August 2005 1 MIC79050
MIC79050 Micrel, Inc.
Typical Applications
Li-Ion
Cell
4.2V 0.75% Over Temp
IN BAT
GND
MIC79050-4.2BS
Regulated or
unregulated
wall adapter
Simplest Battery Charging Solution
4.2V 0.75%
Li-Ion
Cell
IN BAT
FB
GND
EN
MIC79050-4.2BMM
External PWM*
*See Applications Information
Regulated or
unregulated
wall adapter
Pulse-Charging Application
MIC79050
Simple Lithium-Ion Battery Charger
General Description
The MIC79050 is a simple single-cell lithium-ion battery char-
ger. It includes an on-chip pass transistor for high precision
charging. Featuring ultrahigh precision (+0.75% over the 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.
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 ther-
mally-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 temperature range
of –40°C to +125°C.
Features
• 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 SOIC-8, and SOT-223
• Pulse charging capability
Applications
• Li-ion battery charger
• Celluar phones
• Palmtop computers
• PDAs
• Self charging battery packs
Micrel, Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
Ordering Information
Part Number
Voltage
Junction
Temp. Range
Package
Standard Pb-Free
MIC79050-4.2BS MIC79050-4.2YS 4.2V –40ºC to +125ºC SOT-223-3
MIC79050-4.2BM MIC79050-4.2YM 4.2V –40ºC to +125ºC SOIC-8
MIC79050-4.2BMM MIC79050-4.2YMM 4.2V –40ºC to +125ºC MSOP-8
MIC79050 Micrel, Inc.
MIC79050 2 August 2005
Pin Description
Pin No. Pin No. Pin Name Pin Function
SOT-223 SOIC-8
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 BAT Battery Voltage Output
1 EN Enable (Input): TTL/CMOS compatible control input. Logic high = enable; logic low or open =
shutdown.
4 FB Feedback Node
Pin Configuration
IN BAT
GND
1 32
TAB
GND
MIC79050-x.xBS/YS
SOT-223
1
2
3
4
8
7
6
5
GND
GND
GND
GND
EN
IN
BAT
FB
MIC79050-x.xBM/YM
SOIC-8 and MSOP-8
August 2005 3 MIC79050
MIC79050 Micrel, Inc.
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 Parameter Conditions Min Typical Max Units
VBAT Battery Voltage Accuracy variation from nominal VOUT –5°C to +60°C –0.75 +0.75 %
ΔVBAT/ΔT Battery Voltage Note 4 40
ppm/°C
Temperature Coefficient
ΔVBAT/VBAT Line Regulation VIN = VBAT + 1V to 16V 0.009 0.05 %/V
0.1 %/V
ΔVBAT/VBAT Load Regulation IOUT = 100µA to 500mA, Note 5 0.05 0.5 %
0.7 %
VIN – VBAT Dropout Voltage, Note 6 IOUT = 500mA 380 500 mV
600 mV
IGND Ground Pin Current, Notes 7, 8 VEN ≥ 3.0V, IOUT = 100µA 85 130 µA
170 µA
VEN ≥ 3.0V, IOUT = 500mA 11 20 mA
25 mA
IGND Ground Pin Quiescent Current, VEN ≤ 0.4V (shutdown) 0.05 3 µA
Note 8 VEN ≤ 0.18V (shutdown) 0.10 8 µA
PSRR Ripple Rejection f = 120Hz 75 dB
ILIMIT Current Limit VBAT = 0V 750 900 mA
1000 mA
ΔVBAT/ΔPD Thermal Regulation Note 9 0.05 %/W
ENABLE Input
VENL Enable Input Logic-Low Voltage VEN = logic low (shutdown) 0.4 V
0.18 V
VEN = logic high (enabled) 2.0 V
IENL Enable Input Current VENL ≤ 0.4V (shutdown) 0.01 –1 µA
VENL ≤ 0.18V (shutdown) 0.01 –2 µA
IENH VENH ≥ 2.0V (enabled) 5 20 µA
25 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 TA (ambient temperature) is calculated using: PD(max) = (TJ(max) – TA) ÷ θJA. Exceeding the
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.
