MIC2288YMLTR - Micrel, Inc.

April 2005 1 M9999-042205

MIC2288 Micrel, Inc.

MIC2288

1A 1.2MHz PWM Boost Converter in

Thin SOT-23 and 2××

××

×2 MLF™

General Description

The MIC2288 is a 1.2MHz PWM, DC/DC boost switching

regulator available in low-profile Thin SOT-23 and

2mm ×2mm MLF™ package options. High power density is

achieved with the MIC2288’s internal 34V/1A switch, allow-

ing it to power large loads in a tiny footprint.

The MIC2288 implements a constant frequency, 1.2MHz

PWM, current mode control scheme with internal compensa-

tion that offers excellent transient response and output regu-

lation performance. The high frequency operation saves

board space by allowing small, low-profile, external compo-

nents. The fixed frequency PWM topology also reduces

spurious switching noise and ripple to the input power source.

The MIC2288 is available in a low-profile Thin SOT-23-5

package and a 2mm ×2mm MLF™-8 leadless package. The

2mm ×2mm MLF™-8 package option has an output over-

voltage protection feature.

The MIC2288 has a junction temperature range of –40°C to

+125°C.

All support documentation can be found on Micrel’s web

site at www.micrel.com.

Typical Application

10µH

MIC2288BD5

VIN

1-Cell

Li Ion

VOUT

15V

GND

VIN

2.2µF

10µF

2mm ××

××

× 2mm MLF™ Boost Regulator

Features

•2.5V to 10V input voltage range

•Output voltage adjustable to 34V

•Over 1A switch current

•1.2MHz PWM operation

•Stable with ceramic capacitors

•High-efficiency

•<1% line and load regulation

•Low input and output ripple

•<1µA shutdown current

•UVLO

•Output overvoltage protection (MIC2288BML)

•Over temperature shutdown

•Thin SOT-23-5 package option

•2mm × 2mm leadless MLF™-8 package option

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

Applications

•Organic EL power supply

•TFT-LCD bias supply

•12V supply for DSL applications

•Multi-output DC/DC converters

•Positive and negative output regulators

•SEPIC converters

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

MLF and MicroLeadFrame are trademarks of Amkor Technology, Inc.

00.050.1 0.15 0.2

EFFICIENCY (%)

LOAD (A)

15V

OUT

Efficiency

VIN = 4.2V

VIN = 3.2V VIN = 3.6V

MIC2288 Micrel, Inc.

M9999-042205 2April 2005

Pin Description

Pin Number Pin Number

TSOT-23-5 2××

××

×2 MLF™-8 Pin Name Pin Function

17 SW Switch Node (Input): Internal power Bipolar collector.

2GND Ground (Return): Ground.

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

VOUT = 1.24V

1R1











43 EN Enable (Input): Logic high enables regulator. Logic low shuts down regulator.

52 VIN Supply (Input): 2.5V to 10V input voltage.

1OVP Output Overvoltage Protection (Input): Tie this pin to VOUT to clamp the

output voltage to 34V maximum in fault conditions. Tie this pin to ground if

OVP function is not required.

5NCNo Connect: No internal connection to die.

4AGND Analog ground.

8PGND Power ground.

EP GND Exposed backside pad.

Pin Configuration

FB GND

EN VIN

TSOT-23-5 (D5)

OVP

VIN

AGND

PGND

8-Pin MLF™ (ML)

(Top View)

Fused Lead Frame

Ordering Information

Marking Output Overvoltage Junction

Part Number Code Voltage Protection Temp. Range Package Lead Finish

MIC2288BD5 SHAA Adjustable – –40°C to 125°CThin SOT-23-5 Standard

MIC2288YD5 SHAA Adjustable – –40°C to 125°CThin SOT-23-5 Lead Free

MIC2288BML SJA Adjustable 34V –40°C to 125°C2×2 MLF™-8 Standard

MIC2288YML SJA Adjustable 34V –40°C to 125°C2×2 MLF™-8 Lead Free

April 2005 3 M9999-042205

MIC2288 Micrel, Inc.

