MIC23250
4MHz Dual 400mA Synchronous Buck
Regulator with HyperLight Load™
HyperLight Load is a 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
November 2008 M9999-111108-D
General Description
The MIC23250 is a high efficiency 4MHz dual 400mA
synchronous buck regulator with HyperLight Load™ mode.
HyperLight Load™ provides very high efficiency at light
loads and ultra-fast transient response which is perfectly
suited for supplying processor core voltages. An additional
benefit of this proprietary architecture is very low output
ripple voltage throughout the entire load range with the use
of small output capacitors. The fixed output MIC23250 has
a tiny 2mm x 2mm Thin MLF® package that saves
precious board space by requiring only 6 additional
external components to drive both outputs up to 400mA
each.
The device is designed for use with a 1µH inductor and a
4.7µF output capacitor that enables a sub-1mm height.
The MIC23250 has a very low quiescent current of 33µA
with both outputs enabled and can achieve over 85%
efficiency at 1mA. At higher loads the MIC23250 provides a
constant switching frequency around 4MHz while providing
peak efficiencies up to 94%.
The MIC23250 fixed output voltage option is available in a
10-pin 2mm x 2mm Thin MLF®. The adjustable output
options is available in a 12-pin 2.5mm x 2.5mm Thin MLF®.
The MIC23250 is designed to operate over the 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™
• Dual output current 400mA/400mA
• Up to 94% peak efficiency and 85% efficiency at 1mA
• 33µA dual quiescent current
• 1µH inductor with a 4.7µF capacitor
• 4MHz in PWM operation
• Ultra fast transient response
• Low voltage output ripple
• 20mVpp in HyperLight Load™ mode
• 3mV output voltage ripple in full PWM mode
• 0.01µA shutdown current
• Fixed output:10-pin 2mm x 2mm Thin MLF®
• Adjustable output:12-pin 2.5mm x 2.5mm Thin MLF®
• –40°C to +125°C junction temperature range
Applications
• Mobile handsets
• Portable media players
• Portable navigation devices (GPS)
• WiFi/WiMax/WiBro modules
• Digital cameras
• Wireless LAN cards
• USB Powered Devices
____________________________________________________________________________________________________________
Typical Application
0
10
20
30
40
50
60
70
80
90
100
1 10 100 1000
OUTPUT CURRENT (mA)
Efficiency VOUT = 1.8V
L = 1µH
COUT = 4.7µF
VIN = 3.0V
VIN = 2.7V
VIN = 3.6V
VIN = 4.2V
Micrel, Inc. MIC23250
November 2008 2 M9999-111108-D
Ordering Information
Part Number Marking
Code
Nominal
Output
Voltage 1
Nominal
Output
Voltage 2
Junction
Temp. Range
Package Lead
Finish
MIC23250-3BYMT WV3 0.9V 1.1V –40° to +125°C 10-Pin 2mm x 2mm Thin MLF® Pb-Free
MIC23250-C4YMT WV2 1.2V 1.0V –40° to +125°C 10-Pin 2mm x 2mm Thin MLF® Pb-Free
MIC23250-W4YMT WV4 1.2V 1.6V –40° to +125°C 10-Pin 2mm x 2mm Thin MLF® Pb-Free
MIC23250-G4YMT WV5 1.2V 1.8V –40° to +125°C 10-Pin 2mm x 2mm Thin MLF® Pb-Free
MIC23250-GFHYMT WV1 1.575V 1.8V –40° to +125°C 10-Pin 2mm x 2mm Thin MLF® Pb-Free
MIC23250-SKYMT 5WV 2.6V 3.3V –40° to +125°C 10-Pin 2mm x 2mm Thin MLF® Pb-Free
MIC23250-AAYMT 4WV ADJ ADJ –40° to +125°C 12-Pin 2.5mm x 2.5mm Thin MLF® Pb-Free
Notes:
1) Additional voltage options available (0.8V to 3.3V). Contact Micrel for details.
2) Thin MLF® is GREEN RoHS compliant package. Lead finish is NiPdAu. Mold compound is Halogen Free.
