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参数资料
| 型号： | MAX1844ETP+ |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 16/24页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR BUCK PWM CM 20-TQFN |
| 标准包装： | 60 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 600kHz |
| 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： | 20-WFQFN 裸露焊盘 |
| 包装： | 管件 |
High-Speed Step-Down Controller with
Accurate Current Limit for Notebook Computers
Fixed Output Voltages
The MAX1844 ’ s Dual Mode TM operation allows the selec-
tion of common voltages without requiring external com-
ponents (Figure 6). Connect FB to GND for a fixed 2.5V
output or to V CC for a 1.8V output, or connect FB directly
to OUT for a fixed 1V output.
Setting V OUT with a Resistor-Divider
The output voltage can be adjusted from 1V to 5.5V with
a resistor-divider if desired (Figure 7). The equation for
adjusting the output voltage is:
ues lower than this grant no further size-reduction
benefit.
The MAX1844 ’ s pulse-skipping algorithm initiates skip
mode at the critical conduction point. So, the inductor
operating point also determines the load-current value
at which PFM/PWM switchover occurs.
These four factors impact the component selection
process. Selecting components and calculating their
effect on the MAX1844 ’ s operation is best done with a
spreadsheet. Using the formulas provided, calculate the
V OUT = V FB ? 1 +
?
?
?
R1 ?
R2 ?
LIR (the ratio of the inductor ripple current to the
designed maximum load current) for both the minimum
and maximum input voltages. Maintaining an LIR within a
V OUT (V IN - V OUT )
× f × LIR × I
where V FB is 1V.
Design Procedure
Component selection for the MAX1844 is primarily dictat-
ed by the following four criteria:
1) Input voltage range . The maximum value (V IN(MAX) )
must accommodate the worst-case high AC-adapter
voltage. The minimum value (V IN(MIN) ) must account
for the lowest battery voltage after drops due to con-
nectors, fuses, and battery selector switches. Lower
input voltages result in better efficiency.
20% to 50% range is recommended. The use of a
spreadsheet allows quick evaluation of component
selection.
Inductor Selection
The switching frequency and inductor operating point
determine the inductor value as follows:
L =
V IN LOAD(MAX)
Example: I LOAD(MAX) = 8A, V IN = 7V, V OUT = 1.5V,
f = 300kHz, 33% ripple current or LIR = 0.33.
2) Maximum load current . There are two values to con-
sider. The peak load current (I LOAD(MAX) ) determines
the instantaneous component stresses and filtering
L =
1.5V (7V -1.5V)
7V × 300kHz × 0.33 × 8A
= 1.49 μ H
requirements and thus drives output capacitor selec-
tion, inductor saturation rating, and the design of the
current-limit circuit. The continuous load current
(I LOAD ) determines the thermal stresses and thus dri-
ves the selection of input capacitors, MOSFETs, and
other critical heat-contributing components.
3) Switching frequency . This choice determines the
basic trade-off between size and efficiency. The opti-
mal frequency is largely a function of maximum input
voltage, due to MOSFET switching losses that are
proportional to frequency and V IN2 . The optimum fre-
quency is also a moving target, due to rapid improve-
ments in MOSFET technology that are making higher
frequencies more practical (Table 4).
4) Inductor operating point . This choice provides
trade-offs between size vs. efficiency. Low inductor
values cause large ripple currents, resulting in the
smallest size, but poor efficiency and high output rip-
ple. The minimum practical inductor value is one that
causes the circuit to operate at the edge of critical
conduction (where the inductor current just touches
zero with every cycle at maximum load). Inductor val-
Dual Mode is a trademark of Maxim Integrated Products.
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 induc-
tor current (I PEAK ).
I PEAK = I LOAD(MAX) + [(LIR / 2) ? I LOAD(MAX) ]
Most inductor manufacturers provide inductors in stan-
dard values, such as 1.0μH, 1.5μH, 2.2μH, 3.3μH, etc.
Also look for nonstandard values, which can provide a
better compromise in LIR across the input voltage range.
If using a swinging inductor (where the no-load induc-
tance decreases linearly with increasing current), evalu-
ate the LIR with properly scaled inductance values.
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.
16
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相关代理商/技术参数 |
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|---|---|
| MAX1844ETP+ | 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 |
| MAX1844ETP+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 |
| MAX1844ETP-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 |
| MAX1844EVKIT | 功能描述:电源管理IC开发工具 RoHS:否 制造商:Maxim Integrated 产品:Evaluation Kits 类型:Battery Management 工具用于评估:MAX17710GB 输入电压: 输出电压:1.8 V |
| MAX1845EEI | 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 |
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