MIC79050-4.2YMTR - Micrel - Product.Network

September 2001 1 MIC79050

MIC79050 Micrel

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

GND

MIC79050-4.2BMM

External PWM*

*See Applications Information

Regulated or

unregulated

wall adapter

Pulse-Charging Application

MIC79050

Simple Lithium-Ion Battery Charger

Preliminary Information

General Description

The MIC79050 is a simple single-cell lithium-ion battery

charger. It includes an on-chip pass transistor for high preci-

sion 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

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.

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 SOP-8, and SOT-223

• Pulse charging capability

Applications

• Li-ion battery charger

• Celluar phones

• Palmtop computers

• PDAs

• Self charging battery packs

Micrel, Inc. • 1849 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 944-0970 • http://www.micrel.com

Ordering Information

Part Number Voltage Junct. Temp. Range Package

MIC79050-4.2BS 4.2V –40°C to +125°C SOT-223

MIC79050-4.2BM 4.2V –40°C to +125°C SOP-8

MIC79050-4.2BMM 4.2V –40°C to +125°C MSOP-8

MIC79050 Micrel

MIC79050 2 September 2001

Pin Description

Pin No. Pin No. Pin Name Pin Function

SOT-223 SOP-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

132

TAB

GND

MIC79050-x.xBS

SOT-223

GND

BAT

MIC79050-x.xBM

SOP-8 and MSOP-8

September 2001 3 MIC79050

MIC79050 Micrel

Electrical Characteristics

VIN = VBAT + 1.0V; COUT = 4.7µF, I OUT = 100µA; T J = 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 %

∆VBAT/∆T Battery Voltage Note 4 40 ppm/°C

Temperature Coefficient

∆VBAT/VBAT Line Regulation VIN = VBAT + 1V to 16V 0.009 0.05 %/V

0.1 %/V

∆VBAT/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 3µA

Note 8 VEN ≤ 0.18V (shutdown) 0.10 8µA

PSRR Ripple Rejection f = 120Hz 75 dB

ILIMIT Current Limit VBAT = 0V 750 900 mA

1000 mA

∆VBAT/∆PDThermal 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 –1µA

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

SOP-8(θJA)..........................................................63°C/W

SOT-223(θJC)......................................................15°C/W

MIC79050 Micrel

MIC79050 4 September 2001

Typical Characteristics

100

200

300

400

0 100 200 300 400 500

DROPOUT VOLTAGE (mV)

OUTPUT CURRENT (mA)

Dropout Voltage

vs. Output Current

100

200

300

400

500

600

-40 0 40 80 120

DROPOUT VOLTAGE (mV)

TEMPERATURE (C)

Dropout Voltage

vs. Temperature

0246810121416

OUTPUT VOLTAGE (V)

INPUT VOLTAGE (V)

Dropout Characteristics

50mA, 150mA

5mA

0246

OUTPUT VOLTAGE (V)

INPUT VOLTAGE (V)

Dropout Characteristics

250mA 500mA

0 100 200 300 400 500

GROUND CURRENT (mA)

OUTPUT CURRENT (mA)

Output Current

vs. Ground

0.5

1.5

0 4 8 12 16

GROUND CURRENT (mA)

SUPPLY VOLTAGE (V)

Ground Current

vs. Supply Volta

50mA

5mA

0123456

GROUND CURRENT (mA)

SUPPLY VOLTAGE (V)

Ground Current

vs. Supply Volta

500mA

250mA

125mA

100

150

-40 0 40 80 120

GROUND CURRENT (uA)

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

100

200

300

400

500

600

700

800

-40 0 40 80 120

SHORT CIRCUIT CURRENT (mA)

TEMPERATURE (C)

Short Circuit Current

vs. Temperature

September 2001 5 MIC79050

MIC79050 Micrel

-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

Upper

Lower

012345

REVERSE LEAKAGE CURRENT (µA)

OUTPUT VOLTAGE (V)

Reverse Leakage Current

vs. Output Voltage

-5 5 1525354555

REVERSE LEAKAGE CURRENT (µA)

TEMPERATURE (C)

Reverse Leakage Current

vs. Output Voltage

3.0V

3.6V

4.2V

VIN+VEN

FLOATING

-5 5 1525354555

REVERSE LEAKAGE CURRENT (uA)

TEMPERATURE (C)

Reverse Leakage Current

vs. Temperature

3.0V

3.6V

4.2V

VIN+VEN

GROUNDED

MIC79050 Micrel

MIC79050 6 September 2001

Block Diagrams

Current Limit

Thermal Shutdown

GND

Bandgap

Ref.

BAT

MIC79050-x.xBS

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 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

designed to provide constant current, constant voltage charg-

ing 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

typically 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

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-

ling the voltage at the feedback pin the output can be disabled

or forced to the input voltage. Pulling and holding the feed-

back 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.

GND

REF

Bandgap

Ref.

Current Limit

Thermal Shutdown

BAT

MIC79050-x.xBMM/M

5-Pin Version

September 2001 7 MIC79050

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

LM4041

CIM3-1.2

IN BAT

GND

MIC79050-4.2BM

REF

= 1.225V

Impedence

AC Load-line Wall Adapter

10k 4.7µF

End of Charge

MIC6270

VV R1

EOC REF











Figure 1A. Load-Line Charger With End-Of-Charge Termination Circuit.

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

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

wall adapter characteristic with an output current of 350mA at

4.5V. This natural impedance of the wall adapter will limit the

max current into the battery, so no external circuitry is needed

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.

