MIC23303 DATA SHEET (11/05/2015) DOWNLOAD

MIC23303
4MHz PWM 3A Buck Regulator with
HyperLight Load™ and Power Good
General Description
Features
The MIC23303 is a high-efficiency 4MHz 3A synchronous
buck regulator with HyperLight Load™ mode, Power Good
output indicator, and programmable soft-start. HyperLight
Load provides very high efficiency at light loads and ultrafast transient response, which makes the MIC23303
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 tiny 3mm × 3mm
DFN package saves precious board space and requires
only six external components.
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The MIC23303 is designed for use with a very small
inductor, down to 0.33µH, and an output capacitor as small
as 10µF that enables a total solution size less than 1mm in
height.
The MIC23303 has very low quiescent current of 24µA and
can achieve peak efficiency of 93% in continuous
conduction mode. In discontinuous conduction mode, the
MIC23303 can achieve 80% efficiency at 1mA.
The MIC23303 is available in a 12-pin 3mm × 3mm DFN
package with an operating junction temperature range
from –40°C to +125°C.
Datasheets and support documentation are available on
Micrel’s web site at: www.micrel.com.
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Input voltage: 2.7V to 5.5V
Output voltage: down to 0.65
Up to 3A output current
Up to 93% peak efficiency
80% typical efficiency at 1mA
Power Good output
Programmable soft-start
24µA typical quiescent current
4MHz PWM operation in continuous mode
Ultra-fast transient response
Low ripple output voltage
− 35mVpp ripple in HyperLight Load mode
− 5mV output voltage ripple in full PWM mode
Fully-integrated MOSFET switches
0.01µA shutdown current
Thermal-shutdown and current-limit protection
12-pin 3mm × 3mm DFN
–40°C to +125°C junction temperature range
Applications
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Portable media/MP3 players
Portable navigation devices (GPS)
WiFi/WiMax/WiBro modules
Digital Cameras
Wireless LAN cards
Portable applications
Typical Application
HyperLight Load is a trademark of Micrel, 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 6, 2013
090613-2.0
Micrel, Inc.
MIC23303
Ordering Information
Part Number
Marking
Code
Nominal Output
Voltage
Junction
Temperature Range
MIC23303YML
WYA
Adjustable
–40°C to +125°C
Package
(1, 2)
12-Pin 3mm × 3mm DFN
Notes:
1. DFN is a GREEN RoHS compliant package. Lead finish is NiPdAu. Mold compound is Halogen Free.
2. DFN Pin 1 identifier is ● .
Pin Configuration
3mm x 3mm DFN (ML)
(Top View)
Pin Description
Pin Number
(Adjustable)
Pin Name
1, 2
SW
Switch (Output): Internal power MOSFET output switches.
3
PG
Power Good: Open-drain output for the power good indicator. Use a pull-up resistor from
this pin to a voltage source to detect a power good condition.
4
EN
Enable (Input): Logic high enables operation of the regulator. Logic low shuts down the
device. Do not leave floating.
5
SNS
Sense: Connect to VOUT as close to output capacitor as possible to sense output voltage.
6
FB
Feedback: Connect a resistor divider from the output to ground to set the output voltage.
7
SS
Soft Start: Place a capacitor from this pin to ground to program the soft start time. Do not
leave floating, 2.2nF minimum CSS is required.
8
AGND
Analog Ground: Connect to central ground point where all high current paths meet (CIN,
COUT, and PGND) for best operation.
9
AVIN
Supply Voltage (Power Input): Analog control circuitry. Connect to PVIN.
