MIC2285
8MHz PWM Synchronous Buck
Regulator with LDO Standby Mode
Patent Pending
LOWQ is a trademark of Micrel, Inc
MLF and MicroLeadFrame are 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
January 2006
M9999-012406
www.micrel.com
General Description
The Micrel MIC2285 is a high efficiency 8MHz pulse
width modulated (PWM) synchronous buck (step-
down) regulator that features a LOWQ™ LDO standby
mode that draws only 18µA of quiescent current. The
MIC2285 allows an ultra-low noise, small size, and
high efficiency solution for portable power applications.
In PWM mode, the MIC2285 operates with a constant
frequency 8MHz PWM control. Under light load
conditions, such as in system sleep or standby modes,
the PWM switching operation can be disabled to
reduce switching losses. In this light load LOWQ™
mode, the LDO maintains the output voltage and
draws only 18µA of quiescent current. The LDO mode
of operation saves battery life while not introducing
spurious noise and high ripple as experienced with
pulse skipping or bursting mode regulators.
The MIC2285 operates from a 2.7V to 5.5V input
voltage and features internal power MOSFETs that can
supply up to 500mA output current in PWM mode. It
can operate with a maximum duty cycle of 100% for
use in low-dropout conditions.
The MIC2285 is available in the 10-pin 3mm x 3mm
MLF™ package with a junction operating range from
–40°C to +125°C.
Data sheets and support documentation can be found
on Micrel’s web site at: www.micrel.com.
Features
• 2.7 to 5.5V supply/input voltage
• Light load LOWQ™ LDO mode
20µA quiescent current
Low noise, 75µVrms
• 8MHz PWM mode
Output current to 500mA
>90% efficiency
100% maximum duty cycle
• Adjustable output voltage option down to 1V
Fixed output voltage options available
• Ultra-fast transient response
• Uses a tiny 0.47µH inductor
• Enables sub 1mm profile solution
• Fully integrated MOSFET switches
• Micropower shutdown
• Thermal shutdown and current limit protection
• Pb-free 10-pin 3mm x 3mm MLF package
• –40°C to +125°C junction temperature range
Applications
• Cellular phones
• PDAs
• USB peripherals
____________________________________________________________________________________________________
Typical Application
Adjustable Output Buck Regulator with LOWQ™ Mode
0
10
20
30
40
50
60
70
80
90
100
OUTPUT CURRENT (mA)
1.8V
OUT
Efficiency
0 100 200 300 400 500
V
IN
=3.2V
V
IN
=3.6V
V
IN
=4.2V
Micrel, Inc. MIC2285
January 2006
2 M9999-012406
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Ordering Information
Part Number Output
Voltage* Junction
Temperature Range Package Lead Finish
MIC2285YML Adj. –40° to +125°C 10-Pin 3x3 MLF™ Pb-free
Note:
* Other Voltage options available. Contact Micrel for details.
Pin Configur ation
FB EN
A
GND
LDO
BIAS
AV IN
PGND
SW
VIN
LOWQ
5
1
2
3
4
6
10
9
8
7
EP
10-Pin 3mm x 3mm MLF (ML)
Pin Description
Pin Number Pin Name Pin Function
1 AGND Analog (signal) Ground.
2 LDO LDO Output (Output): Connect to V
OUT
for LDO mode operation.
3 BIAS
Internal circuit bias supply. Must be filtered from input voltage through an RC
lowpass filter with a cutoff frequency ≥
()()
100nF20.5Ω2π
1
.
4 AVIN
Analog Supply/Input Voltage (Input): Supply voltage for the analog control
circuitry and LDO input power. Requires bypass capacitor to GND.
5 FB Feedback. Input to the error amplifier. For the Adjustable option, connect to the
external resistor divider network to set the output voltage. For fixed output
voltage options, connect to V
OUT
and an internal resistor network sets the output
voltage.
6 EN
Enable (Input). Logic low will shut down the device, reducing the quiescent
current to less than 5µA.
7
_____
LOWQ Enable LDO Mode (Input): Logic low enables the internal LDO and disables the
PWM operation. Logic high enables the PWM mode and disables the LDO
mode.
8 VIN
Supply/Input Voltage (Input): Supply voltage for the internal switches and
drivers.
9 SW Switch (Output): Internal power MOSFET output switches.
10 PGND Power Ground.
EP GND Ground, backside pad.
