MIC79050 [MICREL]
Simple Lithium-Ion Battery Charger Preliminary Information; 简单的锂离子电池充电器的初步信息
| 型号： | MIC79050 |
| 厂家： | 
MICREL SEMICONDUCTOR |
| 描述： | Simple Lithium-Ion Battery Charger Preliminary Information |
| 文件： | 总20页 (文件大小：104K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
MIC79050
Simple Lithium-Ion Battery Charger
Preliminary Information
General Description
Features
The MIC79050 is a simple single-cell lithium-ion battery
charger. It includes an on-chip pass transistor for high preci-
sioncharging.Featuringultrahighprecision(+0.75%overthe
Li-ion battery charging temperature range) and “zero” off
mode current, the MIC79050 provides a very simple, cost
effective solution for charging lithium-ion battery.
• High accuracy charge voltage:
±0.75% over -5°C to + 60°C (Li-ion charging
temperature range)
• “Zero” off-mode current
• 10µA reverse leakage
• Ultralow 380mV dropout at 500mA
• Wide input voltage range
• Logic controlled enable input (8-pin devices only)
• Thermal shutdown and current limit protection
• Power MSOP-8, Power SOP-8, and SOT-223
• Pulse charging capability
Other features of the MIC79050 include current limit and
thermal shutdown protection. In the event the input voltage to
the charger is disconnected, the MIC79050 also provides
minimal reverse-current and reversed-battery protection.
The MIC79050 is a fixed 4.2V device and comes in the
thermally-enhanced MSO-8, SO-8, and SOT-223 packages.
The 8-pin versions also come equipped with enable and
feedback inputs. All versions are specified over the tempera-
ture range of –40°C to +125°C.
Applications
• Li-ion battery charger
• Celluar phones
• Palmtop computers
• PDAs
• Self charging battery packs
Ordering Information
Part Number
Voltage
4.2V
Junct. Temp. Range
–40°C to +125°C
–40°C to +125°C
–40°C to +125°C
Package
SOT-223
SOP-8
MIC79050-4.2BS
MIC79050-4.2BM
MIC79050-4.2BMM
4.2V
4.2V
MSOP-8
Typical Applications
MIC79050-4.2BS
4.2V ±0.75% Over Temp
Regulated or
unregulated
wall adapter
IN
BAT
Li-Ion
Cell
GND
Simplest Battery Charging Solution
Regulated or
unregulated
wall adapter
MIC79050-4.2BMM
4.2V ±0.75%
IN
BAT
FB
Li-Ion
Cell
EN
External PWM*
GND
*See Applications Information
Pulse-Charging Application
Micrel, Inc. • 1849 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 944-0970 • http://www.micrel.com
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MIC79050
MIC79050
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Pin Configuration
GND
TAB
1
2
3
IN GND
BAT
MIC79050-x.xBS
SOT-223
EN
IN
GND
GND
GND
GND
1
8
7
6
5
2
3
4
BAT
FB
MIC79050-x.xBM
SOP-8 and MSOP-8
Pin Description
Pin No.
SOT-223
Pin No.
SOP-8
Pin Name Pin Function
MSOP-8
1
2
IN
Supply Input
2, TAB
5–8
GND
Ground: SOT-223 pin 2 and TAB are internally connected. SO-8 pins 5 through 8 are
internally connected.
3
3
1
BAT
EN
Battery Voltage Output
Enable (Input): TTL/CMOS compatible control input. Logic high = enable; logic low or open =
shutdown.
4
FB
Feedback Node
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Absolute Maximum Ratings (Note 1)
Operating Ratings (Note 2)
Supply Input Voltage (V ) ............................ –20V to +20V
Supply Input Voltage (V ) ........................... +2.5V to +16V
IN
IN
Power Dissipation (P ) ............... Internally Limited, Note 3
Enable Input Voltage (V ) .................................. 0V to V
D
EN
IN
Junction Temperature (T ) ....................... –40°C to +125°C
Junction Temperature (T ) ....................... –40°C to +125°C
J
J
Lead Temperature (soldering, 5 sec.) ....................... 260°C
Package Thermal Resistance (Note 3) ...............................
