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| 型号： | ZL2008ALBFT1 |
| 厂商： | Intersil |
| 文件页数： | 20/42页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM VM 36-QFN |
| 标准包装： | 1,000 |
| 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 ~ 5.5 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： | 带卷 (TR) |
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ZL2008
P swtop = V INM × t sw × I OUT × f sw
Calculate the RMS current in QL as follows:
P QL = 0 . 05 × V OUT × I OUT
I botrms = I Lrms × 1 ? D
Calculate the desired maximum R DS(ON) as follows:
(EQ. 13)
(EQ. 14)
where Q g is the gate charge of the selected QH and I gdr is the
peak gate drive current available from the ZL2008.
Although the ZL2008 has a typical gate drive current of 3A, use
the minimum guaranteed current of 2A for a conservative
design. Using the calculated switching time, calculate the
switching power loss in QH using:
(EQ. 22)
( I botrms )
R DS ( ON ) =
P QL
2
(EQ. 15)
The total power dissipated by QH is given by Equation 23:
P QHtot = P QH + P swtop
(EQ. 23)
Note that the R DS(ON) given in the manufacturer’s datasheet is
measured at +25°C. The actual R DS(ON) in the end-use
application will be much higher. For example, a Vishay Si7114
MOSFET with a junction temperature of +125°C has an R DS(ON)
that is 1.4 times higher than the value at +25°C. Select a
candidate MOSFET, and calculate the required gate drive current
as follows:
MOSFET THERMAL CHECK
Once the power dissipations for QH and QL have been calculated,
the MOSFETs junction temperature can be estimated. Using the
junction-to-case thermal resistance (R th ) given in the MOSFET
manufacturer’s datasheet and the expected maximum printed
circuit board temperature, calculate the junction temperature as
T j max = T pcb + ( P Q × R th )
I g = f SW × Q g
(EQ. 16)
follows:
(EQ. 24)
P QL = f sw × Q g × V INM
Keep in mind that the total allowed gate drive current for both QH
and QL is 80mA.
MOSFETs with lower R DS(ON) tend to have higher gate charge
requirements, which increases the current and resulting power
required to turn them on and off. Since the MOSFET gate drive
circuits are integrated in the ZL2008, this power is dissipated in
the ZL2008 according to Equation 17:
(EQ. 17)
QH SELECTION
CURRENT SENSING COMPONENTS
Once the current sense method has been selected (refer to
section “Current Limit Threshold Selection” on page 21), 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 15).
GH
In addition to the R DS(ON) loss and gate charge loss, QH also has
switching loss. The procedure to select QH is similar to the
procedure for QL. First, assign 2% to 5% of the output power to
be dissipated in the R DS(ON) of QH using the equation for QL
above. As was done with QL, calculate the RMS current as
ZL
SW
GL
ISENA
ISENB
R1
R2
CL
I toprms = I Lrms × D
P QH = 0 . 05 × V OUT × I OUT
R DS ( ON ) =
( I )
L
follows:
(EQ. 18)
Calculate a starting R DS(ON) as follows, in this example using 5%:
(EQ. 19)
P QH
(EQ. 20)
2
toprms
Select a MOSFET and calculate the resulting gate drive current.
Verify that the combined gate drive current from QL and QH does
not exceed 80mA.
FIGURE 15. 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:
τ RC = τ L / DCR
(EQ. 25)
R 1 ? C L =
DCR
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 .
t SW =
Next, calculate the switching time using:
Q g
I gdr
20
(EQ. 21)
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
FN6859.4
April 29, 2011
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相关代理商/技术参数 |
参数描述 |
|---|---|
| ZL2008EVAL1Z | 功能描述:EVALUATION BOARD FOR ZL2008 RoHS:是 类别:编程器，开发系统 >> 评估板 - DC/DC 与 AC/DC（离线）SMPS 系列:- 产品培训模块:Obsolescence Mitigation Program 标准包装:1 系列:True Shutdown™ 主要目的:DC/DC，步升 输出及类型:1，非隔离 功率 - 输出:- 输出电压:- 电流 - 输出:1A 输入电压:2.5 V ~ 5.5 V 稳压器拓扑结构:升压 频率 - 开关:3MHz 板类型:完全填充 已供物品:板 已用 IC / 零件:MAX8969 |
| ZL20200 | 制造商:ZARLINK 制造商全称:Zarlink Semiconductor Inc 功能描述:Dual Band IS136/AMPS Transceiver |
| ZL20200_06 | 制造商:ZARLINK 制造商全称:Zarlink Semiconductor Inc 功能描述:Dual Band IS136/AMPS Transceiver |
| ZL20200LCE | 制造商:ZARLINK 制造商全称:Zarlink Semiconductor Inc 功能描述:Dual Band IS136/AMPS Transceiver |
| ZL20200LCF | 制造商:ZARLINK 制造商全称:Zarlink Semiconductor Inc 功能描述:Dual Band IS136/AMPS Transceiver |
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