MICREL MIC2285

MIC2285
8MHz PWM Synchronous Buck
Regulator with LDO Standby Mode
General Description
Features
The Micrel MIC2285 is a high efficiency 8MHz pulse
width modulated (PWM) synchronous buck (stepdown) 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.
• 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
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.
Applications
• Cellular phones
• PDAs
• USB peripherals
____________________________________________________________________________________________________
Typical Application
1.8VOUT Efficiency
100
90 VIN =3.2V
80
70
60
50
VIN =3.6V
VIN=4.2V
40
30
20
Adjustable Output Buck Regulator with LOWQ™ Mode
10
0
0
100 200 300 400 500
OUTPUT CURRENT (mA)
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
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Micrel, Inc.
MIC2285
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 Configuration
10 PGND
AGND 1
LDO 2
9 SW
BIAS 3
8 VIN
AVIN 4
7 LOWQ
FB 5
EP
6 EN
10-Pin 3mm x 3mm MLF (ML)
Pin Description
Pin Number
Pin Name
1
AGND
Pin Function
Analog (signal) Ground.
2
LDO
LDO Output (Output): Connect to VOUT 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 ≥
1
.
2π(20.5Ω )(100nF )
Analog Supply/Input Voltage (Input): Supply voltage for the analog control
circuitry and LDO input power. Requires bypass capacitor to GND.
4
AVIN
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 VOUT 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
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
EP
GND
January 2006
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.
Power Ground.
Ground, backside pad.
2
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MIC2285
Absolute Maximum Ratings(1)
Operating Ratings(2)
Supply Voltage (VIN) ............................................ +6V
Output Switch Voltage (VSW) ............................... +6V
Output Switch Current (ISW) ................................... 2A
Logic Input Voltage (VEN,VLOWQ) .............. -0.3V to VIN
Storage Temperature (Ts)................ -60°C to +150°C
ESD Rating(3) ....................................................... 3kV
Supply Voltage (VIN)............................+2.7V to +5.5V
Logic Input Voltage (VEN,VLOWQ) .............. -0.3V to VIN
Junction Temperature (TJ) .............. –40°C to +125°C
Junction Thermal Resistance
3x3 MLF-10L (θJA)................................... 60°C/W
Electrical Characteristics(4)
VIN = VEN = VLOWQ =3.6V; L = 0.47µH; COUT = 10µF; TA = 25°C, unless noted. Bold values indicate –40°C< TJ < +125°C
Parameter
Condition
Min
(turn-on)
2.45
Supply Voltage Range
Under-Voltage Lockout
Threshold
Typ
Max
5.5
V
2.55
2.65
V
2.7
UVLO Hysteresis
100
Units
mV
Quiescent Current, PWM
mode
VFB = 0.9 * VNOM (not switching)
790
900
µA
Quiescent Current, LDO
mode
VLOWQ = 0V;IOUT = 0mA
20
29
µA
Shutdown Current
VEN = 0V
0.01
5
µA
[Adjustable] Feedback
Voltage
± 2% (over temperature)
1
1.02
V
0.98
FB pin input current
1
Current Limit in PWM Mode
VFB = 0.9 * VNOM
Output Voltage Line
Regulation
VOUT > 2V; VIN = VOUT+300mV to 5.5V; ILOAD= 100mA
VOUT < 2V; VIN = 2.7V to 5.5V; ILOAD= 100mA
0.13
Output Voltage Load
Regulation, PWM Mode
20mA < ILOAD < 300mA
0.2
0.8
%
Output Voltage Load
Regulation, LDO Mode
100µA < ILOAD < 50mA
VLOWQ = 0V
0.5
1
%
Maximum Duty Cycle
VFB ≤ 0.4V
PWM Switch ONResistance
ISW = 50mA VFB = 0.7VFB_NOM (High Side Switch)
ISW = -50mA VFB = 1.1VFB_NOM (Low Side Switch)
0.675
1
nA
1.85
A
%
%
100
0.4
Ω
0.4
Oscillator Frequency
7.2
8
8.8
MHz
LOWQ threshold voltage
0.5
0.85
1.3
V
0.1
2
µA
0.85
1.3
V
0.1
2
µA
LOWQ Input Current
Enable Threshold
0.5
Enable Input Current
LDO Dropout Voltage
January 2006
IOUT = 50mA Note 5
110
3
mV
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MIC2285
Parameter
Condition
Min
Output Voltage Noise
LOWQ = 0V; COUT = 10µF, 10Hz to 100kHz
LDO Current Limit
LOWQ = 0V; VOUT = 0V (LDO Mode)
Typ
Max
Units
75
µVrms
120
mA
Over-Temperature
Shutdown
160
°C
Over-Temperature
Hysteresis
20
°C
60
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.
