February 2003
1
MIC3975
MIC3975
Micrel
Ordering Information
Part Number
Voltage
Junction Temp. Range
Package
MIC3975-1.65BMM
1.65V
40
C to +125
C
MSOP-8
MIC3975-1.8BMM
1.8V
40
C to +125
C
MSOP-8
MIC3975-2.5BMM
2.5V
40
C to +125
C
MSOP-8
MIC3975-3.0BMM
3.0V
40
C to +125
C
MSOP-8
MIC3975-3.3BMM
3.3V
40
C to +125
C
MSOP-8
MIC3975-5.0BMM
5.0V
40
C to +125
C
MSOP-8
MIC3975BMM
Adj.
40
C to +125
C
MSOP-8
MIC3975
750mA
Cap Low-Voltage Low-Dropout Regulator
Final Information
General Description
The MIC3975 is a 750mA low-dropout linear voltage regula-
tors that provide low-voltage, high-current output from an
extremely small package. Utilizing Micrel's proprietary Super
eta PNPTM pass element, the MIC3975 offers extremely low
dropout (typically 300mV at 750mA) and low ground current
(typically 6.5mA at 750mA).
The MIC3975 is ideal for PC add-in cards that need to convert
from standard 5V to 3.3V or 3.0V, 3.3V to 2.5V or 2.5V to 1.8V
or 1.65V. A guaranteed maximum dropout voltage of 500mV
over all operating conditions allows the MIC3975 to provide
2.5V from a supply as low as 3.0V and 1.8V or 1.65V from a
supply as low as 2.25V.
The MIC3975 is fully protected with overcurrent limiting,
thermal shutdown, and reversed-battery protection. Fixed
voltages of 5.0V, 3.3V, 3.0, 2.5V, 1.8V, and 1.65V are
available. An adjustable output voltage option is available for
voltages down to 1.24V.
For other voltages, contact Micrel.
Typical Applications
Features
Fixed and adjustable output voltages to 1.24V
300mV typical dropout at 750mA
Ideal for 3.0V to 2.5V conversion
Ideal for 2.5V to 1.8V or 1.65V conversion
Stable with ceramic capacitor
750mA 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 MSOP-8
Applications
Fiber optic modules
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 trademark of Micrel, Inc.
Micrel, Inc. 1849 Fortune Drive San Jose, CA 95131 USA tel + 1 (408) 944-0800 fax + 1 (408) 944-0970 http://www.micrel.com
IN
R1
100k
2.5V
Error
Flag
Output
V
IN
3.3V
10
F
ceramic
EN
OUT
FLG
GND
MIC3975-2.5BMM
ENABLE
SHUTDOWN
2.5V/750mA Regulator with Error Flag
IN
R1
1.5V
V
IN
2.5V
10
F
ceramic
R2
EN
OUT
ADJ
GND
MIC3975BMM
ENABLE
SHUTDOWN
1.5V/750mA Adjustable Regulator
MIC3975
Micrel
MIC3975
2
February 2003
Pin Configuration
1
EN
IN
FLG
OUT
8
GND
GND
GND
GND
7
6
5
2
3
4
MIC3975-x.x
Fixed
MSOP-8 (MM)
1
EN
IN
ADJ
OUT
8
GND
GND
GND
GND
7
6
5
2
3
4
Adjustable
MSOP-8 (MM)
Pin Description
Pin No.
Pin No.
Pin Name
Pin Function
Fixed
Adjustable
1
1
EN
Enable (Input): CMOS-compatible control input. Logic high = enable, logic
low or open = shutdown.
2
2
IN
Supply (Input)
3
FLG
Flag (Output): Open-collector error flag output. Active low = output under-
voltage.
3
ADJ
Adjustment Input: Feedback input. Connect to resistive voltage-divider
network.
