September 2004
1
M9999-091604
MIC37100/37101/37102
Micrel
MIC37100/37101/37102
1A Low-Voltage
Cap LDO Regulator
General Description
The MIC37100, MIC37101, and MIC37102 are 1A low-
dropout, linear voltage regulators that provide low-voltage,
high-current output from an extremely small package. Utiliz-
ing Micrel's proprietary Super
eta PNPTM pass element, the
MIC37100/01/02 offers extremely low dropout (typically
280mV at 1A) and low ground current (typically 11mA at 1A).
The MIC37100 is a fixed output regulator offered in the
SOT-223 package. The MIC37101 and MIC37102 are fixed
and adjustable regulators, respectively, in a thermally en-
hanced power 8-lead SOIC (small outline package) and the
SOT-223 package. The MIC37102 is also available in the S-
PAK power package, for applications that require higher
power dissipation or higher operating ambient temperatures.
The MIC37100/01/02 is ideal for PC add-in cards that need
to convert from standard 5V to 3.3V, 3.3V to 2.5V or 2.5V to
1.8V or lower. A guaranteed maximum dropout voltage of
500mV over all operating conditions allows the
MIC37100/01/02 to provide 2.5V from a supply as low as 3V
and 1.8V from a supply as low as 2.3V.
The MIC37100/01/02 is fully protected with overcurrent lim-
iting and thermal shutdown. Fixed output voltages of 1.5V,
1.65V, 1.8V, 2.5V and 3.3V are available on MIC37100/01
with adjustable output voltages to 1.24V on MIC37102.
For other voltages, contact Micrel.
All support documentation can be found on Micrel's web
site at www.micrel.com.
Typical Applications
Features
Fixed and adjustable output voltages to 1.24V
Cap Regulator, 10
F ceramic output capacitor
stable
280mV typical dropout at 1A
Ideal for 3.0V to 2.5V conversion
Ideal for 2.5V to 1.8V, 1.65V or 1.5V conversion
1A minimum guaranteed output current
1% initial accuracy
Low ground current
Current limiting and thermal shutdown
Reversed-leakage protection
Fast transient response
Low-profile SOT-223 package
Power SO-8 package
S-PAK package (MIC37102 only)
Applications
LDO linear regulator for PC add-in cards
PowerPCTM power supplies
High-efficiency linear power supplies
SMPS post regulator
Multimedia and PC processor supplies
Battery chargers
Low-voltage microcontrollers and digital logic
Super
eta PNP is a registered trademark of Micrel, Inc.
PowerPC is a trademark of IBM Corporation.
Micrel, Inc. 1849 Fortune Drive San Jose, CA 95131 USA tel + 1 (408) 944-0800 fax + 1 (408) 474-1000 http://www.micrel.com
IN
2.5V
V
IN
3.3V
10
F
ceramic
OUT
GND
MIC37100
2.5V/1A Regulator
0
50
100
150
200
250
300
350
0
0.25
0.5
0.75
1
DROPOUT (mV)
OUTPUT CURRENT (A)
Dropout
vs. Output Current
2.5V
OUT
3.3V
OUT
MIC37100/37101/37102
Micrel
M9999-091604
2
September 2004
Ordering Information
Part Number
Voltage
Junction Temp. Range
Package
MIC37100-1.5BS
1.5V
40
C to +125
C
SOT-223
MIC37100-1.65BS
1.65V
40
C to +125
C
SOT-223
MIC37100-1.8BS
1.8V
40
C to +125
C
SOT-223
MIC37100-2.5BS
2.5V
40
C to +125
C
SOT-223
MIC37100-3.3BS
3.3V
40
C to +125
C
SOT-223
MIC37101-1.5BM
1.5V
40
C to +125
C
SOIC-8
MIC37101-1.65BM
1.65V
40
C to +125
C
SOIC-8
MIC37101-1.8BM
1.8V
40
C to +125
C
SOIC-8
MIC37101-2.5BM
2.5V
40
C to +125
C
SOIC-8
MIC37101-3.3BM
3.3V
40
C to +125
C
SOIC-8
MIC37102BM
Adj.
