MIC2250-2YD5 - Micrel, Inc.

MIC2250

High-Efficiency Low EMI

Boost Regulator

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 M9999-041811-B

General Description

The MIC2250 is a general purpose DC/DC boost switching

regulator that features low noise, EMI reduction circuitry,

and high efficiency across a wide output current range.

The MIC2250 is optimized for noise-sensitive hand held

battery powered applications. A proprietary control method

allows low ripple across the output voltage and current

ranges. The MIC2250 incorporates a pseudo-random

dithering function to reduce EMI levels up to 10dB enabled

by the DITH pin.

The MIC2250 is designed for use with inductor values from

4.7µH to 22µH, and is stable with ceramic capacitors from

1µF to 22µF.

The MIC2250 attains a high peak efficiency up to 90% at

100mA and excellent light load efficiency of 80% at 1mA.

High power density is achieved with the MIC2250’s

internal 34V/2A rated switch, allowing it to power large

loads in a tiny footprint.

The MIC2250-1 is available in a 5-pin Thin SOT-23

package with dithering disabled. While the MIC2250-2 is

available in a 5-pin Thin SOT-23 package with dithering

enabled. The MIC2250 is available in 8-pin 2mm x 2mm

MLF® leadless package option with an operating junction

temperature range of –40°C to +125°C.

Data sheets and support documentation can be found on

Micrel’s web site at: www.micrel.com.

Features

• Over 80% efficient for a 300:1 load range

• 2.5V to 5.5V input voltage range

• Output voltage adjustable to 32V

• 52µA (typ) quiescent current

• Constant peak current control reduces output ripple

• EMI reduction circuitry

• Stable with small ceramic capacitors

• <1µA shutdown current

• UVLO and thermal shutdown

• 8-pin 2mm x 2mm leadless MLF® package (MIC2250)

• 5-pin Thin SOT-23 package (MIC2250-1 & -2)

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

Applications

• LCD/OLED display bias supply

• CCD bias supply

• Mobile Phones, PDA, Media Players, GPS PND

• Haptic displays

• Local 5V, 15V, 24V rail

___________________________________________________________________________________________________________

Typical Application

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Ordering Information

Part Number Marking(1) Junction Temp. Range Package(3) Lead Finish

MIC2250YML

(2) –40° to +125°C 8-Pin 2mm x 2mm MLF® Pb-Free

MIC2250-1YD5 AZ1(2) –40° to +125°C 5-Pin Thin SOT-23 Pb-Free

MIC2250-2YD5 AZ2(2) –40° to +125°C 5-Pin Thin SOT-23 Pb-Free

Note:

1. Pin 1 identifier = “•”.

2. Over/Underbar ( /__ ) may not be to scale.

3. MLF® is GREEN RoHs compliant package. Lead finish is NiPdAu. Mold compound is Halogen Free.

Pin Configur ation

8-Pin 2mm x 2mm MLF® (ML)

(Top View) 5-Pin Thin SOT-23 (D5)

(Top View)

Pin Description

Pin Name Pin Number

MIC2250YML Pin Number

MIC2250-1YD5 Pin Number

MIC2250-2YD5 Pin Function

FB 1 3 3 Feedback (Input): 1.24V output voltage sense node.

VOUT = 1.24V (1 + R1/R2)

AGND 2 ― ― Analog Ground. Connect to power ground.

PGND 3 2 2 Power Ground.

SW 4 1 1 Switch Node (Input): Internal power NMOS drain.

NC 5 ― ― Not Internally Connected.

VIN 6 5 5 Supply (Input): 2.5V to 5.5V input voltage.

DITH 7 ― 4 Frequency Dithering (Input): Connect this pin high to

enable pseudo-random on-time dithering to reduce EMI.

Connect this pin-to-ground to disable this function.

EN 8 4 4 Enable (Input): Logic high enables the regulator. Logic

low shuts down the regulator. Do not leave floating.

HS PAD EPAD ― ― Ground (Return): Exposed backside pad. Connect to

power ground.

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Absolute Maximum Ratings(1)

Supply Voltage (VIN).........................................................6V

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

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

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

Switch Current (ISW) ......................................................3.5A

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

ESD Rating(4)................................................. ESD Sensitive

Operating Ratings(2)

Supply Voltage (VIN)......................................... 2.5V to 5.5V

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

Junction Temperature (TJ)(3) .....................–40°C to +125°C

Junction Thermal Resistance

2mm x 2mm MLF®-8 (θJA)..................................90°C/W

Electrical Characteristics(5)

VIN = VEN = 3.6V; VDITH = 0V; VOUT = 15V; IOUT = 40mA; TA = 25°C, unless otherwise noted. Bold values indicate

–40°C ≤ TJ ≤ +85°C.

