MIC37252
2.5A, Low Voltage µCap LDO Regulator
SuperSwitcher and Super ßeta PNP are trademarks 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
February 2006
M9999-021606
(408) 955-1690
General Description
The Micrel MIC37252 is a 2.5A low-dropout linear voltage
regulator that provides a low voltage, high current output
with a minimum of external components. It offers high
precision, low dropout and low ground current.
The MIC37252 operates from an input voltage of 3.0V
to6.0V. It is designed to drive digital circuits requiring low
voltage at high currents (i.e., PLDs, DSP, microcontroller,
etc.). It is available in an adjustable output voltage capable
of 1.24V to 5.5V.
Features of the MIC37252 LDO include thermal and
current limit protection, and reverse current and reverse
battery protection.
Junction temperature range of the MIC37252 is from
–40°C to +125°C.
For higher currents see the MIC3730x family of LDOs.
Features
• 2.5A minimum guaranteed output current
• Ideal for 3.3V to 1.8V conversion
• Stable with ceramic or tantalum capacitor
• ±2.0% initial output tolerance
• Dropout voltage = 550mV @ 2.5A
• Excellent line and load regulation specifications
• Logic controlled shutdown
• Thermal shutdown and current limit protection
• Reverse-leakage protection
• S-Pak and TO-263 packages
Applications
• LDO linear regulator for low-voltage digital IC
• PC add-in cards
• High efficiency linear power supplies
• SMPS post regulator
• Battery charger
____________________________________________________________________________________________________________
Typical Application
Adjustable Regulator
Micrel, Inc. MIC37252
February 2006
2 M9999-021606
(408) 955-1690
Ordering Information
Part Number
Standard RoHS Compliant**
Output
Current Voltage* Junction
Temperature Range Package
MIC37252BR MIC37252WR 2.5A Adj. –40° to +125°C S-Pak-5
MIC37252BU MIC37252WU 2.5A Adj. –40° to +125°C TO-263-5
*For other voltages, please contact Micrel Marketing.
**RoHS compliant with “high melting solder” exemption.
Pin Configur ation
S-PAK5 (R)
TO-263 (U)
Pin Description
Pin Number Pin Name Pin Function
1 EN
Enable (Input): CMOS compatible input. Logic high = enable, logic low =
shutdown.
2 VIN Input voltage which supplies current to the output power device.
3 GND Ground (TAB is connected to ground on S-Pak).
4 VOUT Regulator Output.
5 ADJ Adjustable regulator feedback input. Connect to resistor voltage divider.
Micrel, Inc. MIC37252
February 2006
3 M9999-021606
(408) 955-1690
Absolute Maximum Ratings(1)
Supply Voltage (V
IN
)......................................................6.5V
Enable Input Voltage (V
EN
)............................................6.5V
Power Dissipation .....................................Internally Limited
Junction Temperature .........................–40°C ≤ T
J
≤ +125°C
Storage Temperature ..........................–65°C ≤ T
J
≤ +150°C
Lead Temperature (soldering, 5sec.)......................... 260°C
EDS
(3)
Operating Ratings(2)
Supply voltage (V
IN
) ......................................... 3.0V to 6.0V
Enable Input Voltage (V
EN
).................................. 0V to 6.0V
Junction Temperature Range .............–40°C ≤ T
J
≤ +125°C
Maximum Power Dissipation
(4)
Package Thermal Resistance
S-Pak (θ
JC
) ..........................................................2°C/W
TO-263-5 (θ
JC
).....................................................2°C/W
Electrical Characteristics(5)
T
A
= 25°C with V
IN
= V
OUT
+ 1V; V
EN
= V
IN
; I
L
= 10mA, bold values indicate –40°C< T
J
< +125°C, unless otherwise noted.
