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| 型号： | MAX1714AEEP+T |
| 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-QSOP |
| 产品培训模块： | Lead (SnPb) Finish for COTS Obsolescence Mitigation Program |
| 标准包装： | 2,500 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 600kHz |
| 占空比： | 100% |
| 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-SSOP（0.154"，3.90mm 宽） |
| 包装： | 带卷 (TR) |
High-Speed Step-Down Controller
for Notebook Computers
Inductor Selection
The switching frequency and inductor operating point
determine the inductor value as follows:
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:
L =
V OUT (V IN - V OUT )
V IN ? f ? LIR ? I LOAD(MAX)
V SAG =
( ? I LOAD(MAX) ) 2 ? L
2 ? C F ? DUTY (V IN(MIN) - V OUT )
Example: I LOAD(MAX) = 8A, V IN = 7V, V OUT = 1.5V,
f = 300kHz, 33% ripple current or LIR = 0.33.
where
L = = 1.49 μ H
1.5V (7V - 1.5V)
7V ? 300kHz ? 0.33 ? 8A
DUTY =
K (V OUT + 0.075V) V IN
K (V OUT + 0.075V) V OUT + min off - time
L ? I PEAK
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.
For example, Sumida offers 3.1μH and 4.4μH in their
CDRH125 series. If using a swinging inductor (where the
no-load inductance decreases linearly with increasing
current), evaluate the LIR with properly scaled induc-
tance 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.
Table 4. Frequency Selection Guidelines
FREQUENCY TYPICAL
COMMENTS
(kHz) APPLICATION
and minimum off-time = 400ns typ (see Table 5 for K val-
ues).
The amount of overshoot during a full-load to no-load
transient due to stored inductor energy can be calculated
as: 2
V SOAR ≈
2C OUT V OUT
where I PEAK is the peak inductor current.
Setting the Current Limit
The minimum current-limit threshold must be high
enough to support the maximum load current. The valley
of the inductor current occurs at I LOAD(MAX) minus half
of the ripple current (Figure 4); therefore:
I LIMIT(LOW) > I LOAD(MAX) - (LIR / 2) I LOAD(MAX)
where I LIMIT(LOW) equals minimum current-limit thresh-
old voltage divided by the R DS(ON) of Q2. For the
MAX1714, the minimum current-limit threshold using the
100mV default setting is 90mV. Use the worst-case maxi-
mum value for R DS(ON) from the MOSFET Q2 data sheet,
and add some margin for the rise in R DS(ON) with tem-
perature. A good general rule is to allow 0.5% additional
resistance for each °C of temperature rise.
Examining the 8A circuit example with a maximum
R DS(ON) = 12m ? at high temperature reveals the follow-
ing:
200
TON = V CC
300
TON = Float
450
TON = REF
600
TON = AGND
4-cell Li+ notebook
4-cell Li+ notebook
3-cell Li+ notebook
+5V input
Use for absolute best
efficiency.
Considered mainstream
by current standards.
Useful in 3-cell systems
for lighter loads than the
CPU core or where size is
key.
Good operating point for
compound buck designs
or desktop circuits.
I LIMIT(LOW) = 90mV / 12m ? = 7.5A
This 7.5A is greater than the valley current of 6.7A, so the
circuit can easily deliver the full rated 8A using the default
100mV nominal ILIM threshold.
For an adjustable threshold, connect a two-resistor
divider from REF to AGND, with ILIM connected at the
center tap. The external adjustment range of 0.5V to 2.0V
corresponds to a current-limit threshold of 50mV to
200mV. When adjusting the current limit, use 1% toler-
ance resistors to prevent a significant increase of errors in
16
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相关代理商/技术参数 |
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|---|---|
| MAX1714AEEP-TG068 | 制造商:Rochester Electronics LLC 功能描述: 制造商:Maxim Integrated Products 功能描述: |
| MAX1714AEVKIT | 功能描述:电流型 PWM 控制器 Evaluation Kit for the MAX1714A 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 |
| MAX1714BEEE | 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 |
| MAX1714BEEE+ | 功能描述:电流型 PWM 控制器 Step-Down Controller for Notebook 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 |
| MAX1714BEEE+T | 功能描述:电流型 PWM 控制器 Step-Down Controller for Notebook 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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