MIC23051
4MHz PWM Buck Regulator with
HyperLight Load™ and Voltage Scaling
HyperLight Load is a trademark of Micrel, Inc.
MLF and MicroLeadFrame are registered trademarks of Amkor Technology, Inc. Protected by US Patent No. 7064531
Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
November 2008 M9999-111908-E
General Description
The Micrel MIC23051 is a high efficiency 600mA PWM
synchronous buck (step-down) regulator featuring
HyperLight Load™, a patented switching scheme that
offers best in class light load efficiency and transient
performance while providing very small external
components and low output ripple at all loads.
The MIC23051 has an output voltage scaling feature that
can toggles between two different voltage levels.
The MIC23051 also has a very low typical quiescent
current draw of 20µA and can achieve over 85% efficiency
even at 1mA. The device allows operation with a tiny
inductor ranging from 0.47µH to 2.2µH and uses a small
output capacitor that enables a sub-1mm height solution.
In contrast to traditional light load schemes HyperLight
Load™ architecture does not need to trade off control
speed to obtain low standby currents and in doing so the
device only needs a small output capacitor to absorb the
load transient as the powered device goes from light load
to full load.
At higher loads the MIC23051 provides a constant
switching frequency of greater than 4MHz while providing
peak efficiencies greater than 93%.
The MIC23051 is available in fixed output voltage options
from 0.72V to 3.3V eliminating external feedback
components. The MIC23051 is available in an 8-pin 2mm x
2mm MLF® 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
• Input voltage: 2.7V to 5.5V HyperLight Load™
• 600mA output current
• Fixed output voltage from 0.72V to 3.3V
• Output voltage scaling option
• Ultra fast transient response
• 20µA typical quiescent current
• 4MHz in CCM PWM operation in normal mode
• 0.47µH to 2.2µH inductor
• Low voltage output ripple
– 25mVpp in HyperLight Load mode
– 3mV output voltage ripple in full PWM mode
• >93% efficiency
• ~85% at 1mA
• Micropower shutdown
• Available in 8-pin 2mm x 2mm MLF®
• –40°C to +125°C junction temperature range
Applications
• Cellular phones
• Digital cameras
• Portable media players
• Wireless LAN cards
• WiFi/WiMax/WiBro modules
• USB Powered Devices
____________________________________________________________________________________________________________
Typical Application
50
60
70
80
90
100
1 10 100 1000
OUTPUT CURRENT (mA)
Efficiency V OUT = 1.8V
VOUT = 1.8V
L = 1µH
VIN = 3.3V
VIN = 2.7V
VIN = 3.6V
Micrel, Inc. MIC23051
November 2008 2 M9999-111908-E
Ordering Information
Part Number Marking Voltage
Scaled to
with VSC low
Nominal
Output
Voltage
Junction
Temp. Range Package Lead Finish
MIC23051-CGYML JCG 1.0V 1.8V –40° to +125°C 8-Pin 2x2 MLF® Pb-Free
MIC23051-C4YML JC4 1.0V 1.2V –40° to +125°C 8-Pin 2x2 MLF® Pb-Free
MIC23051-16YML J16 1.15V 1.40V –40° to +125°C 8-Pin 2x2 MLF® Pb-Free
MIC23051-945YML 945 0.95V 1.25V –40° to +125°C 8-Pin 2x2 MLF® Pb-Free
Note
1. Other output voltage combinations (0.72 to 3.3V) available, contact Micrel Marketing for details.
2. MLF® is a GREEN RoHS compliant package. Lead finish is NiPdAu. Mold compound is Halogen Free.
Pin Configur ation
1SW
EN
VS
C
SNS
8PGND
VIN
AGND
CFF
7
6
5
2
3
4
8-Pin 2mm x 2mm MLF®
(Top View)
Pin Description
Pin Number Pin Name Pin Name
1 SW Switch (Output): Internal power MOSFET output switches.
2 EN
Enable (Input). Logic low will shut down the device, reducing the quiescent
current to less than 4µA. Do not leave floating.
3 VSC
Voltage scaling pin (input): A low on this pin will scale the output voltage
down to specified level. Do not leave floating.