40
C to +125
C
SOIC-8
MIC37101-1.5YM
1.5V
40
C to +125
C
SOIC-8 Lead Free
MIC37101-1.65YM
1.65V
40
C to +125
C
SOIC-8 Lead Free
MIC37101-1.8YM
1.8V
40
C to +125
C
SOIC-8 Lead Free
MIC37101-2.5YM
2.5V
40
C to +125
C
SOIC-8 Lead Free
MIC37101-3.3YM
3.3V
40
C to +125
C
SOIC-8 Lead Free
MIC37102YM
Adj.
40
C to +125
C
SOIC-8 Lead Free
MIC37102BR
Adj.
40
C to +125
C
S-PAK-5
Pin Configuration
IN
OUT
GND
1
3
2
TAB
GND
MIC37100-x.x (Fixed)
SOT-223 (S)
1
EN
IN
OUT
FLG
8
GND
GND
GND
GND
7
6
5
2
3
4
MIC37101-x.x (Fixed)
SOIC-8 (M)
1
EN
IN
OUT
ADJ
8
GND
GND
GND
GND
7
6
5
2
3
4
MIC37102 (Adjustable)
SOIC-8 (M)
TA
B
5
ADJ
4
OUT
3
GND
2
IN
1
EN
MIC37102 (Adjustable)
S-PAK-5 (R)
September 2004
3
M9999-091604
MIC37100/37101/37102
Micrel
Pin Description
Pin No.
Pin No.
Pin No.
Pin No.
Pin Name
Pin Function
MIC37100
MIC37101
MIC37102
MIC37102
SOT-223
SOIC-8
SOIC-8
S-PAK
1
1
1
1
EN
Enable (Input): CMOS-compatible control input. Logic high =
enable, logic low or open = shutdown.
2
2
2
IN
Supply (Input).
3
3
3
4
OUT
Regulator Output.
4
FLG
Flag (Output): Open-collector error flag output. Active low =
output under voltage.
4
5
ADJ
Adjustment Input: Feedback input. Connect to resistive
voltage-divider network.
2,
TAB
58
58
3,
TAB
GND
Ground.
MIC37100/37101/37102
Micrel
M9999-091604
4
September 2004
Electrical Characteristics
V
IN
= V
OUT
+ 1V; V
EN
= 2.25V; 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
10mA
1
1
%
10mA
I
OUT
1A, V
OUT
+ 1V
V
IN
6V
2
2
%
Line Regulation
I
OUT
= 10mA, V
OUT
+ 1V
V
IN
6V
0.06
0.5
%
Load Regulation
V
IN
= V
OUT
+ 1V, 10mA
I
OUT
1A,
0.2
1
%
V
OUT
/
T
Output Voltage Temp. Coefficient
(6)
40
ppm/
C
V
DO
Dropout Voltage
(6)
I
OUT
= 100mA,
V
OUT
= 1%
125
200
mV
I
OUT
= 500mA,
V
OUT
= 1%
210
350
mV
I
OUT
= 750mA,
V
OUT
= 1%
250
400
mV
I
OUT
= 1A,
V
OUT
= 1%
280
500
mV
I
GND
Ground Current
(7)
I
OUT
= 100mA, V
IN
= V
OUT
+ 1V
650
mA
I
OUT
= 500mA, V
IN
= V
OUT
+ 1V
3.5
mA
I
OUT
= 750mA, V
IN
= V
OUT
+ 1V
6.7
mA
I
OUT
= 1A, V
IN
= V
OUT
+ 1V
11
25
mA
I
OUT(lim)
Current Limit
V
OUT
= 0V, V
IN
= V
OUT
+ 1V
1.6
2.5
A
Enable Input
V
EN
Enable Input Voltage
logic low (off)
0.8
V
logic high (on)
2.25
V
I
EN
Enable Input Current
V
EN
= 2.25V
1
10
30
A
V
EN
= 0.8V
2
A
4
A
Flag Output
I
FLG(leak)