Micrel, Inc. MIC2285
January 2006
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Absolute Maximum Ratings(1)
Supply Voltage (V
IN
) ............................................ +6V
Output Switch Voltage (V
SW
) ............................... +6V
Output Switch Current (I
SW
) ................................... 2A
Logic Input Voltage (V
EN
,V
LOWQ
) .............. -0.3V to V
IN
Storage Temperature (T
s
)................ -60°C to +150°C
ESD Rating
(3)
....................................................... 3kV
Operating Ratings(2)
Supply Voltage (V
IN
)............................+2.7V to +5.5V
Logic Input Voltage (V
EN
,V
LOWQ
) .............. -0.3V to V
IN
Junction Temperature (T
J
) .............. –40°C to +125°C
Junction Thermal Resistance
3x3 MLF-10L (θ
JA
)................................... 60°C/W
Electrical Characteristics(4)
V
IN
= V
EN
= V
LOWQ
=3.6V; L = 0.47µH; C
OUT
= 10µF; T
A
= 25°C, unless noted. Bold values indicate –40°C< T
J
< +125°C
Parameter Condition Min Typ Max Units
Supply Voltage Range 2.7 5.5 V
Under-Voltage Lockout
Threshold
(turn-on) 2.45 2.55 2.65 V
UVLO Hysteresis 100 mV
Quiescent Current, PWM
mode
V
FB
= 0.9 * V
NOM
(not switching) 790 900 µA
Quiescent Current, LDO
mode
V
LOWQ
= 0V;I
OUT
= 0mA 20 29 µA
Shutdown Current V
EN
= 0V 0.01 5 µA
[Adjustable] Feedback
Voltage
± 2% (over temperature) 0.98 1 1.02 V
FB pin input current 1 nA
Current Limit in PWM Mode V
FB
= 0.9 * V
NOM
0.675 1 1.85 A
Output Voltage Line
Regulation
V
OUT
> 2V; V
IN
= V
OUT
+300mV to 5.5V; I
LOAD
= 100mA
V
OUT
< 2V; V
IN
= 2.7V to 5.5V; I
LOAD
= 100mA
0.13 %
Output Voltage Load
Regulation, PWM Mode
20mA < I
LOAD
< 300mA 0.2 0.8 %
Output Voltage Load
Regulation, LDO Mode
100µA < I
LOAD
< 50mA
V
LOWQ
= 0V
0.5
1 %
Maximum Duty Cycle V
FB
≤ 0.4V 100 %
PWM Switch ON-
Resistance
I
SW
= 50mA V
FB
= 0.7V
FB_NOM
(High Side Switch)
I
SW
= -50mA V
FB
= 1.1V
FB_NOM
(Low Side Switch)
0.4
0.4 Ω
Oscillator Frequency 7.2 8 8.8 MHz
LOWQ threshold voltage 0.5 0.85 1.3 V
LOWQ Input Current 0.1 2 µA
Enable Threshold 0.5 0.85 1.3 V
Enable Input Current 0.1 2 µA
LDO Dropout Voltage I
OUT
= 50mA Note 5 110 mV
Micrel, Inc. MIC2285
January 2006
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Parameter Condition Min Typ Max Units
Output Voltage Noise LOWQ = 0V; C
OUT
= 10µF, 10Hz to 100kHz 75 µVrms
LDO Current Limit LOWQ = 0V; V
OUT
= 0V (LDO Mode) 60 120 mA
Over-Temperature
Shutdown
160
°C
Over-Temperature
Hysteresis
20 °C
Notes
1. Exceeding the absolute maximum rating may damage the device.
2. The device is not guaranteed to function outside its operating rating.
3. Devices are ESD sensitive. Handling precautions recommended. Human body model: 1.5kΩ in series with 100pF.
4. Specification for packaged product only.
5. Dropout voltage is defined as the input-to-output differential at which the output voltage drops 2% below its nominal value that is initially
measured at a 1V differential. For outputs below 2.7V, the dropout voltage is the input-to-output voltage differential with a minimum
input voltage of 2.7V.
