Datasheet

MIC5209
DS20005720A-page 12  2017 Microchip Technology Inc.
4.0 APPLICATIONS INFORMATION
4.1 Enable/Shutdown
Enable is not available on devices in the SOT-223 (S)
package.
Forcing EN (enable/shutdown) high (> 2V) enables the
regulator. EN is compatible with CMOS logic. If the
enable/shutdown feature is not required, connect EN to
IN (supply input).
4.2 Input Capacitor
A 1 µF capacitor should be placed from IN to GND if
there is more than 10 inches of wire between the input
and the AC filter capacitor or if a battery is used as the
input.
4.3 Output Capacitor
An output capacitor is required between OUT and GND
to prevent oscillation. The minimum size of the output
capacitor is dependent upon whether a reference
bypass capacitor is used. 1 µF minimum is
recommended when C
BYP
is not used (see Figure 4-1).
2.2 µF minimum is recommended when C
BYP
is 470 pF
(see Figure 4-2). Larger values improve the regulator’s
transient response.
The output capacitor should have an ESR (equivalent
series resistance) of about 1Ω and a resonant
frequency above 1 MHz. Ultra-low-ESR and ceramic
capacitors can cause a low amplitude oscillation on the
output and/or underdamped transient response. Most
tantalum or aluminum electrolytic capacitors are
adequate; film types will work, but are more expensive.
Since many aluminum electrolytics have electrolytes
that freeze at about –30°C, solid tantalums are
recommended for operation below –25°C.
At lower values of output current, less output
capacitance is needed for output stability. The
capacitor can be reduced to 0.47 µF for current below
10 mA or 0.33 µF for currents below 1 mA.
4.4 No-Load Stability
The MIC5209 will remain stable and in regulation with
no load (other than the internal voltage divider) unlike
many other voltage regulators. This is especially
important in CMOSRAM keep-alive applications.
4.5 Reference Bypass Capacitor
Reference bypass (BYP) is available only on devices in
SOIC-8 and DDPAK packages.
BYP is connected to the internal voltage reference. A
470 pF capacitor (C
BYP
) connected from BYP to GND
quiets this reference, providing a significant reduction
in output noise (ultra-low-noise performance). Because
C
BYP
reduces the phase margin, the output capacitor
should be increased to at least 2.2 µF to maintain
stability.
The start-up speed of the MIC5209 is inversely
proportional to the size of the reference bypass
capacitor. Applications requiring a slow ramp-up of
output voltage should consider larger values of C
BYP
.
Likewise, if rapid turn-on is necessary, consider
omitting C
BYP
.
If output noise is not a major concern, omit C
BYP
and
leave BYP open.
4.6 Thermal Considerations
The SOT-223 has a ground tab that allows it to
dissipate more power than the SOIC-8 (refer to the
Slot-1 Power Supply sub-section for details). At +25°C
ambient, it will operate reliably at 1.6W dissipation with
“worst-case” mounting (no ground plane, minimum
trace widths, and FR4 printed circuit board).
Thermal resistance values for the SOIC-8 represent
typical mounting on a 1”-square, copper-clad, FR4
circuit board. For greater power dissipation, SOIC-8
versions of the MIC5209 feature a fused internal lead
frame and die bonding arrangement that reduces
thermal resistance when compared to standard SOIC-8
packages.
Multilayer boards with a ground plane, wide traces near
the pads, and large supply-bus lines will have better
thermal conductivity and will also allow additional
power dissipation.
For additional heat sink characteristics, refer to
Application Hint 17. For a full discussion of heat sinking
and thermal effects on voltage regulators, refer to the
“Regulator Thermals” section of the Designing with
Low-Dropout Voltage Regulators handbook.
4.7 Low-Voltage Operation
The MIC5209-1.8 and MIC5209-2.5 require special
consideration when used in voltage-sensitive systems.
They may momentarily overshoot their nominal output
voltages unless appropriate output and bypass
capacitor values are chosen.
During regulator power up, the pass transistor is fully
saturated for a short time, while the error amplifier and
voltage reference are being powered up more slowly
from the output (see Functional Diagrams). Selecting
TABLE 4-1: MIC5209 THERMAL
RESISTANCE
Package θ
JA
θ
JC
SOT-223 (S) 62°C/W 15°C/W
SOIC-8 (M) 50°C/W 25°C/W
DDPAK (U) 31.4°C/W 3°C/W
3x3 DFN (ML) 64°C/W 12°C/W