Datasheet

DocID022801 Rev 5 17/42
A7986A Application information
Equation 13
where F
SW
is the switching frequency, 1/(T
ON
+ T
OFF
).
For example, for V
OUT
= 5 V, V
IN
= 24 V, I
O
= 3 A and F
SW
= 250 kHz, the minimum
inductance value to have ΔI
L
= 30% of I
O
is about 18 μH.
The peak current through the inductor is given by:
Equation 14
Therefore, if the inductor value decreases, then the peak current (that must be lower than
the minimum current limit of the device) increases. According to the maximum DC output
current for this product family (3 A), the higher the inductor value, the higher the average
output current that can be delivered, without triggering the overcurrent protection.
In Table 7 below, some inductor part numbers are listed.
6.3 Output capacitor selection
The current in the capacitor has a triangular waveform which generates a voltage ripple
across it. This ripple is due to the capacitive component (charge or discharge of the output
capacitor) and the resistive component (due to the voltage drop across its ESR). So the
output capacitor must be selected in order to have a voltage ripple compliant with the
application requirements.
The amount of the voltage ripple can be calculated starting from the current ripple obtained
by the inductor selection.
Equation 15
Table 7. Inductors
Manufacturer Series Inductor value (μH) Saturation current (A)
Coilcraft
MSS1038 3.8 to 10 3.9 to 6.5
MSS1048 12 to 22 3.84 to 5.34
Wurth
PD Type L 8.2 to 15 3.75 to 6.25
PD Type M 2.2 to 4.7 4 to 6
SUMIDA
CDRH6D226/HP 1.5 to 3.3 3.6 to 5.2
CDR10D48MN 6.6 to 12 4.1 to 5.7
L
MIN
V
OUT
V
F
+
ΔI
MAX
----------------------------
1D
MIN
–
F
SW
-----------------------⋅=
I
LPK ,
I
O
ΔI
L
2
--------+=
ΔV
OUT
ESR ΔI
MAX
⋅
ΔI
MAX
8C
OUT
f
SW
⋅⋅
-------------------------------------+=