MIC2285A
8MHz PWM Synchronous Buck Regulator
with LDO Standby Mode
LOWQ is a registered trademark of Micrel, Inc
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
August 2007
M9999-083107-B
General Description
The Micrel MIC2285A is a high efficiency 8MHz
PWM synchronous buck (step-down) regulator that
features a LOWQ
®
LDO standby mode that draws
only 20µA of quiescent current. The MIC2285A
allows an ultra-low noise, small size, and high
efficiency solution for portable power applications.
In PWM mode, the MIC2285A 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 MIC2285A operates from 2.7V to 5.5V input and
features internal power MOSFETs that can supply
up to 600mA output current in PWM mode. It can
operate with a maximum duty cycle of 100% for use
in low-dropout conditions.
The MIC2285A is available in the 10-pin 2mm x
2mm Thin 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 600mA
– >90% efficiency
– 100% maximum duty cycle
• Adjustable output voltage option down to 1V
– Fixed output voltage options available
• Ultra-fast transient response
• Requires only a 0.47µH inductor
• Enables sub 0.55mm profile solution
• Fully integrated MOSFET switches
• Micropower shutdown
• Thermal shutdown and current limit protection
• 10-pin 2mm x 2mm x 0.55mm 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
0 100 200 300 400 500 600
OUTPUT CURRENT (mA)
2.5V
OUT
Efficiency
V
IN
=3.2V
V
IN
=3.6V
V
IN
=4.2V
Micrel, Inc. MIC2285A
August 2007 2 M9999-083107-B
Ordering Information
Part Number Marking Output
Voltage* Junction
Temperature Range Package Lead Finish
MIC2285AYMT WPA Adj. –40° to +125°C 10-Pin 2x2 Thin MLF
®
Pb-free
Note
* For other voltage options available, please contact Micrel Marketing for details.
MLF® is a GREEN RoHS compliant package. Lead finish is NiPdAu. Mold compound is Halogen Free.
Pin Configur ation
FB EN5
1
A
GND
LDO
BIAS
AVIN
10 PGND
SW
VIN
LOWQ
9
8
7
2
3
4
6
10-Pin 2mm x 2mm Thin MLF
®
(MT)
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 decoupled to signal ground with a 0.1µF
capacitor and should not be loaded.
4 AVIN
Analog Supply 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 Voltage (Input): Supply voltage for the internal switches and drivers.
9 SW Switch (Output): Internal power MOSFET output switches.
10 PGND Power Ground.
Micrel, Inc. MIC2285A
August 2007 3 M9999-083107-B
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
2x2 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
±1%
± 2% (over temperature)
0.99
0.98 1 1.01
1.02 V
V
[Fixed Output] Voltages Nominal V
OUT
tolerance –1
–2
+1
+2
%
%
FB pin input current 1 nA
Current Limit in PWM Mode V
FB
= 0.9 * V
NOM
0.75 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
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. MIC2285A
August 2007 4 M9999-083107-B
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. MIC2285A
August 2007 5 M9999-083107-B
Typical Characteristics – PWM Mode
0
10
20
30
40
50
60
70
80
90
100
0 100 200 300 400 500 600
OUTPUT CURRENT (mA)
2.5VOUT Efficie ncy
V
IN
=3.2V
V
IN
=3.6V
V
IN
=4.2V
0
10
20
30
40
50
60
70
80
90
100
0 100 200 300 400 500 600
OUTPUT CURRENT (mA)
V
IN
=3.2V
V
IN
=3.6V
V
IN
=4.2V
1.8VOUT Efficie ncy
0
10
20
30
40
50
60
70
80
90
100
0 100 200 300 400 500 600
OUTPUT CURRENT (mA)
1.5VOUT Efficiency
V
IN
=3.2V
V
IN
=3.6V
V
IN
=4.2V
0
10
20
30
40
50
60
70
80