Symbol Parameter Condition Min Typ Max Units

VIN Input Voltage Range 2.5 5.5 V

VULVO Under-voltage Lockout VIN rising 1.8 2 2.4 V

IQ Quiescent Current VFB = 1.5V (not switching) 52 80 µA

ISD Shutdown Current VEN = 0V, Note 6 0.1 1 µA

1.20 1.24 1.277 V VFB Feedback Voltage

–40°C ≤ TJ ≤ +85°C 1.19 1.29 V

IFB Feedback Input Current VFB = 1.24V 10 nA

PFM Operation

Tss Soft Start time 1 ms

tSW Switch Off-time VIN = 3.6V 1.6 µs

DMAX Maximum Duty Cycle 75 87 %

tDITH Off-time Dithering VDITH = 3.6V. Percentage from nominal. ±20 %

Line Regulation 3V ≤ VIN ≤ 5V 0.3 2 %

Load Regulation 1mA ≤ IOUT ≤ 40mA 0.1 2 %

ISW Switch Current Limit Note 7 0.9 2 A

RON Switch ON-resistance ISW = 200mA 0.5 1 Ω

ISW Switch Leakage Current VEN = 0V, VSW = 10V 0.01 5 µA

Turn ON 1.5 V VEN,

VDITH

Logic Input Thresholds

Turn OFF 0.4 V

IEN Enable Pin Current VEN = VIN = 5.0V 0.1 2 µA

130 °C T Thermal Shutdown Threshold

Hysteresis 15 °C

Notes:

1. Absolute maximum ratings indicate limits beyond which damage to the component may occur.

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

3. 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.

4. Devices are ESD sensitive. Handling precautions recommended. Human body model, 1.5kΩ in series with 100pF.

5. Specification for packaged product only.

6. ISD = IVIN.

7. Guaranteed by design.

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Typical Characteristics

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Functional Characteristics

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Functional Characteristics (continued)

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Functional Diagram

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Functional Description

VIN

The input supply (VIN) provides power to the internal

MOSFETs and control circuitry for the switch mode

regulator. The operating input voltage range is from 2.5V

to 5.5V. An input capacitor with a minimum voltage

rating of 6.3V is recommended. Refer to the layout

recommendations for details.

A logic level input of 1.5V or higher enables the

regulator. A logic input of 0.4V or less places the

regulator in shutdown mode which reduces the supply

current to less than 1µA. The MIC2250 features built-in

soft start circuitry that reduces in-rush current and

prevents the output voltage from overshooting during

startup. Do not leave the Enable pin floating.

The MIC2250 has an internal MOSFET switch that

connects directly to one end of the inductor (SW pin) and

provides a current path to ground during switching

cycles. The source of the internal MOSFET connects

through a current sense resistor to ground.

PGND

The power ground pin is the high current path to ground.

The current loop for the power ground should be as

small as possible and separate from the analog ground

(AGND). Refer to the layout recommendations for more

details.

AGND

Analog ground (AGND) is the ground path for the biasing

and control circuitry. The current loop for the signal

ground should be separate from the power ground

(PGND) loop. Refer to the layout recommendations for

more details.

DITH

The DITH function is a frequency dithering technique

that reduces EMI noise by spreading the boost

regulators’ noise spectrum. This technique reduces the

EMI peaks by distributing the switching frequency across

a wider spectrum. Connect this pin high to enable the

pseudo-random on-time dithering. Connect this pin to

ground to disable this function.

The feedback pin (FB) allows the regulated output

voltage to be set by applying an external resistor divider

network. The internal reference voltage is 1.24V. The

output voltage is calculated from the following equation:

⎟

⎠

⎞

⎜

⎝

⎛+= R2

11.24VVOUT

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Application Information

Overview

The MIC2250 Boost Regulator utilizes a combination of

PFM & Current Mode Control to achieve very high

efficiency over a wide range of output load. This

innovative design is the basis for the regulator’s high

efficiency, excellent stability, and self compensation

technique. The boost regulator performs a power

conversion that results in an output voltage that is

greater than the input. Operation starts with activating an

internal MOSFET switch which draws current through

the inductor (L1). While one end of the inductor is fixed

at VIN, the other end is switched up and down. While the

switch is on, the current through the inductor increases.

When the switch is off the inductor current continues to

flow through the output diode.

The current flow imposes a voltage across the inductor,

which is added to VIN to produce a higher voltage VOUT.

At low power levels (typically less than 1W), the period

varies between switching cycles, indicative of Pulse

Frequency Modulation (PFM). As the output power

increases beyond approximately 1W, the period between

switching cycles continues to decrease and the power

(switch current) delivered with each cycle increases

indicative of Current Mode control.

PFM Regulation

The error amplifier compares the regulator’s reference

voltage with the feedback voltage obtained from the

output resistor voltage divider network. The resulting

error voltage acts as a correction input signal to the

control block. The control block generates two signals

that turn on and off the output MOSFET switch. An

increase in load current causes VOUT and VFB to

decrease in value. The control loop then changes the

switching frequency to increase the energy transferred to

the output capacitor to regulate the output voltage. A

reduction in load causes VOUT and VFB to increase. Now

the control loop compensates by reducing the effective

switching frequency, thus reducing the amount of energy

delivered to the output capacitor in order to keep the

output voltage within regulation.

