Micrel MIC3975-3.3BMM 750ma ucap low-voltage low-dropout regulator Datasheet

MIC3975
Micrel
MIC3975
750mA µCap Low-Voltage Low-Dropout Regulator
Final Information
General Description
Features
The MIC3975 is a 750mA low-dropout linear voltage regulators that provide low-voltage, high-current output from an
extremely small package. Utilizing Micrel’s proprietary Super
βeta PNP™ 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.
• 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
•
•
•
•
•
•
•
•
For other voltages, contact Micrel.
Fiber optic modules
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
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
Typical Applications
100k
VIN
3.3V
ENABLE
SHUTDOWN
Error
Flag
Output
MIC3975-2.5BMM
IN
OUT
VIN
2.5V
2.5V
R1
EN
FLG
GND
ENABLE
SHUTDOWN
10µF
ceramic
MIC3975BMM
IN
OUT
1.5V
R1
EN
ADJ
GND
R2
10µF
ceramic
1.5V/750mA Adjustable Regulator
2.5V/750mA Regulator with Error Flag
Super βeta 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
February 2003
1
MIC3975
MIC3975
Micrel
Pin Configuration
EN 1
8 GND
EN 1
8 GND
IN 2
7 GND
IN 2
7 GND
FLG 3
6 GND
ADJ 3
6 GND
OUT 4
5 GND
OUT 4
5 GND
MIC3975-x.x
Fixed
MSOP-8 (MM)
Adjustable
MSOP-8 (MM)
Pin Description
Pin No.
Pin No.
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
Pin Name
Pin Function
FLG
Flag (Output): Open-collector error flag output. Active low = output undervoltage.
3
ADJ
Adjustment Input: Feedback input. Connect to resistive voltage-divider
network.
4
4
OUT
Regulator Output
5–8
5–8
GND
Ground
MIC3975
2
February 2003
MIC3975
Micrel
Absolute Maximum Ratings (Note 1)
Operating Ratings (Note 2)
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
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
MSOP-8 (θJA) ...................................................... 80°C/W
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
Max
Units
VOUT
Output Voltage
10mA
10mA ≤ IOUT ≤ 750mA, VOUT + 1V ≤ VIN ≤ 8V
1
2
%
%
Line Regulation
IOUT = 10mA, VOUT + 1V ≤ VIN ≤ 16V
0.06
0.5
%
Load Regulation
VIN = VOUT + 1V, 10mA ≤ IOUT ≤ 750mA,
0.2
1
%
40
100
ppm/°C
IOUT = 100mA, ∆VOUT = –1%
140
200
250
mV
mV
IOUT = 500mA, ∆VOUT = –1%
225
IOUT = 750mA, ∆VOUT = –1%
300
IOUT = 100mA, VIN = VOUT + 1V
400
µA
IOUT = 500mA, VIN = VOUT + 1V
4
mA
IOUT = 750mA, VIN = VOUT + 1V
7.5
15
mA
Current Limit
VOUT = 0V, VIN = VOUT + 1V
1.8
2.5
A
Enable Input Voltage
logic low (off)
0.8
V
∆VOUT/∆T
Output Voltage Temp. Coefficient,
Note 5
VDO
Dropout Voltage, Note 6
IGND
IOUT(lim)
Ground Current, Note 7
Min
Typ
–1
–2
mV
500
mV
Enable Input
VEN
logic high (on)
IEN
Enable Input Current
VEN = 2.25V
2.25
1
V
15
VEN = 0.8V
30
75
µA
µA
2
4
µA
µA
Flag Output
IFLG(leak)
Output Leakage Current
VOH = 16V
0.01
1
2
µA
µA
VFLG(do)
Output Low Voltage
VIN = 2.250V, IOL, = 250µA, Note 9
210
300
400
mV
mV
VFLG
Low Threshold
% of VOUT
High Threshold
% of VOUT
93
99.2
Hysteresis
February 2003
%
1
3
%
%
MIC3975
MIC3975
Symbol
Micrel
Parameter
Condition
Min
Typ
Max
Units
1.228
1.215
1.203
1.240
1.252
1.265
1.277
V
V
V
40
80
120
nA
nA
Adjustable Output Only
Reference Voltage
Note 10
Adjust Pin Bias Current
Reference Voltage
Temp. Coefficient
Note 11
Adjust Pin Bias Current
Temp. Coefficient
20
ppm/°C
0.1
nA/°C
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 ∆VOUT(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 ≤ 750mA, 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.