Micrel, Inc. MIC23250
November 2008 3 M9999-111108-D
Pin Configuration
PGND VIN5
1SNS1
EN1
A
GND
SW1
10 SNS2
EN2
AVIN
SW2
9
8
7
2
3
4
6
SW1 SW25
1FB1
SNS1
EN1
A
GND
12 FB2
SNS2
EN2
AVIN
11
10
9
2
3
4
8
PGND VIN6 7
10-Pin 2mm x 2mm Thin MLF® (MT)
Fixed Output
(Top View)
12-Pin 2.5mmx2.5mm Thin MLF® (MT)
Adjustable Output
(Top View)
Pin Description
Pin Number
(Fixed)
Pin Number
(Adjustable)
Pin Name Pin Function
– 1 FB1
Feedback VOUT1 (Input): Connect resistor divider at this node to set output
voltage. Resistors should be selected based on a nominal VFB of 0.72V.
1 2 SNS1
Sense 1 (Input): Error amplifier input. Connect to feedback resistor network
to set output 1 voltage.
2 3 EN1
Enable 1 (Input): Logic low will shut down output 1. Logic high powers up
output 1. Do not leave unconnected.
3 4 AGND Analog Ground. Must be connected externally to PGND.
4 5 SW1 Switch Node 1 (Output): Internal power MOSFET output.
5 6 PGND Power Ground.
6 7 VIN Supply Voltage (Power Input): Requires close bypass capacitor to PGND.
7 8 SW2 Switch Node 2 (Output): Internal power MOSFET output.
8 9 AVIN Supply Voltage (Power Input): Analog control circuitry. Connect to VIN.
9 10 EN2
Enable 2 (Input): Logic low will shut down output 2. Logic high powers up
output 2. Do not leave unconnected.
10 11 SNS2
Sense 2 (Input): Error amplifier input. Connect to feedback resistor network
to set output 2 voltage.
– 12 FB2
Feedback VOUT2 (Input): Connect resistor divider at this node to set output
voltage. Resistors should be selected based on a nominal VFB of 0.72V.
Micrel, Inc. MIC23250
November 2008 4 M9999-111108-D
Absolute Maximum Ratings(1)
Supply Voltage (VIN).........................................................6V
Output Switch Voltage (VSW) ............................................6V
Logic Input Voltage (VEN1, VEN2) ........................ –0.3V to VIN
Storage Temperature Range (Ts)..............–65°C to +150°C
ESD Rating(3).................................................................. 2kV
Operating Ratings(2)
Supply Voltage (VIN)......................................... 2.7V to 5.5V
Logic Input Voltage (VEN1, VEN2)............................. 0V to VIN
Junction Temperature (TJ) ..................–40°C TJ +125°C
Thermal Resistance
2mm x 2mm Thin MLF-10 (θJA) .........................70°C/W
2.5mm x 2.5mm Thin MLF-12 (θJA) ...................65°C/W
Electrical Characteristics(4)
TA = 25°C with VIN = VEN1 = VEN2 = 3.6V; L = 1µH; COUT = 4.7µF; IOUT = 20mA; only one channel power is enabled, unless
otherwise specified. Bold values indicate –40°C< TJ < +125°C.