Micrel, Inc. MIC2285
January 2006
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Typical Characteristics – PWM Mode
0
10
20
30
40
50
60
70
80
90
100
OUTPUT CURRENT (mA)
2.5V
OUT
Efficiency
0 100 200 300 400 500
V
IN
=3.2V
V
IN
=3.6V
V
IN
=4.2V
0
10
20
30
40
50
60
70
80
90
100
OUTPUT CURRENT (mA)
1.8V
OUT
Efficiency
0 100 200 300 400 500
V
IN
=3.2V
V
IN
=3.6V
V
IN
=4.2V
0
10
20
30
40
50
60
70
80
90
100
OUTPUT CURRENT (mA)
1.5V
OUT
Efficiency
0 100 200 300 400 500
V
IN
=3.2V
V
IN
=3.6V
V
IN
=4.2V
0
10
20
30
40
50
60
70
80
90
100
OUTPUT CURRENT (mA)
0 100 200 300 400 500
1.2V
OUT
Efficiency
V
IN
=3.2V
V
IN
=3.6V
V
IN
=4.2V
0
10
20
30
40
50
60
70
80
90
100
OUTPUT CURRENT (mA)
1.0V
OUT
Efficiency
0 100 200 300 400 500
V
IN
=3.2V
V
IN
=3.6V
V
IN
=4.2V
0.990
0
Load Regulation
0.994
0.998
1.002
1.006
1.010
1.014
1.018
OUTPUT CURRENT (mA)
100 200 300 400 500
V
IN
=3.6V
LowQ=V
IN
600
700
800
900
1000
1100
2.7
INPUT VOLTAGE (V)
Quiescent Current
vs. Input Vol tage
3.1 3.5 3.9 4.3 4.7 5.1 5.5
7.0
7.5
8.0
8.5
9.0
2.7
INPUT VOLTAGE (V)
Frequency
vs. Input Voltage
3.1 3.5 3.9 4.3 4.7 5.1 5.5
0
200
400
600
800
1000
1200
2.7 3.4 4.1 4.8 5.5
CURRENT LIMIT (mA)
SUPPLY VOLTAGE (V)
Peak Current Limit
vs. Supply Voltage
LowQ = V
IN
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
1.3
1.4
1.5
2.7 3.4 4.1 4.8 5.5
ENABLE THRESHOLD (V)
SUPPLY VOLTAGE (V)
Enable Threshold
vs. Supply Voltage
LowQ = V
IN
Micrel, Inc. MIC2285
January 2006
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Typical Characteristics - LDO Mode
0
20
40
60
80
100
120
140
2.7 3.4 4.1 4.8 5.5
CURRENT LIMIT (mA)
SUPPLY VOLTAGE (V)
Current Limit
vs. Supply Voltage
LowQ = 0V
0
20
40
60
80
100
120
140
160
-40 -20 0 20 40 60 80 100 120
DROPOUT VOLTAGE (mV)
TEMPERATURE (°C)
Dropout Voltage
vs. Temperature
V
OUT
= 3.3V
I
OUT
= 50mA
LowQ = 0V
0
10
20
30
40
50
60
70
80
-40 -20 0 20 40 60 80 100 120
DROPOUT VOLTAGE (mV)
TEMPERATURE (°C)
Dropout Voltage
vs. Temperature
V
OUT
= 3.3V
I
OUT
= 25mA
LowQ = 0V
0
5
10
15
20
25
30
35
40
-40 -20 0 20 40 60 80 100 120
DROPOUT VOLTAGE (mV)
TEMPERATURE (°C)
Dropout Voltage
vs. Temperature
V
OUT
= 3.3V
I
OUT
= 10mA
LowQ = 0V
0
1
2
3
4
5
6
7
8
9
-40 -20 0 20 40 60 80 100 120
DROPOUT VOLTAGE (mV)
TEMPERATURE (°C)
Dropout Voltage
vs. Temperature
V
OUT
= 3.3V
I
OUT
= 1mA
LowQ = 0V
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
1.3
1.4
1.5
2.7 3.4 4.1 4.8 5.5
ENABLE THRESHOLD (V)
SUPPLY VOLTAGE (V)
Enable Threshold Voltage
vs. Supply Voltage
LowQ = 0V
Micrel, Inc. MIC2285
January 2006
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Typical Characteristics – LDO Mode (cont.)
15
16
17
18
19
20
21
22
23
24
25
0 20406080100
QUIESCENT CURRENT (µA)
OUTPUT CURRENT (mA)
Quiescent Current
vs. Output Current
V
IN
=3.6V
LowQ = 0V
1.764
1.773
1.782
1.791
1.8
1.809
1.818
1.827
1.836
0 20406080100
OUTPUT VOLTAGE (V)
OUTPUT CURRENT (mA)
Output Voltage
vs. Output Current
V
IN
=3.6V
V
OUT
=1.8V
LowQ = 0V
Micrel, Inc. MIC2285
January 2006
8 M9999-012406
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Functional Diagram
MIC2285 Block Diagram
Micrel, Inc. MIC2285
January 2006
9 M9999-012406
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Functional Characteristics
Load Transient PWM Mode
AC Coupled
(50mV/div)
Output Current
(100mA/div)
Time (20µs/div)
C
OUT
= 4.7µF
Output Volta
g
e
10mA
Load Transient LDO Mode
AC Coupled
(50mV/div)
Output Current
(20mA/div)
Time (20µs/div)
C
OUT
= 4.7µF
Output Volta
g
e
10mA
Enable Transient PWM Mode
Output Volta
g
e
(1V/div)
Enable
(2V/div)
Time (40µs/div)
C
OUT
= 4.7µF
0V
0V
Enable Transient LDO Mode
Output Voltage
(1V/div)
Enable
(2V/div)
Time (40µs/div)
C
OUT
= 4.7µF
0V
0V
Micrel, Inc. MIC2285
January 2006
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Functional Description
VIN
VIN provides power to the MOSFETs for the switch
mode regulator section, along with the current
limiting sensing. Due to the high switching speeds,
a 1µF capacitor is recommended close to VIN and
the power ground (PGND) pin for bypassing. Please
refer to layout recommendations.
