MIC2285
8MHz PWM Synchronous Buck
Regulator with LDO Standby Mode
General Description
The Micrel MIC2285 is a high efficiency 8MHz pulse
width modulated (PWM) synchronous buck (step-
down) 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.
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.
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 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
Applications
•
Cellular phones
•
PDAs
•
USB peripherals
____________________________________________________________________________________________________
Typical Application
1.8V
OUT
Efficiency
100
90
V
IN
=3.2V
80
70
60
50
40
30
20
V
IN
=3.6V
V
IN
=4.2V
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
www.micrel.com
Micrel, Inc.
MIC2285
Ordering Information
Part Number
MIC2285YML
Note:
* Other Voltage options available. Contact Micrel for details.
Output
Voltage*
Adj.
Junction
Temperature Range
–40° to +125°C
Package
10-Pin 3x3 MLF™
Lead Finish
Pb-free
Pin Configuration
AGND 1
LDO 2
BIAS 3
AVIN 4
FB 5
EP
10 PGND
9 SW
8 VIN
7 LOWQ
6 EN
10-Pin 3mm x 3mm MLF (ML)
Pin Description
Pin Number
1
2
3
Pin Name
AGND
LDO
BIAS
Pin Function
Analog (signal) Ground.
LDO Output (Output): Connect to V
OUT
for LDO mode operation.
Internal circuit bias supply. Must be filtered from input voltage through an RC
lowpass filter with a cutoff frequency
≥
4
5
AVIN
FB
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.
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.
Enable (Input). Logic low will shut down the device, reducing the quiescent
current to less than 5µA.
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.
Supply/Input Voltage (Input): Supply voltage for the internal switches and
drivers.
Switch (Output): Internal power MOSFET output switches.
Power Ground.
Ground, backside pad.
6
EN
_____
LOWQ
VIN
SW
PGND
GND
7
8
9
10
EP
January 2006
2
M9999-012406
www.micrel.com
Micrel, Inc.
MIC2285
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
3x3 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
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
0.5
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)
7.2
0.5
100
0.4
0.4
8
0.85
0.1
0.85
0.1
110
8.8
1.3
2
1.3
2
0.675
V
FB
= 0.9 * V
NOM
(not switching)
V
LOWQ
= 0V;I
OUT
= 0mA
V
EN
= 0V
±
2% (over temperature)
0.98
(turn-on)
Condition
Min
2.7
2.45
2.55
100
790
20
0.01
1
1
1
0.13
0.2
0.5
0.8
1
1.85
900
29
5
1.02
Typ
Max
5.5
2.65
Units
V
V
mV
µA
µA
µA
V
nA
A
%
%
%
%
Ω
MHz
V
µA
V
µA
mV
January 2006
3
M9999-012406
www.micrel.com
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