Absolute Maximum Ratings(1)

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

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

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

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

Switch Current (ISW)....................................................... 2A

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

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

Operating Ratings(2)

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

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

Package Thermal Impedance

2mm ×2mm MLF™-8 (θJA) ................................. 93°C/W

Thin SOT-23-5 (θJA) .......................................... 256°C/W

Electrical Characteristics(4)

TA = 25°C, VIN = VEN = 3.6V, VOUT = 10V, IOUT = 20mA, 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

IVIN Quiescent Current VFB = 2V, (not switching) 2.8 5 mA

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

VFB Feedback Voltage (±1%) 1.227 1.24 1.252 V

(±2%) (Over Temp) 1.215 1.265 V

IFB Feedback Input Current VFB = 1.24V –450 nA

Line Regulation 3V ≤ VIN ≤ 5V 0.1 1%

Load Regulation 5mA ≤ IOUT ≤ 40mA 0.2 %

DMAX Maximum Duty Cycle 85 90 %

ISW Switch Current Limit 1.2 A

VSW Switch Saturation Voltage ISW = 1A 550 mV

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

VEN Enable Threshold Turn on 1.5 V

Turn off 0.4 V

IEN Enable Pin Current VEN = 10V 20 40 µA

fSW Oscillator Frequency 1.05 1.2 1.35 MHz

VOVP Output Overvoltage Protection MIC2288 MLF™ package option only 30 32 34 V

TJOvertemperature 150 °C

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, θJA, 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. This device is not guaranteed to operate beyond its specified operating rating.

3. IC devices are inherently ESD sensitive. Handling precautions required. Human body model rating: 1.5K in series with 100pF.

4. Specification for packaged product only.

5. ISD = IVIN.

MIC2288 Micrel, Inc.

M9999-042205 4April 2005

Typical Characteristics

0255075100 125 150

EFFICIENCY (%)

OUTPUT CURRENT (mA)

Efficiency at VOUT = 12V

VIN = 4.2V

VIN = 3.6V

VIN = 3.3V

11.8

11.85

11.9

11.95

12.05

12.1

12.15

12.2

0255075100 125 150

OUTPUT VOLTAGE (V)

LOAD (mA)

Load Re

ulation

IN =

3.6V

1.10

1.12

1.14

1.16

1.18

1.20

1.22

1.24

1.26

1.28

1.30

-40 -20 0 20 40 60 80 100 120

FEEDBACK VOLTAGE (V)

TEMPERATURE (°C)

Feedback Voltage

vs. Tem

erature

0.2

0.4

0.6

0.8

1.2

1.4

1.6

1.8

2.5 4 5.5 7 8.5 10

CURRENT LIMIT (A)

SUPPLY VOLTAGE (V)

Current Limit

vs. Su

Current

0.2

0.4

0.6

0.8

1.0

1.2

1.4

-40 -20 0 20 40 60 80 100 120

CURRENT LIMIT (A)

TEMPERATURE (°C)

Current Limit

vs. Tem

erature

100

150

200

250

300

2.5 4 5.5 7 8.5 10

SWITCH SATURATION VOLTAGE (mV)

SUPPLY VOLTAGE (V)

Switch Saturation

vs. Su

Volta

= 500mA

100

200

300

400

500

600

700

0200 400 600 800 1000

SWITCH SATURATION VOLTAGE (mV)

SWITCH CURRENT (mA)

Switch Saturation

vs. Current

= 3.6V

100

200

300

400

500

600

700

-40 -20 0 20 40 60 80 100 120

SWITCH SATURATION VOLTAGE (mV)

TEMPERATURE (°C)

Switch Saturation

vs. Temperature

VIN = 3.6V

ISW = 500mA

0.8

0.9

1.0

1.1

1.2

1.3

1.4

-40 -20 0 20 40 60 80 100 120

FREQUENCY (MHz)

TEMPERATURE (°C)

