参数资料
| 型号： | ZL6105ALAFTR5546 |
| 厂商： | Intersil |
| 文件页数： | 19/35页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM VM 36-QFN |
| 标准包装： | 100 |
| PWM 型： | 电压模式 |
| 输出数： | 1 |
| 频率 - 最大： | 1.4MHz |
| 占空比： | 95% |
| 电源电压： | 3 V ~ 14 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： | -40°C ~ 85°C |
| 封装/外壳： | 36-VFQFN 裸露焊盘 |
| 包装： | 托盘 |
第1页第2页第3页第4页第5页第6页第7页第8页第9页第10页第11页第12页第13页第14页第15页第16页第17页第18页当前第19页第20页第21页第22页第23页第24页第25页第26页第27页第28页第29页第30页第31页第32页第33页第34页第35页
ZL6105
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 as shown in Equation 26:
τ RC = τ L / DCR
GH
V IN
R 1 ? C L =
L
DCR
(EQ. 26)
ZL
SW
ISENA
GL
V OUT
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 determining the minimum
value of L. Use the typical value for DCR.
ISENB
MOSFET R DS(ON) Sensing
V IN
The value of R 1 should be as small as feasible and no greater
than 5k Ω 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 Equation 27:
GH
SW
ZL
GL
ISENA
ISENB
Inductor DCR Sensing
V OUT
D ( V IN ? max ? V OUT ) + ( 1 ? D ) ? V OUT
R 1 ? min =
2
P R 1 pkg ? max ? δ P
2
(EQ. 27)
(V OUT must be less than 4.0 V)
FIGURE 12. CURRENT SENSING METHODS
Current Limit Threshold Selection
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 Equation 28:
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 condition is imposed on the output. Current
limiting is accomplished by sensing the current through the
C L ? max =
L
R 1 ? min ? DCR
(EQ. 28)
circuit during a portion of the duty cycle.
Output current sensing can be accomplished by measuring the
voltage across a series resistive sensing element according to
Next, 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
Equation 30:
V LIM = I LIM × R SENSE
(EQ. 30)
R 1 ? C L ? DCR ? ?
ε τ = ? ? 1 ?
? 100 %
?
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 as shown in Equation 29.
?
(EQ. 29)
? L avg ?
The value of R 2 should be 2k Ω .
For the r DS(ON) current sensing method, the external low side
MOSFET will act as the sensing element as indicated in
Figure 12.
19
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 ZL6105 supports “lossless” current sensing by measuring
the voltage across a resistive element that is already present in
the circuit. This eliminates additional efficiency losses incurred
by devices that must use an additional series resistance in the
circuit.
To set the current limit threshold, the user must first select a
current sensing method. The ZL6105 incorporates two methods
for current sensing, synchronous MOSFET r DS(ON) sensing and
inductor DC resistance (DCR) sensing; Figure 12 shows a
simplified schematic for each method. The current sensing
method can be selected via the I 2 C/SMBus interface. Please
refer to Application Note AN2033 for details.
FN6906.5
December 19, 2013
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