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参数资料
| 型号： | LT1339ISW#TRPBF |
| 厂商： | Linear Technology |
| 文件页数： | 10/20页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BST PWM CM 20-SOIC |
| 标准包装： | 1,000 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 150kHz |
| 占空比： | 90% |
| 电源电压： | 最高 60V |
| 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： | 20-SOIC（0.295"，7.50mm 宽） |
| 包装： | 带卷 (TR) |
LT1339
APPLICATIO N S I N FOR M ATIO N
R SENSE Selection for Output Current
R SENSE generates a voltage that is proportional to the
inductor current for use by the LT1339 current sense
amplifier. The value of R SENSE is based on the required
load current. The average current limit function has a
typical threshold of 120mV/R SENSE , or:
R SENSE = 120mV/I LIMIT
Operation with V SENSE common mode voltage below 4.5V
may slightly degrade current limit accuracy. See Average
Current Limit Threshold Tolerance vs Common Mode
Voltage curve in the Typical Performance Characteristics
section for more information.
the minimum off-time of the PWM controller. This limits
maximum duty cycle (DC MAX ) to:
DC MAX = 1 – (t DISCH )(f O )
This relation corresponds to the minimum value of the
timing resistor (R CT ), which can be determined according
to the following relation (R CT vs DC MAX graph appears in
the Typical Performance Characteristics section):
R CT(MIN) ≈ [(0.8)(10 –3 )(1 – DC MAX )] –1
Values for R CT > 15k yield maximum duty cycles above
90%. Given a timing resistor value, the value of the timing
capacitor (C CT ) can then be determined for desired oper-
ating frequency (f O ) using the relation:
( 1 / f O ) ? ( ) ?? 10 ? 9 ??
( R CT / 1 . 85 ) +
Output Voltage Programming
Output voltage is programmed through a resistor feed-
back network to V FB (Pin 9) on the LT1339. This pin is the
inverting input of the error amplifier, which is internally
referenced to 1.25V. The divider is ratioed to provide
1.25V at the V FB pin when the output is at its desired value.
C CT ≈
100
1 . 75
( 2 . 5 ) ?? 10 ? 3 ?? ? ( 3 . 375 / R CT )
The output voltage is thus set following the relation:
V OUT = 1.25(1 + R2/R1)
when an external resistor divider is connected to the
output as shown in Figure 1.
A plot of Operating Frequency vs R CT and C CT is shown in
Figure 2. Typical 100kHz operational values are C CT =
1000pF and R CT = 16.9k.
160
V OUT
140
C CT = 1.0nF
LT1339 V FB
SGND
9
R2
R1
120
100
80
C CT = 1.5nF
8
60
1339 ? F01
Figure 1. Programming LT1339 Output Voltage
40
20
C CT = 3.3nF
C CT = 2.2nF
If high value feedback resistors are used, the input bias
current of the V FB pin (1 μ A maximum) could cause a slight
0
0
5
10 15 20
TIMING RESISTOR (k ? )
25
30
increase in output voltage. A Thevenin resistance at the
V FB pin of <5k is recommended.
Oscillator Components R CT and C CT
The LT1339 oscillator creates a modified sawtooth wave
at its timing node (CT) with a slow charge, rapid discharge
characteristic. The rapid discharge time corresponds to
LT1339 ? F02
Figure 2. Oscillator Frequency vs R CT , C CT
Average Current Limit
The average current limit function is implemented using
an external capacitor (C AVG ) connected from I AVG to SGND
that forms a single pole integrator with the 50k ? output
sn1339 1339fas
10
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| LT1341CG | 功能描述:IC TXRX 5V RS232 W/SHTDWN 28SSOP RoHS:否 类别:集成电路 (IC) >> 接口 - 驱动器，接收器，收发器 系列:- 标准包装:27 系列:- 类型:收发器 驱动器/接收器数:3/3 规程:RS232，RS485 电源电压:4.75 V ~ 5.25 V 安装类型:表面贴装 封装/外壳:28-SOIC（0.295"，7.50mm 宽） 供应商设备封装:28-SOIC 包装:管件 |
| LT1341CG#PBF | 功能描述:IC TXRX 5V RS232 W/SHTDWN 28SSOP RoHS:是 类别:集成电路 (IC) >> 接口 - 驱动器，接收器，收发器 系列:- 标准包装:27 系列:- 类型:收发器 驱动器/接收器数:3/3 规程:RS232，RS485 电源电压:4.75 V ~ 5.25 V 安装类型:表面贴装 封装/外壳:28-SOIC（0.295"，7.50mm 宽） 供应商设备封装:28-SOIC 包装:管件 |
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