90
100
0 100 200 300 400 500 600
OUTPUT CURRENT (mA)
1.2VOUT Efficie ncy
V
IN
=3.2V
V
IN
=3.6V
V
IN
=4.2V
0
10
20
30
40
50
60
70
80
90
100
0 100 200 300 400 500 600
OUTPUT CURRENT (mA)
1.0VOUT Efficie ncy
V
IN
=3.2V
V
IN
=3.6V
V
IN
=4.2V
0 100 200 300 400 500 600
OUTPUT CURRENT (mA)
0.990
Load Regulation
0.994
0.998
1.002
1.006
1.010
1.014
1.018
V
IN
=3.6V
LowQ=V
IN
600
700
800
900
1000
1100
2.7
INPUT VOLTAGE (V)
Quiescent Current
vs. Input Voltage
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. MIC2285A
August 2007 6 M9999-083107-B
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. MIC2285A
August 2007 7 M9999-083107-B
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. MIC2285A
August 2007 8 M9999-083107-B
Functional Diagram
MIC2285A Block Diagram
Micrel, Inc. MIC2285A
August 2007 9 M9999-083107-B
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. MIC2285A
August 2007 10 M9999-083107-B
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 V
IN
(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 I
Q
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. MIC2285A
August 2007 11
M9999-083107-B
Applications Information
The MIC2285A 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 18µA 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 MIC2285A 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 600mA 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 MIC2285A is optimized for a 10µF output
capacitor. A larger value can be used to improve
transient response. The MIC2285A 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 their
lower ESR and ESL.
Inductor Selection
The MIC2285A is designed for use with a 0.47µH
inductor. Proper selection should ensure that 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. MIC2285A
August 2007 12
M9999-083107-B
Layout Recommendation
Top
Bottom
Note
The above figures demonstrate the recommended layout for the MIC2285A adjustable option.
Micrel, Inc. MIC2285A
August 2007 13
M9999-083107-B
Adjustable Output
Bill of Materials
Item Part Number Manufacturer Description Qty
06036D105MAT2 AVX
(1)
C1 GRM185R60J105KE21D Murata
(2)
1µF Ceramic Capacitor X5R, 6.3V 0603 1
0201ZD103MAT2 AVX
(1)
C2 GRM033R10J103KA01D Murata
(2)
10nF Ceramic Capacitor, 6.3V 0201 1
C3 VJ0402A101KXAA Vishay
(3)
100pF Ceramic Capacitor 1
AVX
(1)
C4 Murata
(2)
10µF Ceramic Capacitor X5R, 6.3V 0603 1
LQM21PNR47M00 Murata
(2)
0.47µH Inductor, 120mΩ 2.0mm x 1.25mm x 0.5mm
L1 Murata
(2)
0.47µH Inductor, 97mΩ 3.2mm x 2.5mm x 1.55mm 1
Sumida
(4)
0.47µH Inductor, 94mΩ 3.2mm x 3.2mm x 1.55mm
R1 CRCW04021002F Vishay-Dale
(3)
100kΩ 1% 0402 Resistor 1
CRCW04026652F Vishay-Dale
(3)
66.5kΩ 1% 0402 Resistor for 2.5V
OUT
CRCW04021243F Vishay-Dale
(3)
124kΩ 1% 0402 Resistor for 1.8V
OUT
CRCW04022003F Vishay-Dale
(3)
200kΩ 1% 0402 Resistor for 1.5V
OUT
CRCW04024023F Vishay-Dale
(3)
402kΩ 1% 0402 Resistor for 1.2V
OUT
R2
Open for 1.0V
OUT
1
R3 CRCW040220R5F Vishay
(3)
20Ω 1% 0402 Resistor 1
U1 MIC2285AYMT Micrel
(5)
8MHz Synchronous Buck Regulator with LOWQ
®
Mode 1
Notes:
1. AVX: www.avxcorp.com
2. Murata: www.murata.com
3. Vishay: www.vishay.com
4. Sumida: www.sumida.com
5. Micrel, Inc.: www.micrel.com
Micrel, Inc. MIC2285A
August 2007 14
M9999-083107-B
Package Information
10-Pin 2mm x 2mm Thin MLF
®
(MT)
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.
© 2007 Micrel, Incorporated.
