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MIC5209_04 Datasheet, PDF (10/13 Pages) Micrel Semiconductor – 500mA Low-Noise LDO Regulator | |||
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MIC5209
Fixed Regulator Circuits
VIN
MIC5209-x.xBM
2 IN
OUT 3
1 EN
BYP 4
GND
5â8
VOUT
1µF
VIN
MIC5209BM
2 IN
OUT 3
1 EN
ADJ 4
R1
GND
5â8
R2
470pF
Micrel, Inc.
VOUT
2.2µF
Figure 1. Low-Noise Fixed Voltage Regulator
Figure 1 shows a basic MIC5209-x.xBM (SO-8) ï¬xed-voltage
regulator circuit. See Figure 5 for a similar conï¬guration us-
ing the more thermally-efï¬cient MIC5209-x.xBS (SOT-223).
A 1µF minimum output capacitor is required for basic ï¬xed-
voltage applications.
VIN
MIC5209-x.xBM
2 IN
OUT 3
1 EN
BYP 4
GND
5â8
470pF
VOUT
2.2µF
Figure 2. Ultra-Low-Noise Fixed Voltage Regulator
Figure 2 includes the optional 470pF noise bypass capacitor
between BYP and GND to reduce output noise. Note that the
minimum value of COUT must be increased when the bypass
capacitor is used.
Adjustable Regulator Circuits
VIN
MIC5209BM
2 IN
OUT 3
1 EN
ADJ 4 R1
GND
5â8
R2
VOUT
1µF
Figure 3. Low-Noise Adjustable Voltage Regulator
The MIC5209BM/U can be adjusted to a speciï¬c output volt-
age by using two external resistors (Figure 3). The resistors
set the output voltage based on the equation:
VOUT = 1.242V ï£ï£¬1 + RR21
This equation is correct due to the conï¬guration of the
bandgap reference. The bandgap voltage is relative to the
output, as seen in the block diagram. Traditional regula-
tors normally have the reference voltage relative to ground;
therefore, their equations are different from the equation for
the MIC5209BM/U.
Although ADJ is a high-impedance input, for best performance,
R2 should not exceed 470kΩ.
Figure 4. Ultra-Low-Noise Adjustable Application.
Figure 4 includes the optional 470pF bypass capacitor from
ADJ to GND to reduce output noise.
Slot-1 Power Supply
Intelâs Pentium II processors have a requirement for a 2.5V
±5% power supply for a clock synthesizer and its associated
loads. The current requirement for the 2.5V supply is depen-
dant upon the clock synthesizer used, the number of clock
outputs, and the type of level shifter (from core logic levels to
2.5V levels). Intel estimates a worst-case load of 320mA.
The MIC5209 was designed to provide the 2.5V power
requirement for Slot-1 applications. Its guaranteed perfor-
mance of 2.5V ±3% at 500mA allows adequate margin for
all systems, and its dropout voltage of 500mV means that it
operates from a worst-case 3.3V supply where the voltage
can be as low as 3.0V.
VIN
MIC5209-x.xBS
1 IN
OUT 3
VOUT
CIN
0.1µF
GND
2,TAB
COUT
22µF
Figure 5. Slot-1 Power Supply
A Slot-1 power supply (Figure 5) is easy to implement. Only
two capacitors are necessary, and their values are not criti-
cal. CIN bypasses the internal circuitry and should be at least
0.1µF. COUT provides output ï¬ltering, improves transient
response, and compensates the internal regulator control
loop. Its value should be at least 22µF. CIN and COUT may
be increased as much as desired.
Slot-1 Power Supply Power Dissipation
Powered from a 3.3V supply, the Slot-1 power supply of
Figure 5 has a nominal efï¬ciency of 75%. At the maximum
anticipated Slot 1 load (320mA), the nominal power dissipa-
tion is only 256mW.
The SOT-223 package has sufï¬cient thermal characteristics
for wide design margins when mounted on a single layer
copper-clad printed circuit board. The power dissipation of
the MIC5209 is calculated using the voltage drop across the
device à output current plus supply voltage à ground current.
M9999-060906
10
June 2006
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