APU3048M A-POWER [Advanced Power Electronics Corp.], APU3048M Datasheet - Page 7

• Manufacturer Part Number: APU3048M
• Description: DUAL SYNCHRONOUS PWM CONTROLLER CIRCUITRY AND LDO CONTROLLER
• Manufacturer: A-POWER [Advanced Power Electronics Corp.]

Panasonic provides a range of inductors in different val-
ues and low profile for large currents.
Power MOSFET Selection
The selections criteria to meet power transfer require-
ments is based on maximum drain-source voltage (V
gate-source drive voltage (V
rent, On-resistance R
The MOSFET must have a maximum operating voltage
(V
The gate drive requirement is almost the same for both
MOSFETs. Caution should be taken with devices at very
low V
tary MOSFET, which results a shoot-through current.
The total power dissipation for MOSFETs includes con-
duction and switching losses. For the Buck converter
the average inductor current is equal to the DC load cur-
rent. The conduction loss is defined as:
The total conduction loss is defined as:
The R
ered for the worst case operation. This is typically given
in the MOSFET data sheet. Ensure that the conduction
losses and switching losses do not exceed the package
ratings or violate the overall thermal budget.
For this design, AP9408AGH is a good choice. These
devices provide low on-resistance in a compact
TO-252 3Pin package.
The MOSFETs have the following data:
DSS
For Di
For Di
For L
For L
P
P
q = R
P
AP9408AGH
V
I
R
q = 1.5 for 1508C (Junction Temperature)
D
) exceeding the maximum input voltage (V
GS
CON(TOTAL)
COND
COND
DSS
DS(ON)
DS(ON)
= 33A @ 1008C
to prevent undesired turn-on of the complemen-
= 30V
1
2
(Upper Switch) = I
(Lower Switch) = I
DS(ON)
1
2
choose ETQP6F102HFA (10.2mH, 4A)
choose ELLATV6R8M (6.8mH, 4A)
=25% of I
=25% of I
= 10mV @ V
temperature dependency should be consid-
=P
CON
Temperature Dependency
(Upper Switch)q +P
1
2
, we get L
, we get: L
DS(ON)
GS
=10V
and thermal management.
2
2
LOAD
LOAD
GS
), maximum output cur-
1
3R
3R
=9.9mH
2
=5.7mH
DS(ON)
DS(ON)
CON
(Lower Switch)q
3D3q
3(1 - D)3q
IN
).
DSS
),
The total conduction losses for channel 1 is:
The total conduction losses for channel 2 is:
The control MOSFET contributes to the majority of the
switching losses in synchronous Buck converter. The
synchronous MOSFET turns on under zero-voltage con-
dition, therefore the turn on losses for synchronous
MOSFET can be neglected. With a linear approxima-
tion, the total switching loss can be expressed as:
From AP9408AGH data sheet we obtain:
These values are taken under a certain condition test.
For more detail please refer to the AP9408AGH data sheet.
By using equation (6), we can calculate the switching
losses.
P
P
P
Where:
V
t
t
T = Switching Period
I
AP9408AGH
t
t
P
P
LOAD
r
f
r
f
10%
90%
CON1
CON2
SW
DS(OFF)
SW1
SW2
V
= Rise Time
= Fall Time
V
= 5ns
= 6ns
GS
D S
=
= Load Current
Figure 4 - Switching time waveforms.
= 52.8mW
= 22mW
t
= 0.24W
= 0.24W
V
d
(ON)
DS(OFF)
= Drain to Source Voltage at off time
2
3
t
r
+
t
T
r
t
f
t
3 I
d
(OFF)
LOAD
APU3048
---(6)
t
f
7