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| 型号： | MAX1977EEI+ |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 19/32页 |
| 文件大小： | 0K |
| 描述： | IC CNTRLR PS QUAD HI EFF 28QSOP |
| 产品培训模块： | Lead (SnPb) Finish for COTS Obsolescence Mitigation Program |
| 标准包装： | 50 |
| 应用： | 控制器，笔记本电脑电源系统 |
| 输入电压： | 4.5 V ~ 24 V |
| 输出数： | 4 |
| 输出电压： | 3.3V，5V，2 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-QSOP |
| 供应商设备封装： | 28-QSOP |
| 包装： | 管件 |
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High-Efficiency, Quad Output, Main Power-
Supply Controllers for Notebook Computers
tinuous and discontinuous inductor-current operation
(also known as the critical conduction point):
Forced-PWM Mode
The low-noise, forced-PWM ( SKIP = V CC ) mode dis-
2 × L
V +
?
?
I LOAD ( SKIP ) =
K × V OUT _ ? V + ? V OUT _ ?
? ?
ables the zero-crossing comparator, which controls the
low-side switch on-time. Disabling the zero-crossing
detector causes the low-side, gate-drive waveform to
become the complement of the high-side, gate-drive
where K is the on-time scale factor (see the On-Time
One-Shot (t ON ) section). The load-current level at which
PFM/PWM crossover occurs, I LOAD(SKIP) , is equal to 1/2
the peak-to-peak ripple current, which is a function of the
inductor value (Figure 5). For example, in the MAX1777
typical application circuit with V OUT2 = 5V, V+ = 12V,
L = 7.6μH, and K = 5μs, switchover to pulse-skipping
operation occurs at I LOAD = 0.96A or about 1/5 full load.
The crossover point occurs at an even lower value if a
swinging (soft-saturation) inductor is used.
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
inductor value. Generally, low inductor values produce
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).
DC output accuracy specifications refer to the trip level of
the error comparator. When the inductor is in continuous
conduction, the output voltage has a DC regulation high-
er than the trip level by 50% of the ripple. In discontinu-
ous conduction ( SKIP = GND, light load), the output
voltage has a DC regulation higher than the trip level by
approximately 1.5% due to slope compensation.
waveform. The inductor current reverses at light loads
as the PWM loop strives to maintain a duty ratio of
V OUT /V+. The benefit of forced-PWM mode is to keep
the switching frequency fairly constant, but it comes at
a cost: the no-load battery current can be 10mA to
50mA, depending on switching frequency and the
external MOSFETs.
Forced-PWM mode is most useful for reducing audio-
frequency noise, improving load-transient response,
providing sink-current capability for dynamic output
voltage adjustment, and improving the cross-regulation
of multiple-output applications that use a flyback trans-
former or coupled inductor.
Minimum 25kHz Pulse-Skipping Mode
(Ultrasonic Mode)
Leaving SKIP unconnected or connecting SKIP to REF
activates a pulse-skipping mode with a minimum
switching frequency of 25kHz. This ultrasonic pulse-
skipping mode reduces audio-frequency modulation of
the power supply that may occur in Idle Mode at very
light loads. The transition to fixed-frequency PWM oper-
ation is automatic and occurs at the same point as in
Idle Mode. Ultrasonic pulse skipping occurs if no
switching has taken place within the last 28μs. DL_
turns on to induce a regulated negative current in the
inductor. DH_ turns on when the inductor current
reaches the regulated negative current limit. Starting
with a DL_ pulse greatly reduces the ripple current
when compared to starting with a DH_ pulse (Idle
Mode). The output voltage level determines the nega-
tive current limit.
( V REF ? V FB )
? i
? t
=
V+ - V OUT
L
-I PEAK
Calculate the negative ultrasonic current-limit threshold
with the following equation:
V NEG U S = I LX × R ON = × 0 . 467 V
V ILIM _
I LOAD = I PEAK /2
where V FB > V REF , and R ON is the on-resistance of the
synchronous rectifier (MAX1999) or the current-sense
resistor value (MAX1777/MAX1977).
0 ON-TIME
TIME
Figure 5. Pulse- Skipping/Discontinuous Crossover Point
______________________________________________________________________________________
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相关代理商/技术参数 |
参数描述 |
|---|---|
| MAX1977EEI+ | 功能描述:DC/DC 开关控制器 Quad Out Main Power Supply Controller RoHS:否 制造商:Texas Instruments 输入电压:6 V to 100 V 开关频率: 输出电压:1.215 V to 80 V 输出电流:3.5 A 输出端数量:1 最大工作温度:+ 125 C 安装风格: 封装 / 箱体:CPAK |
| MAX1977EEI+T | 功能描述:DC/DC 开关控制器 Quad Out Main Power Supply Controller RoHS:否 制造商:Texas Instruments 输入电压:6 V to 100 V 开关频率: 输出电压:1.215 V to 80 V 输出电流:3.5 A 输出端数量:1 最大工作温度:+ 125 C 安装风格: 封装 / 箱体:CPAK |
| MAX1977EEI-T | 功能描述:DC/DC 开关控制器 RoHS:否 制造商:Texas Instruments 输入电压:6 V to 100 V 开关频率: 输出电压:1.215 V to 80 V 输出电流:3.5 A 输出端数量:1 最大工作温度:+ 125 C 安装风格: 封装 / 箱体:CPAK |
| MAX1977EEI-TG068 | 制造商:Rochester Electronics LLC 功能描述: 制造商:Maxim Integrated Products 功能描述: |
| MAX1978ETM | 功能描述:电压模式 PWM 控制器 RoHS:否 制造商:Texas Instruments 输出端数量:1 拓扑结构:Buck 输出电压:34 V 输出电流: 开关频率: 工作电源电压:4.5 V to 5.5 V 电源电流:600 uA 最大工作温度:+ 125 C 最小工作温度:- 40 C 封装 / 箱体:WSON-8 封装:Reel |
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