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NB650H 参数 Datasheet PDF下载

NB650H图片预览
型号: NB650H
PDF下载: 下载PDF文件 查看货源
内容描述: 高效益分析,快速瞬态, 6A , 28V同步降压转换器, 2位VID [High-Effeciency, Fast-Transient, 6A, 28V Synchronous Step-Down Converters with 2-Bit VID]
分类和应用: 转换器
文件页数/大小: 20 页 / 681 K
品牌: MPS [ MONOLITHIC POWER SYSTEMS ]
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NB650/NB650H – 6A, 28V, FAST-TRANSIENT, SYNCHRONOUS STEP-DOWN CONVERTERS  
Where RO is the equivalent load resistor.  
becomes the reference to the PWM comparator.  
At this point, the soft-start finishes and it enters  
steady-state operation.  
As described in Figure 6, VSLOPE2 in skip mode is  
smaller than VSLOPE1 in PWM mode, so the jitter in  
the skip mode is larger. For less jitter during  
ultra-light–load conditions, select smaller VFB  
resistors, though at the cost of light-load  
efficiency.  
When the EN pin goes low, a 10µA internal  
current source discharges the SS capacitor.  
Once the SS voltage reaches the REF voltage,  
acts as the reference to the PWM comparator.  
The output voltage decreases smoothly with the  
SS voltage until it reaches zero level. Determine  
the SS capacitor as follows:  
VID Input  
Typically, R1 and R2 set the output voltage with  
VFB=0.6V. R2, in this case, is a combination of  
R2A, R2B, and R2C depends on the VID, which  
is active low. The NB650/NB650H can  
dynamically track VID codes as they change. As  
a result, the converter output voltage can change  
without the need to reset either the controller or  
the value of R1 and R2A. As shown in Figure 1,  
R2B and R2C are parallel with R2A. The  
equivalent value of R2 can change due to  
different VID codes. One can get four VOUT  
values depending on the VID codes with the  
details in the application information. The VID  
logic and equivalent R2s are shown in Table 1.  
Table 1: VID Logic  
tSS (ms)×ISS (μA)  
CSS (nF) =  
(12)  
VREF (V)  
If the output capacitors have large capacitance  
values, avoid setting a short SS time. Use a  
minimum value of 4.7nF if the output capacitance  
value exceeds 330µF.  
Power Good  
The NB650/NB650H has power-good (PG)  
output. The PG pin is the open drain of a  
MOSFET. Connect to VCC or another voltage  
source through a resistor (e.g. 100k). The  
MOSFET turns ON after the application of the  
input voltage so that the PG pin is pulled to GND  
before the SS is ready. After the FB voltage  
reaches 90% of the reference voltage, the PG pin  
is pulled high after a delay.  
R2  
VID2  
1
VID1  
1
R2 = R2A  
R2 = R2A //R2B  
R2 = R2A //R2C  
R2 = R2A //R2B //R2C  
1
0
0
0
1
0
The PG delay is determined as follows:  
4 × tSS (ms)  
tPG (ms) =  
(13)  
Enable Control  
9
The NB650/NB650H has a dedicated Enable  
control pin (EN). Pulling this pin high or low  
enables or disables the IC. Tie EN to VIN through  
a resistor for automatic start-up.  
When the FB voltage drops to 90% of the  
reference voltage, the PG pin is pulled low.  
Over-Current Protection and Short-Circuit  
Protection  
Soft Start/Stop  
The NB650/NB650H has cycle-by-cycle over-  
current limit control. The inductor current is  
monitored during the ON state. Once the inductor  
current hits the current limit, the HS-FET turns off.  
At the same time, the over-current protection  
(OCP) timer starts. The OCP timer is set as 50μs.  
If the current limit is hit for every cycle within that  
50μs period, then OCP will trigger.  
The NB650/NB650H employs a soft-start/stop  
(SS) mechanism to ensure smooth output during  
power-up and power shutdown. When the EN pin  
goes high, an internal current source (10μA)  
charges up the SS capacitor. The SS capacitor  
voltage then acts as the VREF voltage to the PWM  
comparator. The output voltage smoothly ramps  
up with the SS voltage. Once the SS voltage  
reaches the same level as the REF voltage, it  
continues ramping up while the REF voltage  
When the output is shorted to ground, the device  
hits its current limit and the FB voltage is less  
than 0.4V. The device treats this as a dead-short  
NB650/NB650H Rev. 1.12  
10/11/2012 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.  
© 2012 MPS. All Rights Reserved.  
www.MonolithicPower.com  
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