Parameter Condition Min Typ Max Units
I
L
= 10mA -2 +2 % Output Voltage Accuracy
10mA < I
OUT
< I
L(max)
, V
OUT
+ 1 ≤ V
IN
≤ 6V -3 +3
%
Output Voltage Line Regulation V
IN
= V
OUT
+ 1.0V to 6.0V, I
L
= 10mA 0.02 0.5 %
Output Voltage Load Regulation I
L
= 10mA to 2.5A 0.2 1 %
I
L
= 1.5A 400 500 mV
V
IN
– V
OUT
; Dropout Voltage,
Note 6 I
L
= 2.5A 550 1000 mV
Ground Pin Current, Note 7 I
L
= 2.5A 40 60 mA
Ground Pin Current in Shutdown V
IL
≤ 0.5V, V
IN
= V
OUT
+ 1V 1.0 µA
Current Limit V
OUT
= 0; V
IN
= 3.3V 3 A
Start-up Time V
EN
= V
IN
, I
OUT
= 10mA, C
OUT
= 47µF 150 250 µs
Enable Input
Regulator enable 2.25 V Enable Input Threshold
Regulator shutdown 0.8 V
V
IL
≤ 0.8V (Regulator shutdown) 2
4
µA
µA
Enable Pin Input Current
V
IH
≥ 2.25V (Regulator enable) 1 10 30 µA
Reference Voltage 1.215
1.202
1.240 1.265
1.277
V
V
Adjust Pin Bias Current 40 80
120
nA
nA
Notes:
1. Exceeding the absolute maximum rating may damage the device.
2. The device is not guaranteed to function outside its operating rating.
3. Device is ESD sensitive. Handling precautions recommended.
4. P
D(max)
= T
J(max)
– T
A
) / θ
JA
, where θ
JA
, depends upon the printed circuit layout. See “Applications Information.”
5. Specification for packaged product only
6. V
DO
= V
IN
– V
OUT
when V
OUT
decreased to 98% of its nominal output voltage with V
IN
= V
OUT
+ 1V. For output voltages below 2V, dropout voltage
specification does not apply due to a minimum input operating voltage of 3V
7. I
GND
is the quiescent current. I
IN
= I
GND
+ I
OUT
.
Micrel, Inc. MIC37252
February 2006
4 M9999-021606
(408) 955-1690
Typical Characteristics
0
10
20
30
40
50
60
70
)Bd(SSRP
FREQUENCY (Hz)
PSRR
100mA
1A
2.5A
10
1100 1k 10k 100k 1M
C
OUT
= 100µF Ceramic
V
IN
= 3.3V
V
OUT
= 1.8V
0
10
20
30
40
50
60
70
)Bd(RRSP
FREQUENCY (Hz)
PSRR
100mA
2.5A
1A
1 10 100 1k 10k 100k 1M
C
OUT
= 47µF
V
IN
= 3.3V
V
OUT
= 1.8V
0
100
200
300
400
500
600
00.511.522.5
)Vm(EGATLOVTUOPORD
OUTPUT CURRENT (A)
Dropout Voltage
V
OUT
= 3.3V
0
100
200
300
400
500
600
-40 -20 0 20 40 60 80 100 120
)Vm(EGATLOVTUOPORD
TEMPERATURE (°C)
Dropout
vs. Temperature
3.3V
OUT
2.5A load
1.75
1.76
1.77
1.78
1.79
1.80
1.81
1.82
1.83
1.84
1.85
-40 -20 0 20 40 60 80 100 120
)V(EGATLOVTUPTUO
TEMPERATURE (°C)
Output Voltage
vs. Temperature
0
2
4
6
8
10
12
14
16
18
-40 -20 0 20 40 60 80 100 120
(TNERRUCELBANEµ)A
TEMPERATURE (°C)
Enable Pin Current
vs. Temperature
100mA Load
0
0.5
1
1.5
2
2.5
3
3.5
4
-40 -20 0 20 40 60 80 100 120
)A(TNERRUCTIUCRICTROHS
TEMPERATURE T
J
(°C)
Short Circuit Current
vs. Temperature
V
OUT
= 0V
V
IN
= 4.3V
0
5
10
15
20
25
30
35
40
45
50
012345
)Am(TNERRUCDNUORG
SUPPLY VOLTAGE (V)
Ground Current
vs. Supply Voltage
0.5A
1.5A
2.5A
0
5
10
15
20
25
30
35
40
45
50
-40 -20 0 20 40 60 80 100 120
)Am(TNERRUCDNUORG
TEMPERATURE (°C)
Ground Current
vs. Temperature
1A Load
10mA Load
2.5A Load
0
5
10
15
20
25
30
35
40
45
50
00.511.522.5
)Am(TNERRUCDNUORG
OUTPUT CURRENT (A)
Ground Current
vs. Output Current
2.490
2.492
2.494
2.496
2.498
2.500
2.502
2.504
2.506
2.508
2.510
00.511.522.5
)V(EGATLOVTUPTUO
OUTPUT CURRENT (A)
Output Voltage
vs. Load Current
2.5V
OUT
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
01234
)V(EGATLOVTUPTUO
SUPPLY VOLTAGE (V)
Dropout Characteristics
0.5A
1.5A
2.5A
Micrel, Inc. MIC37252
February 2006
5 M9999-021606
(408) 955-1690
Functional Characteristics
TIME (400µs/div.)