Parameter Condition Min Typ Max Units
Under-Voltage Lockout Threshold (turn-on) 2.45 2.55 2.65 V
UVLO Hysteresis 60 mV
Quiescent Current
VOUT1, 2 (both Enabled), IOUT1, 2 = 0mA , VSNS1,2 >1.2 * VOUT1, 2
Nominal 33 50 µA
Shutdown Current VEN1, 2 = 0V; VIN = 5.5V 0.01 4 µA
VIN = 3.6V if VOUTNOM < 2.5V, ILOAD = 20mA –2.5 +2.5 %
Output Voltage Accuracy
VIN = 4.5V if VOUTNOM 2.5V, ILOAD = 20mA –2.5 +2.5 %
Feedback Voltage (Adj only) 0.720 V
Current Limit in PWM Mode SNS = 0.9*VOUT NOM 0.410 0.65 1 A
VIN = 3.6V to 5.5V if VOUTNOM < 2.5V, ILOAD = 20mA 0.4 %/V
Output Voltage Line Regulation
VIN = 4.5V to 5.5V if VOUTNOM 2.5V, ILOAD = 20mA 0.4 %/V
20mA < ILOAD < 400mA, VIN = 3.6V if VOUTNOM < 2.5V 0.5 %
Output Voltage Load Regulation
20mA < ILOAD < 400mA, VIN = 5.0V if VOUTNOM 2.5V 0.5 %
PWM Switch ON-Resistance ISW = 100mA PMOS
ISW = -100mA NMOS 0.6
0.8
Frequency ILOAD = 120mA 4 MHz
Soft Start Time VOUT = 90% 260 µs
Enable Threshold 0.5 0.8 1.2 V
Enable Input Current 0.1 2 µA
Over-temperature Shutdown 160 °C
Over-temperature Shutdown
Hysteresis 40
°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. MIC23250
November 2008 5 M9999-111108-D
Typical Characteristics
0
5
10
15
20
25
30
35
40
45
50
2.7
INPUT VOLTAGE (V)
Quiescent Current
vs. Input Voltage
3.2 3.7 4.2 4.7 5.2 5.7
L = 1µH
COUT = 4.7µF
0.01
0.1
1
10
1 10 100 1000
OUTPUT CURRENT (mA)
Switching Frequency
vs. Output Current
VOUT = 1.8V
L = 1µH
COUT = 4.7µF
VIN = 3.6V
VIN = 3.0V
VIN = 4.2V
4MHz
0.01
0.1
1
10
1 10 100 1000
OUTPUT CURRENT (mA)
Switching Frequency
vs. Output Current
VIN = 3.6V
VOUT = 1.8V
COUT = 4.7µF
L = 2.2µH
L = 1µH
L = 4.7µH
4MHz
3.0
3.5
4.0
4.5
5.0
Frequency
vs. Temperature
20 40 60 80
TEMPERATURE (°C)
L = 1µH
COUT = 4.7µF
Load = 120mA
1.70
1.72
1.74
1.76
1.78
1.80
1.82
1.84
1.86
1.88
1.90
1 10 100 1000
OUTPUT CURRENT (mA)
VIN = 3.6V
VIN = 3.0V
VIN = 4.2V
Output Voltage
vs. Output Current
1.72
1.74
1.76
1.78
1.82
1.84
1.86
1.88
2.7
1.70
1.80
1.90
INPUT VOLTAGE (V)
Output Voltage
vs. Input Voltage
3.2 3.7 4.2 4.7 5.2 5.7
L = 1µH
COUT = 4.7µF
Load = 300mA
Load = 1mA
Load = 10mA
Load = 50mA
Load = 150mA
Load = 400mA
1.5
1.6
1.7
1.9
Output Voltage
vs. Temperature
20 40 60 80
TEMPERATURE (°C)
L = 1µH
COUT = 4.7µF
Load = 120mA
1.8
VOUT1 = 1.575V
VOUT2 = 1.8V
0
0.2
0.4
0.6
0.8
1.2
Enable Threshold
vs. Temperature
20 40 60 80
TEMPERATURE (°C)
L = 1µH
COUT = 4.7µF
1.0 VIN = 3.6V
VIN = 2.7V
VIN = 5.5V
0.800
0.825
0.850
0.875
0.900
0.925
0.950
0.975
1.000
2.7
INPUT VOLTAGE (V)
Enable Threshold
vs. Input Voltage
3.2 3.7 4.2 4.7 5.2 5.7
VIN = 3.6V
VOUT = 1.8V
Load = 150mA
Enable OFF
Enable ON
550
600
650
700
2.7
INPUT VOLTAGE (V)
Current Limit
vs. Input Voltage
3.2 3.7 4.2 4.7 5.2 5.7
L = 1µH
COUT = 4.7µF
0
10
20
30
40
50
60
70
80
90
100
1 10 100 1000
OUTPUT CURRENT (mA)
Efficiency VOUT = 1.2V
L = 1µH
COUT = 4.7µF
VIN = 3.0V
VIN = 3.6V
VIN = 4.2V
VIN = 2.7V
0
10
20
30
40
50
60
70
80
90
100
1 10 100 1000
OUTPUT CURRENT (mA)
Efficiency VOUT = 1.575V
L = 1µH
COUT = 4.7µF
VIN = 3.0V
VIN = 3.6V
VIN = 4.2V
VIN = 2.7V
