September 2004 1 M9999-091604
MIC37100/37101/37102 Micrel
MIC37100/37101/37102
1A Low-Voltage µµ
µµ
µCap 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 βeta PNP™ 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
•µµ
µµ
µCap Regulator, 10µµ
µµ
µF 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
• PowerPC™ power supplies
• High-efficiency linear power supplies
• SMPS post regulator
• Multimedia and PC processor supplies
• Battery chargers
• Low-voltage microcontrollers and digital logic
Super βeta 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
10µF
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 OUTGND
132
TAB
GND
MIC37100-x.x (Fixed)
SOT-223 (S)
1EN
IN
OUT
FLG
8 GND
GND
GND
GND
7
6
5
2
3
4
MIC37101-x.x (Fixed)
SOIC-8 (M)
1EN
IN
OUT
ADJ
8 GND
GND
GND
GND
7
6
5
2
3
4
MIC37102 (Adjustable)
SOIC-8 (M)
TAB
5 ADJ
4 OUT
3 GND
2IN
1EN
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
1111ENEnable (Input): CMOS-compatible control input. Logic high =
enable, logic low or open = shutdown.
2 2 2 IN Supply (Input).
3334OUTRegulator 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 5–85–8 3, TAB GND Ground.
MIC37100/37101/37102 Micrel
M9999-091604 4 September 2004
Electrical Characteristics
VIN = VOUT + 1V; VEN = 2.25V; TJ = 25°C, bold values indicate –40°C ≤ TJ ≤ +125°C; unless noted
Symbol Parameter Condition Min Typ Max Units
VOUT Output Voltage 10mA –11%
10mA ≤ IOUT ≤ 1A, VOUT + 1V ≤ VIN ≤ 6V –22%
Line Regulation IOUT = 10mA, VOUT + 1V ≤ VIN ≤ 6V 0.06 0.5 %
Load Regulation VIN = VOUT + 1V, 10mA ≤ IOUT ≤ 1A, 0.2 1 %
∆VOUT/∆T Output Voltage Temp. Coefficient(6) 40 ppm/°C
VDO Dropout Voltage(6) IOUT = 100mA, ∆VOUT = –1% 125 200 mV
IOUT = 500mA, ∆VOUT = –1% 210 350 mV
IOUT = 750mA, ∆VOUT = –1% 250 400 mV
IOUT = 1A, ∆VOUT = –1% 280 500 mV
IGND Ground Current(7) IOUT = 100mA, VIN = VOUT + 1V 650 mA
IOUT = 500mA, VIN = VOUT + 1V 3.5 mA
IOUT = 750mA, VIN = VOUT + 1V 6.7 mA
IOUT = 1A, VIN = VOUT + 1V 11 25 mA
IOUT(lim) Current Limit VOUT = 0V, VIN = VOUT + 1V 1.6 2.5 A
Enable Input
VEN Enable Input Voltage logic low (off) 0.8 V
logic high (on) 2.25 V
IEN Enable Input Current VEN = 2.25V 1 10 30 µA
VEN = 0.8V 2 µA
4µA
Flag Output
IFLG(leak) Output Leakage Current VOH = 6V 0.01 1 µA
2µA
VFLG(do) Output Low Voltage VIN = 2.250V, IOL, = 250µA 210 500 mV
VFLG Low Threshold % of VOUT 93 %
High Threshold % of VOUT 99.2 %
Hysteresis 1%
Absolute Maximum Ratings(1)
Supply Voltage (VIN) ........................................ 0V to +6.5V
Enable Voltage (VEN) .................................................+6.5V
Storage Temperature (TS) .......................–65°C to +150°C
Lead Temperature (soldering, 5 sec.) ....................... 260°C
ESD ................................................................................(3)
Operating Ratings(2)
Supply Voltage (VIN) .................................... +2.25V to +6V
Enable Voltage (VEN) .......................................... 0V to +6V
Maximum Power Dissipation (PD(max)) ...........................(4)
Junction Temperature (TJ) .......................–40°C to +125°C
Package Thermal Resistance
SOT-223 (θJC).....................................................15°C/W
SOIC-8 (θJC) .......................................................20°C/W
S-PAK-5 (θJC) .......................................................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. PD(max) = (TJ(max) – TA) ÷ θJA, where θJA depends upon the printed circuit layout. See
“
Applications Information” section.
5. Output voltage temperature coefficient is ∆VOUT(worst case) ÷ (TJ(max) – TJ(min)) where TJ(max) is +125°C and TJ(min) is –40°C.
6. VDO = VIN – VOUT when VOUT decreases to 98% of its nominal output voltage with VIN = VOUT + 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. IGND is the quiescent current. IIN = IGND + IOUT.