4 SNS Connect to VOUT to sense output voltage.
5 CFF Feed Forward Capacitor. Connect a 560pF capacitor.
6 AGND Analog Ground.
7 VIN Supply Voltage (Input): Requires bypass capacitor to GND.
8 PGND Power Ground.
Micrel, Inc. MIC23051
November 2008 3 M9999-111908-E
Absolute Maximum Ratings(1)
Supply Voltage (VIN).........................................................6V
Output Switch Voltage (VSW) ............................................6V
Output Switch Current (ISW)..............................................2A
Logic Input Voltage (VEN, VLQ)........................... VIN to –0.3V
Storage Temperature Range (Ts)..............–65°C to +150°C
ESD Rating(3).................................................................. 3kV
Operating Ratings(2)
Supply Voltage (VIN)......................................... 2.7V to 5.5V
Logic Input Voltage (VEN)....................................-0.3V to VIN
Junction Temperature (TJ) ..................–40°C TJ +125°C
Thermal Resistance
2x2 MLF-8 (θJA) .................................................90°C/W
Electrical Characteristics(4)
TA = 25°C with VIN = VEN = VSC = 3.6V; L = 1µH; CFF = 560pF; COUT = 4.7µF; IOUT = 20mA unless otherwise specified.
Bold values indicate –40°C< TJ < +125°C. Important design targets are in italics.
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,
Hyper LL mode IOUT = 0mA , SNS > 1.8V 20 35 µA
Shutdown Current VIN = 5.5V; VEN = 0V; 0.01 4 µA
VSC High, VIN = 3.0V, ILOAD = 20mA -2.5 +2.5 %
%
Output Voltage Accuracy
VSC Low, VIN = 3.0V, ILOAD = 20mA -2.5 +2.5 %
%
SNS pin input current VOUT = 1V 1 µA
Current Limit in PWM Mode SNS = 0.9*VNOM 0.65 1 1.7 A
Output Voltage Line Regulation VIN = 3.0V to 5.5V, ILOAD = 20mA, VSC = 3.6V 0.5 %
Output Voltage Load Regulation 20mA < ILOAD < 500mA, VSC = 3.6V 0.3 %
Output Voltage Line Regulation VIN = 3.0V to 5.5V, ILOAD = 20mA, VSC = 0V 0.5 %
Output Voltage Load Regulation 20mA < ILOAD < 500mA, VSC = 0V 0.3 %
Maximum Duty Cycle SNS ≤ VNOM, VOUT = 1.8V 80 89 %
PWM Switch ON-Resistance**
See Design Note
ISW = 100mA PMOS
ISW = -100mA NMOS 0.45
0.5
VSC = 3.6V, ILOAD = 120mA 3.4 4 4.6 MHz
Frequency VSC = 0V, ILOAD = 120mA 3.4 4 4.6 MHz
SoftStart Time VOUT = 90% 650 µs
VSC threshold voltage 0.5 1.2 V
VSC hysteresis 20 mV
VSC from low to high 800 µs
Output transition time VSC from high to low 800
Enable Threshold (turn-on) 0.5 1.2 V
Enable Hysteresis 35 mV
Enable Input Current 0.1 2 µA
Over-temperature Shutdown 165 °C
Over-temperature Shutdown
Hysteresis 20
°C
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, 1.5k in series with 100pF.
