MIC2253-06YML - Micrel, Inc.

MIC2253

3.5A 1MHz High Efficiency

Boost Regulator with OVP and Softstart

MLF and MicroLeadFrame are registered trademarks of Amkor Technology, Inc.

Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com

April 2011 M9999-042011-C

General Description

The MIC2253 is a high power density 1MHz PWM DC/DC

boost regulator. The 3.5A minimum switch current limit

combined with a 1MHz switching frequency allows the

MIC2253 to use smaller inductors and deliver high power

in a tiny solution size.

The 2.5V to 10V input voltage range of MIC2253 allows

direct operation from 1 and 2 cell Li-ion as well as 3 to 4

cell NiCad, NiMH, Alkaline or lithium batteries. Maximum

battery life is assured with a low 0.1µA shutdown current.

The MIC2253 is available in a low profile 12-pin 3mm x

3mm MLF© package. To prevent a high inrush current, a

minimum 1ms soft-start period is set by default and the

MIC2253 has the ability to extend the soft-start period with

an external capacitor.

Datasheet and support documentation can be found on

Micrel’s web site at: www.micrel.com.

Features

• 3.5A minimum switch current

• 1.245V ± 3% feedback voltage

• 2.5V to 10V input voltage

• Output over-voltage protection (OVP)

• Externally programmable soft-start

• Output voltage up to 30V (max)

• Fixed 1MHz operation

• <1% line regulation

• 0.1µA shutdown current

• Over temperature protection

• Under-voltage lockout (UVLO)

• 12-pin 3mm x 3mm leadless MLF® package

• –40°C to +125°C junction temperature range

Applications

• Mobile handsets

• Portable media/MP3 players

• Portable navigation devices (GPS)

• WiFi/WiMax/WiBro modules

• Digital Cameras

• Wireless LAN cards

• USB powered devices

• Portable applications

___________________________________________________________________________________________________________

Typical Application

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April 2011 2 M9999-042011-C

Ordering Information

Part Number Marking

Code(2) OVP Junction Temp. Range Package Lead Finish

MIC2253-06YML 06

2253 6V –40° to +125°C 12-Pin 3x3 MLF® Pb-Free

Note: MLF® is a GREEN RoHS compliant package. Lead finish is NiPdAu. Mold compound is Halogen Free.

Pin Configur ation

12-Pin 3mm x 3mm MLF® (ML)

(Top View)

Pin Description

Pin Number Pin Name Pin Function

1 NC No connect. Not internally connected.

2 SS

Soft start (Input). Connect a capacitor to GND to slowly turn on the device. The

higher the capacitance, the longer the turn-on time.

3 FB

Feedback (Input): Output voltage sense node. Connect external resistors to set

the output voltage. Nominal feedback voltage is 1.245V.

4 AGND Analog Ground

5,6 PGND Power Ground

7,8 SW Switch Node: Internal power BIPOLAR collector.

9 OVP

Over-Voltage Protection (OVP): Connect to the output voltage to clamp the

maximum output voltage. A resistor divider from this pin to ground could be

used to raise the OVP level beyond 6V (max).

10 VIN Supply (Input): 2.5V to 10V for internal circuitry.

11 EN

Enable (Input): Applying 1.5V or greater enables the regulator. Applying a

voltage of 0.4V or less disables the MIC2253. Do not leave floating.

12 COMP

Compensation pin (Input): Add external R and C to GND to stabilize the

converter.

EP HS Pad Exposed Heat-Sink pad.

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Absolute Maximum Ratings(1)

Supply Voltage (VIN).......................................................12V

Switch Voltage (VSW)....................................... –0.3V to 34V

Enable Voltage (VEN)....................................... –0.3V to 12V

FB Voltage (VFB)...............................................................6V

Switch Current (ISW) ..................................Internally Limited

Ambient Storage Temperature (Ts)...........–65°C to +150°C

ESD Rating(3).................................................................. 2kV

Operating Ratings(2)

Supply Voltage (VIN).......................................... 2.5V to 10V

Enable Voltage (VEN).............................................. 0V to VIN

Junction Temperature (TJ) ........................ –40°C to +125°C

Package Thermal Impedance

3mm x 3mm MLF-12 (θJA) .................................60°C/W

Electrical Characteristics(4)

TA = 25°C; VIN = VEN = 3.6V; unless otherwise noted. Bold values indicate –40°C TJ  +125°C.