AVIN
Analog VIN (AVIN) provides power to the LDO
section. AVIN and VIN must be tied together.
Careful layout should be considered to ensure high
frequency switching noise caused by VIN is reduced
before reaching AVIN.
LDO
The LDO pin is the output of the linear regulator and
should be connected to the output. In LOWQ mode
(LOWQ<1.5V), the LDO provides the output voltage.
In PWM mode (LOWQ>1.5V), the LDO pin is high
impedance.
EN
The enable pin provides a logic level control of the
output. In the off state, supply current of the device
is greatly reduced (typically <1µA). Also, in the off
state, the output drive is placed in a "tri-stated"
condition, where both the high side P-channel
Mosfet and the low-side N-channel are in an “off” or
non-conducting state. Do not drive the enable pin
above the supply voltage.
LOWQ
The LOWQ pin provides a logic level control
between the internal PWM mode and the low noise
linear regulator mode. With LOWQ pulled low
(<0.5V), quiescent current of the device is greatly
reduced by switching to a low noise linear regulator
mode that has a typical IQ of 20µA. In linear (LDO)
mode, the output can deliver 60mA of current to the
output. By placing LOWQ high (>1.5V), this
transitions the device into a constant frequency
PWM buck regulator mode. This allows the device
the ability to efficiently deliver up to 500mA of output
current at the same output voltage.
BIAS
The BIAS pin supplies the power to the internal
power to the control and reference circuitry. The
bias is powered from the input voltage through an
RC lowpass filter. The RC lowpass filter frequency
must be ≥
()()
100nF20.5Ω2π
1.
FB
The feedback pin (FB) provides the control path to
control the output. For adjustable versions, a resistor
divider connecting the feedback to the output is used
to adjust the desired output voltage. The output
voltage is calculated as follows:
V
OUT
=V
REF
×R1
R2 +1
⎛
⎝
⎜
⎞
⎠
⎟
where V
REF
is equal to 1.0V.
A feedforward capacitor is recommended for most
designs using the adjustable output voltage option.
To reduce battery current draw, a 100K feedback
resistor is recommended from the output to the FB
pin (R1). Also, a feedforward capacitor should be
connected between the output and feedback (across
R1). The large resistor value and the parasitic
capacitance of the FB pin can cause a high
frequency pole that can reduce the overall system
phase margin. By placing a feedforward capacitor,
these effects can be significantly reduced. Typically
an 82pF small ceramic capacitor is recommended.
SW
The switch (SW) pin connects directly to the inductor
and provides the switching current necessary to
operate in PWM mode. Due to the high speed
switching on this pin, the switch node should be
routed away from sensitive nodes.
PGND
Power ground (PGND) is the ground path for the
high current PWM mode. The current loop for the
power ground should be as small as possible and
separate from the Analog ground (AGND) loop.
Refer to the layout considerations for more details.
AGND
Signal 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
considerations for more details.
Micrel, Inc.
MIC2285
January 2006
11
M9999-012406
www.micrel.com
Applications Information
The MIC2285 is a 500mA PWM power supply that
utilizes a LOWQ™ light load mode to maximize
battery efficiency in light load conditions. This is
achieved with a LOWQ control pin that when pulled
low, shuts down all the biasing and drive current for
the PWM regulator, drawing only 20µA of operating
current. This allows the output to be regulated
through the LDO output, capable of providing 60mA
of output current. This method has the advantage of
producing a clean, low current, ultra-low noise
output in LOWQ™ mode. During LOWQ™ mode,
the SW node becomes high impedance, blocking
current flow. Other methods of reducing quiescent
current, such as pulse frequency modulation (PFM),
or bursting techniques, create large amplitude, low
frequency ripple voltages that can be detrimental to
system operation.
When more than 60mA is required, the LOWQ pin
can be forced high, causing the MIC2285 to enter
PWM mode. In this case, the LDO output makes a
"hand-off" to the PWM regulator with virtually no
variation in output voltage. The LDO output then
turns off allowing up to 500mA of current to be
efficiently supplied through the PWM output to the
load.