Output Leakage Current
V
OH
= 6V
0.01
1
A
2
A
V
FLG(do)
Output Low Voltage
V
IN
= 2.250V, I
OL
, = 250
A
210
500
mV
V
FLG
Low Threshold
% of V
OUT
93
%
High Threshold
% of V
OUT
99.2
%
Hysteresis
1
%
Absolute Maximum Ratings
(1)
Supply Voltage (V
IN
) ........................................ 0V to +6.5V
Enable Voltage (V
EN
) ................................................. +6.5V
Storage Temperature (T
S
) ....................... 65
C to +150
C
Lead Temperature (soldering, 5 sec.) ....................... 260
C
ESD ................................................................................(3)
Operating Ratings
(2)
Supply Voltage (V
IN
) .................................... +2.25V to +6V
Enable Voltage (V
EN
) .......................................... 0V to +6V
Maximum Power Dissipation (P
D(max)
) ........................... (4)
Junction Temperature (T
J
) ....................... 40
C to +125
C
Package Thermal Resistance
SOT-223
(
JC
) ..................................................... 15
C/W
SOIC-8
(
JC
) ....................................................... 20
C/W
S-PAK-5
(
JC
) ....................................................... 2
C/W
September 2004
5
M9999-091604
MIC37100/37101/37102
Micrel
Symbol
Parameter
Condition
Min
Typ
Max
Units
MIC37102 Only
Reference Voltage
1.228
1.240
1.252
V
1.215
1.265
V
Adjust Pin Bias Current
40
80
nA
120
nA
Notes:
1.
Exceeding the absolute maximum ratings may damage the device.
2.
The device is not guaranteed to function outside its operating rating.
3.
Devices are ESD sensitive. Handling precautions recommended.
4.
P
D
(max) = (T
J
(max) T
A
)
JA
, where
JA
depends upon the printed circuit layout. See
"
Applications Information" section.
5.
Output voltage temperature coefficient is
V
OUT
(worst case)
(T
J
(max) T
J
(min)) where T
J
(max) is +125
C and T
J
(min) is 40
C.
6.
V
DO
= V
IN
V
OUT
when V
OUT
decreases to 98% of its nominal output voltage with V
IN
= V
OUT
+ 1V. For output voltages below 2.25V, dropout
voltage is the input-to-output voltage differential with the minimum input voltage being 2.25V. Minimum input operating voltage is 2.25V.
7.
I
GND
is the quiescent current. I
IN
= I
GND
+ I
OUT
.
8.
V
EN
0.8V, V
IN
6V, and V
OUT
= 0V.
