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MAX1718EEI 参数 Datasheet PDF下载

MAX1718EEI图片预览
型号: MAX1718EEI
PDF下载: 下载PDF文件 查看货源
内容描述: 笔记本电脑CPU降压型控制器,用于Intel移动电压定位IMVP- II [Notebook CPU Step-Down Controller for Intel Mobile Voltage Positioning IMVP-II]
分类和应用: 稳压器开关式稳压器或控制器电源电路开关式控制器光电二极管电脑输入元件
文件页数/大小: 35 页 / 694 K
品牌: MAXIM [ MAXIM INTEGRATED PRODUCTS ]
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Notebook CPU Step-Down Controller for Intel  
-
Mobile Voltage Positioning (IMVP II)  
Thus, it is necessary to use forced PWM mode during all  
negative transitions. Most applications should use PWM  
mode exclusively, although there is some benefit to  
REF  
using skip mode while in the low-power suspend state  
(see the Using Skip Mode During Suspend (SKP/SDN =  
MAX1718  
V ) section.)  
CC  
POS  
NEG  
Automatic Pulse-Skipping Switchover  
In skip mode (SKP/SDN high), an inherent automatic  
switchover to PFM takes place at light loads (Figure 6).  
This switchover is effected by a comparator that trun-  
cates the low-side switch on-time at the inductor currents  
zero crossing. This mechanism causes the threshold  
between pulse-skipping PFM and nonskipping PWM  
operation to coincide with the boundary between con-  
tinuous and discontinuous inductor-current operation.  
The load-current level at which PFM/PWM crossover  
Figure 3. Resistive Divider from REF  
occurs, I  
, is equal to 1/2 the peak-to-peak  
LOAD(SKIP)  
ripple current, which is a function of the inductor value  
(Figure 6). For a battery range of 7V to 24V, this thresh-  
old is relatively constant, with only a minor dependence  
on battery voltage:  
DH  
MAX1718  
DL  
K × V  
2 × L  
V
V  
V
BATT  
OUT  
BATT OUT  
I
×
LOAD(SKIP)  
POS  
NEG  
where K is the on-time scale factor (Table 2). For exam-  
ple, in the standard application circuit this becomes:  
3.3µs × 1.25V  
2 × 0.68µH  
12V 1.25V  
×
= 2.7A  
12V  
The crossover point occurs at a lower value if a swing-  
ing (soft-saturation) inductor is used.  
Figure 4. Resistive Divider from OUTPUT  
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.  
DH  
MAX1718  
DL  
POS  
NEG  
MUX  
Current-Limit Circuit  
The current-limit circuit employs a unique valleycurrent-  
sensing algorithm that uses the on-resistance of the  
low-side MOSFET as a current-sensing element. If the  
current-sense signal is above the current-limit thresh-  
old, the PWM is not allowed to initiate a new cycle  
MAX4524  
SEL  
A
B
Figure 5. Programmable Offset Voltage  
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