TNERRUCTUPTUO
).vid/A1(
EGATLOVTUPTUO
).vid/Vm001(
VIN = 3.3V
VOUT = 1.8V
C
OUT
= 47µF
LoadTransient Response
10mA
2A
TIME (400µs/div.)
TNERRUCTUPTUO
).vid/A1(
EGATLOVTUPTUO
).vid/Vm002(
VIN = 3.3V
VOUT = 1.8V
C
OUT
= 47µF
LoadTransient Response
10mA
2.5A
LineTransient Response
TIME (100µs/div.)
EGATLOVTUPTUO
).vid/Vm02(
EGATLOVTUPNI
).vid/V2(
5V
3.3V
Micrel, Inc. MIC37252
February 2006
6 M9999-021606
(408) 955-1690
Application Information
The MIC37252 is a high-performance low-dropout
voltage regulator suitable for moderate to high-current
regulator applications. Its 550mV dropout voltage at full
load makes it especially valuable in battery-powered
systems and as high-efficiency noise filters in post-
regulator applications. Unlike older NPN-pass transistor
designs, where the minimum dropout voltage is limited
by the base-to-emitter voltage drop and collector-to-
emitter saturation voltage, dropout performance of the
PNP output of these devices is limited only by the low
V
CE
saturation voltage.
A trade off for the low dropout voltage is a varying base
drive requirement. Micrel’s Super βeta PNP
®
process
reduces this drive requirement to only 2% to 5% of the
load current.
The MIC37252 regulator is fully protected from damage
due to fault conditions. Current limiting is provided. This
limiting is linear; output current during overload
conditions is constant. Thermal shutdown disables the
device when the die temperature exceeds the maximum
safe operating temperature. Transient protection allows
device (and load) survival even when the input voltage
spikes above and below nominal. The output structure of
these regulators allows voltages in excess of the desired
output voltage to be applied without reverse current flow.
Thermal Design
Linear regulators are simple to use. The most
complicated design parameters to consider are thermal
characteristics. Thermal design requires the following
application-specific parameters:
• Maximum ambient temperature (T
A
)
• Output current (I
OUT
)
• Output voltage (V
OUT
)
• Input voltage (V
IN
)
• Ground current (I
GND
)
First, calculate the power dissipation of the regulator
from these numbers and the device parameters from this
datasheet.
P
D
= (V
IN
– V
OUT
) I
OUT
+ V
IN
I
GND
Where the ground current is approximated by using
numbers from the “Electrical Characteristics” or “Typical
Characteristics.” Then the heat sink thermal resistance is
determined with this formula:
θ
SA
= ((T
J(MAX)
– T
A
)/ P
D
) – (θ
JC
+ θ
CS
)
Where T
J(MAX)
≤ 125°C and θ
CS
is between 0°C and
2°C/W. The heat sink may be significantly reduced in
applications where the minimum input voltage is known
and is large compared with the dropout voltage. Use a
series input resistor to drop excessive voltage and
distribute the heat between this resistor and the
regulator. The low dropout properties of Micrel Super
βeta PNP
®
regulators allow significant reductions in
regulator power dissipation and the associated heat sink
without compromising performance. When this technique
is employed, a capacitor of at least 1.0µF is needed
directly between the input and regulator ground. Refer to
Application Note 9 for further details and examples on
thermal design and heat sink applications.
