MIC5238-1.2YD5 TR Micrel Inc, MIC5238-1.2YD5 TR Datasheet - Page 9

• Manufacturer Part Number: MIC5238-1.2YD5 TR
• Description: 150mA Low Vo, Low Iq LDO ( )
• Manufacturer: Micrel Inc

Specifications of MIC5238-1.2YD5 TR

• Regulator Topology: Positive Fixed
• Voltage - Output: 1.2V
• Voltage - Input: Up to 6V
• Voltage - Dropout (typical): 0.31V @ 150mA
• Number Of Regulators: 1
• Current - Output: 150mA
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: TSOT-23-5, TSOT-5, TSOP-5
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Current - Limit (min): -
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 576-1834-2; MIC5238-1.2YD5TR; MIC5238-1.2YD5TR

Application Information
Enable/Shutdown
The MIC5238 comes with an active-high enable pin that
allows the regulator to be disabled. Forcing the enable pin
low disables the regulator and sends it into a “zero” off-
mode-current state. In this state, current consumed by the
regulator goes nearly to zero. Forcing the enable pin high
enables the output voltage.
Input Bias Capacitor
The input capacitor must be rated to sustain voltages that
may be used on the input. An input capacitor may be
required when the device is not near the source power
supply or when supplied by a battery. Small, surface
mount, ceramic capacitors can be used for bypassing.
Larger values may be required if the source supply has
high ripple.
Output Capacitor
The MIC5238 requires an output capacitor for stability. The
design requires 2.2µF or greater on the output to maintain
stability. The design is optimized for use with low-ESR
ceramic chip capacitors. High ESR capacitors may cause
high frequency oscillation. The maximum recommended
ESR is 3Ω. The output capacitor can be increased without
limit. Larger valued capacitors help to improve transient
response.
X7R/X5R dielectric-type ceramic capacitors are recom-
mended because of their temperature performance. X7R-
type capacitors change capacitance by 15% over their
operating temperature range and are the most stable type
of ceramic capacitors. Z5U and Y5V dielectric capacitors
change value by as much as 50% and 60% respectively
over their operating temperature ranges. To use a ceramic
chip capacitor with Y5V dielectric, the value must be much
higher than a X7R ceramic capacitor to ensure the same
minimum capacitance over the equivalent operating
temperature range.
No-Load Stability
The MIC5238 will remain stable and in regulation with no
load unlike many other voltage regulators. This is especially
important in CMOS RAM keep-alive applications.
Thermal Considerations
The MIC5238 is designed to provide 150mA of continuous
current in a very small package. Maximum power
dissipation can be calculated based on the output current
and the voltage drop across the part. To determine the
maximum power dissipation of the package, use the
junction-to-ambient thermal resistance of the device and
the following basic equation:
Micrel, Inc.
November 2008
P
D(MAX)
=
T
J(max)
θ
JA
-
T
A
9
T
125°C, and T
layout dependent; Table 1 shows the junction-to-ambient
thermal resistance for the MIC5238.
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 MIC5238-1.0BM5 at 50°C
with a minimum footprint layout, the maximum input voltage
for a set output current can be determined as follows.
The junction-to-ambient (θ
minimum footprint is 235°C/W, from Table 1. It is important
that the maximum power dissipation not be exceeded to
ensure proper operation. With very high input-to-output
voltage differentials, the output current is limited by the total
power dissipation. Total power dissipation is calculated
using the following equation:
Since the bias supply draws only 18µA, that contribution
can be ignored for this calculation.
If we know the maximum load current, we can solve for the
maximum input voltage using the maximum power dissipa-
tion calculated for a 50°C ambient, 319mV.
Ground pin current is estimated using the typical
characteristics of the device.
For higher current outputs only a lower input voltage will
work for higher ambient temperatures.
Assuming a lower output current of 20mA, the maximum
input voltage can be recalculated:
Maximum input voltage for a 20mA load current at 50°C
ambient temperature is 16.8V. Since the device has a 6V
rating, it will operate over the whole input range.
J(MAX)
is the maximum junction temperature of the die,
P
P
P
P
319mW = (V
469mW = V
V
319mW = (V
339mW = V
V
P
D
D(MAX)
D
D(MAX)
IN
IN
SOT-23-5
Table 1. SOT-23-5 Thermal Resistance
D(MAX)
Package
= (V
= (V
= 3.07V
= 16.8V
A
D(MAX)
is the ambient operating temperature. θ
= 319mW
= (V
IN
IN
=
– V
– V
125
IN
IN
IN
235
for P
IN
IN
OUT
OUT
– V
(152.8mA)
x 20.2mA
°
– 1V) 150mA + V
– 1V) 20mA + V
C
) I
) I
°
OUT
C/W
-
D
OUT
OUT
50
JA
) I
and solving for the operating
°
) thermal resistance for the
+ V
+ V
OUT
C
IN
IN
+ V
I
θ
Minimum Footprint
GND
x I
JA
IN
GND
IN
Recommended
x I
IN
235°C/W
x 0.2mA
+ V
GND
x 2.8mA
M9999-111209
BIAS
MIC5238
x I
BIAS
JA
is