Note 8: VEN is the voltage externally applied to devices with the EN (enable) input pin. [MSO-8(MM) and SO-8 (M) packages only.]
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 VIN = 16V for t = 10ms.
Absolute Maximum Ratings (Note 1)
Supply Input Voltage (VIN) ..............................–20V to +20V
Power Dissipation (PD) ................ Internally Limited, Note 3
Junction Temperature (TJ) ........................ –40°C to +125°C
Lead Temperature (soldering, 5 sec.) ........................ 260°C
Storage Temperature (TS) ........................ –65°C to +150°C
Operating Ratings (Note 2)
Supply Input Voltage (VIN) ............................ +2.5V to +16V
Enable Input Voltage (VEN) ...................................0V to VIN
Junction Temperature (TJ) ........................ –40°C to +125°C
Package Thermal Resistance (Note 3) ................................
MSOP-8 (θJA) ...................................................... 80°C/W
SOIC-8(θJA) ......................................................... 63°C/W
SOT-223(θJC) ...................................................... 15°C/W
MIC79050 Micrel, Inc.
MIC79050 4 August 2005
Typical Characteristics
0
100
200
300
400
0 100 200 300 400 500
DROPOUT VOLTAGE (mV)
OUTPUT CURRENT (mA)
Dropout Voltage
vs. Output Current
0
100
200
300
400
500
600
-40 0 40 80 120
DROPOUT VOLTAGE (mV)
TEMPERATURE (°C)
Dropout Voltage
vs. Temperature
0
1
2
3
4
5
0 2 4 6 8 10 12 14 16
OUTPUT VOLTAGE (V)
INPUT VOLTAGE (V)
Dropout Characteristics
50mA,150mA
5mA
0
1
2
3
4
5
0246
OUTPUT VOLTAGE (V)
INPUT VOLTAGE (V)
Dropout Characteristics
250mA
500mA
0
2
4
6
8
10
12
0 100 200 300 400 500
GROUND CURRENT (mA)
OUTPUT CURRENT (mA)
Output Current
vs. Ground
0
0.5
1
1.5
04812 16
GROUND CURRENT (mA)
SUPPLY VOLTAGE (V)
Ground Current
vs. Supply Voltage
50mA
5mA
0
5
10
15
20
25
0123456
GROUND CURRENT (mA)
SUPPLY VOLTAGE (V)
Ground Current
vs. Supply Voltage
500mA
250mA
125mA
0
50
100
150
-40 0 40 80 120
GROUND CURRENT (µA)
TEMPERATURE (°C)
Ground Current
vs. Temperature
3.0
3.2
3.4
3.6
3.8
4.0
-40 0 40 80 120
GROUND CURRENT (mA)
TEMPERATURE (°C)
Ground Current
vs. Temperature
11.0
11.5
12.0
12.5
13.0
13.5
-40 0 40 80 120
GROUND CURRENT (mA)
TEMPERATURE (°C)
Ground Current
vs. Temperature
4.190
4.195
4.200
4.205
4.210
-40 -20 0 20 40 60 80 100120140
OUTPUT VOLTAGE (V)
TEMPERATURE (°C)
Battery Voltage
vs. Temperature
0
100
200
300
400
500
600
700
800
-40 0 40 80 120
SHORT CIRCUIT CURRENT (mA)
TEMPERATURE (°C)
Short Circuit Current
vs. Temperature
August 2005 5 MIC79050
MIC79050 Micrel, Inc.
-0.75
-0.25
0.25
0.75
0 200 400 600 800
DRIFT FROM NOMINAL VOUT (%)
TIME (hrs)
Typical Voltage Drift Limits
vs. Time
U
pp
er
Lower
0
5
10
15
20
012345
REVERSE LEAKAGE CURRENT (µA)
OUTPUT VOLTAGE (V)
Reverse Leakage Current
vs. Output Voltage
0
5
10
15
20
-5 5 15 25 35 45 55
REVERSE LEAKAGE CURRENT (µA)
TEMPERATURE (°C)
Reverse Leakage Current
vs. Output Voltage
3.0V
3.6V
4.2V
VIN+VE N
FLOATING
0
5
10
15
20
-5 5 15 25 35 45 55
REVERSE LEAKAGE CURRENT (uA)
TEMPERATURE (°C)
Reverse Leakage Current
vs. Temperature
3.0V
3.6V
4.2V
VIN+VE N
GROUNDED
MIC79050 Micrel, Inc.