MIC37100/37101/37102
Micrel
M9999-091604
6
September 2004
Typical Characteristics
0
10
20
30
40
50
60
70
80
0.01
0.1
1
10
100
1000
PSRR (dB)
FREQUENCY (KHz)
Power Supply
Rejection Ratio
I
OUT
= 1000mA
C
OUT
= 10
F
C
IN
= 0
V
IN
= 5V
V
OUT
= 3.3V
0
10
20
30
40
50
60
70
80
0.01
0.1
1
10
100
1000
PSRR (dB)
FREQUENCY (KHz)
Power Supply
Rejection Ratio
I
OUT
= 1000mA
C
OUT
= 47
F
C
IN
= 0
V
IN
= 5V
V
OUT
= 3.3V
0
10
20
30
40
50
60
70
80
0.01
0.1
1
10
100
1000
PSRR (dB)
FREQUENCY (KHz)
Power Supply
Rejection Ratio
I
OUT
= 1000mA
C
OUT
= 10
F
C
IN
= 0
V
IN
= 3.3V
V
OUT
= 2.5V
0
10
20
30
40
50
60
70
80
0.01
0.1
1
10
100
1000
PSRR (dB)
FREQUENCY (KHz)
Power Supply
Rejection Ratio
I
OUT
= 1000mA
C
OUT
= 47
F
C
IN
= 0
V
IN
= 3.3V
V
OUT
= 2.5V
0
50
100
150
200
250
300
350
0
0.25
0.5
0.75
1
DROPOUT (mV)
OUTPUT CURRENT (A)
Dropout
vs. Output Current
2.5V
OUT
3.3V
OUT
0
50
100
150
200
250
300
350
400
450
-40 -20 0
20 40 60 80 100 120
DROPOUT (mV)
TEMPERATURE (
C)
Dropout
vs. Temperature
2.5VOUT
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.5
1.7
1.9
2.1
2.3
2.5
OUTPUT VOLTAGE (V)
INPUT VOLTAGE (V)
Dropout Characteristics
(1.5V)
10mA Load
1000mA Load
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
1.5
1.7
1.9
2.1
2.3
2.5
2.7
OUTPUT VOLTAGE (V)
INPUT VOLTAGE (V)
Dropout Characteristics
(1.8V)
10mA Load
1000mA Load
0
0.5
1.0
1.5
2.0
2.5
3.0
1.5
2
2.5
3
3.5
OUTPUT VOLTAGE (V)
INPUT VOLTAGE (V)
Dropout Characteristics
(2.5V)
10mA Load
1000mA Load
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
1.5
2
2.5
3
3.5
4
OUTPUT VOLTAGE (V)
INPUT VOLTAGE (V)
Dropout Characteristics
(3.3V)
10mA Load
1000mA Load
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0
1
2
3
4
5
6
GROUND CURRENT (mA)
INPUT VOLTAGE (V)
Ground Current
vs. Supply Voltage (1.5V)
10mA
100mA
0
2
4
6
8
10
12
0
0.25
0.5
0.75
1
GROUND CURRENT (mA)
OUTPUT CURRENT (A)
Ground Current
vs. Output Current
1.5V
OUT
3.3V
OUT
September 2004
7
M9999-091604
MIC37100/37101/37102
Micrel
0
2
4
6
8
10
12
14
16
18
0
1
2
3
4
5
6
GROUND CURRENT (mA)
INPUT VOLTAGE (V)
Ground Current
vs. Supply Voltage (1.5V)
1000mA
750mA
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0
1
2
3
4
5
6
GROUND CURRENT (mA)
INPUT VOLTAGE (V)
Ground Current
vs. Supply Voltage (1.8V)
100mA
10mA
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0
1
2
3
4
5
6
GROUND CURRENT (mA)
INPUT VOLTAGE (V)
Ground Current
vs. Supply Voltage (2.5V)
100mA
10mA
0
5
10
15
20
25
30
0
1
2
3
4
5
6
GROUND CURRENT (mA)
INPUT VOLTAGE (V)
Ground Current
vs. Supply Voltage (2.5V)
1000mA
750mA
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0
1
2
3
4
5
6
GROUND CURRENT (mA)
INPUT VOLTAGE (V)
Ground Current
vs. Supply Voltage (3.3V)
100mA
10mA
0
5
10
15
20
25
0
1
2
3
4
5
6
GROUND CURRENT (mA)
INPUT VOLTAGE (V)