Storage Temperature (T ) ....................... –65°C to +150°C
MSOP-8 (θ ) ......................................................80°C/W
S
JA
SOP-8(θ ) ..........................................................63°C/W
JA
SOT-223(θ ) ......................................................15°C/W
JC
Electrical Characteristics
VIN = VBAT + 1.0V; COUT = 4.7µF, IOUT = 100µA; TJ = 25°C, bold values indicate –40°C ≤ TJ ≤ +125°C; unless noted.
Symbol
VBAT
Parameter
Conditions
Min Typical Max
Units
%
Battery Voltage Accuracy
variation from nominal VOUT –5°C to +60°C
–0.75
+0.75
∆VBAT/∆T
Battery Voltage
Temperature Coefficient
Note 4
40
0.009
0.05
380
85
ppm/°C
∆VBAT/VBAT Line Regulation
∆VBAT/VBAT Load Regulation
VIN = VBAT + 1V to 16V
IOUT = 100µA to 500mA, Note 5
IOUT = 500mA
0.05
0.1
%/V
%/V
0.5
0.7
%
%
VIN – VBAT
Dropout Voltage, Note 6
500
600
mV
mV
IGND
Ground Pin Current, Notes 7, 8
V
EN ≥ 3.0V, IOUT = 100µA
EN ≥ 3.0V, IOUT = 500mA
130
170
µA
µA
V
11
20
25
mA
mA
IGND
Ground Pin Quiescent Current,
Note 8
V
EN ≤ 0.4V (shutdown)
EN ≤ 0.18V (shutdown)
0.05
0.10
75
3
8
µA
µA
dB
V
PSRR
ILIMIT
Ripple Rejection
Current Limit
f = 120Hz
VBAT = 0V
750
900
1000
mA
mA
∆VBAT/∆PD
ENABLE Input
VENL
Thermal Regulation
Note 9
0.05
0.4
%/W
Enable Input Logic-Low Voltage
VEN = logic low (shutdown)
VEN = logic high (enabled)
V
V
0.18
2.0
V
IENL
Enable Input Current
VENL ≤ 0.4V (shutdown)
VENL ≤ 0.18V (shutdown)
VENH ≥ 2.0V (enabled)
0.01
0.01
5
–1
µA
µA
–2
IENH
20
25
µA
µA
Note 1. Exceeding the absolute maximum rating may damage the device.
Note 2. The device is not guaranteed to function outside its operating rating.
Note 3. The maximum allowable power dissipation at any T (ambient temperature) is calculated using: P
= (T
– T ) ÷ θ . Exceeding the
A
D(max)
J(max) A JA
maximum allowable power dissipation will result in excessive die temperature, and the regulator will go into thermal shutdown.
Note 4. Battery voltage temperature coefficient is the worst case voltage change divided by the total temperature range.
Note 5. Regulation is measured at constant junction temperature using low duty cycle pulse testing. Parts are tested for load regulation in the load
range from 100µA to 500mA. Changes in output voltage due to heating effects are covered by the thermal regulation specification.
Note 6. Dropout voltage is defined as the input to battery output differential at which the battery voltage drops 2% below its nominal value measured at
1V differential.
Note 7: Ground pin current is the charger quiescent current plus pass transistor base current. The total current drawn from the supply is the sum of the
load current plus the ground pin current.
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Note 8:
V
is the voltage externally applied to devices with the EN (enable) input pin. [MSO-8(MM) and SO-8 (M) packages only.]
EN
Note 9: Thermal regulation is the change in battery voltage at a time “t” after a change in power dissipation is applied, excluding load or line regulation
effects. Specifications are for a 500mA load pulse at V = 16V for t = 10ms.