Input Capacitor
A minimum 1µF ceramic is recommended on the
VIN pin for bypassing. X5R or X7R dielectrics are
recommended for the input capacitor. Y5V
dielectrics lose most of their capacitance over
temperature and are therefore, not recommended.
A minimum 1µF is recommended close to the VIN
and PGND pins for high frequency filtering. Smaller
case size capacitors are recommended due to their
lower ESR and ESL. Please refer to layout
recommendation section of data sheet for proper
layout of the input capacitor.
Output Capacitor
The MIC2285 is optimized for a 10µF output
capacitor. A larger value can be used to improve
transient response. The MIC2285 utilizes type III
internal compensation and utilizes an internal high
frequency zero to compensate for the double pole
roll off of the LC filter. For this reason, larger output
capacitors can create instabilities. X5R or X7R
dielectrics are recommended for the output
capacitor. Y5V dielectrics lose most of their
capacitance over temperature and are therefore, not
recommended.
In addition to a 10µF, a small 10nF is recommended
close to the load for high frequency filtering. Smaller
case size capacitors are recommended due to there
lower ESR and ESL.
Inductor Selection
The MIC2285 is designed for use with a 0.47µH
inductor. Proper selection should ensure the
inductor can handle the maximum average and peak
currents required by the load. Maximum current
ratings of the inductor are generally given in two
methods; permissible DC current and saturation
current. Permissible DC current can be rated either
for a 40°C temperature rise or a 10% to 20% loss in
inductance. Ensure that the inductor selected can
handle the maximum operating current. When
saturation current is specified, make sure that there
is enough margin that the peak current will not
saturate the inductor. Peak inductor current can be
calculated as follows:
Lf2
V
V
1V
II
IN
OUT
OUT
OUTPK
××
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛−
+=
Micrel, Inc.
MIC2285
January 2006
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M9999-012406
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Layout Recommendation
Component Placement
R1
C3
R2
C4
C1
L1
U1
C2
R5
Evaluation Board Layout
TOP
BOTTOM
Micrel, Inc.
MIC2285
January 2006
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M9999-012406
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Typical Application Circuit with Bill of Materials (BOM)
Adjustable Output
Item Part Number Description Manufacturer Qty
0603D105MAT2A AVX
GRM185R60J105KE21D 1µF 6.3V X5R 0402 Ceramic Capacitor Murata
C1
C1608X5R1A105K 1µF 10V X5R 0402 Ceramic Capacitor TDK
1
C1608X5R0J106K TDK
06036D106MAT2A 10µF 6.3V X5R 0603 Ceramic Capacitor AVX
C4
GRM188R60J106M 10µF 6.3V X7R 0603 Ceramic Capacitor Murata
1
C1005X5R0J104M TDK
04026D104MAT2A
0.1µF 6.3V X5R 0402 Ceramic Capacitor
AVX
C2
GRM155R60J104K 0.1µF 6.3V X7R 0402 Ceramic Capacitor Murata
1
VJ0402A820KXQCW1BC 82pF X7R 0402 Ceramic Capacitor Vishay
C3 C1005COG1H820J 82pF COG 0402 Ceramic Capacitor TDK 1
DO2010-501ML 0.5µH Inductor Colicraft
L1 LQM21PNR47M00 0.47µH Inductor Murata
1
R1
(7)
CRCW04021003F 100kΩ 1% 0402 Resistor Vishay 1
CRCW04026652F 66.5kΩ 1% 0402 Resistor for 2.5V
OUT
Vishay
CRCW04021243F 124kΩ 1% 0402 Resistor for 1.8V
OUT
Vishay
CRCW04022003F 200kΩ 1% 0402 Resistor for 1.5V
OUT
Vishay
CRCW04024993F 499kΩ 1% 0402 Resistor for 1.2V
OUT
Vishay
R2
(7)
Open for 1.0V
OUT
1
R3 CRCW040220R5F 20.5Ω 1% 0402 Resistor Vishay 1
U1 MIC2285YML 8MHz PWM Step-Down Converter/LDO Micrel 1
Notes:
1. AVX: www.avxcorp.com
2. Murata: www.murata.com
3. TDK: www.tdk.com
4. Vishay: www.vishay.com
5. Coilcraft: www.coilcraft.com
6. Micrel, Inc.: www.micrel.com
7. For Adjustable Version Only
Micrel, Inc.
MIC2285
January 2006
14
M9999-012406
www.micrel.com
Package Information
10-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
The 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.
© 2006 Micrel, Incorporated.