MIC3975
4
February 2003
MIC3975
Micrel
Typical Characteristics
Power Supply
Rejection Ratio
80
Power Supply
Rejection Ratio
80
VIN = 5V
VOUT = 3.3V
IOUT = 750mA
COUT = 10µF
CIN = 0
IOUT = 750mA
COUT = 47µF
CIN = 0
40
IOUT = 750mA
COUT = 10µF
CIN = 0
20
0
1E+1
1k 1E+4
10k 1E+5
1M
10 1E+2
100k 1E+6
100 1E+3
FREQUENCY (Hz)
0
1E+1
1k 1E+4
10k 1E+5
1M
10 1E+2
100k 1E+6
100 1E+3
FREQUENCY (Hz)
0
1E+1
1k 1E+4
10k 1E+5
1M
10 1E+2
100k 1E+6
100 1E+3
FREQUENCY (Hz)
Power Supply
Rejection Ratio
Dropout Voltage
vs. Output Current
Dropout Voltage
vs. Temperature
0
1E+1
1k 1E+4
10k 1E+5
1M
10 1E+2
100k 1E+6
100 1E+3
FREQUENCY (Hz)
2.6
OUTPUT VOLTAGE (V)
2.4
2.2
ILOAD =750mA
1.8
1.6
1.4
2
2.3
2.6
2.9
3.2
SUPPLY VOLTAGE (V)
1.8V
200
3.3V
150
100
50
TA = 25°C
3.4
3.2
3.0
ILOAD =750mA
2.8
2.6
3.2
3.6
4.0
SUPPLY VOLTAGE (V)
4.4
Ground Current
vs. Supply Voltage (2.5V)
1.2
1.0
0.8
0.6
0.4
ILOAD =10mA
0.2
0
GROUND CURRENT (mA)
GROUND CURRENT (mA)
ILOAD =100mA
25
20
15
10
5
ILOAD = 750mA
0
0
2
4
6
SUPPLY VOLTAGE (V)
February 2003
8
250
3.3V
0
2
4
SUPPLY VOLTAGE (V)
5
10
9
8
7
6
5
4
3
2
1
0
0
1.8V
2.5V
3.3V
250
500
750
OUTPUT CURRENT (mA)
Ground Current
vs. Supply Voltage (3.3V)
1.4
30
1.6
1.4
1.8V
Ground Current
vs. Output Current
ILOAD =100mA
Ground Current
vs. Supply Voltage (2.5V)
2.0
1.8
300
Dropout Characteristics
(3.3V)
2.4
2.8
3.5
2.5V
350
ILOAD = 750mA
200
-40 -20 0 20 40 60 80 100120140
TEMPERATURE (°C)
250
500
750
OUTPUT CURRENT (mA)
3.6
ILOAD =100mA
2.0
2.5V
0
0
Dropout Characteristics
(2.5V)
2.8
250
DROPOUT VOLTAGE (V)
IOUT = 750mA
COUT = 47µF
CIN = 0
300
GROUND CURRENT (mA)
40
20
400
350
VIN = 3.3V
VOUT = 2.5V
60
PSRR (dB)
40
20
80
OUTPUT VOLTAGE (V)
VIN = 3.3V
VOUT = 2.5V
60
PSRR (dB)
PSRR (dB)
40
20
GROUND CURRENT (mA)
80
VIN = 5V
VOUT = 3.3V
60
DROPOUT VOLTAGE (V)
PSRR (dB)
60
Power Supply
Rejection Ratio
1.2
1.0
ILOAD =100mA
0.8
0.6
ILOAD =10mA
0.4
0.2
0
6
0
2
4
6
SUPPLY VOLTAGE (V)
8
MIC3975
MIC3975
Micrel
1.0
20
15
10
5
0
0
GROUND CURRENT (mA)
9
1
2
3
4
5
SUPPLY VOLTAGE (V)
0.8
0.6
3.3V
0.4
0.2
6
8
7
1.8V
7
3.3V
6
6
ILOAD = 750mA
5
FLAG HIGH
(OK)
3
2
1
0
0.01 0.1
FLAG LOW
(FAULT)
1
10 100 100010000
RESISTANCE (kΩ)
3.0
2.5
1.8V
2.0
1.5
1.0
0.5
ILOAD = 500mA
Short Circuit
vs. Temperature
Typical 3.3V
Device
3.25
3.20
-40 -20 0 20 40 60 80 100 120
TEMPERATURE (°C)
12
ENABLE CURRENT µA)
VIN = 5V
3.3V
Output Voltage
vs. Temperature
