August 2005 1 M9999-082505-B
MIC39100/39101/39102 Micrel
MIC39100/39101/39102
1A Low-Voltage Low-Dropout Regulator
General Description
The MIC39100, MIC39101, and MIC39102 are 1A low-dropout
linear voltage regulators that provide low-voltage, high-current
output from an extremely small package. Utilizing Micrel’s pro-
prietary Super βeta PNP™ pass element, the MIC39100/1/2
offers extremely low dropout (typically 410mV at 1A) and low
ground current (typically 11mA at 1A).
The MIC39100 is a fixed output regulator offered in the
SOT-223 package. The MIC39101 and MIC39102 are fixed
and adjustable regulators, respectively, in a thermally en-
hanced power 8-lead SOIC package.
The MIC39100/1/2 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. A guaranteed maximum dropout voltage of 630mV over
all operating conditions allows the MIC39100/1/2 to provide
2.5V from a supply as low as 3.13V and 1.8V from a supply
as low as 2.43V.
The MIC39100/1/2 is fully protected with overcurrent limit-
ing, thermal shutdown, and reversed-battery protection.
Fixed voltages of 5.0V, 3.3V, 2.5V, and 1.8V are available
on MIC39100/1 with adjustable output voltages to 1.24V on
MIC39102.
For other voltages, contact Micrel.
Typical Applications
Features
• Fixed and adjustable output voltages to 1.24V
• 410mV typical dropout at 1A
Ideal for 3.0V to 2.5V conversion
Ideal for 2.5V to 1.8V conversion
• 1A minimum guaranteed output current
• 1% initial accuracy
• Low ground current
• Current limiting and thermal shutdown
• Reversed-battery protection
• Reversed-leakage protection
• Fast transient response
• Low-profile SOT-223 package
• Power SO-8 package
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 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
IN 2.5V
VIN
3.3V
10µF
tantalum
OUT
GND
MIC39100
2.5V/1A Regulator
IN
R1
100k
2.5V
Error
Flag
Output
VIN
3.3V
10µF
tantalum
EN
OUT
FLG
GND
MIC39101
ENABLE
SHUTDOWN
2.5V/1A Regulator with Error Flag
IN
R1
1.5V
VIN
2.5V
10µF
tantalum
R2
EN
OUT
ADJ
GND
MIC39102
ENABLE
SHUTDOWN
1.5V/1A Adjustable Regulator
MIC39100/39101/39102 Micrel
M9999-082505 2 August 2005
Pin Configuration
IN OUTGND
1 32
TA B
GND
MIC39100-x.x
Fixed
SOT-223 (S)
1EN
IN
OUT
FLG
8 GND
GND
GND
GND
7
6
5
2
3
4
MIC39101-x.x
Fixed
SOIC-8 (M)
1EN
IN
OUT
ADJ
8 GND
GND
GND
GND
7
6
5
2
3
4
MIC39102
Adjustable
SOIC-8 (M)
Pin Description
Pin No. Pin No. Pin No. Pin Name Pin Function
MIC39100 MIC39101 MIC39102
1 1 1 EN Enable (Input): CMOS-compatible control input. Logic high = enable, logic
low or open = shutdown.
2 2 IN Supply (Input)
3 3 3 OUT Regulator Output
4 FLG Flag (Output): Open-collector error flag output. Active low = output under-
voltage.
4 ADJ Adjustment Input: Feedback input. Connect to resitive voltage-divider
network.
