參數(shù)資料
型號： FAN6520AIMX
廠商： FAIRCHILD SEMICONDUCTOR CORP
元件分類： 穩(wěn)壓器
英文描述： Single Synchronous Buck PWM Controller
中文描述： 1 A SWITCHING CONTROLLER, 340 kHz SWITCHING FREQ-MAX, PDSO8
封裝： MS-012AA, SOIC-8
文件頁數(shù)： 11/15頁
文件大?。?/td> 580K
代理商： FAN6520AIMX
PRODUCT SPECIFICATION
FAN6520A
REV. 1.0.2 8/26/04
11
Power MOSFET Selection
For more information on MOSFET selection for synchro-
nous buck regulators, refer to:
AN-6005: Synchronous Buck
MOSFET Loss Calculations.
This Fairchild app note is located at:
http://www.fairchildsemi.com/an/AN/AN-6005.pdf
Losses in a MOSFET are the sum of its switching (P
SW
) and
conduction (P
COND
) losses.
In typical applications, the FAN6520A converter's output
voltage is low with respect to its input voltage, therefore the
lower MOSFET (Q2) is conducting the full load current for
most of the cycle. Therefore choose a MOSFET for Q2
which has low R
DS(ON)
to minimize conduction losses.
In contrast, the high-side MOSFET (Q1) has a much shorter
duty cycle, and its conduction loss will therefore have less of
an impact. Q1, however, sees most of the switching losses,
so Q1’s primary selection criteria should be gate charge.
High-Side Losses
Figure 10 shows a MOSFET’s switching interval, with the
upper graph being the voltage and current on the Drain to
Source and the lower graph detailing V
GS
vs. time with a
constant current charging the gate. The x-axis, therefore, is
also representative of gate charge (Q
G
) . C
ISS
= C
GD
+ C
GS
,
and it controls t1, t2, and t4 timing. C
GD
receives the current
from the gate driver during t3 (as V
DS
is falling). The gate
charge (Q
G
) parameters on the lower graph are either
specified or can be derived from the MOSFET’s datasheet.
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 10).
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
:
Figure 10. Switching Losses and Q
G
Figure 11. Drive Equivalent Circuit
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 its threshold
(V
TH
). For the high-side MOSFET, V
DS
= V
IN
, 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 FAN6520A:
P
GATE
= Q
G
×
VCC
×
F
SW
(17)
where Q
G
is the total gate charge to reach VCC.
P
SW
V
--------2
I
L
×
2
×
t
s
×
F
SW
=
(14)
P
COND
V
IN
---V
I
OUT
2
×
R
DS ON
)
×
=
(15)
V
SP
V
TH
V
GS
t1
t2
t3
4.5V
t4
t5
Q
G(SW)
V
DS
I
D
Q
GS
Q
GD
C
ISS
C
GD
C
ISS
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)
相關PDF資料
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相關代理商/技術參數(shù)
參數(shù)描述
FAN6520AM 功能描述:電壓模式 PWM 控制器 Single Synchronous Buck PWM Controller RoHS:否 制造商:Texas Instruments 輸出端數(shù)量:1 拓撲結構:Buck 輸出電壓:34 V 輸出電流: 開關頻率: 工作電源電壓:4.5 V to 5.5 V 電源電流:600 uA 最大工作溫度:+ 125 C 最小工作溫度:- 40 C 封裝 / 箱體:WSON-8 封裝:Reel
FAN6520AM_Q 功能描述:電壓模式 PWM 控制器 Single Synchronous Buck PWM Controller RoHS:否 制造商:Texas Instruments 輸出端數(shù)量:1 拓撲結構:Buck 輸出電壓:34 V 輸出電流: 開關頻率: 工作電源電壓:4.5 V to 5.5 V 電源電流:600 uA 最大工作溫度:+ 125 C 最小工作溫度:- 40 C 封裝 / 箱體:WSON-8 封裝:Reel
FAN6520AMX 功能描述:電壓模式 PWM 控制器 Single Synchronous Buck PWM Controller RoHS:否 制造商:Texas Instruments 輸出端數(shù)量:1 拓撲結構:Buck 輸出電壓:34 V 輸出電流: 開關頻率: 工作電源電壓:4.5 V to 5.5 V 電源電流:600 uA 最大工作溫度:+ 125 C 最小工作溫度:- 40 C 封裝 / 箱體:WSON-8 封裝:Reel
FAN6520AMX_Q 功能描述:電壓模式 PWM 控制器 Single Synchronous Buck PWM Controller RoHS:否 制造商:Texas Instruments 輸出端數(shù)量:1 拓撲結構:Buck 輸出電壓:34 V 輸出電流: 開關頻率: 工作電源電壓:4.5 V to 5.5 V 電源電流:600 uA 最大工作溫度:+ 125 C 最小工作溫度:- 40 C 封裝 / 箱體:WSON-8 封裝:Reel
FAN6520AMXCT 制造商:Fairchild Semiconductor Corporation 功能描述:
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