MIC23303
4MHz PWM 3A Buck Regula tor w ith
HyperLight Load™ and Power Good
HyperLight Load is a tradem ark 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
General Description
The MIC23303 is a high-efficiency 4MHz 3A synchronous
buck regulator with H yperLight Load™ mode, Po wer Good
output indicator, and programmable soft-start. HyperLight
Load provides very high efficiency at light loads and ultra-
fast transient response, which makes the MIC23303
perfectly suited for supplying processor core voltages. An
additiona l b enef it of th is pro pr ietary architec tur e is v er y lo w
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.
The MIC23303 is designed for use with a very small
inductor, down to 0.33µH, and an output capacitor as small
as 10µF th at e nab les a t ota l solu tio n s i ze less tha n 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.
Features
• Input voltage: 2.7V to 5.5V
• Output voltage: do wn 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
• Portable media/MP3 players
• Portable navigation devices (GPS)
• WiFi/ WiMax/ WiBro modules
• Digital Cameras
• Wireless LAN cards
• Portable applications
Typical Appli cation
Micrel, Inc.
MIC23303
2 090613-2.0
Ordering Information
Part Number Marking
Code Nominal Output
Voltage Junction
Temperature Range Package
MIC23303YML WYA Adjustable –40°C to +125°C 12-Pin 3mm × 3mm DFN (1, 2)
Notes:
1. DFN is a GREEN RoHS compliant package. Lead finis h is NiPdAu. Mold compound is Halogen Free.
2. DFN Pi n 1 identifi er is ● .
Pin Configuration
3mm x 3mm DFN (ML)
(Top View)
Pin Description
Pin Number
(Adjustable) Pin Name Pin Function
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 floati ng, 2.2n F mini mu m 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.
Micrel, Inc.
MIC23303
3 090613-2.0
Absolute Maximum Ratings(3)
Supply Voltage (VIN) .......................................... −0.3V to 6V
Sense Voltage (VSNS) ........................................ −0.3V to VIN
Output Switc h 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
ESD Rating(5) ................................................. ESD Sensitive
Operating Ratings(4)
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 other w ise spe cif i ed.
Bold values indicate –40°C ≤ TJ ≤ +125°C, unless otherwise noted.
Parameter Condition Min. Typ. Max. Units
Supply Voltage Range 2.7 5.5 V
Undervoltage Lockout Threshold (turn-on) 2.3 2.53 2.8 V
Undervoltage Lockout Hysteresis 275 mV
Quiescent Current IOUT = 0mA, SNS > 1.2 × VOUT Nominal 24 40 µA
Shutdown Current VEN = 0V; VIN = 5.5V 0.01 5 µA
Output Voltage Accuracy VIN = 3.6V if VOUTNOM < 2.5V, ILOAD = 20mA
−
2.5 +2.5 %
VIN = 4.5V if VOUTNOM ≥ 2.5V, ILOAD = 20mA
Feedback Regulation Voltage ILOAD = 20mA 0.604 0.62 0.635 V
Current Limit SNS = 0.9 × VOUTNOM 3.5 6.5 10 A
Output Voltage Line Regulation VIN = 3.6V to 5.5V if VOUTNOM < 2.5V, ILOAD = 20mA 0.3 %/V
VIN = 4.5V to 5.5V if VOUTNOM ≥ 2.5V, ILOAD = 20mA
Output Voltage Load Regulation
20mA < ILOAD < 500mA, VIN = 3.6V if VOUTNOM < 2.5V 0.3 %
20mA < ILOAD < 500mA, VIN = 5.0V if VOUTNOM ≥ 2.5V
20mA < ILOAD < 1A, VIN = 3.6V if VOUTNOM < 2.5V 0.7 %
20mA < ILOAD < 1A, VIN = 5.0V if VOUTNOM ≥ 2.5V
PWM Switch O N-Resistance ISW = 100mA PMOS
ISW = −100mA NMOS 0.075
0.055 Ω
Switching Frequency IOUT = 300mA 4 MHz
Maximum Duty Cycle(7, 8) 80 85 %
Soft Start Time VOUT = 90%, CSS = 2.2nF 1.26 ms
Notes:
3. Exceeding the absolute maximum rating may damage the device.
4. The device is not guaranteed to functi on outside its operat i ng rating.
5. Devices are ESD sensitive. Handling precautions recommended. Human body model, 1.5kΩ in series with 100pF.
6. Specific at i on for packaged product only.
7. The maxim um duty cycle is limited by the fixed mandatory off time of 300ns.
8. Guaranteed by desi gn.
Micrel, Inc.
