Datasheet
2017 Microchip Technology Inc. DS20005785A-page 11
MIC5205
regulator circuit. For example, when operating the
MIC5205-3.3YM5 at room temperature with a minimum
footprint layout, the maximum input voltage for a set
output current can be determined as follows:
EQUATION 4-3:
The junction-to-ambient thermal resistance for the
minimum footprint is 220°C/W, from Table 4-1. The
maximum power dissipation must not be exceeded for
proper operation. Using the output voltage of 3.3V and
an output current of 150 mA, the maximum input
voltage can be determined. From the Electrical
Characteristics table, the maximum ground current for
150 mA output current is 2500 µA or 2.5 mA.
EQUATION 4-4:
EQUATION 4-5:
EQUATION 4-6:
V
IN(MAX)
then equates out to 6.23V. Therefore, a 3.3V
application at 150 mA of output current can accept a
maximum input voltage of 6.2V in a SOT-23-5 package.
For a full discussion of heat sinking and thermal effects
on voltage regulators, refer to the Regulator Thermals
section of Microchip’s Designing with Low-Dropout
Voltage Regulators handbook.
4.7 Fixed Regulator Applications
Figure 4-1 includes a 470 pF capacitor for low-noise
operation and shows EN (pin 3) connected to IN (pin 1)
for an application where enable/shutdown is not
required. C
OUT
= 2.2 µF minimum.
FIGURE 4-1: Ultra-Low Noise Fixed
Voltage Application.
Figure 4-2 is an example of a low-noise configuration
where C
BYP
is not required. C
OUT
= 1 µF minimum.
FIGURE 4-2: Low Noise Fixed Voltage
Application.
4.8 Adjustable Regulator Applications
The MIC5205YM5 can be adjusted to a specific output
voltage by using two external resistors (Figure 4-3).
The resistors set the output voltage based on the
following equation:
EQUATION 4-7:
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 470 kΩ or less. A capacitor from ADJ to
ground provides greatly improved noise performance.
P
DMAX
125C 25C–
220C/W
--------------------------------------- - 455mW==
455mW V
IN
3.3V–150mA V
IN
+2.5mA=
455mW V
IN
150mA 495mW– V
IN
+2.5mA=
950mW V
IN
152.5mA=
15
2
3
4
2.2μF
470pF
V
OUT
MIC5205-x.xYM5
V
IN
15
2
34
1.0μF
Enable
Shutdown
EN
V
OUT
MIC5205-x.xYM5
V
IN
V
OUT
1.242V
R2
R1
------ -1+
=