參數(shù)資料
型號(hào): PM6675ASTR
廠商: STMICROELECTRONICS
元件分類: 穩(wěn)壓器
英文描述: 3 A SWITCHING CONTROLLER, QCC24
封裝: 4 X 4 MM, LEAD FREE, VFQFPN-24
文件頁(yè)數(shù): 33/48頁(yè)
文件大?。?/td> 2481K
代理商: PM6675ASTR
PM6675AS
Application information
39/48
In Table 13 some tested polymer capacitors are listed.
8.1.4
MOSFETs selection
In SMPS converters, power management efficiency is a high level requirement, so the
power dissipation on the power switches becomes an important factor in switches selection.
Losses of high-side and low-side MOSFETs depend on their working condition.
Considering the high-side MOSFET, the power dissipation is calculated as:
Equation 40
Maximum conduction losses are approximately given by:
Equation 41
where RDSon is the MOSFET drain-source on-resistance.
Switching losses are approximately given by:
Equation 42
where tON and tOFF are the turn-on and turn-off times of the MOSFET and depend on the
gate-driver current capability and the gate charge Qgate. A greater efficiency is achieved with
low RDSon. Unfortunately low RDSon MOSFETs have a great gate charge.
As general rule, the RDSon
. Q
gate product should be minimized to find out the suitable
MOSFET.
Logic-level MOSFETs are recommended, as long as low-side and high-side gate drivers are
powered by VVCC = +5 V. The breakdown voltage of the MOSFETs (VBRDSS) must be
greater than the maximum input voltage VINmax.
Below some tested high-side MOSFETs are listed.
Table 13.
Evaluated output capacitors
Manufacturer
Series
Capacitance
(F)
Rated voltage
(V)
ESR max
@100kHz (m
)
SANYO
4TPE220MF
220
4 V
15 to 25
4TPE150MI
150
4 V
18
4TPC220M
220
4 V
40
HITACHI
TNCB OE227MTRYF
220
2.5 V
25
switching
conduction
DHighSide
P
+
=
2
MAX
,
LOAD
min
.
IN
OUT
DSon
conduction
I
V
R
P
=
2
f
t
)
2
I
(max)
I
(
V
2
f
t
)
2
I
(max)
I
(
V
P
sw
off
L
LOAD
IN
sw
on
L
LOAD
IN
switching
+
+
=
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