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MIC5190YMM 参数 Datasheet PDF下载

MIC5190YMM图片预览
型号: MIC5190YMM
PDF下载: 下载PDF文件 查看货源
内容描述: 超高速,大电流有源滤波器/ LDO控制器 [Ultra High-Speed, High-Current Active Filter/LDO Controller]
分类和应用: 有源滤波器控制器
文件页数/大小: 13 页 / 464 K
品牌: MICREL [ MICREL SEMICONDUCTOR ]
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MIC5190  
Micrel  
Applications Information  
Designing with the MIC5190  
1
V = idt  
C
Anatomy of a transient response  
Output voltage variation will depend on two factors: loop  
bandwidth and output capacitance. The output capacitance  
will determine how far the voltage will fall over a given time.  
With more capacitance, the drop in voltage will fall at a  
decreased rate. This is the reason that more capacitance  
provides a better transient response for the same given  
bandwidth.  
The measure of a regulator is how accurately and effectively  
it can maintain a set output voltage, regardless of the load's  
power demands. One measure of regulator response is the  
load step. The load step gauges how the regulator responds  
to a change in load current. Figure 2 is a look at the transient  
response to a load step.  
1
V =  
idt  
C  
The time it takes for the regulator to respond is directly  
proportional to its bandwidth gain. Higher bandwidth control  
loops respond quicker causing a reduced drop on the supply  
for the same amount of capacitance.  
1
C
idt  
V =  
di  
dt  
V = L  
Output voltage vs. time  
1
during recovery is  
directly proportional to  
gain vs. frequency.  
V = ∫idt ↓  
1
C
BW  
Final recovery back to the regulated voltage is the final phase  
of transient response and the most important factors are gain  
and time. Higher gain at higher frequency will get the output  
voltage closer to its regulation point quicker. The final settling  
point will be determined by the load regulation, which is  
proportional to DC (0Hz) gain and the associated loss terms.  
Time  
Figure 2. Typical Transient Response  
At the start of a circuit's power demand, the output voltage is  
regulated to its set point, while the load current runs at a  
constant rate. For many different reasons, a load may ask for  
more current without warning. When this happens, the regu-  
lator needs some time to determine the output voltage drop.  
This is determined by the speed of the control loop. So, until  
enough time has elapsed, the control loop is oblivious to the  
voltage change. The output capacitor must bear the burden  
of maintaining the output voltage.  
There are other factors that contribute to large signal tran-  
sient response, such as source impedance, phase margin,  
and PSRR. For example, if the input voltage drops due to  
source impedance during a load transient, this will contribute  
to the output voltage deviation by filtering through to the  
output reduced by the loops PSRR at the frequency of the  
voltage transient. It is straightforward: good input capaci-  
tance reduces the source impedance at high frequencies.  
Having between 35° and 45° of phase margin will help speed  
up the recovery time. This is caused by the initial overshoot  
in response to the loop sensing a low voltage.  
di  
V = L  
dt  
Since this is a sudden change in voltage, the capacitor will try  
to maintain voltage by discharging current to the output. The  
firstvoltagedropisduetotheoutputcapacitor'sESL(equiva-  
lent series inductance). The ESL will resist a sudden change  
incurrentfromthecapacitoranddropthevoltagequickly.The  
amount of voltage drop during this time will be proportional to  
the output capacitor's ESL and the speed at which the load  
steps. Slower load current transients will reduce this effect.  
Compensation  
The MIC5190 has the ability to externally control gain and  
bandwidth.ThisallowstheMIC5190 designto beindividually  
tailored for different applications.  
In designing the MIC5190, it is important to maintain ad-  
equate phase margin. This is generally achieved by having  
the gain cross the 0dB point with a single pole 20dB/decade  
roll-off. The compensation pin is configured as Figure 3  
demonstrates.  
di  
V = L  
dt ↑  
Placing multiple small capacitors with low ESL in parallel can  
help reduce the total ESL and reduce voltage droop during  
highspeedtransients.Forhighspeedtransients,thegreatest  
voltagedeviationwillgenerallybecausedbyoutputcapacitor  
ESL and parasitic inductance.  
Internal  
Error Amplifier  
3.42MΩ  
Driver  
20pF  
di  
V = L ↓  
dt  
External  
Comp  
After the current has overcome the effects of the ESL, the  
output voltage will begin to drop proportionally to time and  
inversely proportional to output capacitance.  
Figure 3. Internal Compensation  
December 2005  
7
M9999-120105