January 2006
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MIC2285
Typical Characteristics – PWM Mode
2.5VOUT Efficiency
1.8VOUT Efficiency
100
100
60
100
90 V IN=3.2V
90
80
70
V IN=3.2V
VIN=3.6V
VIN=4.2V
80
70
60
90 V IN=3.2V
80
VIN=3.6V
70
VIN=3.6V
VIN=4.2V
60
50
50
50
40
40
40
30
20
30
20
30
20
10
0
0
10
100 200 300 400 500
OUTPUT CURRENT (mA)
0
0
1.2VOUT Efficiency
0
0
90
50
50
80
70
60
VIN=4.2V
1.018
VIN=3.2V
1.014
VIN=3.6V
1.010
VIN=4.2V
1.006
40
1.002
30
20
30
20
0.998
10
10
0
0
1100
100 200 300 400 500
OUTPUT CURRENT (mA)
Quiescent Current
vs. Input Voltage
0
0
9.0
1000
Frequency
vs. Input Voltage
900
8.0
800
7.5
600
2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
INPUT VOLTAGE (V)
1.5
0.990
0
100 200 300 400 500
OUTPUT CURRENT (mA)
8.5
700
VIN=3.6V
LowQ=VIN
0.994
1200
CURRENT LIMIT (mA)
40
100 200 300 400 500
OUTPUT CURRENT (mA)
Load Regulation
100
90 V IN=3.2V
80
70
VIN=3.6V
60
VIN=4.2V
10
100 200 300 400 500
OUTPUT CURRENT (mA)
1.0VOUT Efficiency
100
ENABLE THRESHOLD (V)
1.5VOUT Efficiency
7.0
2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
INPUT VOLTAGE (V)
100 200 300 400 500
OUTPUT CURRENT (mA)
Peak Current Limit
vs. Supply Voltage
1000
800
600
400
200
LowQ = VIN
0
2.7
3.4
4.1
4.8
SUPPLY VOLTAGE (V)
5.5
Enable Threshold
vs. Supply Voltage
1.4
1.3
1.2
1.1
1.0
0.9
0.8
0.7
0.6 LowQ = V
IN
0.5
2.7
3.4
4.1
4.8
SUPPLY VOLTAGE (V)
January 2006
5.5
5
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MIC2285
Typical Characteristics - LDO Mode
80
60
40
20
60
50
40
30
20
10
VOUT = 3.3V
IOUT = 25mA
LowQ = 0V
40
DROPOUT VOLTAGE (mV)
DROPOUT VOLTAGE (mV)
Dropout Voltage
vs. Temperature
70
0
-40 -20 0 20 40 60 80 100 120
TEMPERATURE (°C)
DROPOUT VOLTAGE (mV)
100
0
2.7
80
160
120
LowQ = 0V
3.4
4.1
4.8
SUPPLY VOLTAGE (V)
120
100
80
60
40
20
Dropout Voltage
vs. Temperature
9
30
25
20
15
10
VOUT = 3.3V
IOUT = 10mA
LowQ = 0V
5
0
-40 -20 0 20 40 60 80 100 120
TEMPERATURE (°C)
VOUT = 3.3V
IOUT = 50mA
LowQ = 0V
0
-40 -20 0 20 40 60 80 100 120
TEMPERATURE (°C)
5.5
35
Dropout Voltage
vs. Temperature
140
DROPOUT VOLTAGE (mV)
CURRENT LIMIT (mA)
140
Current Limit
vs. Supply Voltage
Dropout Voltage
vs. Temperature
8
7
6
5
4
3
2
1
VOUT = 3.3V
IOUT = 1mA
LowQ = 0V
0
-40 -20 0 20 40 60 80 100 120
TEMPERATURE (°C)
Enable Threshold Voltage
vs. Supply Voltage
ENABLE THRESHOLD (V)
1.5
1.4
1.3
1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
2.7
January 2006
LowQ = 0V
3.4
4.1
4.8
SUPPLY VOLTAGE (V)
6
5.5
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MIC2285
Typical Characteristics – LDO Mode (cont.)
