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| 型号： | MAX8764ETP+ |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 16/23页 |
| 文件大小： | 0K |
| 描述： | IC CNTRL STP DWN HS 20-TQFN |
| 标准包装： | 60 |
| 应用： | 控制器，笔记本电脑电源系统 |
| 输入电压： | 2 V ~ 28 V |
| 输出数： | 1 |
| 输出电压： | 1.8V，2.5V，1 V ~ 5.5 V |
| 工作温度： | 0°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 20-WQFN 裸露焊盘 |
| 供应商设备封装： | 20-TQFN-EP（5x5） |
| 包装： | 管件 |
High-Speed, Step-Down Controller with
Accurate Current Limit for Notebook Computers
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
requirements and thus drives output capacitor selec-
tion, inductor saturation rating, and the design of the
DH
V BATT
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-
MAX8764
DL
CS
OUT
R1
V OUT
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-
FB
R2
GND
Figure 7. Setting V OUT with a Resistor-Divider
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
L =
1.5V (7V -1.5V)
7V × 300kHz × 0.33 × 8A
= 1.49 μ H
V OUT (V IN - V OUT )
V IN × f × LIR × I LOAD(MAX)
zero with every cycle at maximum load). Inductor val-
ues lower than this grant no further size-reduction
benefit.
The MAX8764’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 MAX8764’s operation is best done with a
spreadsheet. Using the formulas provided, calculate the
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
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 =
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.
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:
Example: I LOAD(MAX) = 8A, V IN = 7V, V OUT = 1.5V,
f = 300kHz, 33% ripple current or LIR = 0.33:
16
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相关代理商/技术参数 |
参数描述 |
|---|---|
| MAX8764ETP+ | 功能描述:电流型 PWM 控制器 High-Speed 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 |
| MAX8764ETP+T | 功能描述:电流型 PWM 控制器 High-Speed 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 |
| MAX8764ETP-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 |
| MAX8765AETI+ | 功能描述:电池管理 Multichemistry Battery Charger RoHS:否 制造商:Texas Instruments 电池类型:Li-Ion 输出电压:5 V 输出电流:4.5 A 工作电源电压:3.9 V to 17 V 最大工作温度:+ 85 C 最小工作温度:- 40 C 封装 / 箱体:VQFN-24 封装:Reel |
| MAX8765AETI+T | 功能描述:电池管理 Multichemistry Battery Charger RoHS:否 制造商:Texas Instruments 电池类型:Li-Ion 输出电压:5 V 输出电流:4.5 A 工作电源电压:3.9 V to 17 V 最大工作温度:+ 85 C 最小工作温度:- 40 C 封装 / 箱体:VQFN-24 封装:Reel |
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