10, 11
PVIN
Input Voltage: Connect a capacitor to ground to decouple the noise.
12
PGND
Power Ground.
EP
ePad
Thermal pad: Connect to Ground plane for improved heat sinking.
September 6, 2013
Pin Function
2
090613-2.0
Micrel, Inc.
MIC23303
Absolute Maximum Ratings(3)
Operating Ratings(4)
Supply Voltage (VIN) .......................................... −0.3V to 6V
Sense Voltage (VSNS) ........................................ −0.3V to VIN
Output Switch Voltage (VSW) ............................. −0.3V to VIN
Enable Input Voltage (VEN) .. ..............................−0.3V to VIN
Power Good Voltage (VPG) ................................ −0.3V to VIN
Storage Temperature Range .................... −65°C to +150°C
Lead temperature (soldering, 10s) ............................. 260°C
(5)
ESD Rating ................................................. ESD Sensitive
Supply Voltage (VIN) ........................................ .2.7V to 5.5V
Enable Input Voltage (VEN) .................................... 0V to VIN
Sense Voltage (VSNS) ..................................... 0.65V to 5.5V
Junction Temperature Range (TJ)...... .−40°C ≤ TJ ≤ +125°C
Thermal Resistance
3mm × 3mm DFN-12 (θJA) ................................. 61°C/W
3mm × 3mm DFN-12 (θJC) ................................. 27°C/W
Electrical Characteristics(6)
TA = 25°C; VIN = VEN = 3.6V; VOUT=1.8V; L = 0.33µH; COUT = 44µF unless otherwise specified.
Bold values indicate –40°C ≤ TJ ≤ +125°C, unless otherwise noted.
Parameter
Condition
Min.
2.7
Supply Voltage Range
Undervoltage Lockout Threshold
2.3
(turn-on)
Undervoltage Lockout Hysteresis
IOUT = 0mA, SNS > 1.2 × VOUT Nominal
Shutdown Current
VEN = 0V; VIN = 5.5V
VIN = 3.6V if VOUTNOM < 2.5V, ILOAD = 20mA
VIN = 4.5V if VOUTNOM ≥ 2.5V, ILOAD = 20mA
Feedback Regulation Voltage
ILOAD = 20mA
Current Limit
SNS = 0.9 × VOUTNOM
Output Voltage Line Regulation
Switching Frequency
Maximum Duty Cycle
V
2.8
V
mV
40
µA
0.01
5
µA
+2.5
%
0.62
0.635
V
3.5
6.5
10
A
VIN = 3.6V to 5.5V if VOUTNOM < 2.5V, ILOAD = 20mA
VIN = 4.5V to 5.5V if VOUTNOM ≥ 2.5V, ILOAD = 20mA
20mA < ILOAD < 500mA, VIN = 5.0V if VOUTNOM ≥ 2.5V
20mA < ILOAD < 1A, VIN = 3.6V if VOUTNOM < 2.5V
0.3
%/V
0.3
%
0.7
%
ISW = 100mA PMOS
0.075
ISW = −100mA NMOS
0.055
IOUT = 300mA
(7, 8)
Soft Start Time
5.5
0.604
20mA < ILOAD < 1A, VIN = 5.0V if VOUTNOM ≥ 2.5V
PWM Switch ON-Resistance
Units
24
−2.5
20mA < ILOAD < 500mA, VIN = 3.6V if VOUTNOM < 2.5V
Output Voltage Load Regulation
2.53
Max.
275
Quiescent Current
Output Voltage Accuracy
Typ.
80
VOUT = 90%, CSS = 2.2nF
Ω
4
MHz
85
%
1.26
ms
Notes:
3. Exceeding the absolute maximum rating may damage the device.
4. The device is not guaranteed to function outside its operating rating.
5. Devices are ESD sensitive. Handling precautions recommended. Human body model, 1.5kΩ in series with 100pF.
6. Specification for packaged product only.
7. The maximum duty cycle is limited by the fixed mandatory off time of 300ns.
8. Guaranteed by design.
September 6, 2013
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Micrel, Inc.
MIC23303
Electrical Characteristics(6) (Continued)
TA = 25°C; VIN = VEN = 3.6V; VOUT=1.8V; L = 0.33µH; COUT = 44µF unless otherwise specified.
Bold values indicate –40°C ≤ TJ ≤ +125°C, unless noted.
Parameter
Condition
Power Good Threshold (Rising)
Moving FB from Low to High relative to 0.62V (VFB)
Power Good Threshold Hysteresis
Moving FB from High to Low relative to 0.62V (VFB)
Power Good Delay Time
Rising
160
µs
Power Good Pull-Down