MIC79050 6 August 2005
Block Diagrams
3-Pin Version
Functional Description
The MIC79050 is a high-accuracy, linear battery charging
circuit designed for the simplest implementation of a single
lithium-ion (Li-ion) battery charger. The part can operate
from a regulated or unregulated power source, making it
ideal for various applications. The MIC79050 can take an
unregulated voltage source and provide an extremely ac-
curate termination 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 designed to provide constant current, constant volt-
age charging for Li-ion cells.
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 sustained
without any performance degradation to the output voltage.
The line regulation of the device is typically 0.009%/V; that is,
a 10V change on the input voltage corresponds to a 0.09%
change in output voltage.
Enable
The MIC79050 has an enable pin that allows the charger to
be disabled when the battery is fully charged and the current
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 typi-
cally 12µA or less.
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 am-
plifier. This amplifier compares the voltage at the feedback
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 controlling the voltage at
the feedback pin the output can be disabled or forced to the
input voltage. Pulling and holding the feedback pin low forces
the output low. Holding the feedback pin high forces the pass
element into saturation, where the output will be the input
minus the saturation (dropout) 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.
5-Pin Version
August 2005 7 MIC79050
MIC79050 Micrel, Inc.
Applications Information
Simple Lithium-Ion Battery Charger.
Figure 1A shows a simple, complete lithium-ion battery char-
ger. 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 headroom needed
above 4.2V for the MIC79050 to operate correctly e.g. For
LM4041
CIM3-1.2
IN BAT
FB
GND
EN
MIC79050-4.2BM
VEOC
= VREF (1+ )
Impedence
AC Load-line Wall Adapter
10k 4.7µF
1k
End of Charge
R2
R1
MIC6270
VS
VREF = 1.225V
R1
R2
Figure 1A. Load-Line Charger With End-Of-Charge Termination Circuit.
0
2
4
6
8
0 0.2 0.4 0.6 0.8
SOURCE VOLTAGE (V)
SOURCE CURRENT (A)
Load-Line Source
Characteristics
Figure 1B. Load-Line Characteristics
of AC Wall Adapter
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 wall adapter
characteristic with an output current of 350mA at 4.5V. This
natural impedance of the wall adapter will limit the max cur-
rent into the battery, so no external circuitry is needed to
accomplish this.
If extra impedance is needed to achieve the desired load-
line, extra resistance can easily be added in series with the
MIC79050 IN pin.
MIC79050 Micrel, Inc.
MIC79050 8 August 2005
VEOC
Open Circuit
Charger Voltage
Battery Current (IB)
Battery Voltage (VB)
Unregulated Input
Voltage(VB)
79050 Programmed
Output Voltage
(No LoadVoltage)
End of Charge (VEOC
)
State A
Initial Charge
State B
Voltage Charge
State C
End of Charge
State D
Charge Top
State C
Figure 1C. Charging Cycles
IN BAT
FB
GND
EN
MIC79050-4.2BM
LM4041
CIM3-1.2
5V 5%@
400mA 5%
4.7µF
8.06M
47k
47k
1k
0.050Ω
Q1
10k
R2
MIC6270
MIC7300
10k
1k
Figure 2. Protected Constant-Current Charger
The Charging Cycle (See Figure 1C.)
1. State A: Initial charge. Here the battery’s charging cur-
rent is limited by the wall adapter’s natural impedance.
The battery voltage approaches 4.2V.
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 in-
creases. The MIC6270 and the LM4041 are configured
as a simple voltage monitor, indicating when the 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,
VS reaches VEOC, an end of charge signal is indicated.
4. State D: Top up charge. As soon as enough current
is drawn out of the input source, which pulls the volt-
age lower than the VEOC, the end of charge flag will be
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.