Current Mode Regulation

The control block’s oscillator starts the cycle by setting

the MOSFET switch control flip flop. The switch then

turns on. This flip flop is reset when the switch current

ramp reaches the threshold set by the error amplifier. If

the error amplifier indicates that VFB is either too high or

too low, then the threshold for the comparator measuring

the switch current is appropriately adjusted to bring VOUT

back to within regulation limits. The level of the error

signal also sets the off time of the switch. A higher error

signal (output voltage is low) will reduce off time to

increase energy transfer to the output. A lower error

signal (output voltage is high) will conversely, increase

off time to reduce energy transfer to the output.

Component Selection

Resistors

An external resistive divider network (R1 and R2) with its

center tap connected to the feedback pin sets the output

voltage. The appropriate R1 and R2 values for the

desired output voltage are calculated by:

⎟

⎠

⎞

⎜

⎝

⎛−

1.24V

OUT

Large resistor values are recommended to reduce light

load operating current, and improve efficiency. The table

below gives a good compromise between quiescent

current and accuracy. Additionally, a feedforward

capacitor (CFF) (placed in parallel with R1) may be added

to improve transient performance. Recommended values

are suggested below:

VOUT Suggested R1 CFF

5V to 10V 100k 4.7nF

10V to 15V 240k 2.2nF

15V to 32V 1M 470pF

Figure 1. Typical Application Circuit

Inductor

Inductor selection is a balance between efficiency,

stability, cost, size, and rated current. For most

applications, inductors in the range 4.7uH to 22uH are

recommended. Larger inductance values reduce the

peak-to-peak ripple current, thereby reducing both the

DC losses and the transition losses for better efficiency.

The inductor’s DC resistance (DCR) also plays an

important role. Since the majority of the input current

(minus the MIC2250 operating current) is passed

through the inductor, higher DCR inductors will reduce

efficiency at higher load currents. Figure 2 shows the

comparison of efficiency between a 140mΩ DCR, 4.7uH

inductor and a 190mΩ DCR, 10uH inductor. The switch

current limit for the MIC2250 is typically 2A. The

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saturation current rating of the selected inductor should

be 20-30% higher than the 2A specification for proper

operation.

Figure 2. Efficiency Comparison between Lower

and Higher Inductor Values

Input Capacitor

The boost converter exhibits a triangular current

waveform at its input, so an input capacitor is required to

decouple this waveform and thereby reduce the input

voltage ripple. A 10uF to 22uF ceramic capacitor should

be sufficient for most applications. A minimum input

capacitance of 1uF is recommended. The input capacitor

should be as close as possible to the inductor and the

MIC2250, with short PCB traces for good noise

performance.

Output Capacitor

Output capacitor selection is also a trade-off between

performance, size, and cost. Increasing COUT will lead to

an improved transient response however the size and

cost also increase. X5R and X7R ceramic capacitors are

recommended. For most applications, 2.2uF to 22uF

should be sufficient.

Diode

The MIC2250 requires an external diode for operation.

The diode must be rated for the peak inductor current,

and its reverse voltage rating must be greater than the

output voltage. A Schottky diode is recommended for

lower output voltages due to its lower forward voltage

drop and reverse recovery time. However, at higher

output voltages (>10V), a high speed diode such as

LS4148 can be more efficient as it has the advantage of

considerably lower leakage currents, especially at higher

temperatures. This will greatly improve light load

efficiency when compared to a Schottky diode.

For example: At 70oC ambient temperature, VIN = 2.5V,

VOUT= 24V at no load.

Input current (Vishay SL04 Schottky) = 2.1mA

Input current (Generic LS4148) = 0.37mA

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MIC2250 Schematic

Bill of Materials

Item Part Number Manufacturer Description Qty.

C2012X5R0J106K TDK(1)

VJ0805G106KXYAT Vishay Vitramon(2)

08056D106KAT AVX(3)

GRM21BR60J106M Murata(4)

Capacitor, 10µF, 6.3V, X5R 1

C2012X5R1E225K TDK(1)

08053C225MAT AVX(3)

GRM21R61E225KE36D Murata(4)

Capacitor, 2.2µF, 25V, X5R 1

LS4148 Vishay(2) High Speed Diode, 75V, 300mA

D1 LS04 Vishay(2) Schottky Diode, 40V, 1A 1

VLF5012ST-100M1R0 TDK(1) 10µH

LPS4018-100 Coilcraft(5) 10µH, 10%

CDRH4D28NP-100NC Sumida(6) 10µH, 1.26A

R1 CRCW06031004FKEYE3 Vishay Dale(2) Resistor, 1M, 1%. 1/16W, Size 0603 1

R2 CRCW06039012FKEYE3 Vishay Dale(2) Resistor, 90.1k, 1%. 1/16W, Size 0603 1

U1 MIC2250YML Micrel, Inc.

(7) High-Efficiency Low EMI Boost Regulator 1

Notes:

1. TDK: www.tdk.com.

2. Vishay: www.vishay.com.

3. AVX: www.avx.com.

4. Murata: www.murata.com.

5. Coilcraft: www.coilcraft.com.

6. Sumida: www.sumida.com.

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

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PCB Layout Recommendations

Top Layer

Bottom Layer

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Package Information

8-Pin 2mm x 2mm MLF® (ML)

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5-Pin Thin SOT-23 (D5)

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

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