A7431
DC-DC CONVERTER BUCK (STEP-DOWN)
42V 3A CC/CV
AiT Semiconductor Inc.
www.ait-ic.com
Figure 3: CC/CV Curve（R3=11.5k, R8=52.3k, R2=10k）
Inductor Selection
The inductor maintains a continuous current to the output load. This inductor current has a ripple that is
dependent on the inductance value:
Higher inductance reduces the peak-to-peak ripple current. The trade off for high inductance value is the
increase in inductor core size and series resistance, and the reduction in current handling capability. In
general, select an inductance value L based on ripple current requirement:
V
OUT x (VIN − VOUT)
L =
V
IN
f
SW
I
LOADMAX RIPPLE
K
where VIN is the input voltage, VOUT is the output voltage, fSW is the switching frequency, ILOADMAX is the
maximum load current, and KRIPPLE is the ripple factor. Typically, choose KRIPPLE = 30% to correspond to the
peak-to-peak ripple current being 30% of the maximum load current.
With a selected inductor value the peak-to-peak inductor current is estimated as:
V
OUT x (VIN − VOUT)
ILPK-PK
The peak inductor current is estimated as:
ILPK =ILOADMAX
=
L x VIN x
f
SW
1
+
ILPK-PK
2
The selected inductor should not saturate at ILPK. The maximum output current is calculated as:
1
IOUTMAX = ILIM
-
ILPK-PK
2
LLIM is the internal current limit, which is typically 4.5A, as shown in Electrical Characteristics Table.
REV1.1
- JAN 2016 RELEASED, SEP 2016 UPDATED -
- 8 -
AITSEMI [ AiT Semiconductor ]