4
4
OUT
Regulator Output
58
58
GND
Ground
February 2003
3
MIC3975
MIC3975
Micrel
Electrical Characteristics
(Note 12)
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
750mA, V
OUT
+ 1V
V
IN
8V
2
2
%
Line Regulation
I
OUT
= 10mA, V
OUT
+ 1V
V
IN
16V
0.06
0.5
%
Load Regulation
V
IN
= V
OUT
+ 1V, 10mA
I
OUT
750mA,
0.2
1
%
V
OUT
/
T
Output Voltage Temp. Coefficient,
40
100
ppm/
C
Note 5
V
DO
Dropout Voltage, Note 6
I
OUT
= 100mA,
V
OUT
= 1%
140
200
mV
250
mV
I
OUT
= 500mA,
V
OUT
= 1%
225
mV
I
OUT
= 750mA,
V
OUT
= 1%
300
500
mV
I
GND
Ground Current, Note 7
I
OUT
= 100mA, V
IN
= V
OUT
+ 1V
400
A
I
OUT
= 500mA, V
IN
= V
OUT
+ 1V
4
mA
I
OUT
= 750mA, V
IN
= V
OUT
+ 1V
7.5
15
mA
I
OUT(lim)
Current Limit
V
OUT
= 0V, V
IN
= V
OUT
+ 1V
1.8
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
15
30
A
75
A
V
EN
= 0.8V
2
A
4
A
Flag Output
I
FLG(leak)
Output Leakage Current
V
OH
= 16V
0.01
1
A
2
A
V
FLG(do)
Output Low Voltage
V
IN
= 2.250V, I
OL
, = 250
A, Note 9
210
300
mV
400
mV
V
FLG
Low Threshold
% of V
OUT
93
%
High Threshold
% of V
OUT
99.2
%
Hysteresis
1
%
Absolute Maximum Ratings
(Note 1)
Supply Voltage (V
IN
) ..................................... 20V to +20V
Enable Voltage (V
EN
) .................................................. +20V
Storage Temperature (T
S
) ....................... 65
C to +150
C
Lead Temperature (soldering, 5 sec.) ....................... 260
C
ESD, Note 3
Operating Ratings
(Note 2)
Supply Voltage (V
IN
) .................................. +2.25V to +16V
Enable Voltage (V
EN
) .................................................. +16V
Maximum Power Dissipation (P
D(max)
) .................... Note 4
Junction Temperature (T
J
) ....................... 40
C to +125
C
Package Thermal Resistance
MSOP-8
(
JA
) ...................................................... 80
C/W
MIC3975
Micrel
MIC3975
4
February 2003
Symbol
Parameter
Condition
Min
Typ
Max
Units
Adjustable Output 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 11
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.
P
D(max)
= (T
J(max)
T
A
)
JA
, where
JA
depends upon the printed circuit layout. See "Applications Information."
Note 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.
Note 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.
Note 7.
I
GND
is the quiescent current. I
IN
= I
GND
+ I
OUT
.
Note 8.
V
EN
0.8V, V
IN
8V, and V
OUT
= 0V.
Note 9.
For a 2.5V device, V
IN
= 2.250V (device is in dropout).
Note 10. V
REF
V
OUT
(V
IN
1V), 2.25V
V
IN
16V, 10mA
I
L
750mA, T
J
= T
MAX
.
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 V
IN
= 16V for t = 10ms.
Note 12. Specification for packaged product only.