MIC23303
4 090613-2.0
Electrical Characteristics(6) (Continued)
TA = 25°C; VIN = VEN = 3.6V; VOUT=1.8V; L = 0.33µH; COUT = 44µF unless otherwise spe cif i ed.
Bold values indicate –40°C ≤ TJ ≤ +125°C, unless noted.
Parameter Condition Min. Typ. Max. Units
Power Good Threshold (Rising) Moving FB from Low to High relative to 0.62V (VFB) 85 90 95 %
Power Good Threshold Hysteresis Moving FB from High to Low relative to 0.62V (VFB) 20 %
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 0.4 0.9 1.2 V
Enable Input Current 0.1 2 µA
Overtemperature Shutdown 160 °C
Overtemperature Shutdown
Hysteresis 20 °C
Micrel, Inc.
MIC23303
5 090613-2.0
Typical Characteris tics
Ef ficiency vs. Load
1. 8 V
OUT
0
10
20
30
40
50
60
70
80
90
100
0.0001 0.001 0.01 0.1 110
LOAD CURRENT ( A)
EFFI CIENCY ( % )
V
IN
= 3.6V
VIN = 5V
L = 0. 33µH
C
OUT
= 44µF
Ef ficiency vs. Load
1. 2 VOUT
0
10
20
30
40
50
60
70
80
90
100
0.0001 0.001 0.01 0.1 110
LOAD CURRENT ( A)
EFFI CIENCY ( % )
V
IN
= 3.6V
L = 0. 33µH
C
OUT
= 44µF
V
IN
= 5V
V
IN
= 3V
VOUT Rise Time
vs Css
1
10
100
1000
10000
100000
1000000
1000 10000 100000 1000000
CSS (pF)
RI SE TIM E (µ s )
VIN=3.6V
Current Limit vs.
I nput Volt age
3.00
4.00
5.00
6.00
7.00
8.00
2.5 3.0 3.5 4.0 4.5 5.0 5.5
I NPUT VO L TAGE ( V)
CURRENT LIMIT (A)
VOUT = 1. 8V
L = 0. 33µH
COUT = 44µF
Qui scent Current
vs. Input V olt age
10
12
14
16
18
20
22
24
26
28
30
2.5 33.5 44.5 55.5
I NPUT VO L TAGE ( V)
Q UIESCENT CURRENT (µ A)
TCASE = 25°C
Output Voltage vs.
I nput Volt age
1.15
1.16
1.17
1.18
1.19
1.20
1.21
1.22
1.23
1.24
1.25
2.5 33.5 44.5 55.5
I NPUT VO L TAGE ( V)
O UTPUT VOLTAG E ( V)
IOUT=20mA
IOUT=1mA
L = 0.33µH
C
OUT
= 44µF
Output Voltage vs.
I nput Volt age
1.15
1.16
1.17
1.18
1.19
1.20
1.21
1.22
1.23
1.24
1.25
2.5 33.5 44.5 55.5
I NPUT VO L TAGE ( V)
O UTPUT VOLTAG E ( V)
I
OUT
=500mA
L = 0.33µH
C
OUT
= 44µF
I
OUT
=2A
Output Voltage ( HLL) vs.
Load Current
1.15
1.16
1.17
1.18
1.19
1.20
1.21
1.22
1.23
1.24
1.25
00.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4
LOAD CURRENT ( A)
O UTPUT VOLTAG E ( V)
VIN=3.6V
L = 33µH
C
OUT
= 44µF
Output Voltage (CCM) vs.
Load Current
1.15
1.16
1.17
1.18
1.19
1.20
1.21
1.22
1.23
1.24
1.25
0.4 0.8 1.2 1.6 22.4 2.8 3.2
LOAD CURRENT ( A)
O UTPUT VOLTAG E ( V)
VIN=3.6V
L = 33µH
C
OUT
= 44µF
Micrel, Inc.