Symbol Parameter Condition Min Typ Max Units

VIN Supply Voltage Range 2.5 10 V

VUVLO Under-Voltage Lockout 1.8 2.1 2.4 V

VOVP Over-Voltage Protection 5.25 5.6 6.3 V

IVIN Quiescent Current VFB >1.245V, Not Switching 15 23 mA

ISD Shutdown Current VEN = 0V(5) 0.1 1 µA

VFB Feedback Voltage 1.208 1.245 1.283 V

IFB Feedback Input Current VFB = 1.245V -450 nA

Line Regulation 3.0V ≤ VIN ≤ 4.5V 0.5 %

DMIN Minimum Duty Cycle 10 %

DMAX Maximum Duty Cycle 90 %

ISW Switch Current Limit VIN = 3.6V 3.5 4.75 8 A

VSW Switch Saturation Voltage VIN = 3.6V, ISW = 3.5A 350 500 mV

ISW Switch Leakage Current VEN = 0V, VSW = 10V 0.01 10 µA

TURN ON 1.5

VEN Enable Threshold TURN OFF 0.4 V

IEN Enable Pin Current VEN = 10V 20 40 µA

fSW Oscillator Frequency 0.8 1 1.2 MHz

ISS Soft start VSS = 0V 30 µA

150

°C

TJ Over-Temperature Threshold

Shutdown Hysteresis 10

°C

Notes:

1. Absolute maximum ratings indicate limits beyond which damage to the component may occur. Electrical specifications do not apply when operating

the device outside of its operating ratings. The maximum allowable power dissipation is a function of the maximum junction temperature, TJ(Max), the

junction-to-ambient thermal resistance, θ JA, and the ambient temperature, TA. The maximum allowable power dissipation will result in excessive die

temperature, and the regulator will go into thermal shutdown.

2. The device is not guaranteed to function outside its operating rating.

3. Devices are ESD sensitive. Handling precautions recommended. Human Body Model, 1.5k in series with 100pF.

4. Specification for packaged product only.

5. ISD = IVIN

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Typical Characteristics

Frequency

vs. Input Volt age

500

600

700

800

900

1000

1100

1200

1300

1400

1500

2.5 4.0 5.5 7.0 8.5 10.0

INPUT VOLTAGE (V)

FREQUENCY (kHz)

OUT

= 12V

OUT

= 300mA

L = 2.2µH

C = 22µF

Frequency

vs. Tem p erature

700

800

900

1000

1100

1200

-40-20 0 20406080100120

TEMPERATURE (°C)

FREQUENCY ( kHz)

OUT

= 5V

= 3.6V

Load = 200mA

Feedback Voltage

vs. Temperature

1.20

1.21

1.22

1.23

1.24

1.25

1.26

1.27

1.28

1.29

1.30

-40 -20 0 20 40 60 80 100 120

TEMPERATURE (°C)

FEEDBACK VOLTAGE (V)

OUT

= 5V

= 3.6V

Load = 200mA

Load Regulation

4.90

4.92

4.94

4.96

4.98

5.00

5.02

5.04

5.06

5.08

5.10

0 400 800 1200 1600

OUTPUT CURRENT (mA)

OUTPUT VOLTAGE (V)

OUT

= 5V

L = 2.2µH

C = 22µF

= 25°C

Current Lim it

vs. Input Voltage

4.0

4.1

4.2

4.3

4.4

4.5

4.6

4.7

4.8

4.9

5.0

2.5 4.0 5.5 7.0 8.5 10.0

INPUT VOLTAGE (V)

SW CURRENT LIMIT (A)

VOUT = 12V

L = 2.2µH

C = 22µF

TA = 25°C

Efficiency V

OUT

= 3.8V

100

0 600 1200 1800 2400

OUTPUT CURRENT (mA)

EFFICIENCY (%)

=2.5V

=3V

=3.3V

L = 2.2µH

C = 22µF

= 25°C

Efficien cy V

OUT

=12.0V

0 200 400 600 800 1000 1200

OUTPUT CURRENT (mA)

EFFICIENCY (%)

VIN=3.3V

VIN=4.2V

VIN=5V

L = 2.2µH

C = 22µF

TA = 25°C

Efficiency V

OUT

=15.0V

0 100 200 300 400 500 600 700

OUTPUT CURRENT (mA)

EFFICIENCY (%)

VIN=3.3V VIN=4.2V

VIN=5V

L = 2.2µH

C = 22µF

TA = 25°C

Efficiency V

OUT

=5.0V

0 600 1200 1800 2400

OUTPUT CURRENT (mA)

EFFICIENCY ( %)

