MIC3385
8MHz Inductorless Buck Regulator
with LDO Standby Mode
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
2.5V
OUT
Efficiency
100
90
80
70
60
50
40
30
20
10
0
0
100 200 300 400 500 600
OUTPUT CURRENT (mA)
V
IN
=3.2V
V
IN
=3.6V
V
IN
=4.2V
®
Adjustable Output Buck Regulator with
LOWQ
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
Micrel, Inc.
MIC3385
Ordering Information
Part Number
MIC3385YHL
MIC3385-1.5YHL
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.
Voltage
Adj.
1.5V
Temperature Range
–40° to +125°C
–40° to +125°C
Package
14-Pin 3mm x 3.5mm MLF
®
14-Pin 3mm x 3.5mm MLF
®
Lead Finish
Pb-free
Pb-free
Pin Configuration
FB
VIN
LOWQ
EN
OUT
OUT
OUT
1
2
3
4
5
6
7
14 BIAS
13 LDO
12 AVIN
11 GND
10 SW
9
8
SW
SW
14- Pin 3mm x 3.5mm MLF
®
(ML)
Pin Description
Pin Number
1
2
3
Pin Name
FB
VIN
LOWQ
Pin Function
Feedback. Input to the error amplifier. Connect to the external resistor divider
network to set the output voltage.
Supply Voltage (Input): Supply voltage for the internal switches and drivers.
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.
Enable (Input). Logic low will shut down the device, reducing the quiescent
current to less than 5
µ
A.
Switch Output after inductor.
Switch (Output): Internal power MOSFET output switches before Inductor
Power Ground. Requires input capacitor to GND.
Analog Supply Voltage (Input): Supply voltage for the analog control circuitry and
LDO input power. Requires bypass capacitor to GND.
LDO Output (Output): Connect to V
OUT
for LDO mode operation.
Internal circuit bias supply. Must be de-coupled to signal ground with a 0.1
µ
F
capacitor and should not be loaded.
4
5,6,7
8,9,10
11
12
13
14
EN
OUT
SW
GND
AVIN
LDO
BIAS
February 2008
2
M9999-021908-B
Micrel, Inc.
MIC3385
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
Supply Voltage Range
Under-Voltage Lockout
Threshold
UVLO Hysteresis
Quiescent Current, PWM
mode
Quiescent Current, LDO
mode
Shutdown Current
[Adjustable] Feedback
Voltage
FB pin input current
Current Limit in PWM Mode
Output Voltage Line
Regulation
Output Voltage Load
Regulation, PWM Mode
Output Voltage Load
Regulation, LDO Mode
Maximum Duty Cycle
PWM Switch
ON-Resistance
Oscillator Frequency
LOWQ threshold voltage
LOWQ Input Current
Enable Threshold
Enable Input Current
LDO Dropout Voltage
I
OUT
= 50mA,
Note 5
V
FB
= 0.9 * V
NOM
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
20mA < I
LOAD
< 300mA
100µA < I
LOAD
< 50mA
V
LOWQ
= 0V
V
FB
≤
0.4V
I
SW
= 50mA V
FB
= 0.7V
FB_NOM
(High Side Switch)
I
SW
= -50mA V
FB
= 1.1V
FB_NOM
(Low Side Switch)
V
FB
= 0.9 * V
NOM
(not switching)
V
LOWQ
= 0V;I
OUT
= 0mA
V
EN
= 0V
(turn-on)
Condition
Min
2.7
2.45
Typ
2.55
100
690
16
0.01
Max
5.5
2.65
Units
V
V
mV
900
29
5
1.01
1.02
µA
µA
µA
V
V
nA
A
%
%
%
%
±
1%
±
2% (over temperature)
0.99
0.98
1
1
0.75
1
0.13
0.2
0.1
1.85
100
0.4
0.4
Ω
7.2
0.5
8
0.85
0.1
0.85
0.1
110
8.8
1.3
2
1.3
2
MHz
V
µA
V
µA
mV
0.5
February 2008
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M9999-021908-B
Micrel, Inc.
MIC3385
Parameter
Output Voltage Noise
LDO Current Limit
Over-Temperature
Shutdown
Over-Temperature
Hysteresis
Internal Inductor
Notes:
Condition
LOWQ = 0V; C
OUT
= 10µF, 10Hz to 100kHz
LOWQ = 0V; V
OUT
= 0V (LDO Mode)
Min
Typ
75
Max
Units
µVrms
mA
60
120
160
20
0.47
°
C
°
C
µH
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.
February 2008
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M9999-021908-B
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