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.
LOWQ®
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
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
September 22, 2015
Revision 3.0
Micrel, Inc.
MIC3385
Typical Application
2.5V OUT Efficiency
100
90
80
70
60
50
40
30
20
10
0
0
®
Adjustable Output Buck Regulator with LOWQ Mode
V IN =3.2V
VIN =3.6V
VIN =4.2V
100 200 300 400 500 600
OUTPUT CURRENT (mA)
Ordering Information
Part Number
Voltage
Temperature Range
Package
Lead Finish
MIC3385YHL
Adj.
–40° to +125°C
14-Pin 3mm x 3.5mm MLF
®
MIC3385-1.5YHL
1.5V
–40° to +125°C
14-Pin 3mm x 3.5mm MLF
®
Pb-free
Pb-free
Notes:
1.
MLF® is a GREEN RoHS compliant package. Lead finish is NiPdAu. Mold compound is Halogen Free.
2.
Other voltage options available. Please contact Micrel for details.
September 22, 2015
2
Revision 3.0
Micrel, Inc.
MIC3385
Pin Configuration
FB
1
14 BIAS
VIN
2
13 LDO
LOWQ
3
12 AVIN
EN
4
11 GND
OUT
5
10 SW
OUT
6
9
SW
OUT
7
8
SW
®
14- Pin 3mm x 3.5mm MLF (HL)
Pin Description
Pin Number
Pin Name
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
4
EN
5,6,7
OUT
Switch Output after inductor.
8,9,10
11
SW
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 VOUT 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.
September 22, 2015
Pin Function
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 5µA.
Switch (Output): Internal power MOSFET output switches before Inductor
3
Revision 3.0
Micrel, Inc.
MIC3385
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
(3)
EDS Rating .................................................................. 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
3x3.5 MLF-14 (θJA) ........................................... 55°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.
2.7
Supply Voltage Range
Under-Voltage Lockout
Threshold
Typ.
(turn-on)
2.45
UVLO Hysteresis
2.55
Max.
Units
5.5
V
2.65
V
100
mV
Quiescent Current, PWM
mode
VFB = 0.9 * VNOM (not switching)
690
900
µA
Quiescent Current, LDO
mode
VLOWQ = 0V;IOUT = 0mA
16
29
µA
Shutdown Current
VEN = 0V
0.01
5
µA
[Adjustable] Feedback
Voltage
± 1%
± 2% (over temperature)
1
1.01
1.02
V
V
0.99
0.98
FB pin input current
1
0.75
1
nA
1.85
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
%
Output Voltage Load
Regulation, LDO Mode
100µA < ILOAD < 50mA
VLOWQ = 0V
0.1
%
Maximum Duty Cycle
VFB ≤ 0.4V
PWM Switch
ON-Resistance
ISW = 50mA VFB = 0.7VFB_NOM (High Side Switch)
ISW = -50mA VFB = 1.1VFB_NOM (Low Side Switch)
100
A
%
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
0.5
Enable Threshold
Enable Input Current
LDO Dropout Voltage
September 22, 2015
IOUT = 50mA, Note 5
110
4
mV
Revision 3.0
Micrel, Inc.
MIC3385
Electrical Characteristics(4) (Continued)
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.
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
0.47
µH
60
Internal Inductor
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.
September 22, 2015
5
Revision 3.0
Micrel, Inc.
MIC3385
Typical Characteristics ― PWM Mode
2.5V OUT Efficiency
1.8V OUT Efficiency
100
100
90
90
80
80
70
60
50
V IN =3.2V
VIN =3.6V
VIN =4.2V
70
60
40
30
20
10
0
0
20
10
100 200 300 400 500 600
OUTPUT CURRENT (mA)
0
0
1.2V OUT Efficiency
100
90 V IN =3.2V
80
70
60
50
VIN =3.6V
VIN =4.2V
40
30
20
10
0
0
1100
100
90 V IN =3.2V
80
V IN =3.2V
VIN =3.6V
VIN =4.2V
70
60
50
40
30
50
40
30
100 200 300 400 500 600
OUTPUT CURRENT (mA)
Quiescent Current
vs. Input Voltage
1000
20
10
0
0
1.0V OUT Efficiency
100
90 V IN =3.2V
80
70
VIN =3.6V
60
50
0
0
9.0
VIN =3.6V
VIN =4.2V
100 200 300 400 500 600
OUTPUT CURRENT (mA)
Load Regulation
1.018
1.014
1.010
1.006
VIN =4.2V
1.002
40
30
20
10
100 200 300 400 500 600
OUTPUT CURRENT (mA)
1.5V OUT Efficiency
0.998
VIN =3.6V
/LowQ=V IN
0.994
100 200 300 400 500 600
OUTPUT CURRENT (mA)
0.990
0
100 200 300 400 500 600
OUTPUT CURRENT (mA)
Frequency
vs. Input Voltage
8.5
900
8.0
800
700
600
2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
INPUT VOLTAGE (V)
September 22, 2015
7.5
7.0
2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
INPUT VOLTAGE (V)
6
Revision 3.0
Micrel, Inc.
MIC3385
Typical Characteristics ― LDO Mode
September 22, 2015
7
Revision 3.0
Micrel, Inc.
MIC3385
Typical Characteristics ― LDO Mode (cont.)
September 22, 2015
8
Revision 3.0
Micrel, Inc.
MIC3385
Functional Characteristics
Load Transient LDO Mode
Load
(25mA/div)
Load
(100mA/div)
Output Voltag e
AC Coupled
(50mV/div)
Output Voltag e
AC Coupled
(50mV/div)
Load Transient PWM Mode
COUT = 10µF
Time (100µs/div )
Time (100µs/div )
Enable Transient LDO Mode
Enable
(2V/div)
Enable
(2V/div)
Output Voltag e
(1.5V/div)
Output Voltag e
(1.5V/div)
Enable Transient PWM Mode
COUT = 10µF
COUT = 10µF
Time (40µs/div )
Time (40µs/div )
September 22, 2015
COUT = 10µF
9
Revision 3.0
Micrel, Inc.
MIC3385
Functional Diagram
MIC3385 Block Diagram
September 22, 2015
10
Revision 3.0
Micrel, Inc.
MIC3385
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:
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.
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:
R1
VOUT = VREF ×
+ 1
R2
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.
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.
Feedforward capacitance (CFF) can be calculated as
follows:
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
