MIC5207-1.8BM5 Micrel Semiconductor, MIC5207-1.8BM5 Datasheet - Page 7

• Manufacturer Part Number: MIC5207-1.8BM5
• Description: 180mA Low-Noise LDO Regulator
• Manufacturer: Micrel Semiconductor

MIC5207
Applications Information
Enable/Shutdown
Forcing EN (enable/shutdown) high (> 2V) enables the regu-
lator. EN is compatible with CMOS logic gates.
If the enable/shutdown feature is not required, connect EN
(pin 3) to IN (supply input, pin 1). See Figure 1.
Input Capacitor
A 1 F 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.
Reference Bypass Capacitor
BYP (reference bypass) is connected to the internal voltage
reference. A 470pF capacitor (C
GND quiets this reference, providing a significant reduction in
output noise. C
when using C
generally required to maintain stability.
The start-up speed of the MIC5207 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
consider omitting C
If output noise is not a major concern, omit C
BYP open.
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. 1.0 F minimum is recommended when C
used (see Figure 2). 2.2 F minimum is recommended when
C
regulator’s transient response. The output capacitor value
may be increased without limit.
The output capacitor should have an ESR (effective series
resistance) of about 5
above 1MHz. Ultra-low-ESR 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 electro-
lytes that freeze at about –30 C, solid tantalums are recom-
mended for operation below –25 C.
At lower values of output current, less output capacitance is
required for output stability. The capacitor can be reduced to
0.47 F for current below 10mA or 0.33 F for currents below
1mA.
No-Load Stability
The MIC5207 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 CMOS
RAM keep-alive applications.
Thermal Considerations
The MIC5207 is designed to provide 180mA of continuous
current in a very small package. Maximum power dissipation
can be calculated based on the output current and the voltage
January 2000
BYP
is 470pF (see Figure 1). Larger values improve the
BYP
BYP
BYP
, output capacitors of 2.2 F or greater are
BYP
. Likewise, if rapid turn-on is necessary,
reduces the regulator phase margin;
.
or less and a resonant frequency
BYP
) connected from BYP to
BYP
BYP
and leave
is not
7
drop across the part. To determine the maximum power
dissipation of the package, use the junction-to-ambient ther-
mal resistance of the device and the following basic equation:
T
125 C, and T
layout dependent; Table 1 shows examples of junction-to-
ambient thermal resistance for the MIC5207.
The actual power dissipation of the regulator circuit can be
determined using the equation:
Substituting P
conditions that are critical to the application will give the
maximum operating conditions for the regulator circuit. For
example, when operating the MIC5207-3.3BM5 at room
temperature with a minimum footprint layout, the maximum
input voltage for a set output current can be determined as
follows:
The junction-to-ambient thermal resistance for the minimum
footprint is 220 C/W, from Table 1. The maximum power
dissipation must not be exceeded for proper operation. Using
the output voltage of 3.3V and an output current of 150mA,
the maximum input voltage can be determined. From the
Electrical Characteristics table, the maximum ground current
for 150mA output current is 3000 A or 3mA.
Therefore, a 3.3V application at 150mA of output current can
accept a maximum input voltage of 6V in a SOT-23-5 pack-
age. For a full discussion of heat sinking and thermal effects
on voltage regulators, refer to the Regulator Thermals sec-
tion of Micrel’s Designing with Low-Dropout Voltage Regula-
tors handbook.
Low-Voltage Operation
The MIC5207-1.8 and MIC5207-2.5 require special consid-
eration 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 satu-
rated for a short time, while the error amplifier and voltage
reference are being powered up more slowly from the output
Package
SOT-23-5 (M5)
J(max)
P
455mW = (V
455mW = V
920mW = V
V
P
P
P
D (max)
D(max)
D(max)
D
IN(max)
is the maximum junction temperature of the die,
Table 1. SOT-23-5 Thermal Resistance
= (V
A
IN
= 6.01V
=
D(max)
is the ambient operating temperature.
Minimum Footprint
125˚C 25˚C
425mW
– V
JA
IN
IN
T
IN
Recommended
OUT
J(max)
·150mA – 495mW + V
·153mA
235 C/W
235
– 3.3V) 150mA + V
for P
) I
JA
OUT
– T
D
and solving for the operating
+ V
A
IN
I
GND
Copper Clad
JA
170 C/W
1" Square
IN
IN
·3mA
·3mA
130 C/W
MIC5207
Micrel
JC
JA
is