Quiescent Current
vs. Output Current
1.836
24
23
22
21
20
19
18
17
16
15
0
VIN = 3.6V
LowQ = 0V
20
40
60
80
100
OUTPUT CURRENT (mA)
January 2006
OUTPUT VOLTAGE (V)
QUIESCENT CURRENT (µA)
25
Output Voltage
vs. Output Current
1.827
1.818
1.809
1.8
1.791
1.782
1.773
1.764
0
VIN = 3.6V
VOUT =1.8V
LowQ = 0V
20
40
60
80
100
OUTPUT CURRENT (mA)
7
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MIC2285
Functional Diagram
MIC2285 Block Diagram
January 2006
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MIC2285
Functional Characteristics
Load Transient LDO Mode
Output Current
(20mA/div)
Output Current
(100mA/div)
Output Voltage
AC Coupled
(50mV/div)
Output Voltage
AC Coupled
(50mV/div)
Load Transient PWM Mode
10mA
10mA
COUT = 4.7µF
COUT = 4.7µF
Time (20µs/div)
Time (20µs/div)
Enable Transient LDO Mode
Output Voltage
(1V/div)
0V
Enable
(2V/div)
0V
Enable
(2V/div)
Output Voltage
(1V/div)
Enable Transient PWM Mode
0V
0V
COUT = 4.7µF
COUT = 4.7µF
Time (40µs/div)
Time (40µs/div)
January 2006
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MIC2285
Functional Description
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:
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.
⎛ R1 ⎞
VOUT = VREF × ⎜
+ 1⎟
⎝ R2 ⎠
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.
where VREF 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.
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.
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.
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.
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.
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
1
.
must be ≥
2π (20.5Ω )(100nF )
January 2006
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MIC2285
Applications Information
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.
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.
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:
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.
January 2006
IPK = IOUT
11
⎛
V
VOUT ⎜⎜1 − OUT
VIN
⎝
+
2× f ×L
⎞
⎟
⎟
⎠
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MIC2285
Layout Recommendation
Component Placement
C4
L1
C1
C2
R5
U1
R1
R2
C3
Evaluation Board Layout
TOP
BOTTOM
January 2006
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MIC2285
Typical Application Circuit with Bill of Materials (BOM)
Adjustable Output
Item
Part Number
0603D105MAT2A
C1
GRM185R60J105KE21D
C1608X5R1A105K
C1608X5R0J106K
C4
06036D106MAT2A
GRM188R60J106M
C1005X5R0J104M
C2
04026D104MAT2A
GRM155R60J104K
C3
L1
R1(7)
R2(7)
Description
Manufacturer
1µF 6.3V X5R 0402 Ceramic Capacitor
1µF 10V X5R 0402 Ceramic Capacitor
10µF 6.3V X5R 0603 Ceramic Capacitor
10µF 6.3V X7R 0603 Ceramic Capacitor
0.1µF 6.3V X5R 0402 Ceramic Capacitor
AVX
Murata
1
TDK
TDK
AVX
1
Murata
TDK
AVX
0.1µF 6.3V X7R 0402 Ceramic Capacitor
Murata
VJ0402A820KXQCW1BC
82pF X7R 0402 Ceramic Capacitor
Vishay
C1005COG1H820J
82pF COG 0402 Ceramic Capacitor
TDK
DO2010-501ML
0.5µH Inductor
Colicraft
LQM21PNR47M00
0.47µH Inductor
Murata
CRCW04021003F
100kΩ 1% 0402 Resistor
Vishay
CRCW04026652F
66.5kΩ 1% 0402 Resistor for 2.5VOUT
Vishay
CRCW04021243F
124kΩ 1% 0402 Resistor for 1.8VOUT
Vishay
CRCW04022003F
200kΩ 1% 0402 Resistor for 1.5VOUT
Vishay
CRCW04024993F
499kΩ 1% 0402 Resistor for 1.2VOUT
Vishay
Open
Qty
1
1
1
1
1
for 1.0VOUT
R3
CRCW040220R5F
20.5Ω 1% 0402 Resistor
Vishay
1
U1
MIC2285YML
8MHz PWM Step-Down Converter/LDO
Micrel
1
Notes:
1.
2.
3.
4.
5.
6.
7.
AVX: www.avxcorp.com
Murata: www.murata.com
TDK: www.tdk.com
Vishay: www.vishay.com
Coilcraft: www.coilcraft.com
Micrel, Inc.: www.micrel.com
For Adjustable Version Only
January 2006
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MIC2285
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.
January 2006
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