MIC79050 Micrel

MIC79050 8 September 2001

VEOC

Open Circuit

Charger V oltage

Battery Current (IB)

Battery V oltage (VB)

Unregulated Input

Voltage(VB)

79050 Programmed

Output V oltage

(No Load Voltage)

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

GND

MIC79050-4.2BM

LM4041

CIM3-1.2

5V ±5%@

400mA ±5%

4.7µF

8.06M

47k

0.050Ω

10k

MIC6270

MIC7300 10k

Figure 2. Protected Constant-Current Charger

The Charging Cycle (See Figure 1C.)

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.

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

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 voltage

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.

September 2001 9 MIC79050

MIC79050 Micrel

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 ex-

ceeded. 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 battery 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 minus

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-voltage. 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

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

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.

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-

tion 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

MIC79050-4.2BM

MIC834

SD101

⁄

MIC7122

⁄

MIC7122

IN BAT

GND

8.06M

4.7µF

=124k

=1k

=124k

0.01µF

VDD OUT

GNDINP

=1k

221k

16.2k

16k

10k

5V R

=0.200Ω

I80mV

CC s

=I1.240V R

EOC 1

=×

Figure 3.

MIC79050 Micrel

MIC79050 10 September 2001

again and provide current to the battery until it is fully charged.

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.

Li-Ion

Cell

IN BAT

GND

MIC79050-4.2BMM

VDD OUT

GNDINP

R1100k

4.7µF

MIC834

VIN

GND

REF

=1.240V

VV1

BAT(low) REF

==++





 





Figure 4. Pulse Charging For

Top-off Voltage

Charging Rate

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.

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 operating

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

GND

MIC79050-4.2BMM

VIN

External PWM

Figure 5A.

Li-Ion

Cell

4.7µF

200pF

1kΩ

40kΩ

IN BAT

GND

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

GND

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

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.

IN BAT

GND

MIC79050-4.2BMM

SD101

4.7µF

0.01µF

MIC7300

LM4041CIM3-1.2

16.2k

221k

10k

ImV

CC S

== 80

Figure 7. Constant Current,

September 2001 11 MIC79050

MIC79050 Micrel

Constant Voltage Charger

Simple Charging

The MIC79050 is available in a three-terminal package,

allowing 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 termina-

tion, while a current-limited input supply offers the constant-

current portion 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 SOP-8 and the power MSOP-8

following suit.

Power SOP-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

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, 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 SOP-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 SOP-8 has a θJC

of 20°C/W, this is significantly lower than the standard SOP-

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.

θJA

θJC θCA

printed circuit board

ground plane

heat sink area

SOP-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 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.

100

200

300

400

500

600

700

800

900

0 0.25 0.50 0.75 1.00 1.25 1.50

COPPER AREA (mm2)

POWER DISSIPATION (W)

40°C

50°C

55°C

65°C

75°C

85°C

100°C

∆TJA =

Figure 9. Copper Area vs. Power-SOP

Power Dissipation (∆ (∆

(∆ (∆

(∆TJA)

Where ∆T = Tj(max) – Ta(max)

Tj(max) = 125°C

Ta(max) = maximum ambient operating

temperature

For example, the maximum ambient temperature is 40°C, the

∆T is determined as follows:

∆T = +125°C – 40°C

∆T = +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 fol-

lows: 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 ∆T 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 maximum power

MIC79050 Micrel

MIC79050 12 September 2001

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

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.

100

200

300

400

500

600

700

800

900

0 0.25 0.50 0.75 1.00 1.25 1.50

COPPER AREA (mm2)

POWER DISSIPATION (W)

85°C50°C25°C

TJ = 125°C

Figure 10. Copper Area vs. Power-SOP

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-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

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

100

200

300

400

500

600

700

800

900

0 0.25 0.50 0.75 1.00 1.25 1.50

COPPER AREA (mm2)

POWER DISSIPATION (W)

50°C

55°C

65°C

75°C

85°C

100

Figure 11. Copper Area vs. Power-MSOP

Power Dissipation (∆TJA)

100

200

300

400

500

600

700

800

900

0 0.25 0.50 0.75 1.00 1.25 1.50

COPPER AREA (mm2)

POWER DISSIPATION (W)

85°C50°C25°C

TJ = 125°C

Figure 12. Copper Area vs. Power-MSOP

Power Dissipation (TA)

September 2001 13 MIC79050

MIC79050 Micrel

Package Information

16°

10°

0.84 (0.033)

0.64 (0.025)

1.04 (0.041)

0.85 (0.033)

2.41 (0.095)

2.21 (0.087)

4.7 (0.185)

4.5 (0.177)

6.70 (0.264)

6.30 (0.248)

7.49 (0.295)

6.71 (0.264)

3.71 (0.146)

3.30 (0.130)

3.15 (0.124)

2.90 (0.114)

10°

MAX

0.10 (0.004)

0.02 (0.0008) 0.38 (0.015)

0.25 (0.010)

DIMENSIONS:

MM (INCH)

1.70 (0.067)

1.52 (0.060)

0.91 (0.036) MIN

SOT-223 (S)

45°

0°–8°

0.244 (6.20)

0.228 (5.79)

0.197 (5.0)

0.189 (4.8) SEATING

PLANE

0.026 (0.65)

MAX)

0.010 (0.25)

0.007 (0.18)

0.064 (1.63)

0.045 (1.14)

0.0098 (0.249)

0.0040 (0.102)

0.020 (0.51)

0.013 (0.33)

0.157 (3.99)

0.150 (3.81)

0.050 (1.27)

TYP

PIN 1

DIMENSIONS:

INCHES (MM)

0.050 (1.27)

0.016 (0.40)

8-Pin SOP (M)

MIC79050 Micrel

MIC79050 14 September 2001

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 (0.03)

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)

September 2001 15 MIC79050

MIC79050 Micrel

MIC79050 16 September 2001

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.