MIC5237
500mA Low-Dropout Regulator
Super βeta PNP is a registered trademark of Micrel, Inc.
Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (
408
) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
September 2007
M9999-090607-C
General Description
The MIC5237 is a general-purpose low-dropout regulator
capable of 500mA output current with better than 3%
output voltage accuracy. Using Micrel’s proprietary Super
ßeta PNP
®
process with a PNP pass element, these
regulators feature less than 300mV dropout voltage and
typically 8mA ground current at full load.
Designed for applications that require moderate current
over a broad input voltage range, including hand-held and
battery-powered devices, the MIC5237 is intended for
applications that can tolerate moderate voltage drop at
higher current.
Key features include low ground current to help prolong
battery life, reversed-battery protection, current limiting,
over-temperature shutdown, and thermally efficient
packaging. The MIC5237 is available in fixed output
voltages only.
For space-critical applications and improved performance,
see the MIC5209 and MIC5219. For output current
requirements up to 750m A, see the MIC2937.
Data sheets and support documentation can be found on
Micrel’s web site at: www.micrel.com.
Features
• Guaranteed 500mA output over the full operating
temperature range
• Low 300mV typical dropout voltage at full load
• Extremely tight load and line regulation
• Current and thermal limiting
• Reversed-battery protection
• TO-220 and TO-263 packages
• Low temperature coefficient
• No-load stability
• Low-noise output
Applications
• Portable and laptop computers
• Desktop computer
• Battery chargers
• SMPS post-regulator/dc-to-dc modules
• Consumer and personal electronics
___________________________________________________________________________________________________________
Typical Application
Micrel, Inc. MIC5237
September 2007
2 M9999-090607-C
Ordering Information
Part Number
Standard Pb-Free
Voltage Junction Temp. Range Package
MIC5237-2.5BU MIC5237-2.5YU 2.5V –40° to +125°C TO-263-3
MIC5237-3.3BU MIC5237-3.3YU 3.3V –40° to +125°C TO-263-3
MIC5237-5.0BT MIC5237-5.0YT 5.0V –40° to +125°C TO-220-3
MIC5237-5.0BU MIC5237-5.0YU 5.0V –40° to +125°C TO-263-3
Pin Configur ation
TO-220-3 (T) TO-263-3 (U)
Pin Description
Pin Number Pin Name Pin Function
1 IN Supply Input.
2, TAB GND Ground: TO-220 and TO-263 pin 2 and TAB are internally connected.
3 OUT Regulator Output.
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September 2007
3 M9999-090607-C
Absolute Maximum Ratings(1)
Supply Voltage (V
IN
)..........................................–20 to +20V
Power Dissipation (P
D
)..............................Internally Limited
Lead Temperature (soldering, 5 sec.)........................ 260°C
Operating Ratings
Supply Voltage (V
IN
)...................................... +2.5V to +16V
Junction Temperature (T
J
) ........................ –40°C to +125°C
Package Thermal Resistance
TO-220 (θ
JA
).......................................................55°C/W
TO-220 (θ
JC
) ........................................................3°C/W
TO-263 (θ
JC
) ........................................................3°C/W
Electrical Characteristics
V
IN
= V
OUT
+ 1.0V; C
OUT
= 4.7µF; I
OUT
= 100µA; T
J
= 25°C, bold values indicate –40°C< T
J
< +125°C, unless noted.