Micrel, Inc. MIC23250
November 2008 6 M9999-111108-D
Typical Characteristics (Continued)
0
10
20
30
40
50
60
70
80
90
100
1 10 100 1000
OUTPUT CURRENT (mA)
Efficiency VOUT = 1.8V
L = 1µH
COUT = 4.7µF
VIN = 3.0V
VIN = 2.7V
VIN = 3.6V
VIN = 4.2V
0
10
20
30
40
50
60
70
80
90
100
1 10 100 1000
OUTPUT CURRENT (mA)
Efficiency VOUT = 2.5V
L = 1µH
COUT = 4.7µF
VIN = 3.0V
VIN = 3.6V
VIN = 4.2V
VIN = 2.7V
0
10
20
30
40
50
60
70
80
90
100
1 10 100 1000
OUTPUT CURRENT (mA)
Efficiency VOUT = 3.3V
L = 1µH
COUT = 4.7µF
VIN = 5.0V VIN = 5.5V
VIN = 4.2V
0
10
20
30
40
50
60
70
80
90
100
1 10 100 1000
OUTPUT CURRENT (mA)
Efficiency VOUT = 1.8V
VIN = 3.6V
COUT = 4.7µF
L = 1.0µH
L = 1.5µH
L = 0.47µH
With Various Inductors
0
10
20
30
40
50
60
70
80
90
100
1 10 100 1000
OUTPUT CURRENT (mA)
Dual Output Efficiency
VIN = 3.6V
VIN = 3.3V
VIN = 4.2V
VOUT1 = 1.575V
VOUT2 = 1.8V
Load1 = Load2
L1 = L2 = 1µH
COUT1 = COUT2 = 4.7µF
Micrel, Inc. MIC23250
November 2008 7 M9999-111108-D
Functional Characteristics
Micrel, Inc. MIC23250
November 2008 8 M9999-111108-D
Functional Characteristics (Continued)
Micrel, Inc. MIC23250
November 2008 9 M9999-111108-D
Functional Characteristics (Continued)
Micrel, Inc. MIC23250
November 2008 10 M9999-111108-D
Functional Diagram
MIC23250 Simplified Fixed Output Block Diagram
ISENSE
Current Limit Current Limit
Zero X Zero X
ENABLE
LOGIC
GATE
DRIVES
CONTROL
LOGIC
TON TIMER &
SOFT START
ERROR
COMPARATOR
AVIN
VIN
EN1 EN2
SW2SW1
FB2FB1
PGND AGND
ENABLE
LOGIC
GATE
DRIVES
CONTROL
LOGIC
TON TIMER &
SOFT START ISENSE
ERROR
COMPARATOR
UVLO UVLO
+
-
+
-
REF2REF1
SNS1 SNS2
MIC23250 Simplified Adjustable Output Block Diagram
Micrel, Inc. MIC23250
November 2008 11 M9999-111108-D
Functional Description
VIN
The VIN provides power to the internal MOSFETs for the
switch mode regulator along with the current limit sensing.
The VIN operating range is 2.7V to 5.5V so an input
capacitor with a minimum of 6.3V voltage rating is
recommended. Due to the high switching speed, a
minimum of 2.2µF bypass capacitor placed close to VIN
and the power ground (PGND) pin is required. Based upon
size, performance and cost, a TDK C1608X5R0J475K,
size 0603, 4.7µF ceramic capacitor is highly recommended
for most applications. Refer to the layout
recommendations for details.
AVIN
The analog VIN (AVIN) provides power to the analog
supply circuitry. AVIN and VIN must be tied together.
Careful layout should be considered to ensure high
frequency switching noise caused by VIN is reduced
before reaching AVIN. A 0.01µF bypass capacitor placed
as close to AVIN as possible is recommended. See layout
recommendations for details.
EN1/EN2
The enable pins (EN1 and EN2) control the on and off
states of outputs 1 and 2, respectively. A logic high signal
on the enable pin activates the output voltage of the
device. A logic low signal on each enable pin deactivates
the output. MIC23250 features built-in soft-start circuitry
that reduces in-rush current and prevents the output
voltage from overshooting at start up.