RPG = 5.1k from PG to VOUT
200
mV
Enable Threshold
The voltage on Enable that ensures the part is ON
0.9
1.2
V
Enable Input Current
0.1
2
µA
Overtemperature Shutdown
160
°C
Overtemperature Shutdown
Hysteresis
20
°C
September 6, 2013
4
Min.
Typ.
Max.
Units
85
90
95
%
20
0.4
%
090613-2.0
Micrel, Inc.
MIC23303
Typical Characteristics
Efficiency vs. Load
1.2 VOUT
Efficiency vs. Load
1.8 VOUT
100
100
90
100000
80
VIN = 3.6V
60
50
40
30
20
70
0
0.0001
50
40
30
1000
100
0.001
0.01
0.1
1
10
L = 0.33µH
COUT = 44µF
10
0
0.0001
10
6.00
5.00
VOUT = 1.8V
L = 0.33µH
COUT = 44µF
3.0
3.5
4.0
4.5
10
5.0
30
1.25
28
1.24
26
1.23
24
22
20
18
16
14
1.22
TCASE = 25°C
2.5
3
INPUT VOLTAGE (V)
1.20
1.19
1.17
3.5
4
4.5
5
2.5
Output Voltage (HLL) vs.
Load Current
1.23
1.23
IOUT=500mA
1.21
1.20
1.19
IOUT=2A
1.17
L = 0.33µH
COUT = 44µF
OUTPUT VOLTAGE (V)
1.24
1.23
OUTPUT VOLTAGE (V)
1.25
1.24
1.22
1.22
1.21
1.20
1.19
1.18
1.17
VIN=3.6V
L = 33µH
COUT = 44µF
1.16
1.15
4
4.5
INPUT VOLTAGE (V)
September 6, 2013
5
5.5
4
4.5
5
5.5
1.22
1.21
1.20
1.19
1.18
1.17
VIN=3.6V
L = 33µH
COUT = 44µF
1.16
1.15
3.5
3.5
Output Voltage (CCM) vs.
Load Current
1.25
3
3
INPUT VOLTAGE (V)
1.24
2.5
L = 0.33µH
COUT = 44µF
1.15
5.5
1.25
1.16
IOUT=1mA
1.18
INPUT VOLTAGE (V)
Output Voltage vs.
Input Voltage
1.18
IOUT=20mA
1.21
1.16
10
1000000
Output Voltage vs.
Input Voltage
12
5.5
100000
10000
CSS (pF)
OUTPUT VOLTAGE (V)
QUIESCENT CURRENT (µA)
7.00
2.5
1
Quiscent Current
vs. Input Voltage
8.00
3.00
0.1
VIN=3.6V
1
1000
LOAD CURRENT (A)
Current Limit vs.
Input Voltage
4.00
0.01
0.001
LOAD CURRENT(A)
CURRENT LIMIT (A)
10000
60
20
L = 0.33µH
COUT = 44µF
10
OUTPUT VOLTAGE (V)
VIN = 5V
VIN = 3.6V
RISE TIME (µs)
VIN = 5V
70
EFFICIENCY (%)
EFFICIENCY (%)
1000000
VIN = 3V
90
80
VOUT Rise Time
vs Css
1.15
0
0.05
0.1
0.15
0.2
0.25
0.3
LOAD CURRENT (A)
5
0.35
0.4
0.4
0.8
1.2
1.6
2
2.4
2.8
3.2
LOAD CURRENT (A)
090613-2.0
Micrel, Inc.
MIC23303
Typical Characteristics (Continued)
Output Voltage
vs. Temperature
PG Thresholds vs.
Input Voltage
PG Delay Time
vs. Input Voltage
1.85
160
95
PG Rising
PG THRESHOLD (% of V REF)
140
1.83
1.82
PG DELAY (µs)
OUTPUT VOLTAGE (V)
1.84
1.81
1.80
1.79
1.78
VIN = 3.6V
L = 0.33µH
COUT = 44µF
IOUT = 20mA
1.77
1.76
120
PG Rising
100
80
PG Falling
60
-40
-20
0
20
40
60
80
100
2.5
120
85
80
75
PG Falling
70
65
40
1.75
90
3.0
3.5
4.0
4.5
5.0
2.5
5.5
3.0
Undervoltage Lockout
vs. Temperature
4.0
4.5
5.0
5.5
Enable Thresholds
vs. Temperature
Enable Threshold
vs. Input Voltage
2.6
3.5
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
TEMPERATURE (°C)
1.1
1
1.0
0.95
EN THRESHOLD (V)
2.5
UVLO (V)
2.4
2.3
UVLO OFF
2.2
2.1
EN THRESHOLD (V)
UVLO ON
0.9
0.8
0.7
0.9
0.85
0.8
0.75
0.6
TCASE=25°C
2.0
0.5
-40
-20
0
20
40
60
80
100
120
0.7
2.5
3.0
TEMPERATURE (°C)
Feedback Voltage
vs. Temperature
4.0
4.5
5.0
5.5
-40
10000
1000
0.63
VIN = 5V
0.62
0.61
VIN = 2.7V
0.6
0.59
100
10
VIN=5.5V
VEN=0V
1
-40
-20
0
20
40
60
80
TEMPERATURE (°C)
September 6, 2013
100
120
0
-40
-20
0
20
40
60
80
TEMPERATURE (°C)
6
20
40
60
80
100 120 140
Switching Frequency
vs. Load Current
VIN = 5V
1000
SW FREQUENCY (kHz)
SHUTDOWN CURRENT (nA)
0.64
-20
TEMPERATURE (°C)
Shutdown Current
vs. Temperature
0.65
FEEDBACK VOLTAGE (V)
3.5
INPUT VOLTAGE (V)
100
120
100
VIN = 3V
10
1
0.1
0.0001
VOUT = 1.8V
L = 0.33µH
COUT = 44µF
0.001
0.01
0.1
1
10
LOAD CURRENT (A)
090613-2.0
Micrel, Inc.
MIC23303
Functional Characteristics
September 6, 2013
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090613-2.0
Micrel, Inc.
MIC23303
