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| 型号： | MAX8550AETI+ |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 13/29页 |
| 文件大小： | 0K |
| 描述： | IC PWR SUP DDR INTEG 28TQFN |
| 产品培训模块： | Lead (SnPb) Finish for COTS Obsolescence Mitigation Program |
| 标准包装： | 60 |
| 应用： | 控制器，DDR |
| 输入电压： | 2 V ~ 28 V |
| 输出数： | 2 |
| 输出电压： | 1.8V，2.5V，0.7 V ~ 5.5 V |
| 工作温度： | -40°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： | 管件 |
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Integrated DDR Power-Supply Solution for
Desktops, Notebooks, and Graphic Cards
I LOAD ( SKIP ) = ? OUT IN OUT ?
? ?
? = 1 . 68 A
? ? ?
?
2 × 1 μ H
?
?
?
The on-time one-shot has good accuracy at the operat-
ing points specified in the Electrical Characteristics
table (approximately ±12.5% at 600kHz and 450kHz,
and ±10% at 200kHz and 300kHz). On-times at operat-
ing points far removed from the conditions specified in
the Electrical Characteristics table can vary over a
wider range. For example, the 600kHz setting typically
runs approximately 10% slower with inputs much
greater than 5V due to the very short on-times required.
The constant on-time translates only roughly to a con-
stant switching frequency. The on-times guaranteed in
the Electrical Characteristics table are influenced by
resistive losses and by switching delays in the high-
side MOSFET. Resistive losses, which include the
inductor, both MOSFETs, the output capacitor’s ESR,
and any PC board copper losses in the output and
ground, tend to raise the switching frequency as the
load increases. The dead-time effect increases the
effective on-time, reducing the switching frequency as
one or both dead times are added to the effective on-
time. The dead time occurs only in PWM mode ( SKIP =
V DD ) and during dynamic output-voltage transitions
when the inductor current reverses at light or negative
load currents. With reversed inductor current, the induc-
tor’s EMF causes LX to go high earlier than normal,
extending the on-time by a period equal to the DH-rising
dead time. For loads above the critical conduction point,
where the dead-time effect is no longer a factor, the
actual switching frequency is:
for the default 50mV current-limit threshold), the com-
parator forces DL low (Figure 1). This mechanism caus-
es 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 equal to
half the peak-to-peak ripple current, which is a function
of the inductor value (Figure 2). This threshold is rela-
tively constant, with only a minor dependence on the
input voltage (V IN ):
? V × K ? ? V - V ?
? 2 L ? ? V IN ?
where K is the on-time scale factor (see Table 1). For
example, in the Typical Applications Circuit of Figure 8
(K = 1.7μs, V OUT = 2.5V, V IN = 12V, and L = 1μH), the
pulse-skipping switchover occurs at:
? 2 . 5 V × 1 . 7 μ s ? ? 12 V - 2 .5V ?
12 V
The crossover point occurs at an even lower value if a
swinging (soft-saturation) inductor is used. The switch-
ing waveforms can appear noisy and asynchronous
when light loading causes pulse-skipping operation,
but this is a normal operating condition that results in
f SW =
V OUT + V DROP 1
t ON ( V IN + V DROP 2 )
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 broad-
er efficiency vs. load curve, while higher values result in
where V DROP1 is the sum of the parasitic voltage drops
in the inductor discharge path, including the synchro-
nous rectifier, the inductor, and any PC board resis-
tances; V DROP2 is the sum of the resistances in the
charging path, including the high-side switch (Q1 in the
higher full-load efficiency (assuming that the coil resis-
Table 1. Approximate K-Factor Errors
MINIMUM V IN AT
Typical Applications Circuit ), the inductor, and any PC
board resistances, and t ON is the one-shot on-time (see
the On-Time One-Shot (TON) section.
Automatic Pulse-Skipping Mode
( SKIP = GND)
In skip mode ( SKIP = GND), an inherent automatic
switchover to PFM takes place at light loads (Figure 2).
This switchover is affected by a comparator that trun-
cates the low-side switch on-time at the inductor cur-
rent ’s zero crossing. The zero-crossing comparator
differentially senses the inductor current across the
synchronous-rectifier MOSFET (Q2 in the Typical
Applications Circuit , Figure 8). Once V PGND - V LX
drops below 5% of the current-limit threshold (2.5mV
TON SETTING
200
(TON = AV DD )
300
(TON = OPEN)
450
(TON = REF)
600
(TON = GND)
TYPICAL
K-
FACTOR
(μs)
5.0
3.3
2.2
1.7
K-FACTOR
ERROR
(%)
± 10
± 10
± 12.5
± 12.5
V OUT = 2.5V
(h = 1.5; SEE THE
DROPOUT
PERFORMANCE
SECTION)
3.15
3.47
4.13
5.61
______________________________________________________________________________________
13
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相关代理商/技术参数 |
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|---|---|
| MAX8550AETI+ | 功能描述:电压模式 PWM 控制器 Integrated DDR Power Supply Solution 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 |
| MAX8550AETI+T | 功能描述:电压模式 PWM 控制器 Integrated DDR Power Supply Solution 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 |
| MAX8550AETI-T | 功能描述:PMIC 解决方案 RoHS:否 制造商:Texas Instruments 安装风格:SMD/SMT 封装 / 箱体:QFN-24 封装:Reel |
| MAX8550ETI | 功能描述:PMIC 解决方案 RoHS:否 制造商:Texas Instruments 安装风格:SMD/SMT 封装 / 箱体:QFN-24 封装:Reel |
| MAX8550ETI+ | 功能描述:电压模式 PWM 控制器 Integrated DDR Power Supply Solution 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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