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参数资料
| 型号： | LTC1700EMS#TRPBF |
| 厂商： | Linear Technology |
| 文件页数： | 12/16页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BST PWM CM 10-MSOP |
| 标准包装： | 2,500 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 680kHz |
| 占空比： | 92% |
| 电源电压： | 0.9 V ~ 6 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 ~ 85°C |
| 封装/外壳： | 10-TFSOP，10-MSOP（0.118"，3.00mm 宽） |
| 包装： | 带卷 (TR) |
LTC1700
APPLICATIO N S I N FOR M ATIO N
The efficiency of a switching regulator is equal to the
output power divided by the input power ( × 100%).
Percent efficiency can be expressed as:
% Efficiency = 100%–(L1 + L2 + L3 + ...)
where L1, L2, etc. are the individual losses as a percentage
of input power. It is often useful to analyze individual
losses to determine what is limiting the efficiency and
which change would produce the most improvement.
Although all dissipative elements in the circuit produce
losses, four main sources usually account for most of the
losses in LTC1700 circuits:
1. LTC1700 supply current. This DC supply current, given
in the electrical characteristics, excludes MOSFET drivers
and control current. This supply current results in a small
loss which increases with V OUT .
2. MOSFETs gate charge current results from switching
the gate capacitance of the power MOSFETs. Each time a
MOSFET gate is switched on and then off, a packet of gate
charge Q g moves from V OUT to ground. The resulting
current out from V OUT is typically much larger than the
control circuit current. In continuous mode, I GATECHG =
f(Q g(TOP) + Q g(BOT) ). At high switching frequencies, this
loss becomes increasingly important.
3. DC I 2 R Losses. Since there is no sense resistor needed,
DC I 2 R losses arise only from the resistances of the
MOSFETs and inductor. In continuous mode, the average
current flows through the inductor but is “chopped”
between the synchronous P-channel MOSFET and the
main N-channel MOSFET. If the two MOSFETs have ap-
proximately the same R DS(ON) , then the resistance of one
MOSFET can simply be summed with the resistance of the
inductor to obtain the DC I 2 R loss. For example, if each
R DS(ON) = 0.05 ? and R L = 0.15 ? , then the total resistance
is 0.2 ? . This results in losses ranging from 2% to 8% as
the output current increases from 0.5A to 2A for a 5V
output. I 2 R losses cause the efficiency to drop at high
4. Transition losses apply to the main external MOSFET
and increase at higher operating frequencies and output
voltages. Transition losses can be estimated from:
Transition Loss = 2.5(V OUT ) 2 I O(MAX) C RSS (f)
Other losses including C IN and C OUT ESR dissipative
losses, and inductor core losses, generally account for
less than 2% total loss.
Run/Soft-Start Function
The RUN/SS pin is a dual purpose pin that provides the
soft-start function and a means to shut down the LTC1700.
Soft-start reduces input surge current from V IN by gradu-
ally increasing the internal current limit. Power supply
sequencing can also be accomplished using this pin.
An internal 3.8 μ A current source charges up an external
capacitor C SS . When the voltage on the RUN/SS pin
reaches 0.7V, the LTC1700 begins operating. As the
voltage on RUN/SS continues to ramp from 0.7V to 1V, the
internal current limit is also ramped at a proportional linear
rate. The current limit begins near 0A (at V RUN/SS = 0.7V)
and ends at 0.078/R DS(ON) (V RUN/SS ≈ 2.2V). The output
current thus ramps up slowly, reducing the starting surge
current required from the input power supply. If the RUN/
SS has been pulled all the way to ground, there will be a
delay before the current limit starts increasing and is given
by:
t DELAY = 1.13C SS /I CHG
For input voltages less than 2.3V during the start-up
duration, the soft-start function has no effect on the
internal 60mA current limit. Therefore to fully take advan-
tage of this feature, the soft-start capacitor has to be sized
accordingly to account for the time it takes V OUT to reach
2.3V. An approximate mathematical representation for the
time it takes V OUT to reach 2.3V upon powering up is given
by:
output currents.
t POWER ? UP =
C OUT (2 .3 – V IN – V D )
260 ( L )
– I OUT
2 . 3 – V IN
1700fa
12
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| LTC1701BES5#TRM | 功能描述:IC REG BUCK ADJ 0.5A TSOT23-5 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:升压（升压） 输出类型:可调式 输出数:1 输出电压:1.24 V ~ 30 V 输入电压:1.5 V ~ 12 V PWM 型:电流模式，混合 频率 - 开关:600kHz 电流 - 输出:500mA 同步整流器:无 工作温度:-40°C ~ 85°C 安装类型:表面贴装 封装/外壳:8-SOIC（0.154"，3.90mm 宽） 包装:带卷 (TR) 供应商设备封装:8-SOIC |
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