VIN=2.5V

VIN=3.6V

VIN=4.5V

L = 2.2µH

C = 22µF

TA = 25°C

Quiescent Current

vs. T empera ture

12.0

12.5

13.0

13.5

14.0

14.5

15.0

15.5

16.0

16.5

17.0

-40 -20 0 20 40 60 80 100 120

TEMPERATURE(°C)

QUIESCENT CURR ENT ( mA)

VIN = 3.6V

VFB = 2.5V

Not Switching

Quiescent Current

vs. Input Voltage

11.0

12.0

13.0

14.0

15.0

16.0

17.0

2.5 4.0 5.5 7.0 8.5 10.0

INPUT VOLTAGE (V)

QUIESCENT CURRENT (mA)

VFB = 2.5V

Not Switching

Line Regulation

11.5

11.6

11.7

11.8

11.9

12.0

12.1

12.2

12.3

12.4

12.5

2.54.05.57.08.510.0

INPUT VOLTAGE (V)

OUTPUT VOLTAGE (V)

OUT

= 12V

L = 2.2µH

C = 22µF

= 25°C

Load = 20mA

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Typical Characteristics (Continued)

Enable Threshold

vs. Input Voltage

1.20

1.22

1.24

1.26

1.28

1.30

1.32

1.34

1.36

1.38

1.40

2.5 4.0 5.5 7.0 8.5 10.0

INPUT VOLTAGE (V)

ENABLE THRESHOLD (V)

VOUT = 12V

IOUT = 20mA

L = 2.2µH

C = 22µF

Saturation Voltage

vs. Swi tch Current

100

150

200

250

300

350

400

450

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

SWITCH CURRENT (A)

SATURATIO N V OLTA GE (mV )

= 2.5V

= 25°C

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Functional Characteristics

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Functional Diagram

Functional Description

The MIC2253 is a constant frequency, pulse-width-

modulated (PWM) peak current-mode step-up regulator.

The device’s simplified control scheme is illustrated in the

block diagram above. A reference voltage is fed into the

PWM engine where the duty cycle output of the constant

frequency PWM engine is computed from the error, or

difference, between the REF and FB voltages. The PWM

engine encompasses the necessary circuit blocks to

implement a current-mode boost switching power supply.

The necessary circuit blocks include, but are not limited to,

an oscillator/ramp generator, slope compensation ramp

generator, gm error amplifier, current amplifier, PWM

comparator, and drive logic for the internal 3.5A bipolar

power transistor.

Inside the PWM engine, the oscillator functions as a trigger

for the PWM comparator that turns on the bipolar power

transistor and resets the slope compensation ramp

generator. The current amplifier is used to measure the

power transistor’s current by amplifying the voltage signal

from the sense resistor connected to the emitter of the

bipolar power transistor. The output of the current amplifier

is summed with the output of the slope compensation ramp

generator where the result is connected to one of the inputs

of the PWM comparator.

The gm error amplifier measures the feedback voltage

through the external resistor and amplifies the error

between the detected voltage signal from the feedback

and the internal reference voltage. The output of the gm

error amplifier provides the voltage loop signal that is fed

to the other input of the PWM comparator. When the

current loop signal exceeds the voltage loop signal the

PWM comparator turns off the power transistor. The next

oscillator/clock period initiates the next switching cycle,

maintaining the constant frequency current-mode PWM

control. The enable pin shuts down the output switching

and disables control circuitry to reduce input current-to-

leakage levels. Enable pin input current is approximately

zero, at zero volts.

DC-to-DC PWM Boost Conversion

The MIC2253 is a constant-frequency boost converter. It

can convert a low DC input voltage to a high DC output

voltage. Figure 1 shows a typical circuit. Boost regulation

is achieved by turning on an internal switch, which draws

current through the inductor. When the switch turns off,

the inductor’s magnetic field collapses. This causes the

current to be discharged into the output capacitor

through an external Schottky diode. The Functional

Characteristics show Input Voltage ripple, Output

Voltage ripple, SW Voltage, and Inductor Current for

300mA load current. Regulation is achieved by

modulating the pulse width i.e., pulse-width modulation

(PWM).

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Figure 1. Typical Application Circuit

Duty Cycle Considerations

Duty cycle refers to the switch on-to-off time ratio and can

be calculated as follows for a boost regulator:

OUT

-1=D

However at light loads, the inductor will completely

discharge before the end of a switching cycle. The current

in the inductor reaches zero before the end of the switching

cycle. This is known as discontinuous conduction mode

(DCM). DCM occurs when:

IPEAK

OUT

OUT ×<

where

⎟

⎠

⎞

⎜

⎝

⎛

OUT

INOUT

PEAK V

) V-(V

In DCM, the duty cycle is smaller than in continuous

conduction mode. In DCM the duty cycle is given by:

INOUTOUT

)V(VIL2f

D−××××

The duty cycle required for voltage conversion should be

less than the maximum duty cycle of 90%. Also, in light load

conditions where the input voltage is close to the output

voltage, the minimum duty cycle can cause pulse skipping.

