參數(shù)資料
型號(hào)： LTC1702I
廠商： Linear Technology Corporation
元件分類： 通用總線功能
英文描述： Synchronous 8-Bit Up/Down Binary Counters 24-SOIC 0 to 70
中文描述： 雙550kHz的同步二相開(kāi)關(guān)穩(wěn)壓器控制器
文件頁(yè)數(shù)： 14/36頁(yè)
文件大?。?/td> 350K
代理商： LTC1702I
14
LTC1702
ripple voltage and frequency remain constant at all loads,
easing filtering requirements. Circuits that take advantage
of this behavior can force the LTC1702 to operate in
continuous mode at all loads by tying the FCB (Force
Continuous Bar) pin to ground.
Discontinuous Mode
To minimize the efficiency loss due to reverse current flow
at light loads, the LTC1702 switches to a second mode of
operation: discontinuous mode (Figure 5b). In discontinu-
ous mode, the LTC1702 detects when the inductor current
approaches zero and turns off QB for the remainder of the
switch cycle. During this time, the voltage at the SW pin
will float about V
OUT
, the voltage across the inductor will
be zero, and the inductor current remains zero until the
next switching cycle begins andQT turns on again. This
prevents current from flowing backwards in QB, eliminat-
ing that power loss term. It also reduces the ripple current
in the inductor as the output current approaches zero.
The LTC1702 detects that the inductor current has reached
zero by monitoring the voltage at the SW pin while QB is
APPLICATIO
S I
N
FOR
ATIO
U
W
U
Figure 6. Ringing at SW Causes Discontinuous
Comparator to Trip Early
Figure 5a. Continuous Mode
Figure 5b. Discontinuous Mode
TIME
50ns
BLANK
TIME
0V
0V
5V
DISCONTINUOUS
COMPARATOR
TURNS OFF BG
V
SW
V
BG
1702 F06
TIME
on. Since QB acts like a resistor, SW should ideally be right
at 0V when the inductor current reaches zero. In reality, the
SW node will ring to some degree immediately after it is
switched to ground by QB, causing some uncertainty as to
the actual moment the average current in QB goes to zero.
The LTC1702 minimizes this effect by ignoring the SW
node for a fixed 50ns after QB turns on when the ringing
is most severe, and by including a few millivolts offset in
the comparator that monitors the SW node. Despite these
precautions, some combinations of inductor and layout
parasitics can cause the LTC1702 to enter discontinuous
mode erratically. In many cases, the time that QB turns off
will correspond to a peak in the ringing waveform at the
SW pin (Figure 6). This erratic operation isn’t pretty, but
retains much of the efficiency benefit of discontinuous
mode and maintains regulation at all times.
Burst Mode Operation
Discontinuous mode removes the resistive loss drop term
in QB, but the LTC1702 is still switching QT and QB on and
off once a cycle. Each time an external MOSFET is turned
on, the internal driver must charge its gate to V
CC
. Each
time it is turned off, that charge is lost to ground. At the
high switching frequencies that the LTC1702 operates at,
the charge lost to the gates can add up to tens of milliamps
from V
CC
. As the load current continues to drop, this
quickly become the dominant power loss term, reducing
efficiency once again.
TIME
I
RIPPLE
I
AVERAGE
I
1702 F05a
TIME
I
RIPPLE
I
AVERAGE
I
1702 F05b
相關(guān)PDF資料
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相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
LTC1702IGN 功能描述:IC REG CTRLR BUCK PWM VM 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: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(pán) 包裝:帶卷 (TR) 配用:LM1771EVAL-ND - BOARD EVALUATION LM1771 其它名稱:LM1771SSDX
LTC1702IGN#PBF 功能描述:IC REG CTRLR BUCK PWM VM 24-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(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(pán) 包裝:帶卷 (TR) 配用:LM1771EVAL-ND - BOARD EVALUATION LM1771 其它名稱:LM1771SSDX
LTC1702IGN#TR 功能描述:IC REG CTRLR BUCK PWM VM 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: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(pán) 包裝:帶卷 (TR) 配用:LM1771EVAL-ND - BOARD EVALUATION LM1771 其它名稱:LM1771SSDX
LTC1702IGN#TRPBF 功能描述:IC REG CTRLR BUCK PWM VM 24-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(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(pán) 包裝:帶卷 (TR) 配用:LM1771EVAL-ND - BOARD EVALUATION LM1771 其它名稱:LM1771SSDX
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