Frequency

vs. Tem

erature

100

2.5 4 5.5 7 8.5 10

MAXIMUM DUTY CYCLE (%)

SUPPLY VOLTAGE (V)

Maximum Duty Cycle

vs. Supply Voltage

-40 -20 0 20 40 60 80 100 120

MAXIMUM DUTY CYCLE (%)

TEMPERATURE (°C)

Maximum Duty Cycle

vs. Temperature

VIN = 3.6V

100

200

300

400

500

600

700

-40 -20 0 20 40 60 80 100 120

FEEDBACK CURRENT (nA)

TEMPERATURE (°C)

FB Pin Current

vs. Tem

erature

April 2005 5 M9999-042205

MIC2288 Micrel, Inc.

Function Characteristics

Enable Characteristics

Time (400µs/div)

OUTPUT VOLTAGE

(5V/div)

ENABLE VOLTAGE

(2V/div)

3.6VIN

12VOUT

150mA Load

Output Voltage

Enable Voltage

Line Transient Response

Time (400µs/div)

OUTPUT VOLTAGE

(1mV/div) AC-Coupled

INPUT VOLTAGE

(2V/div)

4.2V

3.2V

12VOUT

150mA Load

Load Transient Response

Time (400µs/div)

OUTPUT VOLTAGE

(100mV/div) AC-Coupled

LOAD CURRENT

(100mA/div)

10mA

150mA

3.6V

12V

OUT

= 10µF

Switching Waveforms

Time (400ns/div)

OUTPUT VOLTAGE

(50mV/div)

INDUCTOR CURRENT

(500mA/div)

SWITCH SATURATION

(5V/div)

Output Voltage

3.6V

12V

OUT

150mA

Inductor Current

(10µH)

MIC2288 Micrel, Inc.

M9999-042205 6April 2005

Functional Description

The MIC2288 is a constant frequency, PWM current mode

boost regulator. The block diagram is shown in Figure 1. The

MIC2288 is composed of an oscillator, slope compensation

ramp generator, current amplifier, gm error amplifier, PWM

generator, and a 1A bipolar output transistor. The oscillator

generates a 1.2MHz clock. The clock’s two functions are to

trigger the PWM generator that turns on the output transistor,

and to reset the slope compensation ramp generator. The

current amplifier is used to measure the switch current by

amplifying the voltage signal from the internal sense resistor.

The output of the current amplifier is summed with the output

of the slope compensation ramp generator. This summed

current-loop signal is fed to one of the inputs of the PWM

generator.

Functional Diagram

GND

PWM

Generator

Ramp

Generator

1.2MHz

Oscillator

ENFB OVP*VIN

1.24V

OVP available on MLF

package option only.

OVP*

VREF

Figure 1. MIC2288 Block Diagram

The gm error amplifier measures the feedback voltage through

the external feedback resistors and amplifies the error be-

tween the detected signal and the 1.24V reference voltage.

The output of the gm error amplifier provides the voltage-loop

signal that is fed to the other input of the PWM generator.

When the current-loop signal exceeds the voltage-loop sig-

nal, the PWM generator turns off the bipolar output transistor.

The next clock period initiates the next switching cycle,

maintaining the constant frequency current-mode PWM con-

trol.

April 2005 7 M9999-042205

MIC2288 Micrel, Inc.

Applications Information

DC-to-DC PWM Boost Conversion

The MIC2288 is a constant-frequency boost converter. It

operates by taking a DC input voltage and regulating a higher

DC output voltage. Figure 2 shows a typical circuit. Boost

regulation is achieved by turning on an internal switch, which

draws current through the inductor (L1). When the switch

turns off, the inductor’s magnetic field collapses, causing the

current to be discharged into the output capacitor through an

external Schottky diode (D1). Voltage regulation is achieved

by modulating the pulse width or pulse-width modulation

(PWM).

10µH

10µF

MIC2288BML

VIN

OUT

GND

OVP

GND

2.2µF

Figure 2. 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:

D1 V

OUT

=−

The duty cycle required for voltage conversion should be less

than the maximum duty cycle of 85%. 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 overshoot slightly over 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 reduces peak

current, which in turn reduces energy transfer in each cycle.