August 2005 9 MIC79050
MIC79050 Micrel, Inc.
Protected Constant-Current Charger
Another form of charging is using a simple wall adapter that
offers a fixed voltage at a controlled, maximum current rating.
The output of a typical charger will source a fixed voltage at a
maximum current unless that maximum current is exceeded. In
the event that the maximum current is exceeded, the voltage
will drop while maintaining that maximum current. Using an
MIC79050 after this type of charger is ideal for lithium-ion bat-
tery charging. The only obstacle is end of charger termination.
Using a simple differential amplifier and a similar comparator
and reference circuit, similar to Figure 1, completes a single
cell lithium-ion battery charger solution.
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 mi-
nus a small voltage drop. When the battery approaches full
charge, the current will taper off. As the current across RS
approaches 50mA, the output of the differential amplifier
(MIC7300) will approach 1.225V, the reference voltage set
by 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
Input voltage sources that have very low output impedances
can be a challenge due to the nature of the source. Using
the circuit in Figure 3 will provide a constant-current and
constant voltage charging algorithm with the appropriate
end-of-charge termination. The main loop consists of an
op-amp controlling the feedback pin through the schottky
diode, D1. The charge current through RS is held constant
by the op-amp circuit until the output draws less than the set
charge-current. At this point, the output goes constant-volt-
age. When the current through RS gets to less than 50mA,
the difference amp output becomes less than the reference
voltage of the MIC834 and the output pulls low. This sets the
output of the MIC79050 less than nominal, stopping current
flow and terminating charge.
Lithium-Ion Battery Charging
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.
For the constant-voltage portion of the charging circuit, an ex-
tremely accurate termination voltage is highly recommended.
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 does not
harm the cell but simply stores less usable energy in the bat-
tery. The charge cycle is completed by disabling the charge
circuit after the termination current drops below a minimum
recommended level, typically 50mA or less, depending on the
manufacturer’s recommendation, or if the circuit times out.
Time Out
The time-out aspect of lithium-ion battery charging can be
added as a safety feature of the circuit. Often times this func-
tion is incorporated in the software portion of an application
using a real-time clock to count out the maximum amount
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.
As a second option, the feedback pin of the MIC79050 can
be 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 again and provide
current to the battery until it is fully charged. This form of
pulse charging is an acceptable way of maintaining the full
charge on a cell until it is ready to be used.
MIC79050-4.2BM
MIC834
SD101
1/2MIC7122
1/2MIC7122
IN BAT
FB
GND
EN
8.06M
4.7µF
R2=124k
R3=1k
R4=124k
0.01µF
VDD OUT
GNDINP
R1=1k
D1
221k
16.2k
16k
10k
5V RS=0.200Ω
ICC=
80mV
RSIEOC
=
1.24V × R1
R2× RS
Figure 3.
MIC79050 Micrel, Inc.
MIC79050 10 August 2005
Li-Ion
Cell
IN BAT
FB
GND
EN
MIC79050-4.2BMM
VDD OUT
GNDINP
R1100k
4.7µF
R2
MIC834
VIN
GND
VREF=1.240V
VBAT(low) = VREF (1+ )
R1
R2
Figure 4. Pulse Charging For
Top-off Voltage
Charging Rate
Lithium-ion cells are typically charged at rates that are frac-
tional 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 determine 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. Charging at rates
greater than 1C are not recommended, or do they decrease
the charge time linearly.
The MIC79050 is capable of providing 500mA of current at its
nominal rated output voltage of 4.2V. If the input is brought
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 operat-
ing temperature. Figure 5 shows a typical configuration for a
PWM-based pulse-charging topology. Two circuits are shown
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).
Li-Ion
Cell
4.7µF
IN BAT
FB
GND
EN
MIC79050-4.2BMM
VIN
External PWM
Figure 5A.
Li-Ion
Cell
4.7µF
200pF
1k
40k
IN BAT
FB
GND
EN
MIC79050-4.2BMM
VIN=4.5V to 16V
MIC4417
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.