Functional Characteristics (Continued)
September 6, 2013
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090613-2.0
Micrel, Inc.
MIC23303
Functional Characteristics (Continued)
September 6, 2013
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090613-2.0
Micrel, Inc.
MIC23303
Functional Diagram
Figure 1. Simplified MIC23303 Functional Block Diagram
September 6, 2013
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090613-2.0
Micrel, Inc.
MIC23303
Functional Description
PVIN
The input supply (PVIN) provides power to the internal
MOSFETs for the switch mode regulator section. The VIN
operating range is 2.7V to 5.5V so an input capacitor, with
a minimum voltage rating of 6.3V, is recommended. Due to
the high switching speed, a minimum 4.7µF bypass
capacitor placed close to PVIN and the power ground
(PGND) pin is required. Refer to the PCB Layout
Recommendations for details.
AVIN
Analog VIN (AVIN) provides power to the internal control
and analog supply circuitry. AVIN and PVIN must be tied
together. Careful layout should be considered to ensure
high frequency switching noise caused by PVIN is reduced
before reaching AVIN. A 1µF capacitor as close to AVIN
as possible is recommended. See PCB Layout
Recommendations for details.
EN
A logic high signal on the enable pin activates the output
voltage of the device. A logic low signal on the enable pin
deactivates the output and reduces supply current to
nominal 0.01µA. MIC23303 features external soft-start
circuitry via the soft start (SS) pin that reduces in-rush
current and prevents the output voltage from overshooting
when EN is driven logic high. Do not leave the EN pin
floating.
SW
The switch (SW) connects directly to one end of the
inductor and provides the current path during switching
cycles. The other end of the inductor is connected to the
load, SNS pin, and output capacitor. Due to the high speed
switching on this pin, the switch node should be routed
away from sensitive nodes whenever possible.
SNS
The sense (SNS) pin is connected to the output of the
device to provide feedback to the control circuitry. The
SNS connection should be placed close to the output
capacitor. Refer to the PCB Layout Recommendations for
more details.
AGND
The analog 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 PCB Layout Recommendations for more
details.
September 6, 2013
11
PGND
The power ground pin 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 as applicable. Refer to the
PCB Layout Recommendations for more details.
PG
The power good (PG) pin is an open-drain output that
indicates logic high when the output voltage is typically
above 90% of its steady state voltage. A pull-up resistor of
more than 5kΩ should be connected from PG to VOUT.
SS
The soft start (SS) pin is used to control the output voltage
ramp-up time. The approximate equation for the ramp time
3
in seconds is 250 × 10 × ln(10) × CSS.
For example, for CSS = 2.2nF, Trise ~ 1.26ms. See the
Typical Characteristics curve for a graphical guide. The
minimum recommended value for CSS is 2.2nF.
FB
The feedback (FB) pin is provided for the adjustable
voltage option (no internal connection for fixed options).
This is the control input for programming the output
voltage. A resistor divider network is connected to this pin
from the output and is compared to the internal 0.62V
reference within the regulation loop.
The output voltage can be programmed between 0.65V
and 3.6V using the following equation:
 R3 
VOUT = VREF ⋅ 1 +