4. Specification for packaged product only.
Micrel, Inc. MIC23051
November 2008 4 M9999-111908-E
Typical Characteristics
50
60
70
80
90
100
1 10 100 1000
OUTPUT CURRENT (mA)
Efficiency VOUT = 1.8V
VOUT = 1.8V
L = 1µH
VIN = 3.3V
VIN = 2.7V
VIN = 3.6V
50
60
70
80
90
1 10 100 1000
OUTPUT CURRENT (mA)
Efficien cy VOUT = 1.2V
VOUT = 1.2V
L = 1µH
VIN = 3.3V
VIN = 2.7V
VIN = 3.6V
50
60
70
80
90
1 10 100 1000
OUTPUT CURRENT (mA)
Efficiency VOUT = 1V
VOUT = 1V
L = 1µH
VIN = 3.3V
VIN = 2.7V
VIN = 3.6V
0
10
20
30
40
Quiescent Curre nt
vs. Temperature
20 40 60 80
TEMPERATURE (°C)
VIN = 3.6V
VOUT = 1.8V
0
5
10
15
20
25
30
35
40
45
50
2.7
INPUT VOLTAGE (V)
Quiescent Curre nt
vs. Input Voltage
3.2 3.7 4.2 4.7 5.2
VIN = 3.6V
VOUT = 1.8V
No Load
2.5
3.0
3.5
4.0
4.5
5.0
5.5
Switchi ng Frequency
vs. Temperature
20 40 60 80
TEMPERATURE (°C)
VIN = 3.6V
VOUT = 1.8V
Load = 150mA
2.5
3.0
3.5
4.0
4.5
5.0
5.5
2.7
INPUT VOLTAGE (V)
Switching Frequency
vs. Input Voltage
3.2 3.7 4.2 4.7 5.2
VIN = 3.6V
VOUT = 1.8V
Load = 150mA
0.60
0.62
0.64
0.66
0.68
0.70
0.72
0.74
0.76
0.78
0.80
Feedback Voltage
vs. Temperature
20 40 60 80
TEMPERATURE (°C)
VIN = 3.6V
VOUT = 1.8V
No Load
1.70
1.75
1.80
1.85
1.90
Output Voltage
vs. Temperature
20 40 60 80
TEMPERATURE (°C)
VIN = 3.6V
VOUT = 1.8V
No Load
1.70
1.75
1.80
1.85
1.90
2.7
INPUT VOLTAGE (V)INPUT VOLTAGE (V)
Output Voltage
vs. Input Voltage
3.2 3.7 4.2 4.7 5.2
Load = 20mA
1.75
1.8
1.85
0 100 200 300 400 500 600
LOAD (mA)
1.70
1.90
Output Voltage
vs. Load
VIN = 3.6V
Micrel, Inc. MIC23051
November 2008 5 M9999-111908-E
Functional Characteristics
Micrel, Inc. MIC23051
November 2008 6 M9999-111908-E
Functional Characteristics (continued)
Micrel, Inc. MIC23051
November 2008 7 M9999-111908-E
Functional Diagram
EN
VIN
SW
PGND
CFF
CONTROL
LOGIC
TIMER &
SOFTSTART
ISENSE
AGND
UVLO
REFERENCE
GATE
DRIVE
SNS
ERROR
COMPARATOR
Current Limit
ZERO 1
R15
R17
VSC
MIC23051 Simplified Block Diagram
Micrel, Inc. MIC23051
November 2008 8 M9999-111908-E
Functional Description
VIN
VIN provides power to the MOSFETs for the switch mode
regulator section and to the analog supply circuitry. Due to
the high switching speeds, a 2.2µF or greater capacitor is
recommended close to VIN and the power ground (PGND)
pin for bypassing. Refer to the layout recommendations for
details.
EN
The enable pin (EN) controls the on and off state of the
device. A logic high on the enable pin activates the
regulator, while a logic low deactivates it. MIC23051
features built-in soft-start circuitry that reduces in-rush
current and prevents the output voltage from overshooting
at start up. Do not leave floating.
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 such as the CFF pin.
SNS
An inductor is connected from the SW pin to the SNS pin.
The SNS pin is the output pin of the device and a minimum
of 2.2µF bypass capacitor should be connected in shunt.
In order to reduce parasitic inductance it is good practice
to place the output bypass capacitor as close to the
inductor as possible.
CFF
The CFF pin is connected to the SNS pin of MIC23051
with a feed-forward capacitor of 560pF. The CFF pin itself
is compared with the internal reference voltage (VREF) of
the device and provides the control path to control the
output. VREF is equal to 0.72V. The CFF pin is sensitive to
noise and should be place away from the SW pin. Refer to
the layout recommendations for details.
VSC
The voltage scaling pin (VSC) is used to switch between
two different voltage levels. A logic high on the VSC pin
will set the output voltage to the higher voltage. A logic low
on the VSC pin will set the output voltage to the lower
voltage. Do not leave floating.