2, TAB 5–8 5–8 GND Ground
Ordering Information
Part Number Voltage Junction Temp. Range Package
Standard RoHS Compliant
MIC39100-1.8BS MIC39100-1.8WS* 1.8V -40°C to +125°C SOT-223
MIC39100-2.5BS MIC39100-2.5WS* 2.5V -40°C to +125°C SOT-223
MIC39100-3.3BS MIC39100-3.3WS* 3.3V -40°C to +125°C SOT-223
MIC39100-5.0BS MIC39100-5.0WS* 5.0V -40°C to +125°C SOT-223
MIC39101-1.8BM MIC39101-1.8YM 1.8V -40°C to +125°C SOIC-8
MIC39101-2.5BM MIC39101-2.5YM 2.5V -40°C to +125°C SOIC-8
MIC39101-3.3BM MIC39101-3.3YM 3.3V -40°C to +125°C SOIC-8
MIC39101-5.0BM MIC39101-5.0YM 5.0V -40°C to +125°C SOIC-8
MIC39102BM MIC39102YM Adj. -40°C to +125°C SOIC-8
* RoHS compliant with ‘high-melting solder’ exemption.
August 2005 3 M9999-082505-B
MIC39100/39101/39102 Micrel
Electrical Characteristics(Note 12)
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 –1 1 %
10mA ≤ IOUT ≤ 1A, VOUT + 1V ≤ VIN ≤ 8V –2 2 %
Line Regulation IOUT = 10mA, VOUT + 1V ≤ VIN ≤ 16V 0.06 0.5 %
Load Regulation VIN = VOUT + 1V, 10mA ≤ IOUT ≤ 1A, 0.2 1 %
ΔVOUT/ΔT Output Voltage Temp. Coefficient, 40 100
ppm/°C
Note 5
VDO Dropout Voltage, Note 6 IOUT = 100mA, ΔVOUT = –1% 140 200 mV
250 mV
IOUT = 500mA, ΔVOUT = –1% 275 mV
IOUT = 750mA, ΔVOUT = –1% 330 500 mV
IOUT = 1A, ΔVOUT = –1% 550 mV
410 630 mV
IGND Ground Current, Note 7 IOUT = 100mA, VIN = VOUT + 1V 400 µA
IOUT = 500mA, VIN = VOUT + 1V 4 mA
IOUT = 750mA, VIN = VOUT + 1V 6.5 mA
IOUT = 1A, VIN = VOUT + 1V 11 20 mA
IOUT(lim) Current Limit VOUT = 0V, VIN = VOUT + 1V 1.8 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 15 30 µA
75 µA
VEN = 0.8V 2 µA
4 µA
Flag Output
IFLG(leak) Output Leakage Current VOH = 16V 0.01 1 µA
2 µA
VFLG(do) Output Low Voltage VIN = 2.250V, IOL, = 250µA, Note 9 210 300 mV
400 mV
VFLG Low Threshold % of VOUT 93 %
High Threshold % of VOUT 99.2 %
Hysteresis 1 %
Absolute Maximum Ratings (Note 1)
Supply Voltage (VIN) .......................................–20V to +20V
Enable Voltage (VEN) ..................................................+20V
Storage Temperature (TS) ........................ –65°C to +150°C
Lead Temperature (soldering, 5 sec.) ........................ 260°C
ESD, Note 3
Operating Ratings (Note 2)
Supply Voltage (VIN) ................................... +2.25V to +16V
Enable Voltage (VEN) ..................................................+16V
Maximum Power Dissipation (PD(max)) ..................... Note 4
Junction Temperature (TJ) ........................ –40°C to +125°C
Package Thermal Resistance
SOT-223 (θJC) ..................................................... 15°C/W
SOIC-8 (θJC) ........................................................ 20°C/W
MIC39100/39101/39102 Micrel
M9999-082505 4 August 2005
Symbol Parameter Condition Min Typ Max Units
MIC39102 Only
Reference Voltage 1.228 1.240 1.252 V
1.215 1.265 V
Note 10 1.203 1.277 V
Adjust Pin Bias Current 40 80 nA
120 nA
Reference Voltage Note 7 20
ppm/°C
Temp. Coefficient
Adjust Pin Bias Current 0.1 nA/°C
Temp. Coefficient
Note 1. Exceeding the absolute maximum ratings may damage the device.
Note 2. The device is not guaranteed to function outside its operating rating.