 R4 
Where: R3 is the top resistor, R4 is the bottom resistor.
Example feedback resistor values:
VOUT
R3
R4
1.2V
274k
294k
1.5V
316k
221k
1.8V
560k
294k
2.5V
324k
107k
3.3V
464k
107k
090613-2.0
Micrel, Inc.
MIC23303
Application Information
The MIC23303 is a high-performance DC-to-DC step down
regulator offering a small solution size. Supporting an
output current up to 3A inside a tiny 3mm x 3mm DFN
package, the IC requires only six external components
while meeting today’s miniature portable electronic device
needs. Using the HyperLight Load switching scheme, the
MIC23303 is able to maintain high efficiency throughout
the entire load range while providing ultra-fast load
transient response. The following sections provide
additional device application information.
Input Capacitor
A 4.7µF ceramic capacitor or greater should be placed
close to the PVIN pin and PGND pin for bypassing. A
Murata GRM188R60J475ME19D, 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 MIC23303 is designed for use with a 10µF or greater
ceramic output capacitor. Increasing the output
capacitance will lower output ripple and improve load
transient response but could also increase solution size or
cost. A low equivalent series resistance (ESR) ceramic
output capacitor such as the Murata GRM21BR60J226ME39L,
size 0805, 22µF ceramic capacitor is recommended based
upon performance, size and cost. Two of these capacitors
in parallel will decrease ESR, resulting in decreased output
voltage ripple. Both the X7R or X5R temperature rating
capacitors are recommended. The Y5V and Z5U
temperature rating capacitors are not recommended due
to their wide variation in capacitance over temperature and
increased resistance at high frequencies.
Inductor Selection
When selecting an inductor, it is important to consider the
following factors (not necessarily in the order of
importance):
•
Inductance
•
Rated current value
•
Size requirements
•
DC resistance (DCR)
September 6, 2013
12
The MIC23303 is designed for use with a 0.33µH to 1.0µH
inductor. For faster transient response and greater
efficiency, a 0.33µH inductor will yield the best result. To
achieve lower output voltage ripple, a higher value inductor
such as a 1µH can be used. However, a greater value
inductor, when operating in low load mode will result in a
higher operating frequency. This effect with increased
DCR will result in a less efficient design.
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 that the inductor selected can handle
the maximum operating current. When saturation current is
specified, make sure that there are enough margins that
the peak current does not cause the inductor to saturate.
Peak current can be calculated as follows:

 1 − VOUT /VIN
IPEAK = IOUT + VOUT 
 2× f ×L




As shown by the calculation above, 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 is somewhat limited by
constant off time control.
The size of the inductor depends on the requirements of
the application. Refer to the Typical Application Schematic
and Bill of Materials 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. The transition between high loads (CCM)
to HyperLight Load (HLL) mode is determined by the
inductor ripple current and the load current.
090613-2.0
Micrel, Inc.
MIC23303
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
handheld devices.
There are two types of losses in switching converters; DC
losses and switching losses. DC losses are simply the
2
power dissipation of I R. Power is dissipated in the highside 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
represents another DC loss.
Figure 2 shows the signals for high-side switch drive
(HSD) for Ton control, the inductor current and the lowside switch drive (LSD) for Toff control.
In HLL mode, the inductor is charged with a fixed Ton
pulse on the high-side switch (HSD). After this, the LSD is
switched on and current falls at a rate VOUT/L. The
controller remains in HLL mode while the inductor falling
current is detected to cross approximately 300mA. When
the LSD (or Toff) time reaches its minimum and the
inductor falling current is no longer able to reach this
300mA threshold, the part is in CCM mode and switching
at a virtually constant frequency.
Compensation
The MIC23303 is designed to be stable with a 0.33µH to
1.0µH inductor with a minimum 10µF ceramic (X5R) output
capacitor. The total feedback resistance should be kept
2
around 500kΩ to reduce the I R losses through the
feedback resistor network, improving efficiency. A feedforward capacitor (CFF) of 33pF is recommended across
the top feedback resistor to reduce the effects of parasitic
capacitance and improve transient performance.
Duty Cycle
The typical maximum duty cycle of the MIC23303 is 85%.
Efficiency Considerations
Efficiency is defined as the amount of useful output power,
divided by the amount of power supplied.
V
×I
Efficiency % =  OUT OUT
V
×
IN IIN

September 6, 2013

 × 100

13
The current required to drive the gates on and off at a
constant 4MHz frequency and the switching transitions
make up the switching losses.
100
Efficiency vs. Load
1.8 VOUT
90
80
EFFICIENCY (%)
Figure 2. HyperLight Load (HLL) and Continuous
Conduction Mode (CCM) Switching Diagram
VIN = 5V
70
VIN = 3.6V
60
50
40
30
20
L = 0.33µH
COUT = 44µF
10
0
0.0001
0.001
0.01
0.1
1
10
LOAD CURRENT(A)
Figure 3. Efficiency under Load
Figure 3 shows an efficiency curve. From no load to
100mA, efficiency losses are dominated by quiescent
current losses, gate drive, and transition losses. By using
HyperLight Load mode, the MIC23303 is able to maintain
high efficiency at low output currents.
Over 300mA, efficiency loss is dominated by MOSFET
RDSON and inductor losses. Higher input supply voltages
will increase the Gate-to-Source voltage 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.
When dealing with inductor losses, inductor selection
becomes increasingly critical in efficiency calculations.
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MIC23303
As the inductors are reduced in size, the DC resistance
(DCR) can become quite significant. The DCR losses can
be calculated as follows:
2
PDCR = IOUT × DCR
From that, the loss in efficiency due to inductor resistance
can be calculated as follows:
 
VOUT × IOUT
Efficiency Loss = 1 − 
  VOUT × IOUT + PDCR
As shown in the previous equation, the load at which the
MIC23303 transitions from HyperLight Load mode to PWM
mode is a function of the input voltage (VIN), output voltage
(VOUT), duty cycle (D), efficiency (η), inductance (L) and
frequency (f). As shown in Figure 4, as the output current
increases, the switching frequency also increases until the
MIC23303 goes from HyperLight Load mode to PWM
mode at approximately 300mA. The MIC23303 will switch
at a relatively constant frequency around 4MHz once the
output current is over 300mA.

