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参数资料
| 型号： | LTC1702IGN |
| 厂商： | Linear Technology |
| 文件页数： | 14/36页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM VM 24-SSOP |
| 标准包装： | 55 |
| 系列： | PolyPhase® |
| PWM 型： | 电压模式 |
| 输出数： | 2 |
| 频率 - 最大： | 750kHz |
| 占空比： | 93% |
| 电源电压： | 3 V ~ 7 V |
| 降压： | 是 |
| 升压： | 无 |
| 回扫： | 无 |
| 反相： | 无 |
| 倍增器： | 无 |
| 除法器： | 无 |
| Cuk： | 无 |
| 隔离： | 无 |
| 工作温度： | -40°C ~ 85°C |
| 封装/外壳： | 24-SSOP（0.154"，3.90mm 宽） |
| 包装： | 管件 |
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LTC1702
APPLICATIO N S I N FOR M ATIO N
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 and QT 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
I RIPPLE
I AVERAGE
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
Figure 5a. Continuous Mode
I RIPPLE
1702 F05a
V SW
V BG
0V
5V
DISCONTINUOUS
COMPARATOR
TURNS OFF BG
50ns
BLANK
TIME
TIME
I AVERAGE
0V
TIME
1702 F06
TIME
Figure 5b. Discontinuous Mode
1702 F05b
Figure 6. Ringing at SW Causes Discontinuous
Comparator to Trip Early
1702fa
14
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相关代理商/技术参数 |
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| LTC1702IGN#PBF | 功能描述:IC REG CTRLR BUCK PWM VM 24-SSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:PolyPhase® 标准包装:4,500 系列:PowerWise® PWM 型:控制器 输出数:1 频率 - 最大:1MHz 占空比:95% 电源电压:2.8 V ~ 5.5 V 降压:是 升压:无 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-40°C ~ 125°C 封装/外壳:6-WDFN 裸露焊盘 包装:带卷 (TR) 配用:LM1771EVAL-ND - BOARD EVALUATION LM1771 其它名称:LM1771SSDX |
| LTC1702IGN#TR | 功能描述:IC REG CTRLR BUCK PWM VM 24-SSOP RoHS:否 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:PolyPhase® 标准包装:4,500 系列:PowerWise® PWM 型:控制器 输出数:1 频率 - 最大:1MHz 占空比:95% 电源电压:2.8 V ~ 5.5 V 降压:是 升压:无 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-40°C ~ 125°C 封装/外壳:6-WDFN 裸露焊盘 包装:带卷 (TR) 配用:LM1771EVAL-ND - BOARD EVALUATION LM1771 其它名称:LM1771SSDX |
| LTC1702IGN#TRPBF | 功能描述:IC REG CTRLR BUCK PWM VM 24-SSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:PolyPhase® 标准包装:4,500 系列:PowerWise® PWM 型:控制器 输出数:1 频率 - 最大:1MHz 占空比:95% 电源电压:2.8 V ~ 5.5 V 降压:是 升压:无 回扫:无 反相:无 倍增器:无 除法器:无 Cuk:无 隔离:无 工作温度:-40°C ~ 125°C 封装/外壳:6-WDFN 裸露焊盘 包装:带卷 (TR) 配用:LM1771EVAL-ND - BOARD EVALUATION LM1771 其它名称:LM1771SSDX |
| LTC1703CG | 功能描述:IC REG SW DUAL SYNC VID 28SSOP RoHS:否 类别:集成电路 (IC) >> PMIC - 稳压器 - 专用型 系列:- 标准包装:43 系列:- 应用:控制器，Intel VR11 输入电压:5 V ~ 12 V 输出数:1 输出电压:0.5 V ~ 1.6 V 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:48-VFQFN 裸露焊盘 供应商设备封装:48-QFN（7x7） 包装:管件 |
| LTC1703CG#PBF | 功能描述:IC REG SW DUAL SYNC VID 28SSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - 专用型 系列:- 标准包装:2,000 系列:- 应用:控制器，DSP 输入电压:4.5 V ~ 25 V 输出数:2 输出电压:最低可调至 1.2V 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:30-TFSOP（0.173"，4.40mm 宽） 供应商设备封装:30-TSSOP 包装:带卷 (TR) |
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