MIC5205
Fixed Regulator Applications
V
IN
MIC5205-x.xBM5
1
2
3
4
5
Micrel
R2
V
OUT
= 1.242V
×
+ 1
R1
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 and
have a different V
OUT
equation.
Resistor values are not critical because ADJ (adjust) has a
high input impedance, but for best results use resistors of
470kΩ or less. A capacitor from ADJ to ground provides
greatly improved noise performance.
V
IN
MIC5205BM5
1
2
3
4
5
V
OUT
2.2µF
470pF
Figure 1. Ultra-Low-Noise Fixed Voltage Application
Figure 1 includes a 470pF capacitor for low-noise operation
and shows EN (pin 3) connected to IN (pin 1) for an applica-
tion where enable/shutdown is not required. C
OUT
= 2.2µF
minimum.
V
IN
MIC5205-x.xBM5
V
OUT
1
2
Enable
Shutdown
3
4
5
V
OUT
R1
R2
2.2µF
1.0µF
EN
470pF
Figure 2. Low-Noise Fixed Voltage Application
Figure 2 is an example of a low-noise configuration where
C
BYP
is not required. C
OUT
= 1µF minimum.
Adjustable Regulator Applications
The MIC5205BM5 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 following equation:
Figure 3. Ultra-Low-Noise
Adjustable Voltage Application
Figure 3 includes the optional 470pF noise bypass capacitor
from ADJ to GND to reduce output noise.
Dual-Supply Operation
When used in dual supply systems where the regulator load
is returned to a negative supply, the output voltage must be
diode clamped to ground.
MIC5205
8
June 2000
MICREL [ MICREL SEMICONDUCTOR ]