8. VEN ≤ 0.8V, VIN ≤ 6V, and VOUT = 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
IOUT = 1000mA
COUT = 10µF
CIN = 0
VIN = 5V
VOUT = 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
IOUT = 1000mA
COUT = 47µF
CIN = 0
VIN = 5V
VOUT = 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
IOUT = 1000mA
COUT = 10µF
CIN = 0
VIN = 3.3V
VOUT = 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
IOUT = 1000mA
COUT = 47µF
CIN = 0
VIN = 3.3V
VOUT = 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 100120
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
0123456
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
1.5VOUT 3.3VOUT
September 2004 7 M9999-091604
MIC37100/37101/37102 Micrel
0
2
4
6
8
10
12
14
16
18
0123456
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
0123456
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
0123456
GROUND CURRENT (mA)
INPUT VOLTAGE
(
V
)
Ground Current
vs. Supply Voltage (2.5V)
100mA
10mA
0
5
10
15
20
25
30
0123456
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
0123456
GROUND CURRENT (mA)
INPUT VOLTAGE
(
V
)
Ground Current
vs. Supply Voltage (3.3V)
100mA
10mA
0
5
10
15
20
25
0123456
GROUND CURRENT (mA)
INPUT VOLTAGE
(
V
)
Ground Current
vs. Supply Voltage (1.8V)
1000mA
750mA
0
5
10
15
20
25
30
0123456
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
-40-200 20406080100120
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 100120
OUTPUT VOLTAGE (V)
TEMPERATURE (°C)
Output Voltage
vs. Tem
p
erature
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 100120
SHORT CIRCUIT CURRENT (A)
TEMPERATURE (°C)
Short Circuit Current
vs. Temperature
2.5VIN
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
3.3VIN 5VIN
2.5VIN
0
50
100
150
200
250
300
350
-40 -20 0 20 40 60 80 100120
FLAG LOW VOLTAGE (mV)
TEMPERATURE
(
°C
)
Flag Low Voltage
vs. Temperature
Fla
g
Current = 250
µ
A
0
1
2
3
4
5
6
0.01 0.1 1 10 100 100010000
FLAG VOLTAGE (V)
RESISTANCE (kΩ)
Error Flag Pull-Up Resistor
Flag High (OK) VIN=5V
Flag Low (FAULT)
0
1
2
3
4
5
6
7
8
9
-40 -20 0 20 40 60 80 100120
ENABLE CURRENT (µA)
TEMPERATURE
(
°C
)
Enable Current
vs. Temperature
2.5VEN
September 2004 9 M9999-091604
MIC37100/37101/37102 Micrel
Functional Characteristics
Load T ransient Response
TIME (400µs/div.)
LOAD CURRENT
(500mA/div) OUTPUT V OLTAGE
(200mV/div)
VIN = 3.3V
VOUT = 2.5V
COUT = 10µF Ceramic
1000mA
100mA
Load T ransient Response
TIME (400µs/div.)
LOAD CURRENT
(500mA/div) OUTPUT V OLTAGE
(200mV/div)
VIN = 3.3V
VOUT = 2.5V
COUT = 10µF Ceramic
1000mA
10mA
Line T ransient Response
TIME (400µs/div.)
OUTPUT V OLTAGE
(50mV/div) INPUT V OLTAGE
(2V/div)
VOUT = 2.5V
COUT = 10µF Ceramic
Load=100mA
5V
3.3V
Enable T ransient Response
TIME (10µs/div.)
OUTPUT VOLTAGE
(1V/div) ENABLE V OLTAGE
(2V/div)
VIN = 3.3V
VOUT = 2.5V
IOUT = 100mA
COUT = 10µF 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
1.240V1.180V
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 VCE 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% 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 µCap
LDO, the MIC37100/01/02 can operate with ceramic output
capacitors as long as the amount of capacitance is 10µF or
greater. For values of output capacitance lower than 10µF,
the recommended ESR range is 200mΩ to 2Ω. The minimum
value of output capacitance recommended for the MIC37100/
01/02 is 4.7µF.
For 10µF or greater the ESR range recommended is less than
1Ω. Ultra-low ESR ceramic capacitors are recommended for
output capacitance of 10µF 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 1µF 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 VIN or VOUT 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 VIN 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 10µF 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 1MΩ, 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 VO 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, θJC
(junction-to-case thermal resistance) and θCA (case-to-ambi-
ent thermal resistance). See Figure 3. θJC is the resistance
from the die to the leads of the package. θCA is the resistance
from the leads to the ambient air and it includes θCS (case-to-
sink thermal resistance) and θSA (sink-to-ambient thermal
resistance).
θJA
θJC θCA
printed circuit board
ground plane
heat sink area
SOIC-8
AMBIENT
Figure 3. Thermal Resistance
Using the power SOIC-8 reduces the θJC dramatically and
allows the user to reduce θCA. The total thermal resistance,
θJA (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 θJC of
20°C/W, this is significantly lower than the standard SOIC-8
which is typically 75°C/W. θCA 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 (mm2)
POWER DISSIPATION (W)
40°C
50°C
55°C
65°C
75°C
85°C
100°C
∆TJA =
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 = TJ(max) – TA(max)
TJ(max) = 125°C
TA(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: PD = (VIN – VOUT) IOUT + VIN ×IGND
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:
PD = (3.3V – 2.5V) × 1A + 3.3V × 11mA
PD = 800mW + 36mW
PD = 836mW
From Figure 4, the minimum amount of copper required to
operate this application at a ∆T of 75°C is 160mm2.
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 160mm2.
The θJA 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)
TA = 85°C50°C25°C
TJ = 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.
