MIC3385
8MHz Inductorless 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
February 2008
M9999-021908-B
General Description
The Micrel MIC3385 is a high efficiency inductorless buck
regulator that features a LOWQ
®
LDO standby mode that
draws only 18µA of quiescent current. The MIC3385
requires no external inductor enabling an ultra-low noise,
small size, and high efficiency solution for portable power
applications.
In PWM mode, the MIC3385 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 MIC3385 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 MIC3385 is available in the 14-pin 3mm x 3.5mm
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 voltage
• Light load LOWQ
®
LDO mode
– 18µA 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
• Ultra-fast transient response
• NO external inductor required
• Enables sub 1mm profile solution
• Fully integrated MOSFET switches
• Micropower shutdown
• Thermal shutdown and current limit protection
• Pb-free 14-pin 3x3.5x0.9mm MLF
®
package
• –40°C to +125°C junction temperature range
Applications
• Slim digital cameras
• MP3 players
• Portable power 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. MIC3385
February 2008
2 M9999-021908-B
Ordering Information
Part Number Voltage Temperature Range Package Lead Finish
MIC3385YHL Adj. –40° to +125°C 14-Pin 3mm x 3.5mm MLF
®
Pb-free
MIC3385-1.5YHL 1.5V –40° to +125°C 14-Pin 3mm x 3.5mm MLF
®
Pb-free
Notes:
MLF® is a GREEN RoHS compliant package. Lead finish is NiPdAu. Mold compound is Halogen Free.
Other voltage options available. Please contact Micrel for details.
Pin Configuration
OUT SW7
3LOWQ
EN
OUT
OUT
12 AVIN
GND
SW
SW
11
10
9
4
5
6
8
1FB
VIN
14 BIAS
LDO132
14- Pin 3mm x 3.5mm MLF
®
(ML)
Pin Description
Pin Number Pin Name Pin Function
1 FB
Feedback. Input to the error amplifier. Connect to the external resistor divider
network to set the output voltage.
2 VIN Supply Voltage (Input): Supply voltage for the internal switches and drivers.
3 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.
4 EN
Enable (Input). Logic low will shut down the device, reducing the quiescent
current to less than 5µA.
5,6,7 OUT Switch Output after inductor.
8,9,10 SW Switch (Output): Internal power MOSFET output switches before Inductor
11 GND
Power Ground. Requires input capacitor to GND.
12 AVIN
Analog Supply Voltage (Input): Supply voltage for the analog control circuitry and
LDO input power. Requires bypass capacitor to GND.
13 LDO LDO Output (Output): Connect to V
OUT
for LDO mode operation.
14 BIAS
Internal circuit bias supply. Must be de-coupled to signal ground with a 0.1µF
capacitor and should not be loaded.
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February 2008
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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
EDS 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
3x3.5 MLF-14 (θ
JA
) ............................................55°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) 690 900 µA
Quiescent Current, LDO
mode
V
LOWQ
= 0V;I
OUT
= 0mA 16 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
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 %
Output Voltage Load
Regulation, LDO Mode
100µA < I
LOAD
< 50mA
V
LOWQ
= 0V
0.1 %
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. MIC3385
February 2008
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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
Internal Inductor 0.47 µH
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. MIC3385
February 2008
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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 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)
1.8VOUT 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)
1.5VOUT 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 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)
1.0VOUT Efficiency
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
Micrel, Inc. MIC3385
February 2008
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Typical Characteristics ― LDO Mode
Micrel, Inc. MIC3385
February 2008
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Typical Characteristics ― LDO Mode (cont.)
Micrel, Inc. MIC3385
February 2008
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Functional Characteristics
Load Transient PWM Mode
AC Coupled
(50mV/div)
Load
(100mA/div)
Time (100µs/div)
C
OUT
= 10µF
Output Volta
g
e
Load Transient LDO Mode
AC Coupled
(50mV/div)
Load
(25mA/div)
Time (100µs/div)
C
OUT
= 10µF
Outpu
t
Volta
g
e
Enable Transient PWM Mode
Output Volta
g
e
(1.5V/div)
Enable
(2V/div)
Time (40µs/div)
C
OUT
= 10µF
Enable Transient LDO Mode
Output Volta
g
e
(1.5V/div)
Enable
(2V/div)
Time (40µs/div)
C
OUT
= 10µF
Micrel, Inc. MIC3385
February 2008
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Functional Diagram
MIC3385 Block Diagram
Micrel, Inc. MIC3385
February 2008
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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 to ground (GND) pin for
bypassing. Please refer to layout recommendations.