IN
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Typical Characteristics
Dropout Voltage
vs. Output Current
Dropout Voltage
vs. Temperature
Dropout Characteristics
400
600
500
400
300
200
100
0
5
4
3
2
1
0
300
200
100
0
5mA
50mA, 150mA
0
100 200 300 400 500
OUTPUT CURRENT (mA)
-40
0
40
80
120
0
2
4
6
8
10 12 14 16
TEMPERATURE (C)
INPUT VOLTAGE (V)
Output Current
vs. Ground
Dropout Characteristics
Ground Current
vs. Supply Voltage
12
10
8
5
1.5
1
4
3
2
1
0
50mA
5mA
250mA
500mA
6
4
0.5
2
0
0
0
100 200 300 400 500
OUTPUT CURRENT (mA)
0
2
4
6
0
4
8
12
16
120
120
INPUT VOLTAGE (V)
SUPPLY VOLTAGE (V)
Ground Current
vs. Temperature
Ground Current
vs. Temperature
Ground Current
vs. Supply Voltage
150
100
50
4.0
3.8
3.6
3.4
3.2
3.0
25
20
15
10
5
500mA
250mA
125mA
0
0
-40
0
40
80
120
-40
0
40
80
0
1
2
3
4
5
6
TEMPERATURE (C)
TEMPERATURE (C)
SUPPLY VOLTAGE (V)
Ground Current
vs. Temperature
Battery Voltage
vs. Temperature
Short Circuit Current
vs. Temperature
13.5
13.0
12.5
12.0
11.5
11.0
4.210
4.205
4.200
4.195
4.190
800
700
600
500
400
300
200
100
0
-40
0
40
80
120
-40 -20
0
20 40 60 80 100120140
-40
0
40
80
TEMPERATURE (C)
TEMPERATURE (C)
TEMPERATURE (C)
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Typical Voltage Drift Limits
vs. Time
Reverse Leakage Current
vs. Output Voltage
Reverse Leakage Current
vs. Output Voltage
0.75
20
15
10
5
20
15
10
5
4.2V
3.6V
3.0V
0.25
Upper
Lower
-0.25
-0.75
VIN+VEN
FLOATING
0
0
0
200
400
600
800
0
1
2
3
4
5
-5
5
15 25 35 45 55
TEMPERATURE (C)
TIME (hrs)
OUTPUT VOLTAGE (V)
Reverse Leakage Current
vs. Temperature
20
15
10
5
4.2V
3.6V
3.0V
VIN+VEN
GROUNDED
0
-5
5
15 25 35 45 55
TEMPERATURE (C)
MIC79050
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Block Diagrams
VBAT
IN
VIN
Bandgap
Ref.
Current Limit
Thermal Shutdown
MIC79050-x.xBS
GND
3-Pin Version
VBAT
IN
VIN
FB
Bandgap
Ref.
EN
Current Limit
Thermal Shutdown
MIC79050-x.xBMM/M
GND
5-Pin Version
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drawn by the battery has approached a minimum and/or the
maximum charging time has timed out. When disabled, the
regulator output sinks a minimum of current with the battery
voltage applied directly onto the output. This current is
typically 12µA or less.
Functional Description
The MIC79050 is a high-accuracy, linear battery charging
circuit designed for the simplest implementation of a single
lithium-ion(Li-ion)batterycharger. Thepartcanoperatefrom
a regulated or unregulated power source, making it ideal for
variousapplications. TheMIC79050cantakeanunregulated
voltage source and provide an extremely accurate termina-
tion voltage. The output voltage varies only 0.75% from
nominal over the standard temperature range for Li-ion
battery charging (–5°C to 60°C). With a minimum of external
components, an accurate constant current charger can be
designedtoprovideconstantcurrent,constantvoltagecharg-
ing for Li-ion cells.
Feedback
The feedback pin allows for external manipulation of the
control loop. This node is connected to an external resistive
divider network, which is connected to the internal error
amplifier. This amplifier compares the voltage at the feed-
back pin to an internal voltage reference. The loop then
corrects for changes in load current or input voltage by
monitoring the output voltage and linearly controlling the
drive to the large, PNP pass element. By externally control-
lingthevoltageatthefeedbackpintheoutputcanbedisabled
or forced to the input voltage. Pulling and holding the feed-
back pin low forces the output low. Holding the feedback pin
highforcesthepasselementintosaturation,wheretheoutput
will be the input minus the saturation (dropout) voltage.