PGND
Power ground (PGND) is the ground path for the high
current PWM mode. The current loop for the power ground
should be as small as possible and separate from the
Analog ground (AGND) loop. Refer to the layout
recommendations for more details.
AGND
Signal ground (AGND) is the ground path for the biasing
and control circuitry. The current loop for the signal ground
should be separate from the Power ground (PGND) loop.
Refer to the layout recommendations for more details.
Micrel, Inc. MIC23051
November 2008 9 M9999-111908-E
Applications Information
Input Capacitor
A minimum of 2.2µF ceramic capacitor should be placed
close to the VIN pin and PGND pin for bypassing. X5R or
X7R dielectrics are recommended for the input capacitor.
Y5V dielectrics, aside from losing most of their
capacitance over temperature, they also become resistive
at high frequencies. This reduces their ability to filter out
high frequency noise.
Output Capacitor
The MIC23051 was designed for use with a 2.2µF or
greater ceramic output capacitor. A low equivalent series
resistance (ESR) ceramic output capacitor either X7R or
X5R is recommended. Y5V and Z5U dielectric capacitors,
aside from the undesirable effect of their wide variation in
capacitance over temperature, become resistive at high
frequencies.
Inductor Selection
Inductor selection will be determined by the following (not
necessarily in the order of importance);
• Inductance
• Rated current value
• Size requirements
• DC resistance (DCR)
The MIC23051 was designed for use with an inductance
range from 0.47µH to 2.2µH. Typically, a 1µH inductor is
recommended for a balance of transient response,
efficiency and output ripple. For faster transient response a
0.47µH inductor may be used. For lower output ripple, a
2.2µH is recommended.
Maximum current ratings of the inductor are generally
given in two methods; permissible DC current and
saturation current. Permissible DC current can be rated
either for a 40°C temperature rise or a 10% to 20% loss in
inductance. Ensure the inductor selected can handle the
maximum operating current. When saturation current is
specified, make sure that there is enough margin so that
the peak current of the inductor does not cause it to
saturate. Peak current can be calculated as follows:
I
PK = IOUT + VOUT (1-VOUT/VIN)/2fL
As shown by the previous calculation, the peak inductor
current is inversely proportional to the switching frequency
and the inductance; the lower the switching frequency or
the inductance the higher the peak current. As input
voltage increases the peak current also increases.
The size of the inductor depends on the requirements of
the application. Refer to the Application Circuit and Bill of
Material for details.
DC resistance (DCR) is also important. While DCR is
inversely proportional to size, DCR can represent a
significant efficiency loss. Refer to the Efficiency
Considerations.
Compensation
The MIC23051 is designed to be stable with a 0.47µH to
2.2µH inductor with a 2.2µF ceramic (X5R) output
capacitor.
Efficiency Considerations
Efficiency is defined as the amount of useful output power,
divided by the amount of power supplied.
100
IV
IV
_%Efficiency
ININ
OUTOUT ×
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
×
×
=
Maintaining high efficiency serves two purposes. It
reduces power dissipation in the power supply, reducing
the need for heat sinks and thermal design considerations
and it reduces consumption of current for battery powered
applications. Reduced current draw from a battery
increases the devices operating time and is critical in hand
held devices.
There are two types of losses in switching converters; DC
losses and switching losses. DC losses are simply the
power dissipation of I2R. Power is dissipated in the high
side switch during the on cycle. Power loss is equal to the
high side MOSFET RDSON multiplied by the Switch
Current2. During the off cycle, the low side N-channel
MOSFET conducts, also dissipating power. Device
operating current also reduces efficiency. The product of
the quiescent (operating) current and the supply voltage is
another DC loss. The current required driving the gates on
and off at a constant 4MHz frequency and the switching
transitions make up the switching losses.
50
60
70
80
90
100
1 10 100 1000
OUTPUT CURRENT (mA)
Efficie ncy VOUT = 1.8V
VOUT = 1.8V
L = 1µH
VIN = 3.3V
VIN = 2.7V
VIN = 3.6V
The Figure above shows an efficiency curve. From no load
to 100mA, efficiency losses are dominated by quiescent
current losses, gate drive and transition losses. By using
the HyperLight Load mode the MIC23051 is able to
maintain high efficiency at low output currents.
