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| 型号： | LT3837EFE#TRPBF |
| 厂商： | Linear Technology |
| 文件页数： | 16/28页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR FLYBK ISO 16-TSSOP |
| 标准包装： | 2,500 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 250kHz |
| 占空比： | 88% |
| 电源电压： | 4.5 V ~ 20 V |
| 降压： | 无 |
| 升压： | 无 |
| 回扫： | 是 |
| 反相： | 无 |
| 倍增器： | 无 |
| 除法器： | 无 |
| Cuk： | 无 |
| 隔离： | 是 |
| 工作温度： | -40°C ~ 125°C |
| 封装/外壳： | 16-TSSOP（0.173"，4.40mm）裸露焊盘 |
| 包装： | 带卷 (TR) |
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LT3837
APPLICATIONS INFORMATION
Setting Feedback Resistive Divider
Use the equation developed in the Operation section for
the feedback divider.
Selecting the Load Compensation Resistor
The expression for R CMP was derived in the Operation
section for primary winding sensing as:
It is recommended that the Thevenin impedance of the
resistors on the FB Pin is roughly 3k for bias current
cancellation and other reasons.
R CMP = K1 ?
R SENSE ? ( 1–DC )
ESR + R DS(ON)
? R1 ? N SP = R S(OUT)
? ? ( 3.3 + 10 ? ( 0.002 + 0.004 ) ?
( 1/ 3 )
1.237 ? ? ?
R1 = ? ? ? ? – 0.7 ? = 22.75k
K1 = ?
? ? = 9 ( 88% ) = 0.417
For the example using primary winding sensing if
ESR = 0.002 and R DS(ON) = 0.004 then:
3k ?
?
? ?
Continuing the example:
? V OUT ? 3.3
? V IN ? Eff
If ESR = 0.002 ? and R DS(ON) = 0.004 ?
So, choose 22.1k.
Current Sense Resistor Considerations
R CMP = 0.417 ?
8.0m ? ? ( 1– 0.52 )
0.002 ? + 0.004 ?
? 22.1k ? ? 0.33
R CMP = K1 ?
? R1 ? N SP orN SF
Theexternalcurrentsenseresistorisusedtocontrolpeak
primary switch current, which controls a number of key
converter characteristics including maximum power and
external component ratings. Use a noninductive current
sense resistor (no wire-wound resistors). Mounting the
resistor directly above an unbroken ground plane con-
nected with wide and short traces keeps stray resistance
and inductance low.
The dual sense pins allow for a fully Kelvined connection.
Make sure that SENSE + and SENSE – are isolated and con-
nect close to the sense resistor to preserve this.
Peak current occurs at 98mV of sense voltage V SENSE . So
the nominal sense resistor is V SENSE /I PK . For example, a
peak switch current of 10A requires a nominal sense resistor
of 0.010Ω. Note that the instantaneous peak power in the
sense resistor is 1W, and that it is rated accordingly. The
use of parallel resistors can help achieve low resistance,
low parasitic inductance and increased power capability.
Size R SENSE using worst-case conditions, minimum L P ,
V SENSE and maximum V IN . Continuing the example, let us
assume that our worst-case conditions yield an I PK 10%
above nominal so I PK = 10.41A . If there is a 5% tolerance
on R SENSE and minimum V SENSE = 80mV, then R SENSE ?
105% = 88mV/10.41A and nominal R SENSE = 8.05mΩ.
Round to the nearest available lower value 8.0mΩ.
= 1.93k ?
This value for R CMP is a good starting point, but empiri-
cal methods are required for producing the best results.
This is because several of the required input variables are
difficult to estimate precisely. For instance, the ESR term
above includes that of the transformer secondary, but its
effective ESR value depends on high frequency behavior,
not simply DC winding resistance. Similarly, K1 appears
as a simple ratio of V IN to V OUT times (differential) ef-
ficiency, but theoretically estimating efficiency is not a
simple calculation.
The suggested empirical method is as follows:
1. Build a prototype of the desired supply including the
actual secondary components.
2. Temporarily ground the C CMP pin to disable the load
compensation function. Measure output voltage while
sweeping output current over the expected range.
Approximate the voltage variation as a straight line,
?V OUT /?I OUT = R S(OUT) .
3. Calculate a value for the K1 constant based on V IN , V OUT
and the measured (differential) efficiency.
4. Compute:
R SENSE
R S(OUT)
3837fd
16
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| LT3837IFE#PBF | 功能描述:IC REG CTRLR FLYBK ISO 16-TSSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:2,500 系列:- PWM 型:电流模式 输出数:1 频率 - 最大:500kHz 占空比:96% 电源电压:4 V ~ 36 V 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 ~ 125°C 封装/外壳:24-WQFN 裸露焊盘 包装:带卷 (TR) |
| LT3837IFE#TRPBF | 功能描述:IC REG CTRLR FLYBK ISO 16-TSSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - DC DC 切换控制器 系列:- 标准包装:2,500 系列:- PWM 型:电流模式 输出数:1 频率 - 最大:500kHz 占空比:96% 电源电压:4 V ~ 36 V 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 ~ 125°C 封装/外壳:24-WQFN 裸露焊盘 包装:带卷 (TR) |
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