Input Voltage
The MIC79050 can operate with an input voltage up to 16V
(20V absolute maximum), ideal for applications where the
input voltage can float high, such as an unregulated wall
adapter that obeys a load-line. Higher voltages can be
sustainedwithoutanyperformancedegradationtotheoutput
voltage.Thelineregulationofthedeviceistypically0.009%/V;
that is, a 10V change on the input voltage corresponds to a
0.09% change in output voltage.
Battery Output
The BAT pin is the output of the MIC79050 and connects
directly to the cell to provide charging current and voltage.
When the input is left floating or grounded, the BAT pin limits
reverse current to <12µA to minimize battery drain.
Enable
The MIC79050 has an enable pin that allows the charger to
be disabled when the battery is fully charged and the current
MIC79050
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June 2000
MIC79050
Micrel
Applications Information
Simple Lithium-Ion Battery Charger.
Figure 1A shows a simple, complete lithium-ion battery
charger. The charging circuit comprises of a cheap wall
adapter, with a load-line characteristic. This characteristic is
always present with cheap adapters due to the internal
impedance of the transformer windings. The load-line of the
unregulated output should be < 4.4V to 4.6V at somewhere
between 0.5C to 1C of the battery under charge. This 4.4 to
4.6V value is an approximate number based on the head-
room needed above 4.2V for the MIC79050 to operate
correctly e.g. For a 500mAhr battery, the output of the semi-
regulated supply should be between 225mA to 500mA ( 0.5C
to 1C ). If it is below 225mA no damage will occur but the
battery will take longer to charge. Figure 1B shows a typical
walladaptercharacteristicwithanoutputcurrentof350mAat
4.5V. This natural impedance of the wall adapter will limit the
maxcurrentintothebattery, sonoexternalcircuitryisneeded
to accomplish this.
If extra impedance is needed to achieve the desired loadline,
extra resistance can easily be added in series with the
MIC79050 IN pin.
Impedence
MIC79050-4.2BM
VS
IN
BAT
FB
4.7µF
EN
10k R1
R2
1k
GND
MIC6270
LM4041
CIM3-1.2
AC Load-line Wall Adapter
End of Charge
R1
R2
V
= V
1+
EOC
REF
VREF = 1.225V
Figure 1A. Load-Line Charger With End-Of-Charge Termination Circuit.
Load-Line Source
Characteristics
8
6
4
2
0
0
0.2
0.4
0.6
0.8
SOURCE CURRENT (A)
Figure 1B. Load-Line Characteristics
of AC Wall Adapter
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MIC79050
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Application Information
End of Charge (VEOC
)
Open Circuit
Charger Voltage
VEOC
Unregulated Input
Voltage(VB)
79050 Programmed
Output Voltage
(No Load Voltage)
Battery Voltage (VB)
Battery Current (IB)
State A
State B
State C
State D
Charge Top
State C
Initial Charge
Voltage Charge
End of Charge
Figure 1C. Charging Cycles
The Charging Cycle (See Figure 1C.)
input voltage has reached such a level so the current in
the battery is low, indicating full charge.
3. State C: End of charge cycle. When the input voltage,
1. State A: Initial charge. Here the battery’s charging
current is limited by the wall adapter’s natural imped-
ance. The battery voltage approaches 4.2V.
V reaches V
an end of charge signal is indicated.
S
EOC,
4. State D: Top up charge. As soon as enough current is
drawn out of the input source, which pulls the voltage
2. State B: Constant voltage charge. Here the battery
voltage is at 4.2V ± 0.75% and the current is decaying in
the battery. When the battery has reached approxi-
mately 1/10th of its 1C rating, the battery is considered
to have reached full charge. Because of the natural
characteristic impedance of the cheap wall adapters, as
the battery voltage decreases so the input voltage
increases. The MIC6270 and the LM4041 are config-
ured as a simple voltage monitor, indicating when the
lower than the V
, the end of charge flag will be
EOC
pulled low and charging will initiate.