This is due to the energy stored in the inductor causing the

output to slightly overshoot the regulated output voltage.

During the next cycle, the error amplifier detects the output

as being high and skips the following pulse. This effect can

be reduced by increasing the minimum load or by

increasing the inductor value. Increasing the inductor value

also reduces the peak current. Minimum duty cycle is

typically 10%.

Over-Voltage Protection (OVP)

The MIC2253 provides a fixed 5.6V overvoltage

protection. The overvoltage functionality will clamp the

output voltage to a safe level in the event that a fault

condition causes the output voltage to increase beyond

control. To ensure the highest level of protection, the

MIC2253 OVP pin will shut the switch off when an

overvoltage condition is detected, saving itself, the

output capacitor, and downstream devices from damage.

Two external resistors can be used to change the OVP

from the range of 6V to 30V. Be careful not to exceed

the 30V rating of the switch. The OVP feature may be

disabled by grounding the OVP pin.

The OVP pin is connected internally to a reference

voltage via a voltage divider circuit. For a 5.6V OVP

setting, connect the OVP pin directly to the output

voltage as shown in Figure 1. To increase the OVP

voltage above 5.6V, an external parallel resistor network

can be configured, as shown in Figure 2, with the

following equation:

R215k

R2)R167k

1.245VOVP ×

+×

×= (

Figure 2. Adjustable OVP Circuit

Note:

1. The maximum value of R2 is 30k.

Soft Start Functionality

The soft start time is dependant up on both CSS and the

comp capacitor values. CCOMP is fixed for stable

operation (typically 10nF); therefore, if any increases in

soft start are desired, this should be done using the CSS

capacitor. The approximate total startup time is given by:

SSSS C85k1msT ×

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Component Selection

Inductor

The MIC2253 is designed to work with a 2.2µH inductor.

This is due to the unavoidable “right half plane zero” effect

for the continuous current boost converter topology. The

frequency at which the right half plane zero occurs can be

calculated as follows:

2ILV

frhpz

OUTOUT

×××

The right half plane zero has the undesirable effect of

increasing gain, while decreasing phase. This requires that

the loop gain is rolled off before this has significant effect on

the total loop response. This can be accomplished by either

reducing inductance (increasing RHPZ frequency) or

increasing the output capacitor value (decreasing loop

gain).

Output Capacitor

Output capacitor selection is a trade-off between

performance, size, and cost. Increasing output capacitance

will lead to an improved transient response, but also an

increase in size and cost. X5R or X7R dielectric ceramic

capacitors are recommended for designs with the MIC2253.

The output capacitor sets the frequency of the dominant

pole and zero in the power stage. The zero is given by:

esr

f××

For ceramic capacitors, the ESR is very small. This puts the

zero at a very high frequency where it can be ignored.

Fortunately, the MIC2253 is current mode in operation

which reduces the need for this output capacitor zero when

compensating the feedback loop.

The frequency of the pole caused by the output capacitor is

given by:

×××

=2VC

OUT

Diode Selection

The MIC2253 requires an external diode for operation. A

Schottky diode is recommended for most applications due

to their lower forward voltage drop and reverse recovery

time. Ensure the diode selected can deliver the peak

inductor current and the maximum reverse voltage is

rated greater than the output voltage.

Input Capacitor

A minimum 2.2µF ceramic capacitor with an X5R or X7R

dielectric is recommended for designing with the

MIC2253. Increasing input capacitance will improve

performance and greater noise immunity on the source.

The input capacitor should be as close as possible to the

inductor and the MIC2253, with short traces for good

noise performance.

Compensation

The comp pin is connected to the output of the voltage

error amplifier. The voltage error amplifier is a

transconductance amplifier. Adding a series RC-to-

ground adds a zero at:

42CR2

fzero

The resistor should be set to approximately 600. The

capacitor typically ranges from 10nF to 100nF.

Adding an optional capacitor from comp pin-to-ground

adds a pole at approximately:

32CR2

fpole

This capacitor typically is 100pF. Generally, an RC to

ground is all that is needed. The RC should be placed as

close as possible to the compensation pin. The capacitor

should be a ceramic with a X5R, X7R, or COG dielectric.

Refer to the MIC2253 evaluation board document for

component location.