3.30
6
2.5V
4.0
3.5
0
-40 -20 0 20 40 60 80 100 120
TEMPERATURE (°C)
3.35
Error Flag
Pull-Up Resistor
FLAG VOLTAGE (V)
1.8V
3.40
2.5V
5
-40 -20 0 20 40 60 80 100120140
TEMPERATURE (°C)
MIC3975
2.5V
5.0
4.5
Ground Current
vs. Temperature
0
-40 -20 0 20 40 60 80 100 120
TEMPERATURE (°C)
Ground Current
vs. Temperature
8
4
ILOAD =10mA
10
SHORT CIRCUIT CURRENT (A)
25
Enable Current
vs. Temperature
VIN = VOUT + 1V
VEN = 2.4V
8
6
4
2
0
-40 -20 0 20 40 60 80 100120140
TEMPERATURE (°C)
6
2.5
2.0
3.3V
1.5
2.5V
1.8V
1.0
0.5
0
-40 -20 0 20 40 60 80 100 120
TEMPERATURE (°C)
250
FLAG VOLTAGE (mV)
GROUND CURRENT (mA)
ILOAD =750mA
OUTPUT VOLTAGE (V)
GROUND CURRENT (mA)
30
Ground Current
vs. Temperature
GROUND CURRENT (mA)
Ground Current
vs. Supply Voltage (3.3V)
200
Flag-Low Voltage
vs. Temperature
FLAG-LOW
VOLTAGE
150
100
VIN = 2.25V
RPULL-UP = 22kΩ
50
0
-40 -20 0 20 40 60 80 100120140
TEMPERATURE (°C)
February 2003
MIC3975
Micrel
Functional Characteristics
OUTPUT VOLTAGE
(200mV/div.)
Load Transient Response
VIN = 3.3V
VOUT = 2.5V
COUT = 10µF Ceramic
VIN = 3.3V
VOUT = 2.5V
COUT = 10µF Ceramic
750mA
LOAD CURRENT
(500mA/div.)
750mA
LOAD CURRENT
(500mA/div.)
OUTPUT VOLTAGE
(200mV/div.)
Load Transient Response
100mA
10mA
TIME (200µs/div.)
TIME (200µs/div.)
OUTPUT VOLTAGE
(50mV/div.)
INPUT VOLTAGE
(1V/div.)
Line Transient Response
5.0V
3.3V
VOUT = 2.5V
COUT = 10µF Ceramic
ILOAD = 10mA
TIME (200µs/div.)
February 2003
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MIC3975
MIC3975
Micrel
Functional Diagrams
OUT
IN
O.V.
ILIMIT
1.180V
FLAG
Ref.
18V
1.240V
EN
Thermal
Shutdown
GND
MIC3975 Fixed Regulator with Flag and Enable Block Diagram
OUT
IN
O.V.
ILIMIT
Ref.
18V
1.240V
ADJ
EN
Thermal
Shutdown
GND
MIC3975 Adjustable Regulator Block Diagram
MIC3975
8
February 2003
MIC3975
Micrel
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 bypassing 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 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 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 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 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 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 designs. 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 respectively. This gives the PNP based regulators a distinct advantage 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.
