參數(shù)資料
型號(hào)： LTC1708EG-PG
廠商： LINEAR TECHNOLOGY CORP
元件分類： 穩(wěn)壓器
英文描述： Dual Adjustable 5-Bit VID High Efficiency, 2-Phase Current Mode Synchronous Buck Regulator Controller
中文描述： 3 A DUAL SWITCHING CONTROLLER, 310 kHz SWITCHING FREQ-MAX, PDSO36
封裝： 0.209 INCH, PLASTIC, SSOP-36
文件頁(yè)數(shù)： 10/32頁(yè)
文件大?。?/td> 358K
代理商： LTC1708EG-PG
10
LTC1708-PG
OPERATIOU
Main Control Loop
The LTC1708 uses a constant frequency, current mode
step-down architecture with the two controller channels
operating 180 degrees out of phase. During normal opera-
tion, each top MOSFET is turned on when the clock for that
channel sets the RS latch, and turned off when the main
current comparator, I
1
, resets the RS latch. The peak
inductor current at which I
1
resets the RS latch is con-
trolled by the voltage on the I
TH
pin, which is the output of
each error amplifier EA. The EAIN pin receives the voltage
feedback signal, which is compared to the internal refer-
ence voltage by the EA. When the load current increases,
it causes a slight decrease in EAIN
relative to the 0.8V
reference, which in turn causes the I
TH
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 I
2
, or
the beginning of the next cycle.
The top MOSFET drivers are biased from floating boot-
strap capacitor C
B
, which normally is recharged during
each off cycle through an external diode when the top
MOSFET turns off. As V
IN
decreases to a voltage close to
V
OUT
, the loop may enter dropout and attempt to turn on
the top MOSFET continuously. The dropout detector de-
tects this and forces the top MOSFET off for about 500ns
every tenth cycle 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 1.2
μ
A
current source to charge soft-start capacitor C
SS
. When
C
SS
reaches 1.5V, the main control loop is enabled with the
I
TH
voltage clamped at approximately 30% of its maximum
value. As C
SS
continues to charge, the I
TH
pin voltage is
gradually released allowing normal, full-current opera-
tion. When both RUN/SS1 and RUN/SS2 are low, all
LTC1708 controller functions are shut down, and the
STBYMD pin determines if the standby 5V and 3.3V
regulators are kept alive.
(Refer to Functional Diagram)
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
controller 1 and 2) select between twomodes of low
current operation. When the FCB pin voltage is below
0.8V, the controller forces continuous PWM current
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 V
INTVCC
–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 synchro-
nous MOSFET(s) when the inductor current goes nega-
tive. This combination of requirements will, at low cur-
rents, force the I
TH
pin below a voltage threshold that will
temporarily inhibit turn-on of both output MOSFETs until
the output voltage drops. There is 60mV of hysteresis in
the burst comparator B tied to the I
TH
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 amplifier
gain block.
Constant Frequency Operation
When the FCB pin is tied to INTV
CC
, Burst Mode operation
is disabled and the forced minimum output current re-
quirement is removed. This provides constant frequency,
discontinuous (preventing reverse inductor current) cur-
rent operation over the widest possible output current
range. This constant frequency operation is not as efficient
as Burst Mode operation, but does provide a lower noise,
constant frequency operating mode down to approxi-
mately 1% of designed maximum output current.
Continuous Current (PWM) Operation
Tying the FCB pin to ground will force continuous current
operation. This is the least efficient operating mode, but
may be desirable in certain applications. The output can
source or sink current in this mode. When sinking current
while in forced continuous operation, current will be
forced back into the main power supply potentially boost-
ing the input supply to dangerous voltage levels—
BEWARE!
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相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
LTC1708EG-PG#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:- 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(wú) 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:6-WDFN 裸露焊盤 包裝:帶卷 (TR) 配用:LM1771EVAL-ND - BOARD EVALUATION LM1771 其它名稱:LM1771SSDX
LTC1708EG-PG#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:- 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(wú) 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:6-WDFN 裸露焊盤 包裝:帶卷 (TR) 配用:LM1771EVAL-ND - BOARD EVALUATION LM1771 其它名稱:LM1771SSDX
LTC1708EG-PG#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:- 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(wú) 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:6-WDFN 裸露焊盤 包裝:帶卷 (TR) 配用:LM1771EVAL-ND - BOARD EVALUATION LM1771 其它名稱:LM1771SSDX
LTC1709EG 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:- 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(wú) 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:6-WDFN 裸露焊盤 包裝:帶卷 (TR) 配用:LM1771EVAL-ND - BOARD EVALUATION LM1771 其它名稱:LM1771SSDX
LTC1709EG#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:- 標(biāo)準(zhǔn)包裝:4,000 系列:- PWM 型:電壓模式 輸出數(shù):1 頻率 - 最大:1.5MHz 占空比:66.7% 電源電壓:4.75 V ~ 5.25 V 降壓:是 升壓:無(wú) 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 ~ 85°C 封裝/外殼:40-VFQFN 裸露焊盤 包裝:帶卷 (TR)
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