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| 型号： | MAX8742EAI+T |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 13/34页 |
| 文件大小： | 0K |
| 描述： | IC CNTRLR PWR SUP 28-SSOP |
| 产品培训模块： | Lead (SnPb) Finish for COTS Obsolescence Mitigation Program |
| 标准包装： | 2,000 |
| 应用： | 控制器，笔记本电脑电源系统 |
| 输入电压： | 4.2 V ~ 30 V |
| 输出数： | 2 |
| 输出电压： | 3.3V，5V，2.5 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-SSOP（0.209"，5.30mm 宽） |
| 供应商设备封装： | 28-SSOP |
| 包装： | 带卷 (TR) |
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500kHz Multi-Output Power-Supply Controllers
with High Impedance in Shutdown
Table 2. Component Suppliers
three signals: the output-voltage error signal with
respect to the reference voltage, the current-sense sig-
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nal, and the slope-compensation ramp (Figure 3). The
PWM controller is a direct-summing type, lacking a tra-
ditional error amplifier and the phase shift associated
with it. This direct-summing configuration approaches
ideal cycle-by-cycle control over the output voltage.
When SKIP = low, idle-mode circuitry automatically
optimizes efficiency throughout the load current range.
Idle mode dramatically improves light-load efficiency
by reducing the effective frequency, which reduces
switching losses. It keeps the peak inductor current
The MAX8741/MAX8742 contain 10 major circuit blocks
(Figure 2).
The two pulse-width-modulation (PWM) controllers
each consist of a dual-mode feedback network and
multiplexer, a multi-input PWM comparator, high-side
and low-side gate drivers, and logic. The MAX8741/
MAX8742 contain fault-protection circuits that monitor
the main PWM outputs for undervoltage and overvolt-
age. A power-on sequence block controls the power-
up timing of the main PWMs and determines whether
one or both of the outputs are monitored for undervoltage
faults. The MAX8742 includes a secondary feedback net-
work and 12V linear regulator to generate a 12V output
from a coupled-inductor flyback winding. The MAX8741
has a secondary feedback input (SECFB) instead, which
allows a quasi-regulated, adjustable output, coupled-
inductor flyback winding to be attached to either the 3.3V
or the 5V main inductor. Bias generator blocks include
the 5V IC internal rail (V L ) linear regulator, 2.5V precision
reference, and automatic bootstrap switchover circuit.
The PWMs share a common 333kHz/500kHz synchroniz-
able oscillator.
These internal IC blocks are not powered directly from
the battery. Instead, the 5V V L linear regulator steps
down the battery voltage to supply both V L and the
gate drivers. The synchronous-switch gate drivers are
directly powered from V L , while the high-side switch
gate drivers are indirectly powered from V L by an exter-
nal diode-capacitor boost circuit. An automatic boot-
strap circuit turns off the 5V linear regulator and powers
the IC from the 5V PWM output voltage if the output is
above 4.5V.
PWM Controller Block
The two PWM controllers are nearly identical. The only
differences are fixed output settings (3.3V vs. 5V), the
V L /CSL5 bootstrap switch connected to the 5V PWM,
and SECFB. The heart of each current-mode PWM con-
troller is a multi-input, open-loop comparator that sums
above 25% of the full current limit in an active cycle,
allowing subsequent cycles to be skipped. Idle mode
transitions seamlessly to fixed-frequency PWM opera-
tion as load current increases.
With SKIP = high, the controller always operates in fixed-
frequency PWM mode for lowest noise. Each pulse from
the oscillator sets the main PWM latch that turns on the
high-side switch for a period determined by the duty fac-
tor (approximately V OUT / V IN ). As the high-side switch
turns off, the synchronous-rectifier latch sets; 60ns later,
the low-side switch turns on. The low-side switch stays on
until the beginning of the next clock cycle.
In PWM mode, the controller operates as a fixed-fre-
quency current-mode controller where the duty ratio is
set by the input/output voltage ratio. The current-mode
feedback system regulates the peak inductor-current
value as a function of the output-voltage error signal. In
continuous-conduction mode, the average inductor
current is nearly the same as the peak current, so the
circuit acts as a switch-mode transconductance ampli-
fier. This pushes the second output LC filter pole, nor-
mally found in a duty-factor-controlled (voltage-mode)
PWM, to a higher frequency. To preserve inner-loop
stability and eliminate regenerative inductor current
“staircasing,” a slope-compensation ramp is summed
into the main PWM comparator to make the apparent
duty factor less than 50%.
The MAX8741/MAX8742 use a relatively low loop gain,
allowing the use of lower-cost output capacitors. The
relative gains of the voltage-sense and current-sense
inputs are weighted by the values of current sources
that bias three differential input stages in the main PWM
comparator (Figure 4). The relative gain of the voltage
comparator to the current comparator is internally fixed
at K = 2:1. The low loop gain results in the 2% typical
load-regulation error. The low value of loop gain helps
reduce output-filter-capacitor size and cost by shifting
the unity-gain crossover frequency to a lower level.
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相关代理商/技术参数 |
参数描述 |
|---|---|
| MAX8743EEI | 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 |
| MAX8743EEI+ | 功能描述:电流型 PWM 控制器 Dual 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 |
| MAX8743EEI+T | 功能描述:电流型 PWM 控制器 Dual 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 |
| MAX8743EEI-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 |
| MAX8743ETX | 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 |
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