MIC23303
6 090613-2.0
Typical Characteris tics (Continued)
Output Voltage
vs. Temperature
1.75
1.76
1.77
1.78
1.79
1.80
1.81
1.82
1.83
1.84
1.85
-40 -20 020 40 60 80 100 120
TEM PERATURE ( °C)
O UTPUT VOLTAG E ( V)
VIN = 3.6V
L = 0.33µH
COUT = 44µ F
IOUT = 20mA
PG Delay Ti me
vs. Input V olt age
40
60
80
100
120
140
160
2.5 3.0 3.5 4.0 4.5 5.0 5.5
I NPUT VO L TAGE ( V)
PG DELAY ( µs)
PG Rising
PG F alling
PG Threshol ds vs.
I nput Volt age
65
70
75
80
85
90
95
2.5 3.0 3.5 4.0 4.5 5.0 5.5
I NPUT VO L TAGE ( V)
PG T HRES HOLD (% o f VREF
)
PG Rising
PG F alling
Undervol tage Lockout
vs. Temperature
2.0
2.1
2.2
2.3
2.4
2.5
2.6
-40 -20 020 40 60 80 100 120
TEM PERATURE ( °C)
UVLO ( V)
UV LO OFF
UV LO ON
Enabl e Threshol d
vs. Input V olt age
0.5
0.6
0.7
0.8
0.9
1.0
1.1
2.5 3.0 3.5 4.0 4.5 5.0 5.5
I NPUT VO L TAGE ( V)
EN THRES HOLD (V)
TCASE=25°C
Enabl e Threshol ds
vs. Temperature
0.7
0.75
0.8
0.85
0.9
0.95
1
-40 -20 020 40 60 80 100 120 140
TEM PERATURE ( °C)
EN THRESHOLD (V)
Feedback Volt age
vs. Temperature
0.59
0.6
0.61
0.62
0.63
0.64
0.65
-40 -20 020 40 60 80 100 120
TEM PERATURE ( °C)
FEEDBACK V OLTAGE (V )
VIN = 2.7V
VIN = 5V
Shut dow n Current
vs. Temperature
1
10
100
1000
-40 -20 020 40 60 80 100 120
TEM PERATURE ( °C)
SHUTDOW N CURRENT (nA)
VIN=5.5V
VEN=0V
Swit ching Frequency
vs. Load Current
0.1
1
10
100
1000
10000
0.0001 0.001 0.01 0.1 110
LOAD CURRENT ( A)
SW FREQUENCY ( kHz )
VIN = 5V
VIN = 3V
VOUT = 1. 8V
L = 0. 33µH
COUT = 44µF
Micrel, Inc.
MIC23303
7 090613-2.0
Functional Characteristics
Micrel, Inc.
MIC23303
8 090613-2.0
Functional Characteristics (Continued)
Micrel, Inc.
MIC23303
9 090613-2.0
Functional Characteristics (Continued)
Micrel, Inc.
MIC23303
10 090613-2.0
Functional Diagram
Figure 1. Simplified MIC23303 Functional Block Diagram
Micrel, Inc.
MIC23303
11 090613-2.0
Functional Description
PVIN
The input supply (PVIN) provides power to the internal
MOSFETs for the switch mode regulator section. The VIN
operatin g range is 2.7V to 5.5V so an input ca pacitor, w ith
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 fr equency s witching n oise c aused b y PVIN is red uced
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 an d con t rol c irc uitry. T he cur rent loop for the s i gna l
ground should be separate from the power ground (PGND)
loop. Ref er to th e PCB La yout Rec omm endations for m ore
details.
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 analo g gr o un d ( AGN D ) loo p as ap pl icabl e. R ef er to t he
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 s teady state voltage. A pull-up r esistor of
more than 5kΩ should be connected from PG to VOUT.
SS
The sof t star t (SS) pin is us ed to c ontrol the output volt age
ramp-up time. T he approx im ate equat ion f or the ram p tim e
in seconds is 250 × 103 × 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:
+⋅= R4
R3
1VV REFOUT
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
Micrel, Inc.
MIC23303
12 090613-2.0
Application Information
The MIC2330 3 is a high-per f ormance DC-to-D C s tep 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 ca pacitor su ch as the Murat a GRM21BR60 J226ME39L,
size 0805, 22µF ceramic capacitor is recommended based
upon performance, size and cost. Two of these capac itors
in parallel will decrease ESR, res ult ing in decreas e d o utput
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 variati on in capac itance ov er tem per ature 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)
The MIC233 03 is design ed 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 f or a 40°C temperatu re rise or a 10% to 20% l oss in
inductance. Ensure that the inductor selected can handle
the max im um oper ating c ur rent. When satur atio n c urr ent 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:
××
−
+= L
f2 /VV
1
VII INOUT
OUTOUTPEAK
As shown by the calculation above, the peak inductor
current is inversely proportional to the switching frequ ency
and the inductance; the lower the switching frequency or
the inductance the higher the peak current. As input
voltage i ncreas es, the p eak curr ent is som ew hat lim ited b y
constant off time control.