Note 3. Devices are ESD sensitive. Handling precautions recommended.
Note 4. PD(max) = (TJ(max) – TA) ÷ θJA, where θJA depends upon the printed circuit layout. See “Applications Information.”
Note 5. Output voltage temperature coefficient is ΔVOUT(worst case) ÷ (TJ(max) – TJ(min)) where TJ(max) is +125°C and TJ(min) is –40°C.
Note 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.
Note 7. IGND is the quiescent current. IIN = IGND + IOUT.
Note 8. VEN ≤ 0.8V, VIN ≤ 8V, and VOUT = 0V.
Note 9. For a 2.5V device, VIN = 2.250V (device is in dropout).
Note 10. VREF ≤ VOUT ≤ (VIN – 1V), 2.25V ≤ VIN ≤ 16V, 10mA ≤ IL ≤ 1A, TJ = TMAX.
Note 11. 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 200mA load pulse at VIN = 16V for t = 10ms.
Note 12. Specification for packaged product only.
August 2005 5 M9999-082505-B
MIC39100/39101/39102 Micrel
Typical Characteristics
0
20
40
60
80
1E+1 1E+2 1E+3 1E+4 1E+5 1E+6
PSRR (dB)
FREQUENCY (Hz)
P ower S upply
R ejection R atio
IOUT = 1A
COUT = 10µF
CIN = 0
VIN = 5V
VOUT = 3.3V
10 100 1k 10k 100k 1M
0
20
40
60
80
1E+1 1E+2 1E+3 1E+4 1E+5 1E+6
PSRR (dB)
FREQUENCY (Hz)
P ower S upply
R ejection R atio
IOUT = 1A
COUT = 47µF
CIN = 0
VIN = 5V
VOUT = 3.3V
10 100 1k 10k 100k 1M
0
20
40
60
80
1E+1 1E+2 1E+3 1E+4 1E+5 1E+6
PSRR (dB)
FREQUENCY (Hz)
P ower S upply
R ejection R atio
IOUT = 1A
COUT = 10µF
CIN = 0
VIN = 3.3V
VOUT = 2.5V
10 100 1k 10k 100k 1M
0
20
40
60
80
1E+1 1E+2 1E+3 1E+4 1E+5 1E+6
PSRR (dB)
FREQUENCY (Hz)
P ower S upply
R ejection R atio
IOUT = 1A
COUT = 47µF
CIN = 0
VIN = 3.3V
VOUT = 2.5V
10 100 1k 10k 100k 1M
0
50
100
150
200
250
300
350
400
450
500
0 250 500 750 1000 1250
DROPOUT VOLTAGE (mV)
OUTPUT CURRENT (mA)
Dropout V oltage
vs . Output C urrent
2.5V
3.3V
TA= 25°C
1.8V
300
350
400
450
500
550
600
-40 -20 0 20 40 60 80 100 120
DROPOUT VOLTAGE (mV)
TEMPERATURE (°C)
Dropout V oltage
vs . T emper ature
3.3V
2.5V
ILOAD = 1A
1.8V
1.4
1.6
1.8
2.0
2.2
2.4
2.6
2.8
2 2.3 2.6 2.9 3.2 3.5
OUTPUT VOLTAGE (V)
SUPPLY VOLTAGE (V)
Dropout C harac teris tic s
(2.5V )
ILOAD =100mA
ILOAD =750mA
ILOAD =1A
2.4
2.6
2.8
3.0
3.2
3.4
3.6
2.8 3.2 3.6 4.0 4.4
OUTPUT VOLTAGE (V)
SUPPLY VOLTAGE (V)
Dropout C harac teris tic s
(3.3V )
ILOAD =100mA
ILOAD =750mA
ILOAD =1A
0
2
4
6
8
10
12
14
0 200 400 600 800 1000
GROUND CURRENT (mA)
OUTPUT CURRENT (mA)
G round C urrent
vs . Output C urrent
2.5V
3.3V
1.8V
0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
02468
GROUND CURRENT (mA)
SUPPLY VOLTAGE (V)
G round C urrent
vs . S upply V oltage (2.5V)
ILOAD =100mA
ILOAD =10mA
0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
02468
GROUND CURRENT (mA)
SUPPLY VOLTAGE (V)
G round C urrent
