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| 型号： | LT1072CP |
| 厂商： | TEXAS INSTRUMENTS INC |
| 元件分类： | 稳压器 |
| 英文描述： | 1.25 A SWITCHING REGULATOR, 47 kHz SWITCHING FREQ-MAX, PDIP8 |
| 封装： | PLASTIC, DIP-8 |
| 文件页数： | 16/19页 |
| 文件大小： | 294K |
| 代理商： | LT1072CP |
LT1072, LT1072HV
1.25-A HIGH-EFFICIENCY SWITCHING REGULATORS
SLVS071A – NOVEMBER 1989 – REVISED AUGUST 1995
6
POST OFFICE BOX 655303
DALLAS, TEXAS 75265
theory of operation
The LT1072 is a current-mode switcher. This means that the switch duty cycle is directly controlled by switch
current rather than by output voltage. Referring to the functional block diagram, the switch is turned on at the
start of each oscillator cycle. It is turned off when the switch current reaches a predetermined level. Control of
output voltage is obtained by using the output of a voltage-sensing error amplifier to set the current trip level.
This technique has several advantages. First, it has immediate response to input-voltage variations, which is
unlike ordinary switchers that have poor input transient response. Second, it reduces the 90
° phase shift at
midfrequencies in the energy-storage inductor. This greatly simplifies closed-loop frequency compensation
under widely varying input-voltage or output-load conditions. Finally, it allows simple pulse-by-pulse current
limiting to provide maximum switch protection under output overload or short conditions. A low-dropout internal
regulator provides a 2.3-V supply for all internal circuitry on the LT1072. This low-dropout design allows input
voltage to vary from 3 V to 60 V with virtually no change in device performance. A 40-kHz oscillator is the basic
clock for all internal timing. It turns on the output switch via the logic and driver circuitry. Special adaptive
antisaturation circuitry detects the onset of saturation in the power switch and adjusts driver current
instantaneously to limit switch saturation. This minimizes driver dissipation and provides very rapid turn off of
the switch.
A 1.2-V band-gap reference biases the positive input of the error amplifier. The negative input is brought out
for output-voltage sensing. This feedback terminal has a second function when pulled low with an external
resistor. It programs the LT1072 to disconnect the main error-amplifier output and connects the output of the
flyback amplifier to the comparator input. The LT1072 will then regulate the value of the flyback pulse with
respect to the supply voltage. This flyback pulse is directly proportional to output voltage in the traditional
transformer-coupled flyback-topology regulator. By regulating the amplitude of the flyback pulse, the output
voltage can be regulated with no direct connection between input and output. The output is fully floating up to
the breakdown voltage of the transformer windings. Multiple floating outputs are easily obtained with additional
windings. A special delay network inside the LT1072 ignores the leakage inductance spike at the leading edge
of the flyback pulse to improve output regulation.
The error signal developed at the comparator input is brought out externally. This terminal (C) has four different
functions. It is used for frequency compensation, current limit adjustment, soft starting, and total regulator
shutdown. During normal regulator operation, this terminal sits at a voltage between 0.9 V (low output current)
and 2 V (high output current). The error amplifiers are current-output (gm) types, so this voltage can be externally
clamped for adjusting current limit. Likewise, a capacitor-coupled external clamp will provide soft start. Switch
duty cycle goes to zero if the C terminal is pulled to ground through a diode. This places the LT1072 in an idle
mode. Pulling the C terminal below 0.15 V causes total regulator shutdown, with only 50-
A supply current for
shutdown-circuitry biasing.
In the P package, the emitters of the power transistors are brought out separately from the ground terminal. This
eliminates errors due to ground-terminal voltage drops and allows the user to reduce the switch-current limit
(2 : 1) by leaving the second emitter (E2) disconnected. The first emitter (E1) should always be connected to the
ground terminal. Note that switch on-state resistance doubles when E2 is left open, so efficiency will suffer
somewhat when switch currents exceed 100 mA. Also, note that chip dissipation will actually
increase with E2
open during normal load operations, even though dissipation in current-limit mode will
decrease.
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相关代理商/技术参数 |
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| LT1072CS8 | 功能描述:IC REG MULTI CONFIG ADJ 8SOIC RoHS:否 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 标准包装:2,500 系列:- 类型:降压（降压） 输出类型:固定 输出数:1 输出电压:1.2V，1.5V，1.8V，2.5V 输入电压:2.7 V ~ 20 V PWM 型:- 频率 - 开关:- 电流 - 输出:50mA 同步整流器:是 工作温度:-40°C ~ 125°C 安装类型:表面贴装 封装/外壳:10-TFSOP，10-MSOP（0.118"，3.00mm 宽）裸露焊盘 包装:带卷 (TR) 供应商设备封装:10-MSOP 裸露焊盘 |
| LT1072CS8#PBF | 功能描述:IC REG MULTI CONFIG ADJ 8SOIC RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 标准包装:250 系列:- 类型:降压（降压） 输出类型:固定 输出数:1 输出电压:1.2V 输入电压:2.05 V ~ 6 V PWM 型:电压模式 频率 - 开关:2MHz 电流 - 输出:500mA 同步整流器:是 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:6-UFDFN 包装:带卷 (TR) 供应商设备封装:6-SON（1.45x1） 产品目录页面:1032 (CN2011-ZH PDF) 其它名称:296-25628-2 |
| LT1072CS8#TR | 功能描述:IC REG MULTI CONFIG ADJ 8SOIC RoHS:否 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 标准包装:2,500 系列:- 类型:降压（降压） 输出类型:固定 输出数:1 输出电压:1.2V，1.5V，1.8V，2.5V 输入电压:2.7 V ~ 20 V PWM 型:- 频率 - 开关:- 电流 - 输出:50mA 同步整流器:是 工作温度:-40°C ~ 125°C 安装类型:表面贴装 封装/外壳:10-TFSOP，10-MSOP（0.118"，3.00mm 宽）裸露焊盘 包装:带卷 (TR) 供应商设备封装:10-MSOP 裸露焊盘 |
| LT1072CS8#TRPBF | 功能描述:IC REG MULTI CONFIG ADJ 8SOIC RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 标准包装:2,500 系列:- 类型:降压（降压） 输出类型:固定 输出数:1 输出电压:1.2V，1.5V，1.8V，2.5V 输入电压:2.7 V ~ 20 V PWM 型:- 频率 - 开关:- 电流 - 输出:50mA 同步整流器:是 工作温度:-40°C ~ 125°C 安装类型:表面贴装 封装/外壳:10-TFSOP，10-MSOP（0.118"，3.00mm 宽）裸露焊盘 包装:带卷 (TR) 供应商设备封装:10-MSOP 裸露焊盘 |
| LT1072CS8PBF | 制造商:Linear Technology 功能描述:DC-DC Converter Step-Up 3-60V SOIC8 |
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