SW1/SW2
The switching pin (SW1 or SW2) connects directly to one
end of the inductor (L1 or L2) and provides the current
path during switching cycles. The other end of the inductor
is connected to the load and SNS pin. Due to the high
speed switching on this pin, the switch node should be
routed away from sensitive nodes.
SNS1/SNS2
The SNS pin (SNS1 or SNS2) is connected to the output
of the device to provide feedback to the control circuitry. A
minimum of 2.2µF bypass capacitor should be connected
in shunt with each output. Based upon size, performance
and cost, a TDK C1608X5R0J475K, size 0603, 4.7µF
ceramic capacitor is highly recommended for most
applications. In order to reduce parasitic inductance, it is
good practice to place the output bypass capacitor as
close to the inductor as possible. The SNS connection
should be placed close to the output bypass capacitor.
Refer to the layout recommendations for more details.
PGND
The power ground (PGND) is the ground path for the high
current in 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
The 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.
FB1/FB2 (Adjustable Output Only)
The feedback pins (FB1/FB2) are two extra pins that can
only be found on the MIC23250-AAYMT devices. It allows
the regulated output voltage to be set by applying an
external resistor network. The internal reference voltage is
0.72V and the recommended value of RBOTTOM is within
10% of 442kΩ. The RTOP resistor is the resistor from the
FB pin to the output of the device and RBOTTOM is the
resistor from the FB pin to ground. The output voltage is
calculated from the equation below. See Compensation
under the Applications Information section for
recommended feedback component values.
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛+= 172.0 BOTTOM
TOP
OUT RR
VV
Micrel, Inc. MIC23250
November 2008 12 M9999-111108-D
Applications Information
The MIC23250 is designed for high performance with a
small solution size. With a dual 400mA output inside a tiny
2mm x 2mm Thin MLF® package and requiring only six
external components, the MIC23250 meets today’s
miniature portable electronic device needs. While small
solution size is one of its advantages, the MIC23250 is big
in performance. Using the HyperLight Load™ switching
scheme, the MIC23250 is able to maintain high efficiency
throughout the entire load range while providing ultra-fast
load transient response. Even with all the given benefits,
the MIC23250 can be as easy to use as linear regulators.
The following sections provide an over view of
implementing MIC23250 into related applications
Input Capacitor
A minimum of 2.2µF ceramic capacitor should be placed
close to the VIN pin and PGND pin for bypassing. A TDK
C1608X5R0J475K, size 0603, 4.7µF ceramic capacitor is
recommended based upon performance, size and cost. A
X5R or X7R temperature rating is recommended for the
input capacitor. Y5V temperature rating capacitors, aside
from losing most of their capacitance over temperature,
can also become resistive at high frequencies. This
reduces their ability to filter out high frequency noise.
Output Capacitor
The MIC23250 was designed for use with a 2.2µF or
greater ceramic output capacitor. Increasing the output
capacitance will lower output ripple and improve load
transient response but could increase solution size or cost.
A low equivalent series resistance (ESR) ceramic output
capacitor such as the TDK C1608X5R0J475K, size 0603,
4.7µF ceramic capacitor is recommended based upon
performance, size and cost. Either the X7R or X5R
temperature rating capacitors are recommended. The Y5V
and Z5U temperature rating 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 MIC23250 was designed for use with an inductance
range from 0.47µH to 4.7µH. 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
4.7µH 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:
⎥
⎦
⎤
⎢
⎣
⎡⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
××
−
+= Lf VV
VII INOUT
OUTOUTPEAK 2
/1
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 MIC23250 is designed to be stable with a 0.47µH to
4.7µH inductor with a minimum of 2.2µF ceramic (X5R)
output capacitor. For the adjustable MIC23250, the total
feedback resistance should be kept around 1M to reduce
current loss down the feedback resistor network. This
helps to improve efficiency. A feed-forward capacitor
(CFF) of 120pF must be used in conjunction with the
external feedback resistors to reduce the effects of
parasitic capacitance that is inherent of most circuit board
layouts. Figure 1 and Table 1 shows the recommended
feedback resistor values along with the recommended
feed-forward capacitor values for the MIC23250 adjustable
device.
