Micrel, Inc. MIC5306
November 2006
7
M9999-112006-B
Applications Information
Input Capacitance
A 1
µ
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.
Output Capacitance
An output capacitor is required between OUT and
GND to prevent oscillation. Larger values improve the
regulator’s transient response. The output capacitor
value may be increased without limit.
The output capacitor should have below ESR 300mΩ
and a resonant frequency 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
electrolytes that freeze at about –30
°
C, solid tant-
alums are recommended for operation below –25
°
C.
Enable
Forcing EN (enable/shutdown) high (>1V) enables the
regulator. 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).
Current Limit
There is overcurrent protection circuitry built into the
MIC5306. Even with the output grounded, current will
be limited to approximately 285mA. Further protection
is provided by thermal shutdown.
Thermal Considerations
The MIC5306 is designed to provide 150mA of
continuous current in a very small package. Maximum
ambient operating temperature can be calculated
based on the output current and the voltage drop
across the part. Given that the input voltage is 3.8V,
the output voltage is 2.8V and the output current
equals 150mA.
The actual power dissipation of the regulator circuit
can be determined using the equation:
P
D
= (V
IN
– V
OUT
) I
OUT
+ V
IN
I
GND
Because this device is CMOS and the ground current
is typically < 50
µ
A over the load range, the power
dissipation contributed by the ground current is < 1%
and can be ignored for this calculation.
P
D
= (3.8V – 2.8V)
⋅
150mA
P
D
= 0.15W
To determine the maximum ambient operating
temperature of the package, use the junction-to-
ambient thermal resistance of the device and the
following basic equation:
P
D
(max) =
T
J
(max) – T
A
JA
T
J
(max) = 125
°
C, the maximum junction temperature
of the die
θ
JA
thermal resistance = 235
°
C/W
Table 1 shows junction-to-ambient thermal resistance
for the MIC5306 in the TSOT23-5 package.
Package
θ
θθ
θ
JA
Recommended
Minimum Footprint
θ
JC
TSOT23-5
235°C/W 2°C/W
Table 1. TSOT23-5 Thermal Resistance
Substituting P
D
for P
D
(max) and solving for the
ambient operating temperature will give the maximum
operating conditions for the regulator circuit. The
junction-to-ambient thermal resistance for the
minimum footprint is 235
°
C/W, from Table 1. The
maximum power dissipation must not be exceeded for
proper operation.
For example, when operating the MIC5306-2.8 at an
input voltage of 3.8V and 150mA load with a minimum
footprint layout, the maximum ambient operating
temperature T
A
can be determined as follows:
0.15W = (125°C - T) / 235C°/W
T = 89.75°C
Therefore, a 2.8V application at 150mA of output
current can accept an ambient operating temperature
of 89.8
°
C in a TSOT23-5 package. For a full
discussion of heat sinking and thermal effects on
voltage regulators, refer to the “Regulator Thermals”
section of Micrel’s
Designing with Low-Dropout
Voltage Regulators
handbook. This information can
be found on Micrel's website at:
http://www.micrel.com/_PDF/other/LDOBk_ds.pdf