Variations on this scheme can be implemented, such as the
circuit shown in Figure 2.
For those designs that have a zero impedance source , see
Figure 3.
5V ±5%@
400mA ±5%
MIC79050-4.2BM
0.050Ω
IN
BAT
FB
EN
4.7µF
10k
R2
8.06M
GND
1k
1k
47k
Q1
MIC7300
10k
MIC6270
47k
LM4041
CIM3-1.2
Figure 2. Protected Constant-Current Charger
MIC79050
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does not harm the cell but simply stores less usable energy
in the battery. The charge cycle is completed by disabling the
charge circuit after the termination current drops below a
minimum recommended level, typically 50mA or less, de-
pending on the manufacturer’s recommendation, or if the
circuit times out.
Applications Information
Protected Constant-Current Charger
Another form of charging is using a simple wall adapter that
offersafixedvoltageatacontrolled, maximumcurrentrating.
The output of a typical charger will source a fixed voltage at
a maximum current unless that maximum current is ex-
ceeded. In the event that the maximum current is exceeded,
thevoltagewilldropwhilemaintainingthatmaximumcurrent.
Using an MIC79050 after this type of charger is ideal for
lithium-ion battery charging. The only obstacle is end of
charger termination. Using a simple differential amplifier and
asimilarcomparatorandreferencecircuit, similartoFigure1,
completes a single cell lithium-ion battery charger solution.
Time Out
The time-out aspect of lithium-ion battery charging can be
added as a safety feature of the circuit. Often times this
function is incorporated in the software portion of an applica-
tionusingareal-timeclocktocountoutthemaximumamount
of time allowed in the charging cycle. When the maximum
recommended charge time for the specific cell has been
exceeded, the enable pin of the MIC79050 can be pulled low,
and the output will float to the battery voltage, no longer
providing current to the output.
Figure 2 shows this solution in completion. The source is a
fixed 5V source capable of a maximum of 400mA of current.
When the battery demands full current (fast charge), the
source will provide only 400mA and the input will be pulled
down. The output of the MIC79050 will follow the input minus
a small voltage drop. When the battery approaches full
Asasecondoption, thefeedbackpinoftheMIC79050canbe
modulated as in Figure 4. Figure 4. shows a simple circuit
where the MIC834, an integrated comparator and reference,
monitors the battery voltage and disables the MIC79050
output after the voltage on the battery exceeds a set vaue.
When the voltage decays below this set threshold, the
MIC834 drives Q1 low allowing the MIC79050 to turn on
againandprovidecurrenttothebatteryuntilitisfullycharged.
This form of pulse charging is an acceptable way of maintain-
ing the full charge on a cell until it is ready to be used.
charge, the current will taper off. As the current across R
S
approaches 50mA, the output of the differential amplifier
(MIC7300)willapproach1.225V,thereferencevoltagesetby
the LM4041. When it drops below the reference voltage, the
output of the comparator (MIC6270) will allow the base of Q1
to be pulled high through R2.
Zero-Output Impedance Source Charging
MIC79050-4.2BMM
Input voltage sources that have very low output impedances
can be a challenge due to the nature of the source. Using the
circuitinFigure3willprovideaconstant-currentandconstant
voltagechargingalgorithmwiththeappropriateend-of-charge
termination. The main loop consists of an op-amp controlling
the feedback pin through the schottky diode, D1. The charge
IN
BAT
FB
VIN
4.7µF
Li-Ion
Cell
EN
GND
MIC834
VDD OUT
100k
R1
R2
INP GND
current throughR isheldconstant bytheop-ampcircuit until
S
GND
the output draws less than the set charge-current. At this
point, the output goes constant-voltage. When the current
R1
R2
V
= V
1+
throughR getstolessthan50mA, thedifferenceampoutput
BAT(low)
REF
S
becomes less than the reference voltage of the MIC834 and
theoutputpullslow.ThissetstheoutputoftheMIC79050less
than nominal, stopping current flow and terminating charge.
