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| 型号： | MAX1845EEI+ |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 18/27页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM CM 28-QSOP |
| 产品培训模块： | Lead (SnPb) Finish for COTS Obsolescence Mitigation Program |
| 标准包装： | 50 |
| PWM 型： | 电流模式 |
| 输出数： | 2 |
| 频率 - 最大： | 540kHz |
| 电源电压： | 4.5 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： | 28-SSOP（0.154"，3.90mm 宽） |
| 包装： | 管件 |
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Dual, High-Efficiency, Step-Down
Controller with Accurate Current Limit
Find a low-loss inductor having the lowest possible DC
resistance that fits in the allotted dimensions. Ferrite
cores are often the best choice, although powdered
iron is inexpensive and can work well at 200kHz. The
core must be large enough not to saturate at the peak
inductor current (I PEAK ):
I PEAK = I LOAD(MAX) + [(LIR / 2) I LOAD(MAX) ]
Transient Response
The inductor ripple current also impacts transient-
response performance, especially at low V IN - V OUT dif-
ferentials. Low inductor values allow the inductor
current to slew faster, replenishing charge removed
from the output filter capacitors by a sudden load step.
The amount of output sag is also a function of the maxi-
mum duty factor, which can be calculated from the on-
time and minimum off-time:
7a). Use the worst-case value for R DS(ON) from the
MOSFET data sheet, and add a margin of 0.5%/°C for
the rise in R DS(ON) with temperature. Use the calculat-
ed R DS(ON) and I L(MIN) from step 1 above to determine
the current-limit threshold voltage. If the default 50mV
threshold is unacceptable, set the threshold value as in
step 2 above.
In all cases, ensure an acceptable current limit consid-
ering current-sense and resistor accuracies.
Output Capacitor Selection
The output filter capacitor must have low enough ESR to
meet output ripple and load-transient requirements, yet
have high enough ESR to satisfy stability requirements.
Also, the capacitance value must be high enough to
absorb the inductor energy going from a full-load to no-
load condition without tripping the OVP circuit.
V SAG =
( Δ I LOAD ( MAX ) ) 2 × L
2 × C F × DUTY ( V IN ( MIN ) - V OUT )
For CPU core voltage converters and other applications
where the output is subject to violent load transients,
the output capacitor’s size depends on how much ESR
DUTY =
R ESR ≤
where:
K (V OUT + 0.075V) V IN
K (V OUT + 0.075V) V OUT + min off - time
where minimum off-time = 400ns typ (Table 4).
The amount of overshoot during a full-load to no-load
transient due to stored inductor energy can be calculat-
ed as:
is needed to prevent the output from dipping too low
under a load transient. Ignoring the sag due to finite
capacitance:
V DIP
I LOAD ( MAX )
In non-CPU applications, the output capacitor’s size
depends on how much ESR is needed to maintain an
acceptable level of output voltage ripple:
V SOAR = L I PEAK 2 / (2 C OUT V OUT )
where I PEAK is the peak inductor current.
Determining the Current Limit
For most applications, set the MAX1845 current limit by
the following procedure:
1) Determine the minimum (valley) inductor current
(I L(MIN) ) under conditions when V IN is small, V OUT is
R ESR ≤
V P ? P
LIR × I LOAD ( MAX )
large, and load current is maximum. The minimum
inductor current is I LOAD minus half the ripple cur-
rent (Figure 4).
2) The sense resistor determines the achievable cur-
rent-limit accuracy. There is a trade-off between cur-
MAX1845
LX
DL
MAX1845
LX
DL
rent-limit accuracy and sense-resistor power
dissipation. Most applications employ a current-
sense voltage of 50mV to 100mV. Choose a sense
resistor such that:
R SENSE = Current-Limit Threshold Voltage / I L(MIN)
Extremely cost-sensitive applications that do not
require high-accuracy current sensing can use the on-
resistance of the low-side MOSFET switch in place of
the sense resistor by connecting CS_ to LX_ (Figure
CS
a)
Figure 7. Current-Sense Configurations
b)
CS
18
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相关代理商/技术参数 |
参数描述 |
|---|---|
| MAX1845EEI+ | 功能描述:电流型 PWM 控制器 Step-Down Controller RoHS:否 制造商:Texas Instruments 开关频率:27 KHz 上升时间: 下降时间: 工作电源电压:6 V to 15 V 工作电源电流:1.5 mA 输出端数量:1 最大工作温度:+ 105 C 安装风格:SMD/SMT 封装 / 箱体:TSSOP-14 |
| MAX1845EEI+T | 功能描述:电流型 PWM 控制器 Step-Down Controller RoHS:否 制造商:Texas Instruments 开关频率:27 KHz 上升时间: 下降时间: 工作电源电压:6 V to 15 V 工作电源电流:1.5 mA 输出端数量:1 最大工作温度:+ 105 C 安装风格:SMD/SMT 封装 / 箱体:TSSOP-14 |
| MAX1845EEI-T | 功能描述:电流型 PWM 控制器 RoHS:否 制造商:Texas Instruments 开关频率:27 KHz 上升时间: 下降时间: 工作电源电压:6 V to 15 V 工作电源电流:1.5 mA 输出端数量:1 最大工作温度:+ 105 C 安装风格:SMD/SMT 封装 / 箱体:TSSOP-14 |
| MAX1845EEI-TG05 | 制造商:Rochester Electronics LLC 功能描述: 制造商:Maxim Integrated Products 功能描述: |
| MAX1845EEI-TG068 | 制造商:Rochester Electronics LLC 功能描述: 制造商:Maxim Integrated Products 功能描述: |
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