vs . S upply V oltage (3.3V)
ILOAD =100mA
ILOAD =10mA
0
5
10
15
20
25
30
35
02468
GROUND CURRENT (mA)
SUPPLY VOLTAGE (V)
G round C urrent
vs . S upply V oltage (2.5V)
ILOAD =1A
MIC39100/39101/39102 Micrel
M9999-082505 6 August 2005
0
0.2
0.4
0.6
0.8
1.0
-40 -20 0 20 40 60 80 100 120
GROUND CURRENT (mA)
TEMPERATURE (°C)
G round C urrent
vs . T emper ature
3.3V
ILOAD =10mA
2.5V
1.8V
0
5
10
15
20
-40 -20 0 20 40 60 80 100 120
GROUND CURRENT (mA)
TEMPERATURE (°C)
G round C urrent
vs . T emper ature
3.3V
2.5V
ILOAD = 1A
1.8V
3.20
3.25
3.30
3.35
3.40
-40 -20 0 20 40 60 80 100 120
OUTPUT VOLTAGE (V)
TEMPERATURE (°C)
Output Voltage
vs . T emperature
T ypical 3.3V
Device
0
0.5
1.0
1.5
2.0
2.5
-40 -20 0 20 40 60 80 100 120
SHORT CIRCUIT CURRENT (A)
TEMPERATURE (°C)
S hort C irc uit
vs . T emper ature
3.3V
2.5V 1.8V
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
-40 -20 0 20 40 60 80 100 120
GROUND CURRENT (mA)
TEMPERATURE (°C)
G round C urrent
vs . T emper ature
3.3V
2.5V
ILOAD = 500mA
1.8V
0
1
2
3
4
5
6
0.01 0.1 1 10 100 1000 10000
FLAG VOLTAGE (V)
RESISTANCE (kΩ)
E rror F lag
P ull-Up R es is tor
VIN = 5V
F LAG HIG H
(OK )
F LAG L OW
(F AUL T )
0
2
4
6
8
10
12
-40 -20 0 20 40 60 80 100 120 140
ENABLE CURRENT (µA)
TEMPERATURE (°C)
E nable C urrent
vs . T emper ature
VIN = V OU T + 1V
VE N = 2.4V
0
50
100
150
200
250
-40 -20 0 20 40 60 80 100 120 140
FLAG VOLTAGE (mV)
TEMPERATURE (°C)
F lag-L ow V oltage
vs . T emper ature
VIN = 2.25V
RP UL L-UP = 22kΩ
F LAG -LO W
V OLT AG E
August 2005 7 M9999-082505-B
MIC39100/39101/39102 Micrel
Functional Characteristics
MIC39100/39101/39102 Micrel
M9999-082505 8 August 2005
Functional Diagrams
Ref. 18V
OV ILIMIT
Thermal
Shut-
down
1.240V
IN OU T
GND
MIC39100
MIC39100 Fixed Regulator Block Diagram
Ref.
18V
O.V.
ILIM IT
Thermal
Shut-
down
1.240V1.180V
E N
IN
FLAG
GND
OUT
MIC39101
MIC39101 Fixed Regulator with Flag and Enable Block Diagram
Ref.
18V
O.V.
ILIM IT
Thermal
Shut-
down
1.240V
E N
IN
GND
OUT
ADJ
MIC39102
MIC39102 Adjustable Regulator Block Diagram
August 2005 9 M9999-082505-B
MIC39100/39101/39102 Micrel
Applications Information
The MIC39100/1/2 is a high-performance low-dropout volt-
age regulator suitable for moderate to high-current voltage
regulator applications. Its 630mV dropout voltage at full load
and overtemperature makes it especially valuable in bat-
tery-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 satura-
tion 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 MIC39100/1/2 regulator is fully protected from damage
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. 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.