Overvoltage Protection

For the MLF™ package option, there is an overvoltage

protection function. If the feedback resistors are discon-

nected from the circuit or the feedback pin is shorted to

ground, the feedback pin will fall to ground potential. This will

cause the MIC2288 to switch at full duty cycle in an attempt

to maintain the feedback voltage. As a result, the output

voltage will climb out of control. This may cause the switch

node voltage to exceed its maximum voltage rating, possibly

damaging the IC and the external components. To ensure the

highest level of protection, the MIC2288 OVP pin will shut the

switch off when an overvoltage condition is detected, saving

itself and other sensitive circuitry downstream.

Component Selection

Inductor

Inductor selection is a balance between efficiency, stability,

cost, size, and rated current. For most applications a 10µH is

the recommended inductor value. It is usually a good balance

between these considerations.

Larger inductance values reduce the peak-to-peak ripple

current, affecting efficiency. This has the effect of reducing

both the DC losses and the transition losses. There is also a

secondary effect of an inductor’s DC resistance (DCR). The

DCR of an inductor will be higher for more inductance in the

same package size. This is due to the longer windings

required for an increase in inductance. Since the majority of

input current (minus the MIC2288 operating current) is passed

through the inductor, higher DCR inductors will reduce effi-

ciency.

To maintain stability, increasing inductor size will have to be

met with an increase in output capacitance. 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:

VLI2

rhpz IN

OUT OUT

=×× ×

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 in-

creasing the output capacitor value (decreasing loop gain).

Output Capacitor

Output capacitor selection is also a trade-off between perfor-

mance, 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 MIC2288. Y5V values

may be used but to offset their tolerance over temperature,

more capacitance is required. The following table shows the

recommended ceramic (X5R) output capacitor value vs.

output voltage.

Output Voltage Recomended Output Capacitance

<6V 22µF

<16V 10µF

<34V 4.7µF

Table 1. Output Capacitor Selection

Diode Selection

The MIC2288 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.

MIC2288 Micrel, Inc.

M9999-042205 8April 2005

Input capacitor

A minimum 1µF ceramic capacitor is recommended for

designing with the MIC2288. 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 MIC2288, with short traces for good

noise performance.

Feedback Resistors

The MIC2288 utilizes a feedback pin to compare the output

to an internal reference. The output voltage is adjusted by

selecting the appropriate feedback resistor network values.

The R2 resistor value must be less than or equal to 5kΩ

(R2 ≤ 5kΩ).The desired output voltage can be calculated

as follows:

VV R1

R2 1

OUT REF

=×+













where VREF is equal to 1.24V.

April 2005 9 M9999-042205

MIC2288 Micrel, Inc.

Application Circuits

4.7µH

22µF

6.3V

1.87k

5.62k

MIC2288BML

VIN

3V to 4.2V

OUT

5V @ 400mA

GND

OVP

GND

4.7µF

6.3V

C1 4.7µF, 6.3V, 0805 X5R Ceramic Capacitor 08056D475MAT AVX

C2 22µF, 6.3V, 0805 X5R Ceramic Capacitor 12066D226MAT AVX

D1 1A, 40V Schotty Diode MBRM140T3 ON Semi.

L1 4.7µH, 650mA Inductor LQH32CN4R7M11 Murata

Figure 3. 3.3VIN to 5VOUT @ 400mA

10µH

10µF

16V

31.6k

MIC2288BML

VIN

3V to 4.2V

OUT

9V @ 180mA

GND

OVP

GND

2.2µF

10V

C1 2.2µF, 10V, 0805 X5R Ceramic Capacitor 08052D225KAT AVX

C2 10µF, 16V, 1206 X5R Ceramic Capacitor 1206YD106MAT AVX

D1 1A, 40V Schotty Diode MBRM140T3 ON Semi.

