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参数资料
| 型号： | LT1939EDD#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 14/24页 |
| 文件大小： | 349K |
| 描述： | IC REG DL BUCK/LINEAR 12DFN |
| 标准包装： | 121 |
| 拓扑： | 降压（降压）（1），线性（LDO）（1） |
| 功能： | 任何功能 |
| 输出数： | 2 |
| 频率 - 开关： | 500kHz ~ 2.4MHz |
| 电压/电流 - 输出 1： | 0.8 V ~ 24.25 V，2A |
| 电压/电流 - 输出 2： | 0.8 V ~ 24.25 V，1A |
| 带 LED 驱动器： | 无 |
| 带监控器： | 无 |
| 带序列发生器： | 无 |
| 电源电压： | 3 V ~ 25 V |
| 工作温度： | -40°C ~ 125°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 12-WFDFN 裸露焊盘 |
| 供应商设备封装： | 12-DFN |
| 包装： | 管件 |
LT1939
14
1939f
surge currents when the input source is applied, tantalum
capacitors should be surge rated. The manufacturer may
also recommend operation below the rated voltage of the
capacitor. Be sure to place the 1糉 ceramic as close as
possible to the V
IN
and GND pins on the IC for optimal
noise immunity.
A nal caution regarding the use of ceramic capacitors for
input bypassing. A ceramic input capacitor can combine
with stray inductance to form a resonant tank circuit. If
power is applied quickly (for example, by plugging the
circuit into a live power source) this tank can ring, doubling
the input voltage and damaging the LT1939. The solution is
to either clamp the input voltage or dampen the tank circuit
by adding a lossy capacitor in parallel with the ceramic
capacitor. For details see Application Note 88.
Output Capacitor Selection
Typically step-down regulators are easily compensated with
an output crossover frequency that is 1/10 of the switch-
ing frequency. This means that the time that the output
capacitor must supply the output load during a transient
step is ~2 or 3 switching periods. With an allowable 5%
drop in output voltage during the step, a good starting
value for the output capacitor can be expressed by:
C
VOUT1
=
MaxLoadStep
Frequency"0.05"V
OUT
1
Example:
V
OUT1
= 3.3V, Frequency = 1MHz, Max Load Step = 2A
C
VOUT1
=
2
1MHz"0.05"
3.3
=12糉
The calculated value is only a suggested starting value.
Increase the value if transient response needs improvement
or reduce the capacitance if size is a priority. The output
capacitor lters the inductor current to generate an output
with low voltage ripple. It also stores energy in order to
satisfy transient loads and to stabilize the LT1939s control
loop. The switching frequency of the LT1939 determines
the value of output capacitance required. Also, the current
mode control loop doesnt require the presence of output
capacitor series resistance (ESR). For these reasons, you
are free to use ceramic capacitors to achieve very low
output ripple and small circuit size. Estimate output ripple
with the following equations:
V
RIPPLE
=
I
L
8"Frequency"C
OUT
1
For ceramic capacitors and,
V
RIPPLE
= 擨
L
" ESR
For electrolytic (tantalum and aluminum)
where 擨
L
is the peak-to-peak ripple current in the
inductor.
The RMS content of this ripple is very low, and the RMS
current rating of the output capacitor is usually not of
concern.
Another constraint on the output capacitor is that it must
have greater energy storage than the inductor; if the stored
energy in the inductor is transferred to the output, you
would like the resulting voltage step to be small compared
to the regulation voltage. For a 5% overshoot, this require-
ment becomes:
C
OUT1
>10"L
I
LIM
V
OUT
1
2
Finally, there must be enough capacitance for good transient
performance. The last equation gives a good starting point.
Alternatively, you can start with one of the designs in this
data sheet and experiment to get the desired performance.
This topic is covered more thoroughly in the section on
loop compensation.
The high performance (low ESR), small size and robust-
ness of ceramic capacitors make them the preferred type
for LT1939 applications. However, all ceramic capacitors
are not the same. As mentioned above, many of the high
value capacitors use poor dielectrics with high tempera-
ture and voltage coef cients. In particular, Y5V and Z5U
types lose a large fraction of their capacitance with ap-
plied voltage and temperature extremes. Because the loop
stability and transient response depend on the value of
C
OUT
, you may not be able to tolerate this loss. Use X7R
and X5R types. You can also use electrolytic capacitors.
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LT1939EDD-TRPBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:Monolithic 2A Step-Down Regulator Plus Linear Regulator/Controller |
| LT1939IDD#PBF | 功能描述:IC REG DL BUCK/LINEAR 12DFN RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - 线性 + 切换式 系列:- 标准包装:2,500 系列:- 拓扑:降压（降压）同步（3），线性（LDO）（2） 功能:任何功能 输出数:5 频率 - 开关:300kHz 电压/电流 - 输出 1:控制器 电压/电流 - 输出 2:控制器 电压/电流 - 输出 3:控制器 带 LED 驱动器:无 带监控器:无 带序列发生器:是 电源电压:5.6 V ~ 24 V 工作温度:-40°C ~ 85°C 安装类型:* 封装/外壳:* 供应商设备封装:* 包装:* |
| LT1939IDD#TRPBF | 功能描述:IC REG DL BUCK/LINEAR 12DFN RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - 线性 + 切换式 系列:- 标准包装:2,500 系列:- 拓扑:降压（降压）同步（3），线性（LDO）（2） 功能:任何功能 输出数:5 频率 - 开关:300kHz 电压/电流 - 输出 1:控制器 电压/电流 - 输出 2:控制器 电压/电流 - 输出 3:控制器 带 LED 驱动器:无 带监控器:无 带序列发生器:是 电源电压:5.6 V ~ 24 V 工作温度:-40°C ~ 85°C 安装类型:* 封装/外壳:* 供应商设备封装:* 包装:* |
| LT1939IDD-PBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:Monolithic 2A Step-Down Regulator Plus Linear Regulator/Controller |
| LT1939IDD-TRPBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:Monolithic 2A Step-Down Regulator Plus Linear Regulator/Controller |
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