RTOP
RBOTTOM
CFF
Figure 1. Feedback Resistor Network
Micrel, Inc. MIC23250
November 2008 13 M9999-111108-D
VOUT (V) RTOP (kΩ) RBOTTOM (kΩ) CFF (pF)
0.8 49 442 120
0.9 111 442 120
1 172 442 120
1.1 233 442 120
1.2 295 442 120
1.3 356 442 120
1.4 417 442 120
1.5 479 442 120
1.6 540 442 120
1.7 602 442 120
1.8 663 442 120
1.9 724 442 120
2 786 442 120
2.1 847 442 120
2.2 909 442 120
2.3 970 442 120
2.4 1031 442 120
2.5 1093 442 120
2.6 1154 442 120
2.7 1216 442 120
2.8 1277 442 120
2.9 1338 442 120
3 1400 442 120
3.1 1461 442 120
3.2 1522 442 120
3.3 1584 442 120
Table 1. Recommended Feedback Component Values
Efficiency Considerations
Efficiency is defined as the amount of useful output power,
divided by the amount of power supplied.
100% ×
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
×
×
=
ININ
OUTOUT IV IV
Efficiency
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 Current
squared. 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.
0
20
40
60
80
100
0.1 1 10 100 1000
LOAD (mA)
Efficiency 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 MIC23250 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
MOSFETs, thereby 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:
DCR Loss = IOUT2 × DCR
From that, the loss in efficiency due to inductor resistance
can be calculated as follows:
100
_
1×
⎥
⎦
⎤
⎢
⎣
⎡
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
+×
×
−=
DOUTOUT
OUTOUT PLIV IV
LossEfficiency
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.
Micrel, Inc. MIC23250
November 2008 14 M9999-111108-D
HyperLight Load Mode™
The MIC23250 uses a minimum on and off time
proprietary control loop (patented by Micrel). 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. This increases the output voltage. If the output
voltage is over the regulation threshold, then the error
comparator turns the PMOS off for a minimum-off-time
until the output drops below the threshold. 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, the MIC23250 works in pulse
frequency modulation (PFM) to regulate the output. As the
output current increases, the off-time decreases, thus
providing more energy to the output. This switching
scheme improves the efficiency of MIC23250 during light
load currents by only switching when it is needed. As the
load current increases, the MIC23250 goes into
continuous conduction mode (CCM) and switches at a
frequency centered at 4MHz. The equation to calculate the
load when the MIC23250 goes into continuous conduction
mode may be approximated by the following formula:
()
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
×
×−
>fL DVV
IOUTIN
LOAD 2
As shown in the previous equation, the load at which
MIC23250 transitions from HyperLight Load™ mode to
PWM mode is a function of the input voltage (VIN), output
voltage (VOUT), duty cycle (D), inductance (L) and
frequency (f). This is illustrated in the graph below. Since
the inductance range of MIC23250 is from 0.47µH to
4.7µH, the device may then be tailored to enter HyperLight
Load™ mode or PWM mode at a specific load current by
selecting the appropriate inductance. For example, in the
graph below, when the inductance is 4.7µH the MIC23250
will transition into PWM mode at a load of approximately
5mA. Under the same condition, when the inductance is
1µH, the MIC23250 will transition into PWM mode at
approximately 70mA.