Over 100mA, efficiency loss is dominated by MOSFET
RDSON and inductor losses. Higher input supply voltages
will increase the Gate to Source threshold on the internal
Micrel, Inc. MIC23051
November 2008 10 M9999-111908-E
MOSFETs, reducing the internal RDSON. This improves
efficiency by reducing DC losses in the device. All but the
inductor losses are inherent to the device. In which case,
inductor selection becomes increasingly critical in
efficiency calculations. As the inductors are reduced in
size, the DC resistance (DCR) can become quite
significant. The DCR losses can be calculated as follows;
L_Pd = IOUT
2 × DCR
From that, the loss in efficiency due to inductor resistance
can be calculated as follows;
100
L_PdIV
IV
1_LossEfficiency
OUTOUT
OUTOUT ×
⎥
⎥
⎦
⎤
⎢
⎢
⎣
⎡
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
+×
×
−=
Efficiency loss due to DCR is minimal at light loads and
gains significance as the load is increased. Inductor
selection becomes a trade-off between efficiency and size
in this case.
HyperLight Load Mode™
MIC23051 uses a minimum on and off time proprietary
control loop. When the output voltage falls below the
regulation threshold, the error comparator begins a
switching cycle that turns the PMOS on and keeps it on for
the duration of the minimum-on-time. When the output
voltage is over the regulation threshold, the error
comparator turns the PMOS off for a minimum-off-time.
The NMOS acts as an ideal rectifier that conducts when
the PMOS is off. Using a NMOS switch instead of a diode
allows for lower voltage drop across the switching device
when it is on. The asynchronous switching combination
between the PMOS and the NMOS allows the control loop
to work in discontinuous mode for light load operations. In
discontinuous mode MIC23051 works in pulse frequency
modulation (PFM) to regulate the output. As the output
current increases, the switching frequency increases. This
improves the efficiency of MIC23051 during light load
currents. As the load current increases, the MIC23051
goes into continuous conduction mode (CCM) at a
constant frequency of 4MHz. The equation to calculate the
load when the MIC23051 goes into continuous conduction
mode may be approximated by the following formula:
⎟
⎠
⎞
⎜
⎝
⎛
×
×−
=f2L
D)V(V
IOUTIN
LOAD
Micrel, Inc. MIC23051
November 2008 11 M9999-111908-E
MIC23051 Typical Application Circuit
Bill of Materials
Item Part Number Manufacturer Description Qty
C1, C2 C1608X5R0J476K TDK(1) 4.7µF Ceramic Capacitor, 6.3V, X5R, Size 0603 2
C3 C1608C0G1H561J TDK(1) 560pF Ceramic Capacitor, 50V, NPO, Size 0603 1
LQM21PN1R0MC0D Murata(2) 1µH, 0.8A, 190m, L2mm x W1.25mm x H0.5mm
LQH32CN1R0M33 Murata(2) 1µH, 1A, 60m, L3.2mm x W2.5mm x H2.0mm
LQM31PN1R0M00 Murata(2) 1µH, 1.2A, 120m, L3.2mm x W1.6mm x H0.95mm
CPL2512T1R0M TDK(1) 1µH, 1.5A, 100m, L2.5mm x W1.5mm x H1.2mm
LQM31PNR47M00 Murata(2) 0.47µH, 1.4A, 80m, L3.2mm x W1.6mm x H0.85mm
L1
MIPF2520D1R5 FDK(3) 1.5µH, 1.5A, 70m, L2.5mm x W2mm x H1.0mm
1
U1 MIC23051-xxYML Micrel, Inc. (4) 4MHz PWM Buck Regulator with HyperLight Load Mode 1
Notes:
1. TDK: www.tdk.com
2. Murata: www.murata.com
3. FDK: www.fdk.co.jp
4. Micrel, Inc: www.micrel.com
Micrel, Inc. MIC23051
November 2008 12 M9999-111908-E
PCB Layout Recommendations
Top Layer
Bottom Layer
Micrel, Inc. MIC23051
November 2008 13 M9999-111908-E
Package Information
8-Pin 2mm x 2mm MLF® (ML)
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.
© 2007 Micrel, Incorporated.
