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
2
L1
10µH
R2
R1
3
1
4
5
MIC2288BD5
VIN
1-Cell
Li Ion
VOUT
15V
EN
SW
FB
GND
VIN
C1
2.2µF
C2
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.
60
65
70
75
80
85
90
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
R2
+
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
SW
31
5
2
4
TSOT-23-5 (D5)
OVP
VIN
EN
AGND
PGND
SW
FB
NC
1
2
3
4
8
7
6
5
EP
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
75
77
79
81
83
85
87
89
91
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
12.05
12.1
12.15
12.2
0255075100 125 150
OUTPUT VOLTAGE (V)
LOAD (mA)
Load Re
g
ulation
V
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
p
erature
0
0.2
0.4
0.6
0.8
1
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
pp
l
y
Current
0
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
p
erature
0
50
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
pp
l
y
Volta
g
e
I
SW
= 500mA
0
100
200
300
400
500
600
700
0200 400 600 800 1000
SWITCH SATURATION VOLTAGE (mV)
SWITCH CURRENT (mA)
Switch Saturation
vs. Current
V
IN
= 3.6V
0
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
p
erature
80
82
84
86
88
90
92
94
96
98
100
2.5 4 5.5 7 8.5 10
MAXIMUM DUTY CYCLE (%)
SUPPLY VOLTAGE (V)
Maximum Duty Cycle
vs. Supply Voltage
85
87
89
91
93
95
97
99
-40 -20 0 20 40 60 80 100 120
MAXIMUM DUTY CYCLE (%)
TEMPERATURE (°C)
Maximum Duty Cycle
vs. Temperature
VIN = 3.6V
0
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
p
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
IN
12V
OUT
C
OUT
= 10µF
Switching Waveforms
Time (400ns/div)
OUTPUT VOLTAGE
(50mV/div)
INDUCTOR CURRENT
(500mA/div)
SWITCH SATURATION
(5V/div)
V
SW
Output Voltage
3.6V
IN
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
CA
PWM
Generator
Ramp
Generator
1.2MHz
Oscillator
SW
ENFB OVP*VIN
1.24V
*
OVP available on MLF
TM
package option only.
g
m
OVP*
Σ
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).
L1
10µH
C2
10µF
R2
R1
MIC2288BML
VIN
V
IN
V
OUT
EN
SW
FB
GND
GND
OVP
GND
C1
2.2µF
D1
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
V
IN
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:
FV
VLI2
rhpz IN
OUT OUT
=×× ×
2
π
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
L1
4.7µH
C2
22µF
6.3V
R2
1.87k
R1
5.62k
MIC2288BML
VIN
V
IN
3V to 4.2V
V
OUT
5V @ 400mA
EN
SW
FB
GND
GND
OVP
GND
C1
4.7µF
6.3V
D1
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
L1
10µH
C2
10µF
16V
R2
5k
R1
31.6k
MIC2288BML
VIN
V
IN
3V to 4.2V
V
OUT
9V @ 180mA
EN
SW
FB
GND
GND
OVP
GND
C1
2.2µF
10V
D1
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
L1
10µH
C2
10µF
16V
R2
5k
R1
42.3k
MIC2288BML
VIN
V
IN
3V to 4.2V
V
OUT
12V @ 100mA
EN
SW
FB
GND
GND
OVP
GND
C1
2.2µF
10V
D1
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
L1
10µH
C2
10µF
16V
R2
5k
R1
54.9k
MIC2288BML
VIN
V
IN
3V to 4.2V
V
OUT
15V @ 100mA
EN
SW
FB
GND
GND
OVP
GND
C1
2.2µF
10V
D1
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
L1
10µH
C2
4.7µF
25V
R2
1k
R1
18.2k
MIC2288BML
VIN
V
IN
3V to 4.2V
V
OUT
24V @ 50mA
EN
SW
FB
GND
GND
OVP
GND
C1
2.2µF
10V
D1
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
L1
10µH
C2
10µF
16V
R2
5k
R1
31.6k
MIC2288BML
VIN
V
IN
5V
V
OUT
9V @ 330mA
EN
SW
FB
GND
GND
OVP
GND
C1
2.2µF
10V
D1
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
L1
10µH
C2
10µF
16V
R2
5k
R1
43.2k
MIC2288BML
VIN
V
IN
5V
V
OUT
12V @ 250mA
EN
SW
FB
GND
GND
OVP
GND
C1
2.2µF
10V
D1
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
L1
10µH
C2
4.7µF
25V
R2
1k
R1
18.2k
MIC2288BML
VIN
VIN
5V
VOUT
24V @ 80mA
EN
SW
FB
GND
GND
OVP
GND
C1
2.2µF
10V
D1
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.
© 2004 Micrel, Incorporated.