 × 100


10000
Switching Frequency
vs. Load Current
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
MIC23303 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 MIC23303 works in pulse
frequency modulation (PFM) to regulate the output. As the
output current increases, the off-time decreases, thus
provides more energy to the output. This switching
scheme improves the efficiency of MIC23303 during light
load currents by only switching when it is needed. As the
load current increases, the MIC23303 goes into
continuous conduction mode (CCM) and switches at a
frequency centered at 4MHz. The equation to calculate the
load when the MIC23303 goes into continuous conduction
mode may be approximated by the following formula:
SW FREQUENCY (kHz)
1000
VIN =5V
100
VIN=3.3V
10
1
0.1
0.0001
VOUT = 1.8V
L = 0.33µH
COUT = 44µF
0.001
0.01
0.1
1
10
LOAD CURRENT (A)
Figure 4. SW Frequency vs. Output Current
Power Dissipation Considerations
As with all power devices, the ultimate current rating of the
output is limited by the thermal properties of the package
and the PCB it is mounted on. There is a simple, Ohm’s
law type relationship between thermal resistance, power
dissipation and temperature which are analogous to an
electrical circuit:
Figure 5. Ohm’s Law Description
 (V − VOUT ) × D × η 
ILOAD >  IN

2L × f


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Micrel, Inc.
MIC23303
From this simple circuit we can calculate VX if we know
ISOURCE, VZ, and the resistor values, RXY and RYZ, using the
equation:
Since effectively all of the power losses (minus the
inductor losses) in the converter are dissipated within the
MIC23303 package, PDISS can be calculated thus:
V X = I SOURCE × (R XY + R YZ ) + VZ


1
2
PDISS = POUT × ( − 1) − I OUT × DCR
η


Thermal circuits can be considered using these same rules
and can be drawn similarly replacing current sources with
power dissipation (in Watts), resistance with thermal
resistance (in °C/W) and voltage sources with temperature
(in °C).
Where:
η = Efficiency taken from efficiency curves and DCR =
Inductor DCR.
RθJC and RθJA are found in the Operating Ratings section
of the datasheet. Where the reel board area differs from
1in square, RθCA (the PCB thermal resistance) values for
various PCB copper areas can be taken from Figure 7
below. This graph is taken from Designing with Low
Dropout Voltage Regulators, which is available from the
Micrel website (LDO Application Hints).
Example:
A MIC23303 is intended to drive a 2A load at 1.8V and is
placed on a printed circuit board which has a ground plane
area of at least 25mm square.
Figure 6. Thermal Circuit Description
Now replacing the variables in the equation for VX, we can
find the junction temperature (TJ) from power dissipation,
ambient temperature, and the known thermal resistance of
the PCB (RθCA) and the package (RθJC).
The voltage source is a Li-ion battery with a lower
operating threshold of 3V and the ambient temperature of
the assembly can be up to 50°C.
Summary of variables:
IOUT = 2A
VOUT = 1.8V
TJ = PDISS × (Rθ JC + Rθ CA ) + TAMB
VIN = 3V to 4.2V
TAMB = 50°C
As can be seen in the diagram, total thermal resistance
RθJA = RθJC + RθCA. Hence this can also be written:
RθJA = 61°C/W from datasheet
η @ 2A = 85% (worst case @ 5V from Figure 3)
TJ = PDISS × (RθJA ) + TAMB
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Micrel, Inc.
MIC23303
Figure 7. PCB Thermal Resistance versus PCB Copper Area
(
)
1


