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| 型号： | ZL2004EVK1 |
| 厂商： | Intersil |
| 文件页数： | 22/42页 |
| 文件大小： | 0K |
| 描述： | KIT EVAL FOR ZL2004 |
| 标准包装： | 1 |
| 系列： | * |
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ZL2004
5.7.9 Current Sensing Components
Once the current sense method has been selected
(Refer to Section 5.8 , “Current Limit Threshold
Selection,” ), the components are selected as follows.
When using the inductor DCR sensing method, the
user must also select an R/C network comprised of R1
and CL (see Figure 14).
V IN
L
C L max
R 1 min DCR
and choose the next-lowest readily available value (eg.:
For C L- max = 1.86μF, C L = 1.5μF is a good choice).
Then substitute the chosen value into the same
equation and re-calculate the value of R 1 . Choose the
1% resistor standard value closest to this re-calculated
value of R 1 . The error due to the mismatch of the two
time constants is
R 1 C L DCR
ZL
PWMH
PWML
ISENA
ISENB
V OUT
1 100 %
L avg
The value of R 2 should be simply five times that of R 1 :
R 2
5 R 1
5.8 Current Limit Threshold Selection
Figure 14. DCR Current Sensing
For the voltage across C L to reflect the voltage across
the DCR of the inductor, the time constant of the
inductor must match the time constant of the RC
network. That is:
It is recommended that the user include a current
limiting mechanism in their design to protect the power
supply from damage and prevent excessive current
from being drawn from the input supply in the event
that the output is shorted to ground or an overload
RC
R 1 C L
L / DCR
L
DCR
condition is imposed on the output. Current limiting is
accomplished by sensing the current through the circuit
during a portion of the duty cycle.
For L , use the average of the nominal value and the
minimum value. Include the effects of tolerance, DC
Bias and switching frequency on the inductance when
Output current sensing can be accomplished by
measuring the voltage across a series resistive sensing
element according to the following equation:
determining the minimum value of L . Use the typical
value for DCR .
V LIM
I LIM
R SENSE
The value of R 1 should be as small as feasible and no
greater than 5 k ? for best signal-to-noise ratio. The
designer should make sure the resistor package size is
appropriate for the power dissipated and include this
loss in efficiency calculations. In calculating the
minimum value of R 1 , the average voltage across C L
(which is the average I OUT ?DCR product) is small and
can be neglected. Therefore, the minimum value of R 1
may be approximated by the following equation:
Where:
I LIM is the desired maximum current that should
flow in the circuit
R SENSE is the resistance of the sensing element
V LIM is the voltage across the sensing element at the
point the circuit should start limiting the output
current.
The ZL2004 supports “lossless” current sensing, by
measuring the voltage across a resistive element that is
V OUT
R 1
min
D V IN
max
2
P R 1 pkg max
1 D V OUT
P
2
,
already present in the circuit. This eliminates
additional efficiency losses incurred by devices that
must use an additional series resistance in the circuit.
where P R1pkg- max is the maximum power dissipation
specification for the resistor package and δ P is the
derating factor for the same parameter (eg.: P R1pkg- max =
0.0625W for 0603 package, δ P = 50% @ 85°C). Once
R 1- min has been calculated, solve for the maximum
value of C L from
22
To set the current limit threshold, the user must first
select a current sensing method. The ZL2004
incorporates one method for current sensing, inductor
DC resistance (DCR) sensing; Figure 14 shows a
simplified schematic for DCR method.
The current sensing method and current limit threshold
FN6846.3
February 15, 2011
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相关代理商/技术参数 |
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|---|---|
| ZL2005 | 制造商:INTERSIL 制造商全称:Intersil Corporation 功能描述:Digital-DC? Integrated Power Management and Conversion IC |
| ZL2005ALNF | 制造商:Intersil Corporation 功能描述:DIGITAL DC-DC CONTROLLER W/ DRIVERS - TRAY100 - Trays 制造商:Intersil Corporation 功能描述:IC REG CNTRLR BUCK PWM 36-QFN 制造商:Intersil Corporation 功能描述:Digital DC-DC Controller w/ Drivers - BULK 50 |
| ZL2005ALNFT | 功能描述:电压模式 PWM 控制器 DIGTL DC-DC CNTRLR W/DRVRS TR100 RoHS:否 制造商:Texas Instruments 输出端数量:1 拓扑结构:Buck 输出电压:34 V 输出电流: 开关频率: 工作电源电压:4.5 V to 5.5 V 电源电流:600 uA 最大工作温度:+ 125 C 最小工作温度:- 40 C 封装 / 箱体:WSON-8 封装:Reel |
| ZL2005ALNFT1 | 功能描述:电压模式 PWM 控制器 DIGTL DC-DC CNTRLR W/DRVRS TR1K RoHS:否 制造商:Texas Instruments 输出端数量:1 拓扑结构:Buck 输出电压:34 V 输出电流: 开关频率: 工作电源电压:4.5 V to 5.5 V 电源电流:600 uA 最大工作温度:+ 125 C 最小工作温度:- 40 C 封装 / 箱体:WSON-8 封装:Reel |
| ZL2005P | 制造商:INTERSIL 制造商全称:Intersil Corporation 功能描述:Digital-DC? Controller with Drivers and POLA/DOSA Trim |
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