VREF=1.240V
Figure 4. Pulse Charging For
Top-off Voltage
Lithium-Ion Battery Charging
Charging Rate
Single lithium-ion cells are typically charged by providing a
constant current and terminating the charge with constant
voltage. The charge cycle must be initiated by ensuring that
the battery is not in deep discharge. If the battery voltage is
below 2.5V, it is commonly recommended to trickle charge
the battery with 5mA to 10mA of current until the output is
above 2.5V. At this point the battery can be charged with
constant current until it reaches its top off voltage (4.2V for a
typical single lithium-ion cell) or a time out occurs.
Lithium-ion cells are typically charged at rates that are
fractional multiples of their rated capacity. The maximum
varies between 1C – 1.3C (1× to 1.3× the capacity of the cell).
The MIC79050 can be used for any cell size. The size of the
cell and the current capability of the input source will deter-
mine the overall circuit charge rate. For example, a 1200mAh
battery charged with the MIC79050 can be charged at a
maximum of 0.5C. There is no adverse effects to charging at
lower charge rates; that charging will just take longer. Charg-
ing at rates greater than 1C are not recommended, or do they
decrease the charge time linearly.
For the constant-voltage portion of the charging circuit, an
extremely accurate termination voltage is highly recom-
mended. The higher the accuracy of the termination circuit,
the more energy the battery will store. Since lithium-ion cells
do not exhibit a memory effect, less accurate termination
The MIC79050 is capable of providing 500mA of current at its
nominal rated output voltage of 4.2V. If the input is brought
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MIC79050
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below the nominal output voltage, the output will follow the
input, less the saturation voltage drop of the pass element. If
the cell draws more than the maximum output current of the
device, the output will be pulled low, charging the cell at
600mA to 700mA current. If the input is a fixed source with a
low output impedance, this could lead to a large drop across
the MIC79050 and excess heating. By driving the feedback
pin with an external PWM-circuit, the MIC79050 can be used
to pulse charge the battery to reduce power dissipation and
bring the device and the entire unit down to a lower operating
temperature. Figure 5 shows a typical configuration for a
PWM-basedpulse-chargingtopology.Twocircuitsareshown
in Figure 5: circuit a uses an external PWM signal to control
the charger, while circuit b uses the MIC4417 as a low duty-
cycle oscillator to drive the base of Q1. (Consult the battery
manufacturer for optimal pulse-charging techniques).
Regulated Input Source Charging
Whenprovidingaconstant-current,constant-voltage,charger
solution from a well-regulated adapter circuit, the MIC79050
can be used with external components to provide a constant
voltage, constant-current charger solution. Figure 7 shows a
configuration for a high-side battery charger circuit that
monitors input current to the battery and allows a constant
current charge that is accurately terminated with the
MIC79050. The circuit works best with smaller batteries,
charging at C rates in the 300mA to 500mA range. The
MIC7300 op-amp compares the drop across a current sense
resistor and compares that to a high-side voltage reference,
the LM4041, pulling the feedback pin low when the circuit is
in the constant-current mode. When the current through the
resistor drops and the battery gets closer to full charge, the
output of the op-amp rises and allows the internal feedback
network of the regulator take over, regulating the output to
4.2V.
MIC79050-4.2BMM
VIN
IN
BAT
FB
MIC79050-4.2BMM
RS
4.7µF
Li-Ion
Cell
EN
IN
BAT
FB
4.7µF
GND
EN
GND
16.2k
221k
MIC7300
External PWM
LM4041CIM3-1.2
80mV
SD101
I
=
CC
Figure 5A.
R
S
MIC79050-4.2BMM
10k
0.01µF
VIN=4.5V to 16V
IN
BAT
FB
4.7µF
1kΩ
EN
Li-Ion
Cell
GND
Figure 7. Constant Current,
Constant Voltage Charger
MIC4417
Simple Charging
40kΩ
200pF
The MIC79050 is available in a three-terminal package,
allowing for extremely simple battery charging. When used
withacurrent-limited,low-powerinputsupply,theMIC79050-
4.2BS completes a very simple, low-charge-rate, battery-
charger circuit. It provides the accuracy required for termina-
tion, while a current-limited input supply offers the constant-
current portion of the algorithm.