Ground Current
vs. Supply Voltage (1.8V)
1000mA
750mA
0
5
10
15
20
25
30
0
1
2
3
4
5
6
GROUND CURRENT (mA)
INPUT VOLTAGE (V)
Ground Current
vs. Supply Voltage (3.3V)
750mA
500mA
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
-40 -20 0
20 40 60 80 100 120
GROUND CURRENT (mA)
TEMPERATURE (
C)
Ground Current
vs. Temperature
2.5VOUT
IOUT=10mA
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
-40 -20 0
20 40 60 80 100 120
GROUND CURRENT (mA)
TEMPERATURE (
C)
Ground Current
vs. Temperature
2.5VOUT
IOUT=500mA
0
2
4
6
8
10
12
14
16
-40 -20 0
20 40 60 80 100 120
GROUND CURRENT (mA)
TEMPERATURE (
C)
Ground Current
vs. Temperature
2.5VOUT
IOUT=1000mA
2.4
2.45
2.5
2.55
2.6
-40 -20 0
20 40 60 80 100 120
OUTPUT VOLTAGE (V)
TEMPERATURE (
C)
Output Voltage
vs. Temperature
2.5VOUT
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.25
3
3.75
4.5
5.25
6
SHORT CIRCUIT CURRENT (A)
SUPPLY VOLTAGE (V)
Short Circuit Current
vs. Supply Voltage
MIC37100/37101/37102
Micrel
M9999-091604
8
September 2004
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
-40 -20 0
20 40 60 80 100 120
SHORT CIRCUIT CURRENT (A)
TEMPERATURE (
C)
Short Circuit Current
vs. Temperature
2.5V
IN
0
0.2
0.4
0.6
0.8
1.0
0 0.5 1 1.5 2 2.5 3 3.5 4
FLAG VOLTAGE (V)
FLAG CURRENT (mA)
Flag Voltage
vs. Flag Current
3.3V
IN
5V
IN
2.5V
IN
0
50
100
150
200
250
300
350
-40 -20 0
20 40 60 80 100 120
FLAG LOW VOLTAGE (mV)
TEMPERATURE (
C)
Flag Low Voltage
vs. Temperature
Flag Current = 250
A
0
1
2
3
4
5
6
0.01
0.1
1
10
100 1000 10000
FLAG VOLTAGE (V)
RESISTANCE (k
)
Error Flag Pull-Up Resistor
Flag High (OK)
V
IN
=5V
Flag Low (FAULT)
0
1
2
3
4
5
6
7
8
9
-40 -20 0
20 40 60 80 100 120
ENABLE CURRENT (
A)
TEMPERATURE (
C)
Enable Current
vs. Temperature
2.5V
EN
September 2004
9
M9999-091604
MIC37100/37101/37102
Micrel
Functional Characteristics
Load Transient Response
TIME (400
s/div.)
LO
AD CURRENT
(500mA/div)
OUTPUT V
O
L
T
A
G
E
(200mV/div)
V
IN
= 3.3V
V
OUT
= 2.5V
C
OUT
= 10
F Ceramic
1000mA
100mA
Load Transient Response
TIME (400
s/div.)
LO
AD CURRENT
(500mA/div)
OUTPUT V
O
L
T
A
G
E
(200mV/div)
V
IN
= 3.3V
V
OUT
= 2.5V
C
OUT
= 10
F Ceramic
1000mA
10mA
Line Transient Response
TIME (400
s/div.)
OUTPUT V
O
L
T
A
G
E
(50mV/div)
INPUT V
O
L
T
A
G
E
(2V/div)
V
OUT
= 2.5V
C
OUT
= 10
F Ceramic
Load=100mA
5V
3.3V
Enable Transient Response
TIME (10
s/div.)
OUTPUT
V
O
L
T
A
G
E
(1V/div)
ENABLE V
O
L
T
A
G
E
(2V/div)
V
IN
= 3.3V
V
OUT
= 2.5V
I
OUT
= 100mA
C
OUT
= 10
F Ceramic
MIC37100/37101/37102
Micrel
M9999-091604
10
September 2004
Functional Diagrams
Ref.
Thermal
Shut-
down
1.240V
IN
OUT
MIC37100
MIC37100 Fixed Regulator Block Diagram
Ref.
Thermal
Shut-
down
1.240V
1.180V
EN
IN
FLAG
GND
OUT
MIC37101
MIC37101 Fixed Regulator with Flag and Enable Block Diagram
Ref.
