MIC2245
4MHz PWM Synchronous Buck
Regulator with LDO Standby Mode
General Description
The Micrel MIC2245 is a high efficiency 4MHz pulse
width modulated (PWM) synchronous buck (step-
down) regulator that features a
LOWQ™
LDO
standby mode that draws only 18µA of quiescent
current. The MIC2245 allows an ultra-low noise,
small size, and high efficiency solution for portable
power applications.
In PWM mode, the MIC2245 operates with a
constant frequency 4MHz 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 MIC2245 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 MIC2245 is available in the 10-pin 3mm x 3mm
MLF™ package with a junction operating range from
–40°C to +125°C.
Data sheet 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
•
4MHz PWM mode
Output current to 500mA
>92% efficiency
100% maximum duty cycle
•
Adjustable output voltage option down to 1V
Fixed output voltage options available
•
Ultra-fast transient response
•
Uses a tiny 1µH inductor
•
Fully integrated MOSFET switches
•
Micropower shutdown operation
•
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
80
70
60
50
40
30
20
10
0
0
V
IN
=3.2V
V
IN
=3.6V
V
IN
=4.2V
Adjustable Output Buck Regulator with
LOWQ™
Mode
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.
MIC2245
Ordering Information
Part Number
MIC2245YML
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.
MIC2245
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 = 1.0µH; C
OUT
= 4.7µF; 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)
3.6
0.5
100
0.4
0.4
4
0.85
0.1
0.85
0.1
110
4.4
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
710
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
Micrel, Inc.
MIC2245
Parameter
Output Voltage Noise
LDO Current Limit
Over-Temperature
Shutdown
Over-Temperature
Hysteresis
Notes
1.
2.
3.
4.
5.
Condition
LOWQ = 0V; C
OUT
= 4.7µF, 10Hz to 100kHz
LOWQ = 0V; V
OUT
= 0V (LDO Mode)
Min
Typ
75
Max
Units
µVrms
mA
°C
°C
60
120
160
20
Exceeding the absolute maximum rating may damage the device.
The device is not guaranteed to function outside its operating rating.
Devices are ESD sensitive. Handling precautions recommended. Human body model: 1.5kΩ in series with 100pF.
Specification for packaged product only.
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
4
M9999-012406
www.micrel.com
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