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| 型号： | LT3689EMSE#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 16/34页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK ADJ 0.7A 16MSOP |
| 标准包装： | 37 |
| 类型： | 降压（降压） |
| 输出类型： | 可调式 |
| 输出数： | 1 |
| 输出电压： | 0.8 V ~ 34.2 V |
| 输入电压： | 3.6 V ~ 36 V |
| PWM 型： | 电流模式，Burst Mode? |
| 频率 - 开关： | 500kHz ~ 2MHz |
| 电流 - 输出： | 700mA |
| 同步整流器： | 无 |
| 工作温度： | -40°C ~ 125°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 16-TFSOP（0.118"，3.00mm 宽）裸露焊盘 |
| 包装： | 管件 |
| 供应商设备封装： | 16-MSOP，裸露焊盘 |
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LT3689/LT3689-5
APPLICATIONS INFORMATION
(1 ? DC)(V OUT + V D )
? I L =
I SW(PK) = I L(PK) = I OUT +
I OUT(MAX) = I LIM ?
? I L
= 1.15A ? (1 ? 0.28 ? DC) ?
1.4 ( V OUT + V D )
L MIN =
Chooseaninductorusingthepreviousinductorselection
equation to guarantee 700mA of output current. If using
a smaller inductor, check the DA current limit equation to
verify that the DA circuitry will not lower the switching
frequency.
When the switch is off, the potential across the inductor
is the output voltage plus the catch diode drop. This gives
the peak-to-peak ripple current in the inductor:
L ? f SW
where f SW is the switching frequency of the LT3689 and L
is the value of the inductor. The peak inductor and switch
current is:
? I L
2
To maintain output regulation, this peak current must be
less than the LT3689’s switch current limit I LIM . I LIM is at
least 1.5A for at low duty cycles and decreases linearly
to 0.87A at DC = 85%. The maximum output current is a
function of the chosen inductor value.
? I L
2
2
Choosing an inductor value so that the ripple current is
small will allow a maximum output current near the switch
current limit.
One approach to choosing the inductor is to start with the
preceding simple rule, determine the available inductors,
and choose one to meet cost or space goals. Next, use
these equations to check that the LT3689 will be able to
deliver the required output current. Note again that these
equations assume that the inductor current is continu-
ous. Discontinuous operation occurs when I OUT is less
than ? I L /2.
Of course, such a simple design guide will not always
result in the optimum inductor for the application. A larger
value inductor provides a slightly higher maximum load
current and will reduce the output voltage ripple. If the
load is lower than 0.7A, decrease the value of the inductor
and operate with a higher ripple current. This allows the
use of a physically smaller inductor, or one with a lower
DCR resulting in higher efficiency. There are graphs in
the Typical Performance Characteristics section of this
data sheet that show the maximum load current as a
function of input voltage for several popular output volt-
ages. Low inductance may result in discontinuous mode
operation, which is okay but further reduces maximum
load current. For details of maximum output current and
discontinuous mode operation, see Linear Technology
Application Note 44. Finally, for duty cycles greater than
50% (V OUT / V IN > 0.5), a minimum inductance is required
to avoid subharmonic oscillations:
f SW
where L MIN is in μH, V OUT and V D are in volts, and f SW
is in MHz.
Input Capacitor
Bypass the input of the LT3689 circuit with a ceramic
capacitor of an X7R or X5R type. Y5V types have poor
performance over temperature and applied voltage, and
should not be used. The minimum value of input capaci-
tance depends on the switching frequency. Use an input
capacitor of 1μF or more for switching frequencies be-
tween 1MHz to 2.2MHz, and 2.2μF or more for frequen-
cies lower than 1MHz. If the input power source has high
impedance, or there is significant inductance due to long
wires or cables, additional bulk capacitance may be nec-
essary. This can be provided with a lower performance
electrolytic capacitor. Step-down regulators draw current
from the input supply in pulses with very fast rise and
fall times. The input capacitor is required to reduce the
resulting voltage ripple at the LT3689 input and to force
this very high frequency switching current into a tight local
loop, minimizing EMI. A ceramic capacitor is capable of
this task, but only if it is placed close to the LT3689 and
the catch diode (see the PCB Layout section). A second
precaution regarding the ceramic input capacitor concerns
the maximum input voltage rating of the LT3689. A ceramic
input capacitor combined with trace or cable inductance
forms a high quality (under damped) tank circuit. If the
3689fe
16
For more information www.linear.com/LT3689
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相关代理商/技术参数 |
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| LT3689EMSE-TRPBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:700mA Step-Down Regulator with Power-On Reset and Watchdog Timer |
| LT3689EUD#PBF | 功能描述:IC REG BUCK ADJ 0.7A 16QFN RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 开关稳压器 系列:- 设计资源:Design Support Tool 标准包装:1 系列:- 类型:升压（升压） 输出类型:固定 输出数:1 输出电压:3V 输入电压:0.75 V ~ 2 V PWM 型:- 频率 - 开关:- 电流 - 输出:100mA 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:SOT-23-5 细型，TSOT-23-5 包装:剪切带 (CT) 供应商设备封装:TSOT-23-5 其它名称:AS1323-BTTT-30CT |
| LT3689EUD#TRPBF | 功能描述:IC REG BUCK ADJ 0.7A 16QFN 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 |
| LT3689EUD-5#PBF | 功能描述:IC REG BUCK 5V 0.7A 16QFN 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 |
| LT3689EUD-5#TRPBF | 功能描述:IC REG BUCK 5V 0.7A 16QFN 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 |
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