Thermal
Shut-
down
1.240V
EN
IN
GND
OUT
ADJ
MIC37102
MIC37102 Adjustable Regulator Block Diagram
September 2004
11
M9999-091604
MIC37100/37101/37102
Micrel
Applications Information
The MIC37100/01/02 is a high-performance low-dropout
voltage regulator suitable for moderate to high-current volt-
age regulator applications. Its 500mV dropout voltage at full
load and overtemperature makes it especially valuable in
battery-powered systems and as high-efficiency noise filters
in post-regulator applications. Unlike older NPN-pass tran-
sistor 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
eta PNPTM process reduces
this drive requirement to only 2% of the load current.
The MIC37100/01/02 regulator is fully protected from dam-
age due to fault conditions. Linear current limiting is provided.
Output current during overload conditions is constant. Ther-
mal shutdown disables the device when the die temperature
exceeds the maximum safe operating temperature. The
output structure of these regulators allows voltages in excess
of the desired output voltage to be applied without reverse
current flow.
MIC37100-x.x
IN
OUT
GND
C
IN
C
OUT
V
IN
V
OUT
Figure 1. Capacitor Requirements
Output Capacitor
The MIC37100/01/02 requires an output capacitor to main-
tain stability and improve transient response. As a
Cap
LDO, the MIC37100/01/02 can operate with ceramic output
capacitors as long as the amount of capacitance is 10
F or
greater. For values of output capacitance lower than 10
F,
the recommended ESR range is 200m
to 2
. The minimum
value of output capacitance recommended for the MIC37100/
01/02 is 4.7
F.
For 10
F or greater the ESR range recommended is less than
1
. Ultra-low ESR ceramic capacitors are recommended for
output capacitance of 10
F or greater to help improve tran-
sient response and noise reduction at high frequency.
X7R/X5R dielectric-type ceramic capacitors are recom-
mended because of their temperature performance. X7R-
type capacitors change capacitance by 15% over their oper-
ating 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 capaci-
tor with Y5V dielectric, the value must be much higher than an
X7R ceramic capacitor to ensure the same minimum capaci-
tance over the equivalent operating temperature range.
Input Capacitor
An input capacitor of 1
F or greater is recommended when
the device is more than 4 inches away from the bulk ac supply
capacitance or when the supply is a battery. Small, surface
mount, ceramic chip capacitors can be used for bypassing.
Larger values will help to improve ripple rejection by bypass-
ing the input to the regulator, further improving the integrity of
the output voltage.
Error Flag
The MIC37101 features an error flag (FLG), which monitors
the output voltage and signals an error condition when this
voltage drops 5% below its expected value. The error flag is
an open-collector output that pulls low under fault conditions
and may sink up to 10mA. Low output voltage signifies a
number of possible problems, including an overcurrent fault
(the device is in current limit) or low input voltage. The flag
output is inoperative during overtemperature conditions. A
pull-up resistor from FLG to either V
IN
or V
OUT
is required for
proper operation. For information regarding the minimum and
maximum values of pull-up resistance, refer to the graph in
the "Typical Characteristics" section of the data sheet.
Enable Input
The MIC37101 and MIC37102 versions feature an active-
high enable input (EN) that allows on-off control of the
regulator. Current drain reduces to "zero" when the device is
shutdown, with only microamperes of leakage current. The
EN input has TTL/CMOS compatible thresholds for simple
logic interfacing. EN may be directly tied to V
IN
and pulled up
to the maximum supply voltage
Transient Response and 3.3V to 2.5V or 2.5V to 1.8V,
1.65V or 1.5V Conversion
The MIC37100/01/02 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 10
F output
capacitor, 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 de-
signs. When converting from 3.3V to 2.5V or 2.5V to 1.8V, or
lower, the NPN based regulators are already operating in
dropout, with typical dropout requirements of 1.2V or greater.