L1 10µH, 650mA Inductor LQH43CN100K03 Murata

Figure 4. 3.3VIN – 4.2VIN to 9VOUT @ 180mA

10µH

10µF

16V

42.3k

MIC2288BML

VIN

3V to 4.2V

OUT

12V @ 100mA

GND

OVP

GND

2.2µF

10V

C1 2.2µF, 10V, 0805 X5R Ceramic Capacitor 08052D225KAT AVX

C2 10µF, 16V, 1206 X5R Ceramic Capacitor 1206YD106MAT AVX

D1 1A, 40V Schotty Diode MBRM140T3 ON Semi.

L1 10µH, 650mA Inductor LQH43CN100K03 Murata

Figure 5. 3.3VIN – 4.2VIN to 12VOUT @ 100mA

10µH

10µF

16V

54.9k

MIC2288BML

VIN

3V to 4.2V

OUT

15V @ 100mA

GND

OVP

GND

2.2µF

10V

C1 2.2µF, 10V, 0805 X5R Ceramic Capacitor 08052D225KAT AVX

C2 10µF, 16V, 1206 X5R Ceramic Capacitor 1206YD106MAT AVX

D1 1A, 40V Schotty Diode MBRM140T3 ON Semi.

L1 10µH, 650mA Inductor LQH43CN100K03 Murata

Figure 6. 3.3VIN – 4.2VIN to 15VOUT @ 100mA

10µH

4.7µF

25V

18.2k

MIC2288BML

VIN

3V to 4.2V

OUT

24V @ 50mA

GND

OVP

GND

2.2µF

10V

C1 2.2µF, 10V, 0805 X5R Ceramic Capacitor 08052D225KAT AVX

C2 4.7µF, 25V, 1206 X5R Ceramic Capacitor 12063D475MAT AVX

D1 1A, 40V Schotty Diode MBRM140T3 ON Semi.

L1 10µH, 650mA Inductor LQH43CN100K03 Murata

Figure 7. 3.3VIN – 4.2VIN to 24VOUT @ 50mA

10µH

10µF

16V

31.6k

MIC2288BML

VIN

OUT

9V @ 330mA

GND

OVP

GND

2.2µF

10V

C1 2.2µF, 10V, 0805 X5R Ceramic Capacitor 08052D225KAT AVX

C2 10µF, 16V, 1206 X5R Ceramic Capacitor 1206YD106MAT AVX

D1 1A, 40V Schotty Diode MBRM140T3 ON Semi.

L1 10µH, 650mA Inductor LQH43CN100K03 Murata

Figure 8. 5VIN to 9VOUT @ 330mA

MIC2288 Micrel, Inc.

M9999-042205 10 April 2005

10µH

10µF

16V

43.2k

MIC2288BML

VIN

OUT

12V @ 250mA

GND

OVP

GND

2.2µF

10V

C1 2.2µF, 10V, 0805 X5R Ceramic Capacitor 08052D225KAT AVX

C2 10µF, 16V, 1206 X5R Ceramic Capacitor 1206YD106MAT AVX

D1 1A, 40V Schotty Diode MBRM140T3 ON Semi.

L1 10µH, 650mA Inductor LQH43CN100K03 Murata

Figure 9. 5VIN to 12VOUT @ 250mA

10µH

4.7µF

25V

18.2k

MIC2288BML

VIN

VOUT

24V @ 80mA

GND

OVP

GND

2.2µF

10V

C1 2.2µF, 10V, 0805 X5R Ceramic Capacitor 08052D225KAT AVX

C2 4.7µF, 25V, 1206 X5R Ceramic Capacitor 12066D475MAT AVX

D1 1A, 40V Schotty Diode MBRM140T3 ON Semi.

L1 10µH, 650mA Inductor LQH32CN4R7M11 Murata

Figure 10. 5VIN to 24VOUT @ 80mA

April 2005 11 M9999-042205

MIC2288 Micrel, Inc.

Package Information

All Dimensions are in millimeters

5-Pin TSOT (D5)

8-Pin 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

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.