參數(shù)資料
型號(hào)： LTC1929CG
廠商： LINEAR TECHNOLOGY CORP
元件分類： 穩(wěn)壓器
英文描述： Isolated Flyback Switching Regulator with 9V Output
中文描述： 3 A DUAL SWITCHING CONTROLLER, 310 kHz SWITCHING FREQ-MAX, PDSO28
封裝： 0.209 INCH, PLASTIC, SSOP-28
文件頁(yè)數(shù)： 9/24頁(yè)
文件大?。?/td> 233K
代理商： LTC1929CG
9
LTC1929
but it is very dependent on inductance selected. As induc-
tance increases, core losses go down. Unfortunately,
increased inductance requires more turns of wire and
therefore copper losses will increase.
Ferrite designs have very low core loss and are preferred
at high switching frequencies, so design goals can con-
centrate on copper loss and preventing saturation. Ferrite
core material saturates “hard,” which means that induc-
tance collapses abruptly when the peak design current is
exceeded. This results in an abrupt increase in inductor
ripple current and consequent output voltage ripple. Do
not allow the core to saturate!
Molypermalloy (from Magnetics, Inc.) is a very good, low
loss core material for toroids, but it is more expensive than
ferrite. A reasonable compromise from the same manu-
facturer is Kool M
μ
. Toroids are very space efficient,
especially when you can use several layers of wire. Be-
cause they lack a bobbin, mounting is more difficult.
However, designs for surface mount are available which
do not increase the height significantly.
Power MOSFET, D1 and D2 Selection
Two external power MOSFETs must be selected for each
controller with the LTC1929: One N-channel MOSFET for
the top (main) switch, and one N-channel MOSFET for the
bottom (synchronous) switch.
The peak-to-peak drive levels are set by the INTV
CC
volt-
age. This voltage is typically 5V during start-up (see
EXTV
CC
Pin Connection). Consequently, logic-level thresh-
old MOSFETs must be used in most applications. The only
exception is if low input voltage is expected (V
IN
< 5V);
then, sublogic-level threshold MOSFETs (V
GS(TH)
< 3V)
should be used. Pay close attention to the BV
DSS
specifi-
cation for the MOSFETs as well; most of the logic-level
MOSFETs are limited to 30V or less.
Selection criteria for the power MOSFETs include the “ON”
resistance R
DS(ON)
, reverse transfer capacitance C
RSS
,
input voltage, and maximum output current. When the
LTC1929 is operating in continuous mode the duty factors
for the top and bottom MOSFETs of each output stage are
given by:
MainSwitchDutyCycle
V
V
OUT
IN
=
SynchronousSwitchDutyCycle
V
V
V
IN
OUT
IN
=
–
The MOSFET power dissipations at maximum output
current are given by:
P
V
V
I
R
k V
( )
I
C
f
MAIN
OUT
IN
MAX
2
DS ON
(
IN
MAX
2
RSS
=
(
+
(
)
)( )
+
1
2
2
δ
)
P
V
V
V
I
R
SYNC
IN
OUT
IN
MAX
2
DS ON
(
=
+
(
)
–
)
1
2
δ
where
δ
is the temperature dependency of R
DS(ON)
and k
is a constant inversely related to the gate drive current.
Both MOSFETs have I
2
R losses but the topside N-channel
equation includes an additional term for transition losses,
which peak at the highest input voltage. For V
IN
< 20V the
high current efficiency generally improves with larger
MOSFETs, while for V
IN
> 20V the transition losses rapidly
increase to the point that the use of a higher R
DS(ON)
device
with lower C
RSS
actual provides higher efficiency. The
synchronous MOSFET losses are greatest at high input
voltage when the top switch duty factor is low or during a
short-circuit when the synchronous switch is on close to
100% of the period.
The term (1 +
δ
) is generally given for a MOSFET in the
form of a normalized R
DS(ON)
vs. Temperature curve, but
δ
= 0.005/
°
C can be used as an approximation for low
voltage MOSFETs. C
RSS
is usually specified in the MOS-
FET characteristics. The constant k = 1.7 can be used to
estimate the contributions of the two terms in the main
switch dissipation equation.
The Schottky diodes, D1 and D2 shown in Figure 1 conduct
during the dead-time between the conduction of the two
large power MOSFETs. This helps prevent the body diode
APPLICATIU
W
U
U
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LTC1929CG#TR 功能描述:IC REG CTRLR BUCK PWM CM 28-SSOP RoHS:否 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標(biāo)準(zhǔn)包裝:2,500 系列:- PWM 型:電流模式 輸出數(shù):1 頻率 - 最大:500kHz 占空比:96% 電源電壓:4 V ~ 36 V 降壓:無(wú) 升壓:是 回掃:無(wú) 反相:無(wú) 倍增器:無(wú) 除法器:無(wú) Cuk:無(wú) 隔離:無(wú) 工作溫度:-40°C ~ 125°C 封裝/外殼:24-WQFN 裸露焊盤 包裝:帶卷 (TR)
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LTC1929CG-PG#25123 制造商:Linear Technology 功能描述:
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