February 2003
5
MIC3975
MIC3975
Micrel
Typical Characteristics
0
20
40
60
80
1E+1 1E+2 1E+3 1E+4 1E+5 1E+6
PSRR (dB)
FREQUENCY (Hz)
Power Supply
Rejection Ratio
I
OUT
= 750mA
C
OUT
= 10
F
C
IN
= 0
V
IN
= 5V
V
OUT
= 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)
Power Supply
Rejection Ratio
I
OUT
= 750mA
C
OUT
= 47
F
C
IN
= 0
V
IN
= 5V
V
OUT
= 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)
Power Supply
Rejection Ratio
I
OUT
= 750mA
C
OUT
= 10
F
C
IN
= 0
V
IN
= 3.3V
V
OUT
= 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)
Power Supply
Rejection Ratio
I
OUT
= 750mA
C
OUT
= 47
F
C
IN
= 0
V
IN
= 3.3V
V
OUT
= 2.5V
10
100
1k
10k
100k
1M
0
50
100
150
200
250
300
350
0
250
500
750
DROPOUT VOLTAGE (V)
OUTPUT CURRENT (mA)
Dropout Voltage
vs. Output Current
3.3V
1.8V
2.5V
T
A
= 25
C
200
250
300
350
400
-40 -20 0 20 40 60 80 100120140
DROPOUT VOLTAGE (V)
TEMPERATURE (
C)
Dropout Voltage
vs. Temperature
3.3V
2.5V
I
LOAD
= 750mA
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 Characteristics
(2.5V)
ILOAD
=100mA
ILOAD
=750mA
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 Characteristics
(3.3V)
ILOAD
=100mA
ILOAD
=750mA
0
1
2
3
4
5
6
7
8
9
10
0
250
500
750
GROUND CURRENT (mA)
OUTPUT CURRENT (mA)
Ground Current
vs. Output Current
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
0
2
4
6
8
GROUND CURRENT (mA)
SUPPLY VOLTAGE (V)
Ground Current
vs. Supply Voltage (2.5V)
ILOAD
=
100mA
ILOAD
=
10mA
0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
0
2
4
6
8
GROUND CURRENT (mA)
SUPPLY VOLTAGE (V)
Ground Current
vs. Supply Voltage (3.3V)
ILOAD
=100mA
ILOAD
=10mA
0
5
10
15
20
25
30
0
2
4
6
GROUND CURRENT (mA)
SUPPLY VOLTAGE (V)
Ground Current
vs. Supply Voltage (2.5V)
ILOAD
= 750mA
MIC3975
Micrel
MIC3975
6
February 2003
0
5
10
15
20
25
30
0
1
2
3
4
5
6
GROUND CURRENT (mA)
SUPPLY VOLTAGE (V)
Ground Current
vs. Supply Voltage (3.3V)
ILOAD
=750mA
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)
Ground Current
vs. Temperature
3.3V
ILOAD
=
10mA
2.5V
1.8V
5
6
6
7
7
8
8
9
-40 -20 0 20 40 60 80 100120140
GROUND CURRENT (mA)
TEMPERATURE (
C)
Ground Current
vs. Temperature
3.3V
2.5V
I
LOAD
= 750mA
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. Temperature
Typical 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)
Short Circuit
vs. Temperature
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)
Ground Current
vs. Temperature
3.3V
2.5V
I
LOAD
= 500mA
1.8V
0
1
2
3
4
5
6
0.01 0.1
1
10
100 100010000
FLAG VOLTAGE (V)
RESISTANCE (k
)
Error Flag
Pull-Up Resistor
V
IN
= 5V
FLAG HIGH
(OK)
FLAG LOW
(FAULT)
0
2
4
6
8
10
12
-40 -20 0 20 40 60 80 100120140
ENABLE CURRENT
A)
TEMPERATURE (
C)
Enable Current
vs. Temperature
V
IN
= V
OUT
+ 1V
V
EN
= 2.4V
0
50
100
150
200
250
-40 -20 0 20 40 60 80 100120140
FLAG VOLTAGE (mV)
TEMPERATURE (
C)
Flag-Low Voltage
vs. Temperature
V
IN
= 2.25V
R
PULL-UP
= 22k
FLAG-LOW
VOLTAGE
February 2003
7
MIC3975
MIC3975
Micrel
Functional Characteristics
Load Transient Response
TIME (200
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
750mA
100mA
Load Transient Response
TIME (200
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
750mA
10mA
V
OUT
= 2.5V
C
OUT
= 10
F Ceramic
I
LOAD
= 10mA
3.3V
5.0V
Line Transient Response
TIME (200
s/div.)
INPUT V
O
L
T
A
G
E
(1V/div
.
)
OUTPUT V
O
L
T
A
G
E
(50mV/div
.
)
MIC3975
Micrel
MIC3975
8
February 2003
Functional Diagrams
Ref.
18V
O.V.
I
LIMIT
Thermal
Shut-
down
1.240V
1.180V
EN
IN
FLAG
GND
OUT
MIC3975 Fixed Regulator with Flag and Enable Block Diagram
Ref.
