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參數資料
| 型號： | FAN5234 |
| 廠商： | Fairchild Semiconductor Corporation |
| 英文描述： | Terminal Block; Pitch Spacing:0.197"; Mounting Type:PC Board RoHS Compliant: Yes |
| 中文描述： | 移動友好的PWM / PFM控制器 |
| 文件頁數： | 11/15頁 |
| 文件大?。?/td> | 537K |
| 代理商： | FAN5234 |
FAN5234
PRODUCT SPECIFICATION
REV. 1.0.10 5/3/04
11
Assuming switching losses are about the same for both the
rising edge and falling edge, Q1's switching losses, occur
during the shaded time when the MOSFET has voltage
across it and current through it.
These losses are given by:
P
UPPER
= P
SW
+ P
COND
where:
P
UPPER
is the upper MOSFET's total losses, and P
SW
and
P
COND
are the switching and conduction losses for a given
MOSFET. R
DS(ON)
is at the maximum junction temperature
(T
J
). t
S
is the switching period (rise or fall time) and is t2+t3
(Figure 8).
The driver’s impedance and C
ISS
determine t2 while t3’s
period is controlled by the driver's impedance and Q
GD
.
Since most of t
S
occurs when V
GS
= V
SP
we can use a
constant current assumption for the driver to simplify the
calculation of t
S
:
C
ISS
Figure 8. Switching losses and Q
G
Figure 9. Drive Equivalent Circuitt
Most MOSFET vendors specify Q
GD
and Q
GS
. Q
G(SW)
can
be determined as: Q
G(SW)
= Q
GD
+ Q
GS
– Q
TH
where Q
TH
is
the gate charge required to get the MOSFET to it's threshold
(V
TH
). For the high-side MOSFET, V
DS
= VIN, which can
be as high as 20V in a typical portable application. Care
should also be taken to include the delivery of the
MOSFET's gate power (P
GATE
)
in calculating the power
dissipation required for the FAN5234:
P
GATE
= Q
G
×
VCC
×
F
SW
(17)
where Q
G
is the total gate charge to reach VCC.
Low-Side Losses
Q2, however, switches on or off with its parallel shottky
diode conducting, therefore V
DS
≈
0.5V. Since P
SW
is pro-
portional to V
DS
, Q2's switching losses are negligible and
we can select Q2 based on R
DS(ON)
only.
Conduction losses for Q2 are given by::
where R
DS(ON)
is the R
DS(ON)
of the MOSFET at the highest
operating junction temperature and
is the minimum duty cycle for the converter.
Since D
MIN
< 20% for portable computers, (1-D)
≈
1
produces a conservative result, further simplifying the
calculation.
The maximum power dissipation (P
D(MAX)
) is a function of
the maximum allowable die temperature of the low-side
MOSFET, the
θ
J-A
, and the maximum allowable ambient
temperature rise:
θ
J-A
, depends primarily on the amount of PCB area that can
be devoted to heat sinking (see FSC app note AN-1029 for
SO-8 MOSFET thermal information).
P
SW
V
--------2
I
L
×
2
×
t
S
×
F
SW
=
(15a)
P
COND
V
V
IN
--------------
I
OUT
2
×
R
DS ON
)
×
=
(15b)
V
SP
V
TH
t1
t2
t3
4.5V
t4
t5
Q
G(SW)
V
DS
I
D
Q
GS
Q
GD
V
GS
C
RSS
C
ISS
C
ISS
= C
GS
|| C
GD
C
GD
R
D
R
GATE
C
GS
HDRV
5V
SW
VIN
G
t
S
Q
DRIVER
)
I
Q
DRIVER
)
V
SP
R
GATE
+
–
R
------------VCC
≈
=
(16)
P
COND
1
D
–
(
)
I
OUT
2
×
R
DS ON
)
×
=
(18)
D
V
V
IN
--------------
=
P
D MAX
)
T
-------------------------------------------------
T
)
–
J
A
–
=
(19)
相關PDF資料 |
PDF描述 |
|---|---|
| FAN5235 | System Electronics Regulator for Mobile PCs |
| FAN5236MTC | Dual Mobile-Friendly DDR / Dual-output PWM Controller |
| FAN5236MTCX | Dual Mobile-Friendly DDR / Dual-output PWM Controller |
| FAN5236QSC | Dual Mobile-Friendly DDR / Dual-output PWM Controller |
| FAN5236QSCX | Dual Mobile-Friendly DDR / Dual-output PWM Controller |
相關代理商/技術參數 |
參數描述 |
|---|---|
| FAN5234_10 | 制造商:FAIRCHILD 制造商全稱:Fairchild Semiconductor 功能描述:Dual Mobile-Friendly PWM / PFM Controller |
| FAN5234MTC | 功能描述:開關變換器、穩壓器與控制器 PWM Controller RoHS:否 制造商:Texas Instruments 輸出電壓:1.2 V to 10 V 輸出電流:300 mA 輸出功率: 輸入電壓:3 V to 17 V 開關頻率:1 MHz 工作溫度范圍: 安裝風格:SMD/SMT 封裝 / 箱體:WSON-8 封裝:Reel |
| FAN5234MTC_Q | 功能描述:開關變換器、穩壓器與控制器 PWM Controller RoHS:否 制造商:Texas Instruments 輸出電壓:1.2 V to 10 V 輸出電流:300 mA 輸出功率: 輸入電壓:3 V to 17 V 開關頻率:1 MHz 工作溫度范圍: 安裝風格:SMD/SMT 封裝 / 箱體:WSON-8 封裝:Reel |
| FAN5234MTCX | 功能描述:開關變換器、穩壓器與控制器 PWM Controller RoHS:否 制造商:Texas Instruments 輸出電壓:1.2 V to 10 V 輸出電流:300 mA 輸出功率: 輸入電壓:3 V to 17 V 開關頻率:1 MHz 工作溫度范圍: 安裝風格:SMD/SMT 封裝 / 箱體:WSON-8 封裝:Reel |
| FAN5234QSC | 功能描述:開關變換器、穩壓器與控制器 PWM Controller RoHS:否 制造商:Texas Instruments 輸出電壓:1.2 V to 10 V 輸出電流:300 mA 輸出功率: 輸入電壓:3 V to 17 V 開關頻率:1 MHz 工作溫度范圍: 安裝風格:SMD/SMT 封裝 / 箱體:WSON-8 封裝:Reel |
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