− 1) − 22 × 20mΩ = 0.56W
PDISS = 1.8 × 2 × (
0.85


The worst case switch and inductor resistance will
increase at higher temperatures, so a margin of 20% can
be added to account for this.
PDISS = 0.56 × 1.2 = 0.67W
Therefore:
TJ = 0.67W. (61°C/W) + 50°C
TJ = 91°C
This is well below the maximum 125°C.
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MIC23303
Typical Application Schematic
Bill of Materials
Item
Part Number
06036D475KAT2A
C1
GRM188R60J475ME19D
C1608X5R0J475M
06035C222KAT2A
C2
C3, C8
GRM188R71H222MA01D
Manufacturer
Murata
(10)
4.7µF/6.3V, X5R, 0603
1
2.2nF/50V, X7R, 0603
1
22µF/6.3V, X5R, 0805
1
(11)
TDK
AVX
Murata
TDK
08056D226MAT2A
AVX
C2012X5R0J226M
Qty.
AVX
C1608X7R1H222K
GRM21BR60J226ME39L
Description
(9)
Murata
TDK
Notes:
9. AVX: www.avx.com .
10. Murata: www.murata.com.
11. TDK: www.tdk.com.
September 6, 2013
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Micrel, Inc.
MIC23303
Bill of Materials (Continued)
Item
C4
Part Number
06035A330KAT2A
GRM1885C1H330JA01D
06036D105KAT2A
C6
C7
GRM188R60J105KA01D
AVX
Murata
Murata
TDK
06035D104KAT2A
AVX
GRM188R71H104KA930
0520CDMCDSNP-R33MC
744373240033
Description
Qty.
33pF/50V, 0603
1
1µF/6.3V, X5R, 0603
1
0.1µF/6.3V, X5R, 0603
1
AVX
C1608X5R0J105K
C1608X5R1H104K
L1
Manufacturer
Murata
TDK
Sumida
Wurth
(12)
Vishay/Dale
0.33µH/5.6A, 8mΩ
0.33µH/8.0A, 8.6mΩ
(13)
(14)
1
R1, R2
CRCW060310K0FKEA
10K,1%, 1/10W, 0603
2
R3
CRCW0603560KFKEA
Vishay/Dale
560K,1%, 1/10W, 0603
1
R4
CRCW0603294KFKEA
Vishay/Dale
294K,1%, 1/10W, 0603
1
R5
CRCW060310R0FKEA
Vishay/Dale
10Ω,1%, 1/10W, 0603
1
IC1
MIC23303YML
4MHz 3A Buck Regulator with HyperLight
Load Mode and Power Good
1
(15)
Micrel, Inc
Notes:
12. Sumida: www.Sumida.com.
13. Wurth: www.we-online.com.
14. Vishay: www.vishay.com.
15. Micrel, Inc.: www.micrel.com.
September 6, 2013
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Micrel, Inc.
MIC23303
PCB Layout Recommendations
Top Layer
Bottom Layer
September 6, 2013
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090613-2.0
Micrel, Inc.
MIC23303
Package Information (16)
12-Pin 3mm x 3mm DFN (ML)
Note:
16. Package information is correct as of the publication date. For updates and most current information, go to www.micrel.com.
September 6, 2013
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Micrel, Inc.
MIC23303
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
Micrel makes no representations or warranties with respect to the accuracy or completeness of the information furnished in this data sheet. This
information is not intended as a warranty and Micrel does not assume responsibility for its use. Micrel reserves the right to change circuitry,
specifications and descriptions at any time without notice. No license, whether express, implied, arising by estoppel or otherwise, to any intellectual
property rights is granted by this document. Except as provided in Micrel’s terms and conditions of sale for such products, Micrel assumes no liability
whatsoever, and Micrel disclaims any express or implied warranty relating to the sale and/or use of Micrel products including liability or warranties
relating to fitness for a particular purpose, merchantability, or infringement of any patent, copyright or other intellectual property right.
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.
© 2002 Micrel, Incorporated.
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