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參數(shù)資料
| 型號： | LTC3731H |
| 廠商： | Linear Technology Corporation |
| 英文描述： | 3-Phase, 600kHz, Synchronous Buck Switching Regulator Controller |
| 中文描述： | 3相，600kHz的，同步降壓開關(guān)穩(wěn)壓器控制器 |
| 文件頁數(shù)： | 10/32頁 |
| 文件大?。?/td> | 323K |
| 代理商： | LTC3731H |
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10
LTC3731H
3731hf
OPERATIOU
Main Control Loop
The IC uses a constant frequency, current mode step-
down architecture. During normal operation, each top
MOSFET is turned on each cycle when the oscillator sets
the RS latch, and turned off when the main current
comparator, I
1
, resets each RS latch. The peak inductor
current at which I
1
resets the RS latch is controlled by the
voltage on the I
TH
pin, which is the output of the error
amplifier EA. The EAIN pin receives a portion of output
voltage feedback signal through the external resistive
divider and is compared to the internal reference voltage.
When the load current increases, it causes a slight de-
crease in the EAIN pin voltage
relative to the 0.6V refer-
ence, which in turn causes the I
TH
voltage to increase until
each inductor’s average current matches one third of the
new load current (assuming all three current sensing
resistors are equal). In Burst Mode operation and Stage
Shedding mode, after each top MOSFET has turned off, the
bottom MOSFET is turned on until either the inductor
current starts to reverse, as indicated by current compara-
tor I
2
, or the beginning of the next cycle.
The top MOSFET drivers are biased from floating boot-
strap capacitor C
B
, which is normally recharged through
an external Schottky diode when the top FET is turned off.
When V
IN
decreases to a voltage close to V
OUT
, however,
the loop may enter dropout and attempt to turn on the top
MOSFET continuously. The dropout detector counts the
number of oscillator cycles that the bottom MOSFET
remains off and periodically forces a brief on period to
allow C
B
to recharge.
The main control loop is shut down by pulling the RUN/SS
pin low. Releasing RUN/SS allows an internal 1.5
μ
A
current source to charge soft-start capacitor C
SS
. When
C
SS
reaches 1.5V, the main control loop is enabled and the
internally buffered I
TH
voltage is clamped but allowed to
ramp as the voltage on C
SS
continues to ramp. This “soft-
start” clamping prevents abrupt current from being drawn
from the input power source. When the RUN/SS pin is low,
all functions are kept in a controlled state. The RUN/SS pin
is pulled low when the supply input voltage is below 4V,
when the undervoltage lockout pin (UVADJ) is below 1.2V,
or when the IC die temperature rises above 160
°
C.
(Refer to Functional Diagram)
Low Current Operation
The FCB pin is a logic input to select between three modes
of operation.
A) Burst Mode Operation
When the FCB pin voltage is below 0.6V, the controller
performs as a continuous, PWM current mode synchro-
nous switching regulator. The top and bottom MOSFETs
are alternately turned on to maintain the output voltage
independent of direction of inductor current. When the
FCB pin is below V
CC
– 1.5V but greater than 0.6V, the
controller performs as a Burst Mode switching regulator.
Burst Mode operation sets a minimum output current level
before turning off the top switch and turns off the synchro-
nous MOSFET(s) when the inductor current goes nega-
tive. This combination of requirements will, at low current,
force the I
TH
pin below a voltage threshold that will
temporarily shut off both output MOSFETs until the output
voltage drops slightly. There is a burst comparator having
60mV of hysteresis tied to the I
TH
pin. This hysteresis
results in output signals to the MOSFETs that turn them on
for several cycles, followed by a variable “sleep” interval
depending upon the load current. The resultant output
voltage ripple is held to a very small value by having the
hysteretic comparator after the error amplifier gain block.
B) Stage Shedding Operation
When the FCB pin is tied to the V
CC
pin, Burst Mode
operation is disabled and the forced minimum inductor
current requirement is removed. This provides constant
frequency, discontinuous current operation over the wid-
est possible output current range. At approximately 10%
of maximum designed load current, the second and third
output stages are shut off and the phase 1 controller alone
is active in discontinuous current mode. This “stage
shedding” optimizes efficiency by eliminating the gate
charging losses and switching losses of the other two
output stages. Additional cycles will be skipped when the
output load current drops below 1% of maximum de-
signed load
current in order to maintain the output volt-
age. This stage shedding operation is not as efficient as
Burst Mode operation at very light loads, but does provide
lower noise, constant frequency operating mode down to
very light load conditions.
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| LTC3731HG | 功能描述:IC REG CTRLR BUCK PWM CM 36-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 |
| LTC3731HG#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 36-SSOP RoHS:是 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 |
| LTC3731HG#TR | 功能描述:IC REG CTRLR BUCK PWM CM 36-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 |
| LTC3731HG#TRPBF | 功能描述:IC REG CTRLR BUCK PWM CM 36-SSOP RoHS:是 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 |
| LTC3731HUH#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 32-QFN RoHS:是 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 |
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