To convert down to 2.5V or 1.8V without operating in dropout,
NPN-based regulators require an input voltage of 3.7V at the
very least. The MIC37100 regulator will provide excellent
performance with an input as low as 3.0V or 2.5V respec-
tively. This gives the PNP based regulators a distinct advan-
tage over older, NPN based linear regulators.
MIC37100/37101/37102
Micrel
M9999-091604
12
September 2004
Minimum Load Current
The MIC37100/01/02 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 regulation.
Adjustable Regulator Design
IN
R1
V
OUT
V
IN
C
OUT
R2
EN
OUT
ADJ
GND
MIC37102
ENABLE
SHUTDOWN
V
1.240V 1
R1
R2
OUT
=
+
Figure 2. Adjustable Regulator with Resistors
The MIC37102 allows programming the output voltage any-
where between 1.24V and the 6V maximum operating rating
of the family. Two resistors are used. Resistors can be quite
large, up to 1M
, because of the very high input impedance
and low bias current of the sense comparator: The resistor
values are calculated by:
R1 R2
V
1.240
1
OUT
=
-
Where V
O
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).
Power SOIC-8 Thermal Characteristics
One of the secrets of the MIC37101/02's performance is its
power SO-8 package featuring half the thermal resistance of
a standard SO-8 package. Lower thermal resistance means
more output current or higher input voltage for a given
package size.
Lower thermal resistance is achieved by joining the four
ground leads with the die attach paddle to create a single-
piece electrical and thermal conductor. This concept has
been used by MOSFET manufacturers for years, proving
very reliable and cost effective for the user.
Thermal resistance consists of two main elements,
JC
(junction-to-case thermal resistance) and
CA
(case-to-ambi-
ent thermal resistance). See Figure 3.
JC
is the resistance
from the die to the leads of the package.
CA
is the resistance
from the leads to the ambient air and it includes
CS
(case-to-
sink thermal resistance) and
SA
(sink-to-ambient thermal
resistance).
JA
JC
CA
printed circuit board
ground plane
heat sink area
SOIC-8
AMBIENT
Figure 3. Thermal Resistance
Using the power SOIC-8 reduces the
JC
dramatically and
allows the user to reduce
CA
. The total thermal resistance,
JA
(junction-to-ambient thermal resistance) is the limiting
factor in calculating the maximum power dissipation capabil-
ity of the device. Typically, the power SOIC-8 has a
JC
of
20
C/W, this is significantly lower than the standard SOIC-8
which is typically 75
C/W.
CA
is reduced because pins 5
through 8 can now be soldered directly to a ground plane
which significantly reduces the case-to-sink thermal resis-
tance and sink to ambient thermal resistance.
Low-dropout linear regulators from Micrel are rated to a
maximum junction temperature of 125
C. It is important not
to exceed this maximum junction temperature during opera-
tion of the device. To prevent this maximum junction tempera-
ture from being exceeded, the appropriate ground plane heat
sink must be used.
September 2004
13
M9999-091604
MIC37100/37101/37102
Micrel
0
100
200
300
400
500
600
700
800
900
0
0.25 0.50 0.75 1.00 1.25 1.50
COPPER AREA (mm
2
)
POWER DISSIPATION (W)
40
C
50
C
55
C
65
C
75
C
85
C
100
C
T
JA
=
Figure 4. Copper Area vs. Power SO-8
Power Dissipation
Figure 4 shows copper area versus power dissipation with
each trace corresponding to a different temperature rise
above ambient.
From these curves, the minimum area of copper necessary
for the part to operate safely can be determined. The maxi-
mum allowable temperature rise must be calculated to deter-
mine operation along which curve.
T = T
J
(max) T
A
(max)
T
J
(max) = 125
C
T
A
(max) = maximum ambient operating temperature
For example, the maximum ambient temperature is 50
C, the
T is determined as follows:
T = 125
C 50
C
T = 75
C
Using Figure 4, the minimum amount of required copper can
be determined based on the required power dissipation.
