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参数资料
| 型号： | LT3845MPFE#TRPBF |
| 厂商： | Linear Technology |
| 文件页数： | 17/26页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM CM 16TSSOP |
| 标准包装： | 2,500 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 500kHz |
| 电源电压： | 4 V ~ 60 V |
| 降压： | 是 |
| 升压： | 无 |
| 回扫： | 无 |
| 反相： | 无 |
| 倍增器： | 无 |
| 除法器： | 无 |
| Cuk： | 无 |
| 隔离： | 无 |
| 工作温度： | -55°C ~ 125°C |
| 封装/外壳： | 16-TSSOP（0.173"，4.40mm）裸露焊盘 |
| 包装： | 带卷 (TR) |
LT3845
APPLICATIONS INFORMATION
The maximum ESR required to meet a ΔV OUT design
requirement can be calculated by:
The V FB pin input bias current is typically 25nA, so use
of extremely high value feedback resistors could cause a
V OUT
V IN(MAX)
ESR(MAX)=
( V OUT )(L)(f SW )
V OUT ? 1–
converter output that is slightly higher than expected. Bias
current error at the output can be estimated as:
ΔV OUT(BIAS) = 25nA ? R2
Supply UVLO and Shutdown
Worst-case ΔV OUT occurs at highest input voltage. Use
paralleled multiple capacitors to meet the ESR require-
ments. Increasing the inductance is an option to lower the
ESR requirements. For extremely low ΔV OUT , an additional
LC ?lter stage can be added to the output of the supply.
Application Note 44 has some good tips on sizing an ad-
ditional output ?lter.
Output Voltage Programming
The SHDN pin has a precision voltage threshold with
hysteresis which can be used as an undervoltage lockout
threshold (UVLO) for the power supply. Undervoltage
lockout keeps the LT3845 in shutdown until the supply
input voltage is above a certain voltage programmed by
the user. The hysteresis voltage prevents noise from falsely
tripping UVLO.
Resistors are chosen by ?rst selecting R B . Then
A resistive divider sets the DC output voltage according
to the following formula:
R A = R B ?
V SUPPLY(ON)
1.35V
–1
R2 = R1
V OUT
1.231V
–1
V SUPPLY(ON) is the input voltage at which the undervoltage
lockout is disabled and the supply turns on.
The external resistor divider is connected to the output
of the converter as shown in Figure 3. Tolerance of the
Example: Select R B = 49.9kΩ, V SUPPLY(ON) = 14.5V (based
on a 15V minimum input voltage)
feedback resistors will add additional error to the output
voltage.
Example: V OUT = 12V; R1 = 10kΩ
12V
R2 = 10k 1 = 87.48k use 86.6k 1%
1.231V
R A = 49.9k ?
= 486.1k
14.5V
1.35V
(499k
–1
resistor is selected)
L1
V OUT
V SUPPLY
R2
C OUT
R A
V FB PIN
R1
3845 F03
Figure 3. Output Voltage Feedback Divider
SHDN PIN
R B
3845 F04
Figure 4. Undervoltage Feedback Divider
3845fd
17
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相关代理商/技术参数 |
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|---|---|
| LT3846 | 制造商:LINER 制造商全称:Linear Technology 功能描述:Current Mode PWM Controller |
| LT3846J | 制造商:Linear Technology 功能描述:Current Mode PWM Controller 200mA 16-Pin CDIP |
| LT3846N | 制造商:LINER 制造商全称:Linear Technology 功能描述:Current Mode PWM Controller |
| LT3847 | 制造商:LINER 制造商全称:Linear Technology 功能描述:Current Mode PWM Controller |
| LT3847J | 制造商:Linear Technology 功能描述:Current Mode PWM Controller 200mA 16-Pin CDIP |
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