Figure 5B. PWM Based Pulse-charging
Applications
Figure 6 shows another application to increase the output
current capability of the MIC79050. By adding an external
PNP power transistor, higher output current can be obtained
while maintaining the same accuracy. The internal PNP now
becomes the driver of a darlington array of PNP transistors,
obtaining much higher output currents for applications where
the charge rate of the battery is much higher.
Thermal Considerations
The MIC79050 is offered in three packages for the various
applications. The SOT-223 is most thermally efficient of the
threepackages,withthepowerSOP-8andthepowerMSOP-8
following suit.
Power SOP-8 Thermal Characteristics
MIC79050-4.2BMM
One of the secrets of the MIC79050’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.
IN
BAT
FB
4.7µF
EN
GND
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
Figure 6. High Current Charging
MIC79050
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MIC79050
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900
800
700
600
500
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300
200
100
0
been used by MOSFET manufacturers for years, proving
very reliable and cost effective for the user.
∆TJA
=
Thermal resistance consists of two main elements, θ , or
JC
thermal resistance junction to case and θ , thermal resis-
CA
tance case to ambient (Figure 8). θ is the resistance from
JC
the die to the leads of the package. θ is the resistance from
CA
the leads to the ambient air and it includes θ , thermal
CS
resistance case to sink, and θ , thermal resistance sink to
SA
ambient. Using the power SOP-8 reduces the θ dramati-
JC
0
0.25 0.50 0.75 1.00 1.25 1.50
POWER DISSIPATION (W)
cally and allows the user to reduce θ . The total thermal
CA
resistance, θ , junctiontoambientthermalresistance, isthe
limiting factor in calculating the maximum power dissipation
JA
Figure 9. Copper Area vs. Power-SOP
Power Dissipation (∆T
)
JA
capabilityofthedevice. Typically, thepowerSOP-8hasaθ
JC
of 20°C/W, this is significantly lower than the standard SOP-
Where ∆T = T
– T
a(max)
j(max)
8 which is typically 75°C/W. θ is reduced because pins 5-
CA
T
T
= 125°C
j(max)
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.
= maximum ambient operating
a(max)
temperature
Forexample, themaximumambienttemperatureis40°C, the
∆T is determined as follows:
∆T = +125°C – 40°C
∆T = +85°C
SOP-8
Using Figure 9, 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:
θJA
ground plane
heat sink area
θJC
θCA
P = (Vin-Vout)*Iout + Vin*Ignd
D
For example, using the charging circuit in Figure 7, assume
the input is a fixed 5V and the output is pulled down to 4.2V
at a charge current of 500mA. The power dissipation in the
MIC79050 is calculated as follows:
AMBIENT
printed circuit board
Figure 8. Thermal Resistance
P = (5V – 4.2V)*0.5A + 5V*0.012A
D
The MIC79050 is 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.
P = 0.460W
D
From Figure 9, the minimum amount of copper required to
2
operate this application at a ∆T of 85C is less than 50mm .
Quick Method
Figure 9 shows curves of copper area versus power dissipa-
tion, each trace corresponding to different temperature rises
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.
Determine the power dissipation requirements for the design
along with the maximum ambient temperature at which the
devicewillbeoperated. RefertoFigure10, whichshowssafe
operatingcurvesfor3differentambienttemperatures:+25°C,
+50°C and +85°C. From these curves, the minimum amount
ofcoppercanbedeterminedbyknowingthemaximumpower
dissipation required. If the maximum ambient temperature is
+40°C and the power dissipation is as above, 0.46W, the
curve in Figure 10 shows that the required area of copper is
2
50mm .
The θ of this package is ideally 63°C/W, but it will vary
JA
depending upon the availability of copper ground plane to
which it is attached.