IN BAT 4.7µF
FB
GND
EN
MIC79050-4.2BMM
Figure 6. High Current Charging
Regulated Input Source Charging
When providing a constant-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 moni-
tors 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.
IN BAT
FB
GND
EN
MIC79050-4.2BMM
SD101
4.7µF
0.01µF
MIC7300
LM4041CIM3-1.2
16.2k
221k
10k
RS
ImV
R
CC
S
== 80
Figure 7. Constant Current,
Constant Voltage Charger
August 2005 11 MIC79050
MIC79050 Micrel, Inc.
Simple Charging
The MIC79050 is available in a three-terminal package, allow-
ing for extremely simple battery charging. When used with a
current-limited, low-power input supply, the MIC79050-4.2BS
completes a very simple, low-charge-rate, battery-charger
circuit. It provides the accuracy required for termination, while
a current-limited input supply offers the constant-current por-
tion of the algorithm.
Thermal Considerations
The MIC79050 is offered in three packages for the various
applications. The SOT-223 is most thermally efficient of
the three packages, with the power SOIC-8 and the power
MSOP-8 following suit.
Power SOIC-8 Thermal Characteristics
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 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, or
thermal resistance junction to case and θCA, thermal resis-
tance case to ambient (Figure 8). 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, thermal
resistance case to sink, and θSA, thermal resistance sink to
ambient. Using the power SOIC-8 reduces the θJC dramati-
cally and allows the user to reduce θCA. The total thermal
resistance, θ JA, junction to ambient thermal resistance, is the
limiting factor in calculating the maximum power dissipation
capability 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 5-8 can now be soldered directly to a ground plane, which
significantly reduces the case to sink thermal resistance and
sink to ambient thermal resistance.
qJA
qJC
qCA
printed circuit board
ground plane
heat sink area
SOIC-8
AMBIENT
Figure 8. Thermal Resistance
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.
Figure 9 shows curves of copper area versus power dis-
sipation, 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.
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)
∆TJ A =
Figure 9. Copper Area vs. Power-SOIC
Power Dissipation (∆TJA)
Where ΔT = Tj(max) – Ta(max)
Tj(max) = 125°C
Ta(max) = maximum ambient operating
temperature
For example, the maximum ambient temperature is 40°C,
the ΔT is determined as follows:
ΔT = +125°C – 40°C
ΔT = +85°C
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 follows:
PD = (Vin-Vout)*Iout + Vin*Ignd
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:
PD = (5V – 4.2V)*0.5A + 5V*0.012A
PD = 0.460W
From Figure 9, the minimum amount of copper required to
operate this application at a ΔT of 85C is less than 50mm2.
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 10 , which shows
safe operating curves for 3 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
MIC79050 Micrel, Inc.
MIC79050 12 August 2005
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 50mm2.
The θJA of this package is ideally 63°C/W, but it will vary
depending upon the availability of copper ground plane to
which it is attached.
0
100
200
300
400
500
600
700
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
TJ= 125°C
Figure 10. Copper Area vs. Power-SOIC
Power Dissipation (TA)
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, reducing thermal resistance and increasing power
dissipation capability.
The same method of determining the heat sink area used
for the power-SOIC-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
operating curves for 3 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
+25°C and the power dissipation is 1W, the curve in Figure
12v shows that the required area of copper is 500mm2,when
using the power MSOP-8
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)
Figure 11. Copper Area vs. Power-MSOP
Power Dissipation (ΔTJA)
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
TJ= 125°C
Figure 12. Copper Area vs. Power-MSOP
Power Dissipation (TA)
August 2005 13 MIC79050
MIC79050 Micrel, Inc.
Package Information
SOT-223 (S)
8-Pin SOIC (M)
MIC79050 Micrel, Inc.
MIC79050 14 August 2005
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-Pin MSOP (MM)
MICREL INC. 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA
TEL + 1 (408) 944-0800 FAX + 1 (408) 474-1000 WEB http://www.micrel.com
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.
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 a Purchaser's own risk and Purchaser agrees to fully indemnify
Micrel for any damages resulting from such use or sale.
© 2000 Micrel, Inc.