0.01
0.1
1
10
1 10 100 1000
OUTPUT CURRENT (mA)
Switching Frequency
vs. Output Current
VIN = 3.6V
VOUT = 1.8V
COUT = 4.7µF
L = 2.2µH
L = 1µH
L = 4.7µH
4MHz
Micrel, Inc. MIC23250
November 2008 15 M9999-111108-D
MIC23250 Typical Application Circuit (Fixed Output)
Bill of Materials
Item Part Number Manufacturer Description Qty
C1, C2, C3 C1608X5R0J475K TDK(1) 4.7µF Ceramic Capacitor, 6.3V, X5R, Size 0603 3
C4 VJ0603Y103KXXAT Vishay(2) 0.01µF Ceramic Capacitor, 25V, X7R, Size 0603 1
R1, R2 CRCW06031002FKEA Vishay(2) 10k, 1%, 1/16W, Size 0603 Optional
LQM21PN1R0MC0D Murata(3) 1µH, 0.8A, 190m, L2mm x W1.25mm x H0.5mm
LQH32CN1R0M33 Murata(3) 1µH, 1A, 60m, L3.2mm x W2.5mm x H2.0mm
LQM31PN1R0M00 Murata(3) 1µH, 1.2A, 120m, L3.2mm x W1.6mm x H0.95mm
GLF251812T1R0M TDK(1) 1µH, 0.8A, 100m, L2.5mm x W1.8mm x H1.35mm
LQM31PNR47M00 Murata(3) 0.47µH, 1.4A, 80m, L3.2mm x W1.6mm x H0.85mm
MIPF2520D1R5 FDK(4) 1.5µH, 1.5A, 70m, L2.5mm x W2mm x H1.0mm
L1, L2
EPL2010-102 Coilcraft(5) 1.0µH, 1.0A, 86m, L2.0mm x W1.8mm x H1.0mm
2
U1 MIC23250-xxYMT Micrel, Inc.(6) 4MHz Dual 400mA Fixed Output Buck Regulator
with HyperLight Load™ Mode 1
Notes:
1. TDK: www.tdk.com
2. Vishay: www.vishay.com
3. Murata: www.murata.com
4. FDK: www.fdk.co.jp
5. Coilcraft: www.coilcraft.com
6. Micrel, Inc: www.micrel.com
Micrel, Inc. MIC23250
November 2008 16 M9999-111108-D
PCB Layout Recommendations (Fixed Output)
Top Layer
Bottom Layer
Micrel, Inc. MIC23250
November 2008 17 M9999-111108-D
MIC23250 Typical Application Circuit (Adjustable Output)
Bill of Materials
Item Part Number Manufacturer Description Qty
C1, C2, C3 C1608X5R0J475K TDK(1) 4.7µF Ceramic Capacitor, 6.3V, X5R, Size 0603 3
C4 VJ0603Y103KXXAT Vishay(2) 0.01µF Ceramic Capacitor, 25V, X7R, Size 0603 1
C5, C6 VJ0603Y121KXAAT Vishay(2) 120pF Ceramic Capacitor, 50V, X7R, Size 0603 2
R1, R2 CRCW06031002FKEA Vishay(2) 10k, 1%, 1/16W, Size 0603 Optional
R3, R5 CRCW06036653FKEA Vishay(2) 665k, 1%, 1/16W, Size 0603 2
R4, R6 CRCW06034423FKEA Vishay(2) 442k, 1%, 1/16W, Size 0603 2
LQM21PN1R0MC0D Murata(3) 1µH, 0.8A, 190m, L2mm x W1.25mm x H0.5mm
LQH32CN1R0M33 Murata(3) 1µH, 1A, 60m, L3.2mm x W2.5mm x H2.0mm
LQM31PN1R0M00 Murata(3) 1µH, 1.2A, 120m, L3.2mm x W1.6mm x H0.95mm
GLF251812T1R0M TDK(1) 1µH, 0.8A, 100m, L2.5mm x W1.8mm x H1.35mm
LQM31PNR47M00 Murata(3) 0.47µH, 1.4A, 80m, L3.2mm x W1.6mm x H0.85mm
MIPF2520D1R5 FDK(4) 1.5µH, 1.5A, 70m, L2.5mm x W2mm x H1.0mm
L1, L2
EPL2010-102 Coilcraft(5) 1.0µH, 1.0A, 86m, L2.0mm x W1.8mm x H1.0mm
2
U1 MIC23250-AAYMT Micrel, Inc.(6) 4MHz Dual 400mA Adjustable Output
Buck Regulator with HyperLight Load™ Mode 1
Notes:
1. TDK: www.tdk.com
2. Vishay: www.vishay.com
3. Murata: www.murata.com
4. FDK: www.fdk.co.jp
5. Coilcraft: www.coilcraft.com
6. Micrel, Inc: www.micrel.com
Micrel, Inc. MIC23250
November 2008 18 M9999-111108-D
PCB Layout Recommendations (Adjustable Output)
Top Layer
Bottom Layer
Micrel, Inc. MIC23250
November 2008 19 M9999-111108-D
Package Information (Fixed Output)
10-Pin 2mm x 2mm Thin MLF® (MT)
Micrel, Inc. MIC23250
November 2008 20 M9999-111108-D
Package Information (Adjustable Output)
12-Pin 2.5mm x 2.5mm Thin MLF® (MT)
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.
