inductor saturation current should be much greater
than the maximum inductor peak current I
Equation 16
Using soft saturation inductors it's possible to choose inductors with saturation current limit
nearly to I
Table 11.
Output capacitor
The selection of the output capacitor is based on the ESR value Rout and the voltage rating
rather than on the capacitor value Cout.
The output capacitor has to satisfy the output voltage ripple requirements. Lower inductor
value can reduce the size of the choke but increases the inductor current ripple ∆I
Since the voltage ripple V
Equation 17
A low ESR capacitor is required to reduce the output voltage ripple. Switching sections can
work correctly even with 20 mV output ripple.
However, to reduce jitter noise between the two switching sections it's preferable to work
with an output voltage ripple greater than 30 mV. If lower output ripple is required, a further
compensation network is needed (see Closing the integrator loop paragraph).
Finally the output capacitor choice deeply impacts on the load transient response (see Load
transient response paragraph). Below there is a list of some capacitor manufacturers.
Manufacturer
Coilcraft
Coilcraft
TDK
peak
Inductor manufacturer
. Below there is a list of some inductor manufacturers.
RLF12560
SER1360
Series
MLC
RIPPLEout
∆
I
L
I
peak
(max)
Inductor value
is given by:
V
0.7 to 4.5
=
RIPPLEout
=
1 to 10
1 to 8
I
(uH)
LOAD
V
IN
peak
max
f
(max)
sw
=
:
−
×
R
L
V
out
OUT
+
∆
×
I
∆
L
RMS current
×
13.6 to 17.3
(max)
7.5 to 14.4
I
2
L
V
6 to 9.5
V
IN
OUT
(A)
max
`
Saturation current
Design guidelines
7.5 to 18.5
11.5 to 26
7 to 31
(A)
L
.
31/47