June 2000
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MIC79050
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300
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100
0
900
800
700
600
500
400
300
200
100
0
T
= 125°C
85°C
T
= 125°C
85°C
J
J
50°C 25°C
50°C 25°C
0
0.25 0.50 0.75 1.00 1.25 1.50
POWER DISSIPATION (W)
0
0.25 0.50 0.75 1.00 1.25 1.50
POWER DISSIPATION (W)
Figure 10. Copper Area vs. Power-SOP
Figure 12. Copper Area vs. Power-MSOP
Power Dissipation (T )
Power Dissipation (T )
A
A
Power MSOP-8 Thermal Characteristics
The power-MSO-8 package follows the same idea as the
power-SO-8 package, using four ground leads with the die
attach paddle to create a single-piece electrical and thermal
conductor,reducingthermalresistanceandincreasingpower
dissipation capability.
The same method of determining the heat sink area used for
the power-SOP-8 can be applied directly to the power-
MSOP-8. The same two curves showing power dissipation
versus copper area are reproduced for the power-MSOP-8
and they can be applied identically.
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 12, which shows safe
operatingcurvesfor3differentambienttemperatures,+25°C,
+50°C and +85°C. From these curves, the minimum amount
ofcoppercanbedeterminedbyknowingthemaximumpower
dissipation required. If the maximum ambient temperature is
+25°C and the power dissipation is 1W, the curve in Figure
2
12v shows that the required area of copper is 500mm ,when
using the power MSOP-8
900
800
700
600
500
400
300
200
100
0
0
0.25 0.50 0.75 1.00 1.25 1.50
POWER DISSIPATION (W)
Figure 11. Copper Area vs. Power-MSOP
Power Dissipation (∆T
)
JA
MIC79050
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June 2000
MIC79050
Micrel
Package Information
3.15 (0.124)
2.90 (0.114)
C
L
7.49 (0.295)
6.71 (0.264)
3.71 (0.146)
3.30 (0.130)
C
L
2.41 (0.095)
2.21 (0.087)
1.04 (0.041)
0.85 (0.033)
4.7 (0.185)
4.5 (0.177)
DIMENSIONS:
MM (INCH)
1.70 (0.067)
1.52 (0.060)
16°
10°
6.70 (0.264)
6.30 (0.248)
0.10 (0.004)
0.38 (0.015)
10°
MAX
0.02 (0.0008)
0.25 (0.010)
0.84 (0.033)
0.64 (0.025)
0.91 (0.036) MIN
SOT-223 (S)
0.026 (0.65)
MAX)
PIN 1
0.157 (3.99)
0.150 (3.81)
DIMENSIONS:
INCHES (MM)
0.020 (0.51)
0.013 (0.33)
0.050 (1.27)
TYP
45°
0.0098 (0.249)
0.0040 (0.102)
0.010 (0.25)
0.007 (0.18)
0°–8°
0.197 (5.0)
0.189 (4.8)
0.050 (1.27)
0.016 (0.40)
SEATING
PLANE
0.064 (1.63)
0.045 (1.14)
0.244 (6.20)
0.228 (5.79)
8-Pin SOP (M)
June 2000
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MIC79050
MIC79050
Micrel
0.122 (3.10)
0.112 (2.84)
0.199 (5.05)
0.187 (4.74)
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
0.007 (0.18)
0.005 (0.13)
0.008 (0.20)
0.004 (0.10)
5° MAX
0° MIN
0.012 (0.03)
0.012 (0.03) R
0.039 (0.99)
0.0256 (0.65) TYP
0.035 (0.89)
0.021 (0.53)
8-Pin MSOP (MM)
MIC79050
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June 2000
MIC79050
Micrel
June 2000
17
MIC79050
MIC79050
Micrel
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
This information is believed to be accurate and reliable, however no responsibility is assumed by Micrel for its use nor for any infringement of patents or
other rights of third parties resulting from its use. No license is granted by implication or otherwise under any patent or patent right of Micrel Inc.
© 2000 Micrel Incorporated
MIC79050
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MIC79050
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