APE3312GN3 Advanced Power Electronics Corp., APE3312GN3 Datasheet - Page 17

• Manufacturer Part Number: APE3312GN3
• Manufacturer: Advanced Power Electronics Corp.

Specifications of APE3312GN3

• Vin(min): 3
• Vin(max): 28
• Vout(min): 0.75
• Vout(max): 5.5
• Iout(max): 8
• Power Good: ?
• Otp: ?
• Ocp: ?
• Ovp: ?
• Package: DFN 3x3-10L

APPLICATION INFORMATION
Inductor Selection
The inductor value determines the ripple current and the ripple voltage of the converter. This inductor choice
provides trade-offs between size vs. efficiency. Low inductor values cause large ripple currents, resulting in
the smallest size, but poor efficiency and high output noise. The inductor selection is based on the ripple
current which is typically set between 1/4 to 1/2 of the maximum load current. The switching frequency and
ripple current determine the inductor which can be calculated as follows:
The
Output Capacitor Selection
The output capacitor must have high enough ESR to satisfy the
important parameters of capacitor are the ESR, the capacitance value, the RMS ripple current rating, and the
voltage rating. For the output capacitor of APE3312, ESR is the most important parameter. Determine ESR to
meet the required ripple voltage as follow:
A minimum ESR is required to generate the required ripple voltage for regulation. Due to the pseudo fixed
frequency PWM mode not contain an error amplifier in the loop; a sufficient feedback signal needs to be
provided from output ripple. The VFB required 15mV ripple signal at least. That will generate output ripple
∆V
The capacitor is usually selected by ESR and voltage rating rather than by capacitance value. The conductive
polymer capacitors are recommended to proper high capacitance and low ESR.
MOSFET Selection
Choose a high side MOSFET that has conduction loss equal to the switching loss at the optimum input
voltage for maximum efficiency. Choose a low-side MOSFET that has the lowest R
APE3312 DL gate driver can drive low-side MOSFET. The current ability of the N-channel MOSFET must be
more than the peak switching current. The voltage rating V
1.25 times the maximum input voltage. Low R
MOSFET is for reducing the switching loss. But most of time, this two factors are trade-off. Consider the
system requirement and define the MOSFETs rating.
L
ESR
I ∆
=
L
OUT
V
=
ripple current can be given by:
(
f
m
OUT
SW
(
= (VOUT/0.7) × 15 mV
V
Ω
IN
×
L
)
(
V
_
=
Advanced Power
Electronics Corp.
f ×
I ∆
V
IN
∆
OUT
L
SW
_
V
I ∆
V
×
OUT
OUT
L
V
× )
×
IN
V
V
IN
)
OUT
DS-ON
MOSFET is for reducing the conduction loss. Low C
DS
of the N-channel MOSFET should be at least
ripple requirements
DS-ON
for loop stability. The
. Ensure that the
APE3312
ISS
17