The size of the inductor depends on the requirements of
the applic ation. Refer to th e Typica l Applicat ion Sche matic
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.
Micrel, Inc.
MIC23303
13 090613-2.0
Figure 2. HyperLight Load (HLL) and Continuous
Conduction Mode (CCM) Switching Diagram
Figure 2 shows the signals for high-side switch drive
(HSD) for Ton control, the inductor current and the low-
side 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 induct or with a minimum 10µF c eram ic (X5R ) output
capacitor. The total feedback resistance should be kept
around 500kΩ to reduce the I2R losses through the
feedback resistor network, improving efficiency. A feed-
forward capacitor (CFF) of 33pF is recommended across
the top feedback resistor to reduce the effects of parasitic
capacitance and improve transient performance.
Du ty C yc le
The typical maximum duty cycle of the MIC23303 is 85%.
Efficiency Considerations
Effic iency is def ined as t he am ount of useful output pow er,
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 f or heat s ink s and therm al desi gn cons idera tions ,
and it reduces consum ption of current for batter y-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
power dissipation of I2R. Power is dissipated in the high-
side switch dur ing 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.
The current required to drive the gates on and off at a
constant 4MHz frequency and the switching transitions
make up the switching losses.
Eff iciency vs. Load
1. 8 VOUT
0
10
20
30
40
50
60
70
80
90
100
0.0001 0.001 0.01 0.1 110
LOAD CURRENT( A)
EFFICI ENCY ( %)
V
IN
= 3.6V
VIN = 5V
L = 0. 33µH
C
OUT
= 44µF
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.
Micrel, Inc.
MIC23303
14 090613-2.0
As the inductors are reduced in size, the DC resistance
(DCR) can become quite significant. The DCR losses can
be calculated as follows:
PDCR = IOUT2 × DCR
From that, the loss in efficiency due to inductor resistance
can be calculated as follows:
100
P
IV IV
1Loss
Efficiency
DCR
OUT
OUT
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
MIC23303 uses a minimum on and off time proprietary
control loop (pat ented by Micrel). W hen 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 PMO S off for a minim um-off-time until the o utpu t 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
frequenc y m odulation (PF M) to regulate th e 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
frequenc y center ed at 4MH z. The equat ion to c alculat e the
load when t he MIC23303 goes into continuous conduction
mode may be approximated by the following formula:
×
η××−
>f2L D)V(V
I
OUT
IN
LOAD
As shown in the previous equation, the load at which the
MIC2330 3 transit ions f rom HyperLight L oad m ode to PW M
mode is a f unc t ion of th e in put vo lta ge (V IN), out put v ol tage
(VOUT), duty cycle (D), efficiency (η), inductance (L) and
frequency (f). As shown in Figure 4, as the output current
increases , the switch ing frequenc y also incre ases 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.
Switching Frequency
vs. Load Current
0.1
1
10
100
1000
10000
0.0001 0.001 0.01 0.1 110
LOA D CURRENT ( A)
SW FRE QUENCY ( k Hz )
V
IN
=5V
V
IN=3.3V
V
OUT
= 1. 8V
L = 0. 33µH
C
OUT
= 44µF
Figure 4. SW Frequency vs. Output Current
Power Dissipation Considerations
As with a ll po wer dev ices, t he ult im ate curr ent rati ng 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
Micrel, Inc.
MIC23303
15 090613-2.0
From this simple circuit we can calculate VX if we know
ISOURCE, VZ, and the res istor values, R XY and RYZ, using the
equation:
( )
ZYZ
XY
SOURCEXVRR
IV +
+
×=
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 s ources with tem perature
(in °C).
Figure 6. Thermal Circuit Description
Now replac ing the variable s in the equation for VX, we can
find the junction temperature (TJ) from power dissipation,
ambient tem perature, and t he known th erm al resistance of
the PCB (RθCA) and the package (RθJC).