18V
O.V.
I
LIMIT
Thermal
Shut-
down
1.240V
EN
IN
GND
OUT
ADJ
MIC3975 Adjustable Regulator Block Diagram
February 2003
9
MIC3975
MIC3975
Micrel
Applications Information
The MIC3975 is a high-performance low-dropout voltage
regulator suitable for moderate to high-current voltage regu-
lator 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 transistor de-
signs, 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 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 MIC3975 regulator is fully protected from damage due to
fault conditions. Linear current limiting is provided. Output
current during overload conditions is constant. Thermal shut-
down disables the device when the die temperature exceeds
the maximum safe operating temperature. Transient protec-
tion allows device (and load) survival even when the input
voltage spikes above and below nominal. The output struc-
ture of these regulators allows voltages in excess of the
desired output voltage to be applied without reverse current
flow.
MIC3975x.x
IN
OUT
GND
C
IN
C
OUT
V
IN
V
OUT
Figure 1. Capacitor Requirements
Output Capacitor
The MIC3975 requires an output capacitor for stable opera-
tion. As a
Cap LDO, the MIC3975 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
MIC3975 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 MIC3975 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 MIC3975 features 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 microam-
peres 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 or
1.65V Conversion
The MIC3975 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
1.65V, 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 MIC3975 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.
Minimum Load Current
The MIC3975 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.
MIC3975
Micrel
MIC3975
10
February 2003
Adjustable Regulator Design
IN
R1
V
OUT
V
IN
C
OUT
R2
EN
OUT
ADJ
GND
MIC3975
ENABLE
SHUTDOWN
V
1.240V 1
R1
R2
OUT
=
+
Figure 2. Adjustable Regulator with Resistors
The MIC3975 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 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 MSOP-8 Thermal Characteristics
One of the secrets of the MIC3975's performance is its power
MSO-8 package featuring half the thermal resistance of a
standard MSO-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).
Using the power MSOP-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 MSOP-8 has a
JA
of
80
C/W, this is significantly lower than the standard MSOP-8
which is typically 160
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.
JA
JC
CA
printed circuit board
ground plane
heat sink area
MSOP-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 maxi-
mum allowable temperature rise must be calculated to deter-
mine 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 (mm
2
)
POWER DISSIPATION (W)
40
C
50
C
55
C
65
C
75
C
85
C
100
C
Figure 4. Copper Area vs. Power-MSOP
Power Dissipation (
T
JA
)
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)
85
C
50
C 25
C
T
J
= 125
C
Figure 5. Copper Area vs. Power-MSOP
Power Dissipation (T
A
)
February 2003
11
MIC3975
MIC3975
Micrel
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 750mA, then our power dissipation is as follows:
P
D
= (3.3V 2.5V)
750mA + 3.3V
7.5mA
P
D
= 600mW + 25mW
P
D
= 625mW
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,
625mW, the curve in Figure 5 shows that the required area of
copper is 160mm
2
.
The
JA
of this package is ideally 80
C/W, but it will vary
depending upon the availability of copper ground plane to
which it is attached.
MIC3975
Micrel
MIC3975
12
February 2003
Package Information
0.008 (0.20)
0.004 (0.10)
0.039 (0.99)
0.035 (0.89)
0.021 (0.53)
0.012 (0.03) R
0.0256 (0.65) TYP
0.012 (0.30) R
5
MAX
0
MIN
0.122 (3.10)
0.112 (2.84)
0.120 (3.05)
0.116 (2.95)
0.012 (0.3)
0.007 (0.18)
0.005 (0.13)
0.043 (1.09)
0.038 (0.97)
0.036 (0.90)
0.032 (0.81)
DIMENSIONS:
INCH (MM)
0.199 (5.05)
0.187 (4.74)
8-Lead MSOP (MM)
MICREL, INC.
1849 FORTUNE DRIVE
SAN JOSE, CA 95131
USA
TEL
+ 1 (408) 944-0800
FAX
+ 1 (408) 944-0970
WEB
http://www.micrel.com
The information furnished by Micrel in this datasheet 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.
2003 Micrel, Incorporated.
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