MIC5209 MICREL [Micrel Semiconductor], MIC5209 Datasheet - Page 9

• Manufacturer Part Number: MIC5209
• Description: 500mA Low-Noise LDO Regulator
• Manufacturer: MICREL [Micrel Semiconductor]

Fixed Regulator Circuits
Figure 1 shows a basic MIC5209-x.xBM (SO-8) fixed-voltage
regulator circuit. See Figure 5 for a similar configuration
using the more thermally-efficient MIC5209-x.xBS (SOT-223).
A 1 F minimum output capacitor is required for basic fixed-
voltage applications.
Figure 2 includes the optional 470pF noise bypass capacitor
between BYP and GND to reduce output noise. Note that the
minimum value of C
capacitor is used.
Adjustable Regulator Circuits
The MIC5209BM/U can be adjusted to a specific output
voltage by using two external resistors (Figure 3). The resis-
tors set the output voltage based on the equation:
This equation is correct due to the configuration of the
bandgap reference. The bandgap voltage is relative to the
output, as seen in the block diagram. Traditional regulators
normally have the reference voltage relative to ground;
therefore, their equations are different from the equation for
the MIC5209BM/U.
August 2, 2000
MIC5209
Figure 2. Ultra-Low-Noise Fixed Voltage Regulator
Figure 3. Low-Noise Adjustable Voltage Regulator
Figure 1. Low-Noise Fixed Voltage Regulator
V
OUT
V
V
IN
= 1.242V
IN
V
IN
2
1
MIC5209-x.xBM
2
1
IN
EN
OUT
MIC5209BM
IN
EN
MIC5209-x.xBM
2
1
IN
EN
GND
5–8
must be increased when the bypass
1
GND
5–8
+
GND
OUT
ADJ
OUT
BYP
5–8
R2
R1
OUT
BYP
470pF
3
4
3
4
R1
R2
3
4
1µF
V
OUT
2.2µF
V
1µF
OUT
V
OUT
9
Although ADJ is a high-impedance input, for best perfor-
mance, R2 should not exceed 470k .
Figure 4 includes the optional 470pF bypass capacitor from
ADJ to GND to reduce output noise.
Slot-1 Power Supply
Intel’s Pentium II processors have a requirement for a 2.5V
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.
A Slot-1 power supply (Figure 5) is easy to implement. Only
two capacitors are necessary, and their values are not critical.
C
0.1 F. C
response, and compensates the internal regulator control
loop. Its value should be at least 22 F. C
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 efficiency of 75%. At the maximum
anticipated Slot 1 load (320mA), the nominal power dissipa-
tion is only 256mW.
The SOT-223 package has sufficient thermal characteristics
for wide design margins when mounted on a single layer
copper-clad printed circuit board. The power dissipation of
5% power supply for a clock synthesizer and its associated
IN
Figure 4. Ultra-Low-Noise Adjustable Application.
bypasses the internal circuitry and should be at least
OUT
V
IN
Figure 5. Slot-1 Power Supply
0.1µF
provides output filtering, improves transient
V
2
1
C
IN
IN
EN
MIC5209BM
IN
GND
1
MIC5209-x.xBS
5–8
IN
OUT
ADJ
470pF
GND
3
4
2,TAB
OUT
R1
R2
3
IN
C
22µF
V
OUT
and C
OUT
2.2µF
V
OUT
OUT
MIC5209
may be
Micrel