Symbol Parameter Condition Min Typ Max Units
V
OUT
Output Voltage Accuracy variation from nominal V
OUT
–3
–5
3
5
%
%
∆V
OUT
/∆T Output Voltage
Temperature Coefficient
Note 2 40 ppm/°C
∆V
OUT
/V
OUT
Line Regulation V
IN
= V
OUT
+ 1V to 16V
0.015
0.05
0.1
%/V
%/V
∆V
OUT
/V
OUT
Load Regulation I
OUT
= 100µA to 500mA, Note 3 0.05
0.5
0.7
%
%
I
OUT
= 100µA 10 70
90
mV
mV
I
OUT
= 50mA 115 190
280
mV
mV
I
OUT
= 150mA 165 350
450
mV
mV
V
IN
– V
OUT
Dropout Voltage, Note 4
I
OUT
= 500mA 300 600
700
mV
mV
I
OUT
= 100µA 80 130
170
µA
µA
I
OUT
= 50mA 350 650
900
µA
µA
I
OUT
= 150mA 1.8 2.5
3.0
mA
mA
I
GND
Ground Pin Current, Note 5
I
OUT
= 500mA 8 15
20
mA
mA
PSRR Ripple Rejection f = 120Hz 75 dB
I
LIMIT
Current Limit V
OUT
= 0V 700 900
1000
mA
mA
∆V
OUT
/∆P
D
Thermal Regulation Note 6 0.05 %/W
e
no
Output Noise V
OUT
= 5.0V, I
OUT
= 50Ma, C
OUT
= 2.2µF 500 nV/√Hz
Micrel, Inc. MIC5237
September 2007
4 M9999-090607-C
Notes:
1. Absolute maximum ratings indicate limits beyond which damage to the component may occur. Electrical specifications do not apply when operating
the device outside of its operating ratings. The maximum allowable power dissipation is a function of the maximum junction temperature, T
J(max)
, the
junction-to-ambient thermal resistance, θ
JA
, and the ambient temperature, T
A
. The maximum allowable power dissipation at any ambient temperature
is calculated using: P
D(max)
= (T
J(max)
–T
A
) ÷ θ
JA
. Exceeding the maximum allowable power dissipation will result in excessive die temperature, and the
regulator will go into thermal shutdown. See the “Thermal Considerations” section for details.
2. Output voltage temperature coefficient is defined as the worst case voltage change divided by the total temperature range.
3. Regulation is measured at constant junction temperature using low duty cycle pulse testing. Parts are tested for load regulation in the load range from
100µA to 500mA. Changes in output voltage due to heating effects are covered by the thermal regulation specification.
4. Dropout voltage is defined as the input to output differential at which the output voltage drops 2% below its nominal value measured at 1Vdifferential.
5. Ground pin current is the regulator quiescent current plus pass transistor base current. The total current drawn from the supply is the sum of the load
current plus the ground pin current.
6. Thermal regulation is defined as the change in output voltage at a time “t” after a change in power dissipation is applied, excluding load or line
regulation effects. Specifications are for a 500mA load pulse at V
IN
= 16V for t = 10ms.
Micrel, Inc. MIC5237
September 2007
5 M9999-090607-C
Typical Characteristics
-100
-80
-60
-40
-20
0
1E+11E+21E+31E+41E+51E+6 1E+7
)Bd(RRSP
FREQUENCY (Hz)
Power Suppl
y
Rejection Ratio
I
OUT
= 100µA
C
OUT
= 1µF
V
IN
= 6V
V
OUT
= 5V
10 100 1k 10k 100k 1M 10M -100
-80
-60
-40
-20
0
1E+11E+21E+31E+41E+51E+61E+7
)Bd(RRSP
FREQUENCY (Hz)
Power Suppl
y
Rejection Ratio
I
OUT
= 1mA
C
OUT
= 1µF
V
IN
= 6V
V
OUT
= 5V
10 100 1k 10k 100k 1M 10M -100
-80
-60
-40
-20
0
1E+11E+21E+31E+41E+51E+61E+
7
)Bd(RRSP
FREQUENCY (Hz)
Power Suppl
y
Rejection Ratio
I
OUT
= 100mA
C
OUT
= 1µF
V
IN
= 6V
V
OUT
= 5V
10 100 1k 10k 100k 1M 10M
0
10
20
30
40
50
60
0 0.1 0.2 0.3 0.4
)Bd(NOITCEJERELPPIR
VOLTAGE DROP (V)
Power Supply Ripple Rejection
vs. Voltage Drop
I
OUT
= 100mA
10mA
1mA
C
OUT
= 1µF
0.0001
0.001
0.01
0.1
1
10
1E+1 1E+2 1E+3 1E+4 1E+51E+6 1E+7
(ESIONµ/V )zH
FREQUENCY (Hz)
Noise Performance
10mA
1mA
100mA
10 100 1k 10k 100k 1M 10M
V
OUT
= 5V
C
OUT
= 10µF
electrolytic
Micrel, Inc. MIC5237
September 2007
6 M9999-090607-C
Block Diagram
Fixed Regulator
Micrel, Inc. MIC5237
September 2007
7 M9999-090607-C
Application Information
The MIC5237 is intended for general-purpose use and can
be implemented in a wide variety of applications where
500mA of output current is needed. It is available in several
voltage options for ease of use. For voltage options that are
not available on the MIC5237, consult the MIC5209 for a
500mA adjustable LDO regulator, or the MIC5219 for
applications that require only short-duration peak output
current.
