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參數(shù)資料
| 型號： | LTC3737 |
| 廠商： | Linear Technology Corporation |
| 英文描述： | No RSENSE Low EMI, Synchronous DC/DC Controller with Output Tracking |
| 中文描述： | 無檢測電阻低EMI，同步DC / DC控制器的輸出跟蹤 |
| 文件頁數(shù)： | 17/28頁 |
| 文件大?。?/td> | 372K |
| 代理商： | LTC3737 |
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17
LTC3808
3808f
satisfied, the capacitance is adequate for filtering. The
output ripple (
V
OUT
) is approximated by:
≈
+
V
I
ESR
f C
OUT
RIPPLE
OUT
1
8
where f is the operating frequency, C
OUT
is the output
capacitance and I
RIPPLE
is the ripple current in the induc-
tor. The output ripple is highest at maximum input voltage
since I
RIPPLE
increase with input voltage.
Setting Output Voltage
The LTC3808 output voltage is set by an external feedback
resistor divider carefully placed across the output, as
shown in Figure 3. The regulated output voltage is deter-
mined by:
V
V
R
R
OUT
B
A
=
+
0 6
.
1
For most applications, a 59k resistor is suggested for R
A
.
In applications where minimizing the quiescent current is
critical, R
A
should be made bigger to limit the feedback
divider current. If R
B
then results in very high impedance,
it may be beneficial to bypass R
B
with a 50pF to 100pF
capacitor C
FF
.
Once the controller is enabled, the start-up of V
OUT
is
controlled by the state of the TRACK/SS pin. If the TRACK/
SS pin is connected to V
IN
, the start-up of V
OUT
is con-
trolled by internal soft-start, which slowly ramps the
positive reference to the error amplifier from 0V to 0.6V,
allowing V
OUT
to rise smoothly from 0V to its final value.
The default internal soft-start time is around 1ms. The
soft-start time can be changed by placing a capacitor
between the TRACK/SS pin and GND. In this case, the soft-
start time will be approximately:
t
C
mV
A
μ
1
SS
SS
=
600
where 1
μ
A is an internal current source which is always
on.
When the voltage on the TRACK/SS pin is less than the
internal 0.6V reference, the LTC3808 regulates the V
FB
voltage to the TRACK/SS pin voltage instead of 0.6V.
Therefore the start-up of V
OUT
can ratiometrically track an
external voltage V
X
, according to a ratio set by a resistor
divider at TRACK/SS pin (Figure 5a). The ratiometric
relation between V
OUT
and V
X
is (Figure 5c):
V
V
R
R
R
R
R
R
OUT
X
TA
A
A
B
TB
TA
=
+
+
APPLICATIU
W
U
U
LTC3808
V
FB
V
OUT
R
B
C
FF
R
A
3808 F03
Figure 3. Setting Output Voltage
Run and Soft-Start/Tracking Functions
The LTC3808 has a low power shutdown mode which is
controlled by the RUN pin. Pulling the RUN pin below 1.1V
puts the LTC3808 into a low quiescent current shutdown
mode (I
Q
= 9
μ
A). Releasing the RUN pin, an internal 0.7
μ
A
(at V
IN
= 4.2V) current source will pull the RUN pin up to
V
IN
, which enables the controller. The RUN pin can be
driven directly from logic as showed in Figure 4.
3.3V OR 5V
3808 F04
LTC3808
RUN
LTC3808
RUN
Figure 4. RUN Pin Interfacing
LTC3808
V
FB
V
OUT
V
X
TRACK/SS
R
B
R
A
3808 F5a
R
TB
R
TA
Figure 5a. Using the TRACK/SS Pin to Track V
X
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| LTC3737EGN | 功能描述:IC REG CTRLR BUCK PWM CM 24-SSOP RoHS:否 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:PolyPhase® 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 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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| LTC3737EGN#TR | 功能描述:IC REG CTRLR BUCK PWM CM 24-SSOP RoHS:否 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:PolyPhase® 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 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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| LTC3737EUF | 功能描述:IC REG CTRLR BUCK PWM CM 24-QFN RoHS:否 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 切換控制器 系列:PolyPhase® 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 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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