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参数资料
| 型号： | LTC1778EGN |
| 厂商： | Linear Technology |
| 文件页数： | 12/24页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM CM 16-SSOP |
| 标准包装： | 100 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 电源电压： | 4 V ~ 36 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： | 16-SSOP（0.154"，3.90mm 宽） |
| 包装： | 管件 |
LTC1778/LTC1778-1
APPLICATIO S I FOR ATIO
Because the voltage at the I ON pin is about 0.7V, the
current into this pin is not exactly inversely proportional to
V IN , especially in applications with lower input voltages.
To correct for this error, an additional resistor R ON2
due to a dropping input voltage for example, then the
output will drop out of regulation. The minimum input
voltage to avoid dropout is:
connected from the I ON pin to the 5V INTV CC supply will
further stabilize the frequency.
V IN ( MIN ) = V OUT
t ON + t OFF (MIN)
t ON
R ON 2 =
5 V
0 . 7 V
R ON
A plot of maximum duty cycle vs frequency is shown in
Figure 5.
? I L = ? OUT ? ? 1 ? OUT ?
Changes in the load current magnitude will also cause
frequency shift. Parasitic resistance in the MOSFET
switches and inductor reduce the effective voltage across
the inductance, resulting in increased duty cycle as the
load current increases. By lengthening the on-time slightly
as current increases, constant frequency operation can be
maintained. This is accomplished with a resistive divider
from the I TH pin to the V ON pin and V OUT . The values
required will depend on the parasitic resistances in the
specific application. A good starting point is to feed about
25% of the voltage change at the I TH pin to the V ON pin as
shown in Figure 4a. Place capacitance on the V ON pin to
filter out the I TH variations at the switching frequency. The
Inductor Selection
Given the desired input and output voltages, the inductor
value and operating frequency determine the ripple
current:
? V ? ? V ?
? f L ? ? V IN ?
Lower ripple current reduces core losses in the inductor,
ESR losses in the output capacitors and output voltage
2.0
resistor load on I TH reduces the DC gain of the error amp
and degrades load regulation, which can be avoided by
using the PNP emitter follower of Figure 4b.
Minimum Off-time and Dropout Operation
The minimum off-time t OFF(MIN) is the smallest amount of
time that the LTC1778 is capable of turning on the bottom
1.5
1.0
0.5
DROPOUT
REGION
MOSFET, tripping the current comparator and turning the
0
0
0.25 0.50 0.75
1.0
MOSFET back off. This time is generally about 250ns. The
minimum off-time limit imposes a maximum duty cycle of
t ON /(t ON + t OFF(MIN) ). If the maximum duty cycle is reached,
R VON1
30k
DUTY CYCLE (V OUT /V IN )
1778 F05
Figure 5. Maximum Switching Frequency vs Duty Cycle
R VON1
3k
V OUT
R VON2
100k
R C
C VON
0.01 μ F
V ON
LTC1778
I TH
V OUT
INTV CC
10k
Q1
2N5087
R VON2
10k
C VON
0.01 μ F
R C
V ON
LTC1778
I TH
C C
(4a)
(4b)
C C
1778 F04
Figure 4. Correcting Frequency Shift with Load Current Changes
1778fb
12
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相关代理商/技术参数 |
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|---|---|
| LTC1778EGN#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 16-SSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:2,500 系列:- PWM 型:电流模式 输出数:1 频率 - 最大:500kHz 占空比:96% 电源电压:4 V ~ 36 V 降压:无 升压:是 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:24-WQFN 裸露焊盘 包装:带卷 (TR) |
| LTC1778EGN#TR | 功能描述:IC REG CTRLR BUCK PWM CM 16-SSOP RoHS:否 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:2,500 系列:- PWM 型:电流模式 输出数:1 频率 - 最大:500kHz 占空比:96% 电源电压:4 V ~ 36 V 降压:无 升压:是 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:24-WQFN 裸露焊盘 包装:带卷 (TR) |
| LTC1778EGN#TRPBF | 功能描述:IC REG CTRLR BUCK PWM CM 16-SSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:2,500 系列:- PWM 型:电流模式 输出数:1 频率 - 最大:500kHz 占空比:96% 电源电压:4 V ~ 36 V 降压:无 升压:是 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:24-WQFN 裸露焊盘 包装:带卷 (TR) |
| LTC1778EGN-1 | 功能描述:IC REG CTRLR BUCK PWM CM 16-SSOP RoHS:否 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:2,500 系列:- PWM 型:电流模式 输出数:1 频率 - 最大:500kHz 占空比:96% 电源电压:4 V ~ 36 V 降压:无 升压:是 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:24-WQFN 裸露焊盘 包装:带卷 (TR) |
| LTC1778EGN-1#PBF | 功能描述:IC REG CTRLR BUCK PWM CM 16-SSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 特色产品:LM3753/54 Scalable 2-Phase Synchronous Buck Controllers 标准包装:1 系列:PowerWise® PWM 型:电压模式 输出数:1 频率 - 最大:1MHz 占空比:81% 电源电压:4.5 V ~ 18 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:-5°C ~ 125°C 封装/外壳:32-WFQFN 裸露焊盘 包装:Digi-Reel® 产品目录页面:1303 (CN2011-ZH PDF) 其它名称:LM3754SQDKR |
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