Power dissipation in a linear regulator is calculated as fol-
lows:
P
D
= (V
IN
V
OUT
) I
OUT
+ V
IN
I
GND
If we use a 2.5V output device and a 3.3V input at an output
current of 1A, then our power dissipation is as follows:
P
D
= (3.3V 2.5V)
1A + 3.3V
11mA
P
D
= 800mW + 36mW
P
D
= 836mW
From Figure 4, the minimum amount of copper required to
operate this application at a
T of 75
C is 160mm
2
.
Quick Method
Determine the power dissipation requirements for the design
along with the maximum ambient temperature at which the
device will be operated. Refer to Figure 5, which shows safe
operating curves for three different ambient temperatures:
25
C, 50
C and 85
C. From these curves, the minimum
amount of copper can be determined by knowing the maxi-
mum power dissipation required. If the maximum ambient
temperature is 50
C and the power dissipation is as above,
836mW, the curve in Figure 5 shows that the required area of
copper is 160mm
2
.
The
JA
of this package is ideally 63
C/W, but it will vary
depending upon the availability of copper ground plane to
which it is attached.
0
100
200
300
400
500
600
700
800
900
0
0.25 0.50 0.75 1.00 1.25 1.50
COPPER AREA (mm
2
)
POWER DISSIPATION (W)
T
A
= 85
C
50
C
25
C
T
J
= 125
C
Figure 5. Copper Area vs. Power-SOIC
Power Dissipation
MIC37100/37101/37102
Micrel
M9999-091604
14
September 2004
Package Information
16
10
0.84 (0.033)
0.64 (0.025)
1.04 (0.041)
0.85 (0.033)
2.41 (0.095)
2.21 (0.087)
4.7 (0.185)
4.5 (0.177)
6.70 (0.264)
6.30 (0.248)
7.49 (0.295)
6.71 (0.264)
3.71 (0.146)
3.30 (0.130)
3.15 (0.124)
2.90 (0.114)
10
MAX
0.10 (0.004)
0.02 (0.0008)
0.38 (0.015)
0.25 (0.010)
C
L
DIMENSIONS:
MM (INCH)
C
L
1.70 (0.067)
1.52 (0.060)
0.91 (0.036) MIN
SOT-223 (S)
45
0
8
0.244 (6.20)
0.228 (5.79)
0.197 (5.0)
0.189 (4.8)
SEATING
PLANE
0.026 (0.65)
MAX
)
0.010 (0.25)
0.007 (0.18)
0.064 (1.63)
0.045 (1.14)
0.0098 (0.249)
0.0040 (0.102)
0.020 (0.51)
0.013 (0.33)
0.157 (3.99)
0.150 (3.81)
0.050 (1.27)
TYP
PIN 1
DIMENSIONS:
INCHES (MM)
0.050 (1.27)
0.016 (0.40)
8-Lead SOIC (M)
September 2004
15
M9999-091604
MIC37100/37101/37102
Micrel
0.375 (9.52)
0.365 (9.27)
0.360 (9.14)
0.350 (8.89)
0.080 (2.03)
0.070 (1.78)
0.010 BSC
(0.25 BSC)
0.045 (1.14)
0.035 (0.89)
0.316 BSC
(8.03 BSC)
0.256 BSC
(6.50 BSC)
0.031 (0.79)
0.025 (0.63)
0.005 (0.13)
0.001 (0.03)
6
0
0.010 BSC
(0.25 BSC)
0.067 BSC
(1.70 BSC)
0.031 (0.89)
0.041 (1.14)
0.420 (10.67)
0.410 (10.41)
0.050 (1.27)
0.030 (0.76)
0.320 (8.13)
0.310 (7.87)
DIMENSIONS:
INCH (MM)
0.080 (2.03)
0.070 (1.78)
5 Lead S-PAK (R)
MICREL, INC.
1849 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 at Purchaser's own risk and Purchaser agrees to
fully indemnify Micrel for any damages resulting from such use or sale.
2004 Micrel, Incorporated.
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