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| 型号： | MAX8744AETJ+T |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 21/36页 |
| 文件大小： | 0K |
| 描述： | IC CNTRLR PWR SUP QUAD 32TQFN |
| 标准包装： | 2,500 |
| 应用： | 控制器，笔记本电脑电源系统 |
| 输入电压： | 6 V ~ 26 V |
| 输出数： | 4 |
| 输出电压： | 3.3V，5V，1 V ~ 26 V |
| 工作温度： | 0°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 32-WFQFN 裸露焊盘 |
| 供应商设备封装： | 32-TQFN-EP（5x5） |
| 包装： | 带卷 (TR) |
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High-Efficiency, Quad-Output, Main Power-
Supply Controllers for Notebook Computers
Table 4. FSEL Configuration Table
sense voltage exceeds the idle mode current-sense
threshold. Under light-load conditions, the on-time dura-
FSEL
LDO5
REF
GND
SWITCHING FREQUENCY (kHz)
500
300
200
tion depends solely on the idle mode current-sense
threshold, which is 20% ( SKIP = GND) of the full-load
current-limit threshold set by ILIM, or the low-noise cur-
rent-sense threshold, which is 10% ( SKIP = REF) of the
full-load current-limit threshold set by ILIM. This forces
Frequency Selection (FSEL)
The FSEL input selects the PWM mode switching fre-
quency. Table 4 shows the switching frequency based
on FSEL connection. High-frequency (500kHz) operation
optimizes the application for the smallest component
size, trading off efficiency due to higher switching losses.
This may be acceptable in ultraportable devices where
the load currents are lower. Low-frequency (200kHz)
operation offers the best overall efficiency at the expense
of component size and board space.
Forced-PWM Mode
The low-noise forced-PWM mode ( SKIP = LDO5) dis-
ables the zero-crossing comparator, which controls the
low-side switch on-time. This forces the low-side gate-
drive waveform to be constantly the complement of the
high-side gate-drive waveform, so the inductor current
reverses at light loads while DH_ maintains a duty factor
of V OUT /V IN . The benefit of forced-PWM mode is to keep
the switching frequency fairly constant. However, forced-
PWM operation comes at a cost: the no-load 5V supply
current remains between 20mA to 50mA, depending on
the external MOSFETs and switching frequency.
Forced-PWM mode is most useful for avoiding audio-
the controller to source a minimum amount of power with
each cycle. To avoid overcharging the output, another
on-time cannot begin until the output voltage drops
below the feedback threshold. 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.
Automatic Pulse-Skipping Crossover
In skip mode, an inherent automatic switchover to PFM
takes place at light loads (Figure 4). This switchover is
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_ to CSL_. Once V CSH _ - V CSL _ drops
below the 3mV zero-crossing, current-sense threshold,
the comparator forces DL_ low (Figure 3). This mecha-
nism causes the threshold between pulse-skipping
PFM and nonskipping PWM operation to coincide with
the boundary between continuous and discontinuous
inductor-current operation (also known as the “critical
conduction ” point). The load-current level at which
PFM/PWM crossover occurs, I LOAD(SKIP) , is given by:
frequency noise and improving load-transient
response. Since forced-PWM operation disables the
zero-crossing comparator, the inductor current revers-
es under light loads.
Light-Load Operation Control ( SKIP )
The MAX8744A/MAX8745A include a light-load operat-
ing mode control input ( SKIP ) used to enable or dis-
able the zero-crossing comparator for both switching
regulators. When the zero-crossing comparator is
I LOAD ( SKIP ) =
(V IN ? V OUT )V OUT
2 V IN f OSC L
enabled, the regulator forces DL_ low when the cur-
rent-sense inputs detect zero inductor current. This
keeps the inductor from discharging the output capaci-
tors and forces the regulator to skip pulses under light-
load conditions to avoid overcharging the output. When
the zero-crossing comparator is disabled, the regulator
is forced to maintain PWM operation under light-load
conditions (forced PWM).
t ON(SKIP) =
V OUT
V IN f OSC
I PK
I LOAD = I PK /2
Idle Mode Current-Sense Threshold
When pulse-skipping mode is enabled, the on-time of the
step-down controller terminates when the output voltage
0
ON-TIME
TIME
exceeds the feedback threshold and when the current-
Figure 4. Pulse-Skipping/Discontinuous Crossover Point
______________________________________________________________________________________
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相关代理商/技术参数 |
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| MAX8744AEVKIT+ | 制造商:Maxim Integrated Products 功能描述:MAX8744A EVAL KIT - Rail/Tube |
| MAX8744ETJ+ | 功能描述:电流型 PWM 控制器 Quad-Out Main Power Supply 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 |
| MAX8744ETJ+T | 功能描述:电流和电力监控器、调节器 Quad-Out Main Power Supply Controller RoHS:否 制造商:STMicroelectronics 产品:Current Regulators 电源电压-最大:48 V 电源电压-最小:5.5 V 工作温度范围:- 40 C to + 150 C 安装风格:SMD/SMT 封装 / 箱体:HPSO-8 封装:Reel |
| MAX8744EVKIT | 制造商:Maxim Integrated Products 功能描述:HIGH-EFFICIENCY QUAD OUTPUT MAIN - Rail/Tube |
| MAX8744EVKIT+ | 制造商:Maxim Integrated Products 功能描述:HIGH-EFFICIENCY QUAD OUTPUT MAIN - Rail/Tube |
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