Applications Information
The MIC3975 is a high-performance low-dropout voltage
regulator suitable for moderate to high-current voltage regulator applications. Its 500mV dropout voltage at full load and
overtemperature makes it especially valuable in batterypowered systems and as high-efficiency noise filters in postregulator applications. Unlike older NPN-pass transistor designs, where the minimum dropout voltage is limited by the
base-to-emitter voltage drop and collector-to-emitter saturation voltage, dropout performance of the PNP output of these
devices is limited only by the low 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 MIC3975 regulator is fully protected from damage due to
fault conditions. Linear current limiting is provided. Output
current during overload conditions is constant. Thermal shutdown disables the device when the die temperature exceeds
the maximum safe operating temperature. Transient protection allows device (and load) survival even when the input
voltage spikes above and below nominal. The output structure of these regulators allows voltages in excess of the
desired output voltage to be applied without reverse current
flow.
VIN
MIC3975x.x
IN
CIN
VOUT
OUT
GND
COUT
Figure 1. Capacitor Requirements
Output Capacitor
The MIC3975 requires an output capacitor for stable operation. As a µCap LDO, the MIC3975 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
MIC3975 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 transient response and noise reduction at high frequency.
X7R/X5R dielectric-type ceramic capacitors are recommended because of their temperature performance. X7Rtype capacitors change capacitance by 15% over their operating temperature range and are the most stable type of
ceramic capacitors. Z5U and Y5V dielectric capacitors change
value by as much as 50% and 60% respectively over their
operating temperature ranges. To use a ceramic chip capacitor with Y5V dielectric, the value must be much higher than an
X7R ceramic capacitor to ensure the same minimum capacitance over the equivalent operating temperature range.
February 2003
9
MIC3975
MIC3975
Micrel
sink thermal resistance) and θSA (sink-to-ambient thermal
resistance).
Using the power MSOP-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 capability of the device. Typically, the power MSOP-8 has a θJA of
80°C/W, this is significantly lower than the standard MSOP-8
which is typically 160°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.
Adjustable Regulator Design
VIN
MIC3975
OUT
IN
VOUT
R1
ENABLE
SHUTDOWN
EN
ADJ
GND
R2
COUT
 R1
VOUT = 1.240V 1 +

 R2 
Figure 2. Adjustable Regulator with Resistors
The MIC3975 allows programming the output voltage anywhere 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:
V

R1 = R2  OUT − 1
 1.240 
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 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 singlepiece 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-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-
MSOP-8
θJA
θJC
printed circuit board
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.
100°C
900
800
COPPER AREA (mm2)
40°C
50°C
55°C
65°C
75°C
85°C
COPPER AREA (mm2)
700
600
500
400
300
200
100
0
0
700
TJ = 125°C
85°C
50°C 25°C
600
500
400
300
200
100
0
0
0.25 0.50 0.75 1.00 1.25 1.50
POWER DISSIPATION (W)
Figure 4. Copper Area vs. Power-MSOP
∆TJA)
Power Dissipation (∆
MIC3975
ground plane
heat sink area
AMBIENT
900
800
θCA
0.25 0.50 0.75 1.00 1.25 1.50
POWER DISSIPATION (W)
Figure 5. Copper Area vs. Power-MSOP
Power Dissipation (TA)
10
February 2003
MIC3975
Micrel
∆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 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 750mA, then our power dissipation is as follows:
PD = (3.3V – 2.5V) × 750mA + 3.3V × 7.5mA
PD = 600mW + 25mW
PD = 625mW
From Figure 4, the minimum amount of copper required to
operate this application at a ∆T of 75°C is 160mm2.
February 2003
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 maximum 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 160mm2.
The θJA 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.
11
MIC3975
MIC3975
Micrel
Package Information
0.199 (5.05)
0.187 (4.74)
0.122 (3.10)
0.112 (2.84)
DIMENSIONS:
INCH (MM)
0.120 (3.05)
0.116 (2.95)
0.036 (0.90)
0.032 (0.81)
0.043 (1.09)
0.038 (0.97)
0.012 (0.30) R
0.012 (0.3)
0.0256 (0.65) TYP
0.008 (0.20)
0.004 (0.10)
5° MAX
0° MIN
0.007 (0.18)
0.005 (0.13)
0.012 (0.03) R
0.039 (0.99)
0.035 (0.89)
0.021 (0.53)
8-Lead MSOP (MM)
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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.
MIC3975
12
February 2003
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