Input Capacitor
A 1µF 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 Capacitor
An output capacitor is required between OUT and GND to
prevent oscillation. 1µF minimum is recommended for
standard applications. Larger values improve the
regulator’s transient response. The output capacitor value
may be increased without limit.
The output capacitor should have an ESR (equivalent
series resistance) of about 5Ω or less and a resonant
frequency above 1MHz. Ultra low-ESR capacitors can
cause low-amplitude oscillations and/or under-damped
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
0.47µF for current below 10mA or 0.33µF for currents
below 1mA.
For 2.5V applications a 22µF output capacitor is recom-
mended to reduce startup voltage overshoot.
No-Load Stability
The MIC5237 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.
Thermal Considerations
Proper thermal design can be accomplished with some
basic design criteria and some simple equations. The
following information is required to implement a regulator
design.
V
IN
= input voltage
V
OUT
= output voltage
I
OUT
= output current
T
A
= ambient operating temperature
I
GND
= ground current
The regulator ground current, I
GND
, can be measured or
read from the data sheet. Assuming the worst case
scenario is good design procedure, and the corresponding
ground current number can be obtained from the data
sheet. First, calculate the power dissipation of the device.
This example uses the MIC5237-5.0BT, a 13V input, and
500mA output current, which results in 20mA of ground
current, worst case. The power dissipation is the sum of
two power calculations: voltage drop × output current and
input voltage × ground current.
P
D
= [(V
IN
– V
OUT
) × I
OUT
] + (V
IN
× I
GND
)
P
D
= [(13V – 5V) × 500mA] + (13V × 20mA)
P
D
= 4.260W
From this number, the heat sink thermal resistance is
determined using the regulator’s maximum operating
junction temperature (T
J(max)
) and the ambient temperature
(T
A
) along with the power dissipation number already
calculated.
T
J(MAX)
= 125°C
θ
JC
= junction-to-case thermal resistance
θ
CS
= case-to-sink thermal resistance
θ
JA
= junction-to-ambient thermal resistance
θ
SA
= sink-to-ambient thermal resistance
To determine the heat sink thermal resistance, the junction-
to-case thermal resistance of the device must be used
along with the case-to-heat sink thermal resistance. These
numbers show the heat-sink thermal resistance required at
T
A
=25°C that does not exceed the maximum operating
junction temperature.
D
AJ(max)
JA P
T - T
θ=
θ
SA
=
θ
JA
- θ
JC
θ
CS
is approximately 1°C/W and θ
JC
for the TO-220 is
3°C/W in this example.
4.260W
25 - 125
θ
JA
=
θ
JA
= 23.5°C/W
θ
SA
= 23.5°C/W – (3°C/W + 1°C/W)
θ
SA
= 19.5°C/W
Therefore, a heat sink with a thermal resistance of
19.5°C/W will allow the part to operate safely and it will not
exceed the maximum junction temperature of the device.
The heat sink can be reduced by limiting power dissipation,
by reducing the input voltage or output current. Either the
TO-220 or TO-263 package can operate reliably at 2W of
power dissipation without a heat sink. Above 2W, a heat
sink is recommended.
For a full discussion on voltage regulator thermal effects,
please refer to “Thermal Management” in Micrel’s
Designing with Low-Dropout Voltage Regulators handbook.
Micrel, Inc. MIC5237
September 2007
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Package Information
3-Pin TO-220 (T)
3-Pin TO-263 (U)
Micrel, Inc. MIC5237
September 2007
9 M9999-090607-C
MICREL, INC. 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA
TEL +1 (408) 944-0800 FAX +1 (408) 474-1000 WEB http://www.micrel.com
The information furnished by Micrel in this data sheet is believed to be accurate and reliable. However, no responsibility is assumed by Micrel for its
use. Micrel reserves the right to change circuitry and specifications at any time without notification to the customer.
Micrel Products are not designed or authorized for use as components in life support appliances, devices or systems where malfunction of a product
can reasonably be expected to result in personal injury. Life support devices or systems are devices or systems that (a) are intended for surgical implant
into the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significant injury to the user. A
Purchaser’s use or sale of Micrel Products for use in life support appliances, devices or systems is a Purchaser’s own risk and Purchaser agrees to fully
indemnify Micrel for any damages resulting from such use or sale.
© 2000 Micrel, Incorporated.
