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| 型号： | MAX8717ETI+T |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 17/30页 |
| 文件大小： | 0K |
| 描述： | IC CNTRLR PWR SUP 28-TQFN |
| 标准包装： | 2,500 |
| 应用： | 控制器，笔记本电脑电源系统 |
| 输入电压： | 4 V ~ 26 V |
| 输出数： | 2 |
| 输出电压： | 3.3V，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： | 28-WFQFN 裸露焊盘 |
| 供应商设备封装： | 28-TQFN-EP（5x5） |
| 包装： | 带卷 (TR) |
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Interleaved High-Efficiency, Dual Power-Supply
Controllers for Notebook Computers
the switching frequency remains constant and the
no-load supply current is typically between 8mA and
20mA per phase, depending on external MOSFETs and
switching frequency.
Light-Load Operation Control ( SKIP_ )
The MAX8716/MAX8717/MAX8756/MAX8757 include
I LOAD = LOAD(SKIP)
SKIP_ inputs that enable the corresponding outputs to
operate in discontinuous mode. Connect SKIP_ to GND
or REF as shown in Table 4 to enable or disable the
zero-crossing comparators of either controller. When
the zero-crossing comparator is enabled, the controller
forces DL_ low when the current-sense inputs detect
zero inductor current. This keeps the inductor from dis-
charging the output capacitors and forces the con-
troller to skip pulses under light-load conditions to
t ON(SKIP) =
V OUT
V IN x f OSC
I LOAD(SKIP)
I
2
avoid overcharging the output. During skip mode, the
V DD current consumption is reduced and efficiency is
improved. During low-noise skip mode, the no-load rip-
0
ON-TIME
TIME
ple amplitude is two times smaller and the no-load
switching frequency is four times higher, although the
light-load efficiency is somewhat lower.
Table 3. FSEL Configuration Table
Figure 4. Pulse-Skipping/Discontinuous Crossover Point
Automatic Pulse-Skipping Crossover
In skip mode, an inherent automatic switchover to PFM
takes place at light loads (Figure 4). This switchover is
FSEL
V CC
REF
GND
MAX8717/
MAX8757 (kHz)
500
300
200
MAX8756 (kHz)
400
300
250
affected by a comparator that truncates the low-side
switch on-time at the inductor current’s zero crossing.
The zero-crossing comparator senses the inductor cur-
rent across CSH_ and CSL_. Once V CSH - V CSL _ drops
below the 3mV zero-crossing, current-sense threshold,
the comparator forces DL_ low (Figure 3). This mecha-
Idle Mode Current-Sense Threshold
When pulse-skipping mode is enabled, the on-time of
the step-down controller terminates when the output
voltage exceeds the feedback threshold and when the
current-sense voltage exceeds the Idle Mode current-
sense threshold. Under light-load conditions, the on-
nism causes the threshold between pulse-skipping PFM
and nonskipping PWM operation to coincide with the
boundary between continuous and discontinuous induc-
tor-current operation (also known as the “critical conduc-
tion” point). The load-current level at which PFM/PWM
crossover occurs, I LOAD(SKIP) , is determined by:
time duration depends solely on the Idle Mode
current-sense threshold ( SKIP_ = GND), which is 20%
of the full-load current-limit threshold set by ILIM_, or
I LOAD ( SKIP ) =
(V IN ? V OUT )V OUT
2 LV IN ? OSC
the low-noise current-sense threshold ( SKIP_ = REF),
which is 10% for the MAX8716/MAX8717/MAX8757 and
5% for the MAX8756 of the full-load current-limit thresh-
old set by ILIM_. This forces the controller to source a
minimum amount of power with each cycle. To avoid
overcharging the output, another on-time cannot begin
until output voltage drops below the feedback thresh-
old. Since the zero-crossing comparator prevents the
switching regulator from sinking current, the controller
must skip pulses. Therefore, the controller regulates the
valley of the output ripple under light-load conditions.
The switching waveforms may appear noisy and asyn-
chronous when light loading causes pulse-skipping
operation, but this is a normal operating condition that
results in high light-load efficiency. Trade-offs in PFM
noise vs. light-load efficiency are made by varying the
inductance. Generally, low inductance produces a
broader efficiency vs. load curve, while higher values
result in higher full-load efficiency (assuming that the
coil resistance remains fixed) and less output voltage
ripple. Penalties for using higher inductor values
include larger physical size and degraded load-tran-
sient response (especially at low input-voltage levels).
______________________________________________________________________________________
17
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相关代理商/技术参数 |
参数描述 |
|---|---|
| MAX8717EVKIT | 制造商:Maxim Integrated Products 功能描述:HIGH-EFFICIENCY DUAL POWER-SUPPLY - Rail/Tube |
| MAX8718ETA | 制造商:Maxim Integrated Products 功能描述:HIGH-VOLTAGE LOW-POWER LINEAR REGU - Rail/Tube |
| MAX8718ETA+ | 制造商:Maxim Integrated Products 功能描述: |
| MAX8718ETA-T | 功能描述:低压差稳压器 - LDO RoHS:否 制造商:Texas Instruments 最大输入电压:36 V 输出电压:1.4 V to 20.5 V 回动电压（最大值）:307 mV 输出电流:1 A 负载调节:0.3 % 输出端数量: 输出类型:Fixed 最大工作温度:+ 125 C 安装风格:SMD/SMT 封装 / 箱体:VQFN-20 |
| MAX8719ETA | 制造商:Maxim Integrated Products 功能描述:HIGH-VOLTAGE LOW-POWER LINEAR REGU - Rail/Tube |
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