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參數(shù)資料
| 型號： | LTC3728LIGN-1 |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | 3 A DUAL SWITCHING CONTROLLER, 590 kHz SWITCHING FREQ-MAX, PDSO28 |
| 封裝： | 0.150 INCH, PLASTIC, SSOP-28 |
| 文件頁數(shù)： | 2/32頁 |
| 文件大?。?/td> | 475K |
| 代理商： | LTC3728LIGN-1 |
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LTC3728L-1
10
3728l1fc
OPERATION
Main Control Loop
The LTC3728L-1 is a constant frequency, current mode
step-down controller with two channels operating 180
degrees out of phase. During normal operation, each top
MOSFET is turned on when the clock for that channel sets
the RS latch, and turned off when the main current com-
parator, I1, resets the RS latch. The peak inductor current
at which I1 resets the RS latch is controlled by the voltage
on the ITH pin, which is the output of each error amplier
EA. The VOSENSE pin receives the voltage feedback signal,
which is compared to the internal reference voltage by the
EA. When the load current increases, it causes a slight
decrease in VOSENSE relative to the 0.8V reference, which
in turn causes the ITH voltage to increase until the average
inductor current matches the new load current. After the
top MOSFET has turned off, the bottom MOSFET is turned
on until either the inductor current starts to reverse, as
indicated by current comparator I2, or the beginning of
the next cycle.
The top MOSFET drivers are biased from oating bootstrap
capacitor CB, which normally is recharged during each off
cycle through an external diode when the top MOSFET
turns off. As VIN decreases to a voltage close to VOUT, the
loop may enter dropout and attempt to turn on the top
MOSFET continuously. The dropout detector detects this
and forces the top MOSFET off for about 400ns every tenth
cycle to allow CB to recharge.
The main control loop is shut down by pulling the RUN/SS
pin low. Releasing RUN/SS allows an internal 1.2μA cur-
rent source to charge soft-start capacitor CSS. When CSS
reaches 1.5V, the main control loop is enabled with the ITH
voltage clamped at approximately 30% of its maximum
value. As CSS continues to charge, the ITH pin voltage is
gradually released allowing normal, full-current operation.
When both RUN/SS1 and RUN/SS2 are low, all controller
functions are shut down, including the 5V regulator.
Low Current Operation
The FCB pin is a multifunction pin providing two func-
tions: 1) to provide regulation for a secondary winding
by temporarily forcing continuous PWM operation on
both controllers; and 2) to select between
two modes
of low current operation. When the FCB pin voltage is
below 0.8V, the controller forces continuous PWM cur-
rent mode operation. In this mode, 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 VINTVCC – 2V but greater
than 0.8V, the controller enters Burst Mode operation.
Burst Mode operation sets a minimum output current
level before inhibiting the top switch and turns off the
synchronous MOSFET(s) when the inductor current goes
negative. This combination of requirements will, at low
currents, force the ITH pin below a voltage threshold that
will temporarily inhibit turn-on of both output MOSFETs
until the output voltage drops. There is 60mV of hyster-
esis in the burst comparator B tied to the ITH pin. This
hysteresis produces 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
amplier gain block.
Frequency Synchronization
The phase-locked loop allows the internal oscillator to
be synchronized to an external source via the PLLIN pin.
The output of the phase detector at the PLLFLTR pin is
also the DC frequency control input of the oscillator that
operates over a 260kHz to 550kHz range corresponding
to a DC voltage input from 0V to 2.4V. When locked, the
PLL aligns the turn on of the top MOSFET to the rising
edge of the synchronizing signal. When PLLIN is left
open, the PLLFLTR pin goes low, forcing the oscillator to
minimum frequency.
Constant Frequency Operation
When the FCB pin is tied to INTVCC, Burst Mode opera-
tion is disabled and the forced minimum output current
requirement is removed. This provides constant frequency,
discontinuous current (preventing reverse inductor cur-
rent) operation over the widest possible output current
range. This constant frequency operation is not as efcient
(Refer to Functional Diagram)
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| LTC3728LIGN-1#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 28-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(zhǔn)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 |
| LTC3728LIGN-1#TRPBF | 功能描述:IC REG CTRLR BUCK PWM CM 28-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(zhǔn)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 |
| LTC3728LIUH#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(zhǔn)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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