AVIN
Analog VIN (AVIN) provides power to the LDO
subsection and the bias through an internal 6Ω resistor.
AVIN and VIN must be tied together. Careful layout
should be considered to ensure that 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 18µA. 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 600mA 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 input voltage through an RC lowpass filter. The RC
lowpass filter frequency is:
≥
()( )
100nF202
1
Ω
π
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.
Feedforward capacitance (CFF) can be calculated as
follows:
160kHzR12
1
C
FF
××
=
π
For fixed options a feedforward capacitor from the output
to the FB pin is required. Typically a 100pF 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.
GND
Combines PGND and SGND
Power ground (PGND) is the ground path for the high
current PWM mode. Signal ground (SGND) is the
ground path for the biasing and control circuitry.
Micrel, Inc. MIC3385
February 2008
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M9999-021908-B
Application Information
The MIC3385 is a 600mA 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. It is
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 MIC3385 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 recommendations for proper
layout of the input capacitor.
Output Capacitor
The MIC3385 is optimized for a 10µF output capacitor. A
larger value can be used to improve transient response
The MIC3385 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.
Micrel, Inc. MIC3385
February 2008
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Layout Recommendations
Top Layer
Bottom Layer
Note:
The above figures demonstrate the recommended layout for the MIC3385 adjustable option.
Micrel, Inc. MIC3385
February 2008
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R4
10K
R1
Option
R2
Option
C4
10µF/3.6V
C3
82pF/50V
J5
OUT
J1
Vin 5.5 Max
J2
GND
J3
LOWQ
12
JP1
1X2
C2
0.1µF/6.3V
EN
J4
J6
GND
C1
10µF/6.3V
R3
Vin
Vin
R5
10K
VIN
2
EN
4
BIAS
14
AVin
12
SW
8, 9, 10
5, 6, 7
OUT
LOWQ
3
GND
11
FB
1
LDO
13
U1
MIC3385YHL
MIC3385 Adjustable Output Schematic
Bill of Materials
Item Part Number Manufacturer Description Qty.
C1608X5R0J106K TDK
(1)
JMK107BJ106MA-T Taiyo Yuden
(2)
10µF Ceramic Capacitor X5R, 6.3V 2
C1, C4
GRM188R60J106M Murata
(3)
10µF Ceramic Capacitor X7R, 6.3V 2
C1005X5R0J104M TDK
(1)
04026D104MAT2A AVX
(4)
1µF Ceramic Capacitor X5R, 6.3V 1
C2
VJ0402Y104KXQPW1BC Vishay
(5)
1µF Ceramic Capacitor X7R, 6.3V 1
C1005COG1H820J TDK
(1)
82pF Ceramic Capacitor COG, 50V 1
C3 VJ0402A80KXQPW1BC Vishay
(5)
82pF Ceramic Capacitor COG, 10V 1
R1 CRCW04021003FKEYE3 Vishay
(5)
100K, 1% 0402, 1/16W (Optional) 1
R2 CRCW04021243FKEYE3 Vishay
(5)
124K, 1% 0402, 1/16W (Optional) 1
R3 CRCW060320R0FKEYE3 Vishay
(5)
20Ω, 1% 0603, 1/16W 1
R4, R5 CRCW06031002FKEYE3 Vishay
(5)
10K, 1% 0603, 1/16W 1
U1 MIC3385YHL Micrel, Inc.
(6)
8MHz Power System Module w/LDO Standby Mode 1
Notes:
1. TDK: www.tdk.com
2. Taiyo Yuden, Inc.: www.t-yuden.com
3. Murata: www.murata.com
4. AVX: www.avxcorp.com
5. Vishay: www.website.com
6. Micrel, Inc.: www.micrel.com
Micrel, Inc. MIC3385
February 2008
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M9999-021908-B
Package Information
14-Pin 3mm x 3.5mm HMLF (HL)
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.