Output Capacitor
The MIC37252 requires an output capacitor for stable
operation. As a µCap LDO, the MIC37252 can operate
with ceramic output capacitors as long as the amount of
capacitance is 47µF or greater. For values of output
capacitance lower than 47µF, the recommended ESR
range is 200mΩ to 2Ω. The minimum value of output
capacitance recommended for theMIC37252 is 10µF.
For 47µF or greater the ESR range recommended is
less than1Ω. Ultra-low ESR, ceramic capacitors are
recommended for output capacitance of 47µF or greater
to help improve transient response and noise reduction
at high frequency. X7R/X5R dielectric-type ceramic
capacitors are recommended 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 withY5V dielectric, the value must be
much higher than an X7Rceramic capacitor to ensure
the same minimum capacitance over the equivalent
operating temperature range. The MIC37252 has
excellent transient response to variations in input voltage
and load current. The device has been designed to
respond quickly to load current variations and input
voltage variations. Large output capacitors are not
required to obtain this performance. A standard 47µF
output capacitor is all that is required. Larger values help
to improve performance even further.
Input Capacitor
An input capacitor of 1.0µF or greater is recommended
when the device is more than 4 inches away from the
bulk supply capacitance, or when the supply is a battery.
Small, surface-mount chip capacitors can be used for
the bypassing. The capacitor should be place within 1” of
the device for optimal performance. Larger values will
help to improve ripple rejection by bypassing the input to
the regulator, further improving the integrity of the output
voltage.
Micrel, Inc. MIC37252
February 2006
7 M9999-021606
(408) 955-1690
Transient Response and 5V to 3.3V or 3.3V to
1.8VConversions
The MIC37252 has excellent transient response to
variations in input voltage and load current. The device
has been designed to respond quickly to load current
variations and input voltage variations. Large output
capacitors are not required to obtain this performance.
A standard 10µF output capacitor, preferably tantalum,
is all that is required. Larger values help to improve
performance even further.
By virtue of its low dropout voltage, this device does not
saturate into dropout as readily as similar NPN-based
designs. When converting from 3.3V to 1.8V, the NPN-
based regulators are already operating in dropout, with
typical dropout requirements of 2V or greater. To convert
down to1.8V without operating in dropout, NPN-based
regulators require an input voltage of 3.8V at the very
least. The MIC37252 regulator will provide excellent
performance with an input as low as 3.0V. This gives the
PNP-based regulators a distinct advantage over older
NPN-based linear regulators.
Minimum Load Current
The MIC37252 regulator is specified between finite
loads. If the output current is too small, leakage currents
dominate and the output voltage rises. A 10mA minimum
load current is necessary for proper operation.
Enable Input
The MIC37252 also features an enable input for on/off
control of the device. Its shutdown state draws “zero”
current (only microamperes of leakage). The enable
input is TTL/CMOS compatible for simple logic interface,
but can be connected to up to VIN. When enabled, it
draws approximately 15µA.
Adjustable Regulator Design
Figure 2. Adjustable Regu lato r with Resistors
The MIC37252 allows programming of the output voltage
anywhere between 1.24V and the 5.5V maximum
operating rating of the family. Two resistors are used.
Resistors values are recommended to be less than 10kΩ
in value to improve stability. The resistor values can be
sized to draw the mini-mum load current for this device.
The resistor values are calculated by:
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛−= 1
1.240
V
R2R1
OUT
Where V
OUT
is the desired output voltage. Figure 2
shows component definition. Applications with widely
varying load currents may scale the resistors to draw the
minimum load current required for proper operation (see
above).
Micrel, Inc. MIC37252
February 2006
8 M9999-021606
(408) 955-1690
Package Information
5-Pin S-PAK (R)
1θ
θ1
3θ
4θ
1θ
2θ
3θ
4θ
2θ
1θ
5-Pin TO-263 (U)
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.
© 2002 Micrel, Incorporated.