Feedback Resistors

The feedback pin (FB) provides the control path to the

control the output. The FB pin is used to compare the

output to an internal reference. Output voltages are

adjusted by selecting the appropriate feedback network

values. The desired output voltage can be calculated as

follows:

⎟

⎠

⎞

⎜

⎝

⎛+⋅= 1

REFOUT

where VREF is equal to 1.245V.

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MIC2253 Sample Schematic

Micrel, Inc. MIC2253

April 2011 11 M9999-042011-C

Bill of Materials

Item Part Number Manufacturer Description Qty.

C1608X5R1C225K TDK(1) Capacitor, 2.2µF, 16V, X5R, 0603 size

GRM188R61C225KE15 Murata(2) Capacitor, 2.2µF, 16V, X5R, 0603 size

CL10A225K08NNN Samsung(3) Capacitor, 2.2µF, 16V, X5R, 0603 size

C1608X7R1H104K/10 TDK Capacitor, 0.1µF, 16V, X7R, 0603 size

GRM188R71H104KA93 Murata Capacitor, 0.1µF, 16V, X7R, 0603 size

CL10B104KB8NNN Samsung Capacitor, 0.1µF, 16V, X7R, 0603 size

C1608C0G1H101J TDK Capacitor, 100pF, 50V, C0G, 0603 size

GRM1885C1H101JA01 Murata Capacitor, 100pF, 50V, C0G, 0603 size

CL10C101JB8NNN Samsung Capacitor, 100pF, 50V, C0G, 0603 size

06035A101AT2A AVX(4) Capacitor, 100pF, 50V, C0G, 0603 size

C1608X5R1H103K TDK Capacitor, 10nF, 50V, X5R, 0603 size

CL10B103KB8NNN Samsung Capacitor, 10nF, 50V, X5R, 0603 size

06035C103KA12A AVX Capacitor, 10nF, 50V, X5R, 0603 size

CL21A226MPCLRNC Samsung Capacitor, 22µF, 10V, X5R, 0805 size C5

LMK212BJ226MG-T Taiyo Yuden(5) Capacitor, 22µF, 10V, X5R, 0805 size 1

SK32 MCC(6) Schottky Diode, 3A, 20V D1

SK34 MCC Schottky Diode, 3A, 40V 1

LTF5022T-2R2N3R2 TDK Inductor, 2.2µH, 3.4A, 5.2 x 5.0 x 2.2mm

RLF7030T-2R2M TDK Inductor, 2,2µH, 5.4A, 6.8 x 7.3 x 3.2mm

MOS6020-222ML Coilcraft(7) Inductor, 2.2µH, 3.56A, 6.0 x 7.1 x 2.4mm

R1 CRCW06031002FRTI Vishay(8) Resistor, 10k, 1%, 1/16W, 0603 size 1

R2 CRCW06036200FRTI Vishay Resistor, 620, 1%, 1/16W, 0603 size 1

R4 CRCW06031003FRTI Vishay Resistor, 100k, 1%, 1/16W, 0603 size 1

R5 CRCW06033092FRTI Vishay Resistor, 30.9k, 1%, 1/16W, 0603 size 1

U1 MIC2253-06YML Micrel, Inc.(9) 1MHz High Efficiency Boost Regulator with OVP and

Softstart 1

Notes:

1. TDK: www.tdk.com

2. Murata: www.murata.com

3. Samsung: www.sem.samsung.com

4. AVX: www.avx.com

5. Taiyo Yuden: www.t-yuden.com

6. MCC: www.mccsemi.com

7. Coilcraft: www.coilcraft.com

8. Vishay: www.vishay.com

9. Micrel, Inc.: www.micrel.com

Micrel, Inc. MIC2253

April 2011 12 M9999-042011-C

Recommended Layout

Top Layout

Bottom Layout

Micrel, Inc. MIC2253

April 2011 13 M9999-042011-C

Package Information

12-Pin 3mm x 3mm MLF® (ML)

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

Micrel makes no representations or warranties with respect to the accuracy or completeness of the information furnished in this data sheet. This

information is not intended as a warranty and Micrel does not assume responsibility for its use. Micrel reserves the right to change circuitry,

specifications and descriptions at any time without notice. No license, whether express, implied, arising by estoppel or otherwise, to any intellectual

property rights is granted by this document. Except as provided in Micrel’s terms and conditions of sale for such products, Micrel assumes no liability

whatsoever, and Micrel disclaims any express or implied warranty relating to the sale and/or use of Micrel products including liability or warranties

relating to fitness for a particular purpose, merchantability, or infringement of any patent, copyright or other intellectual property right.

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

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