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| 型号： | LT3430IFE-1#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 25/28页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK ADJ 3A 16TSSOP |
| 标准包装： | 95 |
| 类型： | 降压（降压） |
| 输出类型： | 可调式 |
| 输出数： | 1 |
| 输出电压： | 1.2 V ~ 54 V |
| 输入电压： | 5.5 V ~ 60 V |
| PWM 型： | 电流模式 |
| 频率 - 开关： | 100kHz |
| 电流 - 输出： | 3A |
| 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-TSSOP（0.173"，4.40mm）裸露焊盘 |
| 包装： | 管件 |
| 供应商设备封装： | 16-TSSOP-EP |
| 产品目录页面： | 1331 (CN2011-ZH PDF) |
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LT3430/LT3430-1
APPLICATIONS INFORMATION
D2 ?
MMSD914TI
L1*
0.68 μ F 10 μ H
LT3430
+
4.7 μ F
C C
R2
L MIN =
2 ( f )( V IN OUT ) ? I P OUT ? 1 + OUT F ? ?
? ? ( V + V ) ? ?
?
? ?
?
( 40 ) ( 3 ) 2
4 ( 40 + 12 )( 40 + 12 + 0 . 52 )
C2
INPUT BOOST
5.5V TO V IN V SW
44V
FB
C3 GND V C
D1
100V 30BQ060
CER
C F R C 4.12k
* INCREASE L1 FOR HIGHER CURRENT APPLICATIONS.
D4
7V
R1
36.5k
D3
30BQ015
C1
100 μ F
16V TANT
OUTPUT**
–12V, 0.5A
3430 F15
Minimum inductor continuous mode:
( V IN )( V OUT )
+ V – I
V IN
For a 40V to –12V converter using the LT3430/LT3430-
1 with peak switch current of 3A and a catch diode of
0.52V:
2
I CONT = = 1 . 148 A
L MIN = = 6 . 7 μ H
SEE APPLICATIONS INFORMATION
** MAXIMUM LOAD CURRENT DEPENDS ON MINIMUM INPUT VOLTAGE
AND INDUCTOR SIZE. SEE APPLICATIONS INFORMATION
Figure 15. Positive-to-Negative Converter
INDUCTOR VALUE
The criteria for choosing the inductor is typically based on
ensuring that peak switch current rating is not exceeded.
This gives the lowest value of inductance that can be
used, but in some cases (lower output load currents) it
may give a value that creates unnecessarily high output
ripple voltage.
The dif?culty in calculating the minimum inductor size
needed is that you must ?rst decide whether the switcher
will be in continuous or discontinuous mode at the critical
point where switch current reaches 3A. The ?rst step is to
use the following formula to calculate the load current above
which the switcher must use continuous mode. If your
load current is less than this, use the discontinuous mode
formula to calculate minimum inductor needed. If load
current is higher, use the continuous mode formula.
Output current where continuous mode is needed:
For a load current of 0.5A, this says that discontinuous
mode can be used and the minimum inductor needed is
found from:
2 ( 12 )( 0 . 5 )
( 200 ? 10 3 )( 3 ) 2
In practice, the inductor should be increased by about
30% over the calculated minimum to handle losses and
variations in value. This suggests a minimum inductor of
10μH for this application.
Ripple Current in the Input and Output Capacitors
Positive-to-negative converters have high ripple current in
the input capacitor. For long capacitor lifetime, the RMS
value of this current must be less than the high frequency
ripple current rating of the capacitor. The following formula
will give an approximate value for RMS ripple current. This
formula assumes continuous mode and large inductor
value . Small inductors will give somewhat higher ripple
current, especially in discontinuous mode. The exact for-
mulas are very complex and appear in Application Note
44, pages 29 and 30. For our purposes here I have simply
( V IN P ) 2
) ( I
I CONT >
2
4 ( V IN + V OUT )( V IN + V OUT + V F )
added a fudge factor (ff). The value for ff is about 1.2 for
higher load currents and L ≥15μH. It increases to about
2.0 for smaller inductors at lower load currents.
L MIN =
Minimum inductor discontinuous mode:
2(V OUT )(I OUT )
( f )( I P ) 2
ff = 1.2 to 2.0
Capacitor I RMS = ( ff )( I OUT )
V OUT
V IN
The output capacitor ripple current for the positive-to-
negative converter is similar to that for a typical buck
regulator—it is a triangular waveform with peak-to-peak
34301fa
25
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| LT3431EFE#PBF | 功能描述:IC REG BUCK ADJ 3A 16TSSOP 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 |
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