( )
AMB
CAJCDISSJTRRPT +θ+θ
×=
As can be seen in the diagram, total thermal resistance
RθJA = RθJC + RθCA. He nc e this can also be wr itte n:
()
AMBJA
DISSJTRP
T+
θ×
=
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:
DCRI)1
1
(PP 2
OUTOUT
DISS ×
−
−
η
×=
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 websi te (LDO Application Hints).
Example:
A MIC23303 is intended to drive a 2A load at 1.8V and is
placed on a pr inted c ircuit board wh ich has a gro und pla ne
area of at least 25mm square.
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
VIN = 3V to 4.2V
TAMB = 50°C
RθJA = 61°C/W from datasheet
η
@ 2A = 85% (worst case @ 5V from Figure 3)
Micrel, Inc.
MIC23303
16 090613-2.0
Figure 7. PCB Thermal Resistance versus PCB Copper Area
( )
Ω×−
−××= m202)1
85.01
(28.1P 2
DISS
= 0.56W
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.
Micrel, Inc.
MIC23303
17 090613-2.0
Typical Appli cation Schematic
Bill of Materials
Item Part Number Manufacturer Description Qty.
C1
06036D475KAT2A AVX
(9)
4.7µF/6.3V, X5R, 0603 1 GRM188R60J475ME19D Murata
(10)
C1608X5R0J475M TDK
(11)
C2
06035C222KAT2A AVX
2.2nF/50V, X7R, 0603 1 GRM188R71H222MA01D Murata
C1608X7R1H222K TDK
C3, C8
08056D226MAT2A AVX
22µF/6.3V, X5R, 0805 1 GRM21BR60J226ME39L Murata
C2012X5R0J226M TDK
Notes:
9. AVX: www.avx.com .
10. Murata: www.murata.com.
11. TDK: www.tdk.com.
Micrel, Inc.
MIC23303
18 090613-2.0
Bill of Materials (Continued)
Item Part Number Manufacturer Description Qty.
C4 06035A330KAT2A AVX 33pF/50V, 0603 1
GRM1885C1H330JA01D Murata
C6
06036D105KAT2A AVX
1µF/6.3V, X5R, 0603 1 GRM188R60J105KA01D Murata
C1608X5R0J105K TDK
C7
06035D104KAT2A AVX
0.1µF/6.3V, X5R, 0603 1 GRM188R71H104KA930 Murata
C1608X5R1H104K TDK
L1 0520CDMCDSNP-R33MC Sumida
(12)
0.33µH/5.6A, 8mΩ 1
744373240033 Wurth(13) 0.33µH/8.0A, 8.6mΩ
R1, R2 CRCW060310K0FKEA Vishay/Dale(14) 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 Micrel, Inc(15) 4MHz 3A Buck Regulator with HyperLight
Load Mode and Power Good 1
Notes:
12. Sumida: www.Sumida.com.
13. Wurth: www.we-online.com.
14. Vishay: www.vishay.com.
15. Micrel, Inc.: www.micrel.com.
Micrel, Inc.
MIC23303
19 090613-2.0
PCB Layout Recommendations
Top Layer
Bottom Layer
Micrel, Inc.
MIC23303
20 090613-2.0
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.
Micrel, Inc.
MIC23303
21 090613-2.0
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 representati ons or warranties with respect to the accuracy or completeness of the information furnished in this data sheet. This
informat i on is not intended as a warranty and Micrel does not assume responsibilit y for its use. Micrel reserves the right to change circuitry,
specificat i ons and descript i ons at any time without notice. No license, whether express , im plied, arisi ng by estoppel or otherwise, t o any intellectual
property rights is granted by this document. Except as provided in Micrel’s term s and condit i ons of sale for such products, Micrel assumes no liabil ity
whatsoever, and Micrel disclaims any express or impli ed warranty relat i ng to the sale and/or use of Micrel products including l i abi l ity or warranties
relating to fitness for a particular purpose, merchantability, or infringement of any patent, copyright or other int el l ect ual property right.
Micrel Products are not designed or authorized for use as components in life support appliances, devic es or systems where m alfunction 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 signific ant inj ury t o the user. A
Purchaser’s use or sale of Micrel Products for use in life support appliances, devices or syst ems is a Purchaser’s own risk and Purchaser agrees to fully
indemnify Micrel f or any damages resulting from such use or sale.
© 2002 Micrel, Incorporated.