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參數(shù)資料
| 型號： | LTC1735 |
| 廠商： | Linear Technology Corporation |
| 元件分類： | 基準電壓源/電流源 |
| 英文描述： | RADIATION HARDENED HIGH EFFICIENCY, 5 AMP SWITCHING REGULATORS |
| 中文描述： | 抗輻射高效，5安培開關(guān)穩(wěn)壓器 |
| 文件頁數(shù)： | 11/32頁 |
| 文件大?。?/td> | 373K |
| 代理商： | LTC1735 |
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11
LTC1735
capacitor reaches 1.19V, C
OSC
is reset to ground. The
process then repeats.
The value of C
OSC
is calculated from the desired operating
frequency assuming no external clock input on the FCB
pin:
C
pF
Frequency
OSC
(
)
. (
1 6110
)
–
=
11
7
A graph for selecting C
OSC
versus frequency is shown in
Figure 2. The maximum recommended switching fre-
quency is 550kHz .
The internal oscillator runs at its nominal frequency (f
O
)
when the FCB pin is pulled high to INTV
CC
or connected to
ground. Clocking the FCB pin above and below 0.8V will
cause the internal oscillator to injection lock to an external
clock signal applied to the FCB pin with a frequency
between 0.9f
O
and 1.3f
O
. The clock high level must exceed
1.3V for at least 0.3
μ
s and the clock low level must be less
than 0.3V for at least 0.3
μ
s. The top MOSFET turn-on will
synchronize with the rising edge of the clock.
Attempting to synchronize to too high an external fre-
quency (above 1.3f
O
) can result in inadequate slope com-
pensation and possible loop instability. If this condition
exists simply lower the value of C
OSC
so f
EXT
= f
O
according
to Figure 2.
When synchronized to an external clock, Burst Mode
operation is disabled but the inductor current is not
APPLICATIU
W
U
U
allowed to reverse. The 25% minimum inductor current
clamp present in Burst Mode operation is removed,
providing constant frequency discontinuous operation
over the widest possible output current range. In this
mode the synchronous MOSFET is forced on once every
10 clock cycles to recharge the bootstrap capacitor. This
minimizes audible noise while maintaining reasonably
high efficiency.
Inductor Value Calculation
The operating frequency and inductor selection are inter-
related in that higher operating frequencies allow the use
of smaller inductor and capacitor values. So why would
anyone ever choose to operate at lower frequencies with
larger components The answer is efficiency. A higher
frequency generally results in lower efficiency because of
MOSFET gate charge losses. In addition to this basic trade
off, the effect of inductor value on ripple current and low
current operation must also be considered.
The inductor value has a direct effect on ripple current. The
inductor ripple current
I
L
decreases with higher induc-
tance or frequency and increases with higher V
IN
or V
OUT
:
I
f L
( )( )
V
V
V
L
OUT
OUT
IN
=
1
1
–
Accepting larger values of
I
L
allows the use of low
inductances, but results in higher output voltage ripple
and greater core losses. A reasonable starting point for
setting ripple current is
I
L
= 0.3 to 0.4(I
MAX
). Remember,
the maximum
I
L
occurs at the maximum input voltage.
The inductor value also has an effect on low current
operation. The transition to low current operation begins
when the inductor current reaches zero while the bottom
MOSFET is on. Burst Mode operation begins when the
average inductor current required results in a peak current
below 25% of the current limit determined by R
SENSE
.
Lower inductor values (higher
I
L
) will cause this to occur
at higher load currents, which can cause a dip in efficiency
in the upper range of low current operation. In Burst Mode
operation, lower inductance values will cause the burst
frequency to decrease.
Figure 2. Timing Capacitor Value
OPERATING FREQUENCY (kHZ)
0
100
200
300
400
500
600
C
O
1735 F02
100.0
87.5
75.0
62.5
50.0
37.5
25.0
12.5
0
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| LTC1735CF | 功能描述:IC REG CTRLR BUCK PWM CM 20TSSOP RoHS:否 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標準包裝:4,500 系列:PowerWise® PWM 型:控制器 輸出數(shù):1 頻率 - 最大:1MHz 占空比:95% 電源電壓:2.8 V ~ 5.5 V 降壓:是 升壓:無 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 工作溫度:-40°C ~ 125°C 封裝/外殼:6-WDFN 裸露焊盤 包裝:帶卷 (TR) 配用:LM1771EVAL-ND - BOARD EVALUATION LM1771 其它名稱:LM1771SSDX |
| LTC1735CF#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 20TSSOP RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標準包裝:2,000 系列:- PWM 型:電流模式 輸出數(shù):1 頻率 - 最大:1MHz 占空比:50% 電源電壓:9 V ~ 10 V 降壓:無 升壓:是 回掃:是 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 工作溫度:-40°C ~ 85°C 封裝/外殼:8-TSSOP（0.173"，4.40mm 寬） 包裝:帶卷 (TR) |
| LTC1735CF#TR | 功能描述:IC REG CTRLR BUCK PWM CM 20TSSOP RoHS:否 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標準包裝: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 升壓:是 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 工作溫度:-40°C ~ 125°C 封裝/外殼:24-WQFN 裸露焊盤 包裝:帶卷 (TR) |
| LTC1735CF#TRPBF | 功能描述:IC REG CTRLR BUCK PWM CM 20TSSOP RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:- 標準包裝: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 升壓:是 回掃:無 反相:無 倍增器:無 除法器:無 Cuk:無 隔離:無 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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