MIC39100-x.x
IN OU T
GN D
CIN
COUT
VIN VOUT
Figure 1. Capacitor Requirements
Output Capacitor
The MIC39100/1/2 requires an output capacitor to maintain
stability and improve transient response. Proper capaci-
tor selection is important to ensure proper operation. The
MIC39100/1/2 output capacitor selection is dependent upon
the ESR (equivalent series resistance) of the output capacitor
to maintain stability. When the output capacitor is 10µF or
greater, the output capacitor should have an ESR less than
2Ω. This will improve transient response as well as promote
stability. Ultra-low-ESR capacitors (<100mΩ), such as ceramic
chip capacitors, may promote instability. These very low ESR
levels may cause an oscillation and/or underdamped transient
response. A low-ESR solid tantalum capacitor works extremely
well and provides good transient response and stability over
temperature. Aluminum electrolytics can also be used, as
long as the ESR of the capacitor is <2Ω.
The value of the output capacitor can be increased without
limit. Higher capacitance values help to improve transient
response and ripple rejection and reduce output noise.
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 MIC39101 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 MIC39101 and MIC39102 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
Conversion
The MIC39100/1/2 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 satu-
rate into dropout as readily as similar NPN-based designs.
When converting from 3.3V to 2.5V or 2.5V to 1.8V, the NPN
based regulators are already operating in dropout, with typi-
cal 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 MIC39100 regulator will provide excellent performance
with an input as low as 3.0V or 2.5V respectively. This gives
the PNP based regulators a distinct advantage over older,
NPN based linear regulators.
Minimum Load Current
The MIC39100/1/2 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.
MIC39100/39101/39102 Micrel
M9999-082505 10 August 2005
Adjustable Regulator Design
IN
R1
VOUT
VIN
COUT
R2
EN
OUT
ADJ
GND
MIC39102
ENABLE
SHUTDOWN
V 1.240V 1 R1
R2
OUT = +
Figure 2. Adjustable Regulator with Resistors
The MIC39102 allows programming the output voltage any-
where between 1.24V and the 16V 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 MIC39101/2’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 pack-
age 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 (junc-
tion-to-case thermal resistance) and θCA (case-to-ambient
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).
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 resistance
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 operation
of the device. To prevent this maximum junction temperature
from being exceeded, the appropriate ground plane heat sink
must be used.
JA
JC
CA
printed circuit board
ground plane
heat sink area
SOIC-8
AMBIENT
Figure 3. Thermal Resistance
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 maximum
allowable temperature rise must be calculated to determine
operation along which curve.
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)
4
0
°C
5
0
°C
5
5
°C
6
5
°C
7
5
°C
8
5
°C
1
00
°C
∆TJ A =
Figure 4. Copper Area vs. Power-SOIC
Power Dissipation
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)
TA= 85°C
50°C
25°C
TJ= 125°C
Figure 5. Copper Area vs. Power-SOIC
Power Dissipation
August 2005 11 M9999-082505-B
MIC39100/39101/39102 Micrel
ΔT = TJ(max) – TA(max)
TJ(max) = 125°C
TA(max) = maximum ambient operating temperature
For example, the maximum ambient temperature is 50°C,
the ΔT is determined as follows:
ΔT = 125°C – 50°C
ΔT = 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 follows:
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 ΔT 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.
MIC39100/39101/39102 Micrel
M9999-082505 12 August 2005
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
DI MEN SIO NS:
MM (INCH)
C
L
1.70 (0.067)
1.52 (0.060)
0.91 (0.036) MIN
SOT-223 (S)
8-Lead SOIC (M)
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This 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.
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© 2005 Micrel Incorporated