MIC23450
3MHz, PWM, 2A Triple Buck Regulator
with HyperLight Load® and Power Good
HyperLight Load is a registered 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
November 5
, 2013
110513-1.1
General Description
The MIC23450 is a high-efficiency, 3MHz, triple 2A,
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 5mm x 5mm QFN package
saves board space and requires only five external
components for each channel.
The MIC23450 is designed for use with a very small
inductor, down to 0.47µH, and an output capacitor as small
as 2.2µF that enables a total solution size, less than 1mm
height.
The MIC23450 has a very-low quiescent current of 23µA
each channel and achieves as high as 81% efficiency at
1mA. At higher loads, the MIC23450 provides a constant
switching frequency around 3MHz while achieving peak
efficiencies up to 93%.
The MIC23450 is available in 32-pin 5mm x 5mm QFN
package with an operating junction temperature range
from –40°C to +125°C.
Datasheets and support documentation can be found on
Micrel’s web site at: www.micrel.com.
Features
• Input voltage: 2.7V to 5.5V
• 3 independent 2A outputs
• Up to 93% peak efficiency
• 81% typical efficiency at 1mA
• Three independent Power Good Indicators
• 23µA typical quiescent current (per channel)
• 3MHz PWM operation in continuous mode
• Ultra-fast transient response
• Low voltage output ripple
− 30mVPP ripple in HyperLight Load mode
− 5mV output voltage ripple in full PWM mode
• Fully integrated MOSFET switches
• 0.01µA shutdown current (per channel)
• Thermal-shutdown and current-limit protection
• Output voltage as low as 1V
• 32-pin 5mm x 5mm QFN
• –40°C to +125°C junction temperature range
Applications
• Solid state drives (SSD)
• µC/µP, FPGA, and DSP power
• Test and measurement systems
• Set-top boxes and DTV
• High-performance servers
• Security/surveillance cameras
• 5V POL applications
_________________________________________________________________________________________________________________________
Typical Application
Micrel, Inc.
MIC23450
November
5, 2013 2 110513-1.1
Ordering Information
Part Number Marking Nominal Output
Voltage
Junction Temperature
Range(1) Package(2, 3) Lead Finish
MIC23450-AAAYML AAA ADJ/ADJ/ADJ –40C to +125°C 32-Pin 5mm × 5mm QFN Pb-Free
Notes:
1. Other options available. Contact Micrel for details.
2. QFN is a Green, RoHS-compliant package. Lead finish is NiPdAu. Mold compound is Halogen Free.
3. QFN • = Pin 1 identifier.
Pin Configuration
32-Pin 5mm
×
5mm QFN (ML)
−
Adjustable
Top View
Pin Description
Pin Number Pin Name Pin Function
26, 23, 21 SW1, 2, 3 Switch (Output). Internal power MOSFET output switches for Output 1/2/3.
30, 3, 8 EN1, 2, 3 Enable (Input). Logic high enables operation of regulator 1/2/3. Logic low will shut down the
device. Do not leave floating.
31, 4, 9 SNS1, 2, 3 Sense. Connect to VOUT1,2,3 as close to output capacitor as possible to sense output voltage.
32, 5, 10 FB1, 2, 3 Feedback. Connect a resistor Divider from output 1/2/3 to ground to set the output voltage.
1, 6, 12 PG1, 2, 3 Power Good. Open Drain output for the power good indicator for output 1/2/3. Place a resistor
between this pin and a voltage source to detect a power good condition.
2, 7, 11 AGND1, 2, 3 Analog Ground. Connect to quiet ground point away from high-current paths, e.g., COUT for
best operation. Must be connected externally to PGND.
27, 29, 14 PVIN1, 2, 3 Power Input Voltage. Connect a capacitor to PGND to localize loop currents and decouple
switching noise.
28, 15, 13 AVIN1, 2, 3 Analog Input Voltage. Connect a capacitor to AGND to decouple noise.
24, 22, 18 PGND1, 2, 3 Power Ground.
16, 17, 19, 20, 25 NC No Connect.
ePAD ePad Connect to ground plane to ensure good thermal properties.
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MIC23450
November
5, 2013 3 110513-1.1
Absolute Maximum Ratings(1)
Supply Voltage (PVIN, AVIN) .................................. −0.3 to 6V
Sense (VSNS1, VSNS2, VSNS3). ................................. −0.3 to 6V
Power Good (PG1, PG2, PG3) ............................ −0.3 to 6V
Output Switch Voltage (VSW1, VSW2, VSW3) ......... −0.3V to 6V
Enable Input Voltage (VEN1, VEN2, VEN3) ............ −0.3V to VIN
Storage Temperature Range .................... −65°C to +150°C
ESD Rating(3) ................................................. ESD Sensitive
Operating Ratings(2)
Supply Voltage (VIN) ..................................... +2.7V to +5.5V
Enable Input Voltage (VEN1, VEN2, VEN3) ................. 0V to VIN
Output Voltage Range (VSNS1, VSNS2, VSNS3) ... +1V to +3.3V
Junction Voltage Range (TJ) ............... −40°C ≤ TJ ≤ +125°C
Thermal Resistance
32-Pin 5mm × 5mm QFN (θJA) ......................... +30°C/W
32-Pin 5mm × 5mm QFN (θJC) ........................ +10°C/W
Electrical Characteristics(4)
TA = +25°C; VIN = VEN1, VEN2, VEN3 = 3.6V; L1 = L2 = L3 = 1µH; COUT1, COUT2, COUT3 = 4.7µF, unless otherwise specified.
Bold values indicate –40°C ≤ TJ ≤ +125°C, unless noted.
Parameter Condition Min. Typ. Max. Units
Supply Voltage Range 2.7 5.5 V
Undervoltage Lockout Threshold Turn-On 2.45 2.55 2.65 V
Undervoltage Lockout Hysteresis 75 mV
Quiescent Current IOUT = 0mA, SNS > 1.2 × VOUTNOM 69 120 µA
Per Channel Shutdown Current VEN1, VEN2, VEN3 = 0V; VIN = 5.5V 0.01 5 µA
Output Voltage Accuracy VIN = 3.6V if VOUT(NOM) < 2.5V, ILOAD = 20mA
−
2.5
+
2.5 %
VIN = 4.5V if VOUT(NOM) ≥ 2.5V, ILOAD = 20mA
Feedback Voltage
(VFB1, VFB2, VFB3) .604 0.62 .635 V
Peak Current Limit IOUT1, IOUT2, IOUT3
SNS1, SNS2, SNS3 = 0.9 × VOUTNOM 2 4.5 A
Foldback Current Limit 1.8 A
Output Voltage Line Regulation
(VOUT1, VOUT2, VOUT3)
VIN = 3.6V to 5.5V if VOUTNOM1, 2, 3 < 2.5V, ILOAD = 20mA 0.3 %/V
VIN = 4.5V to 5.5V if VOUTNOM1, 2, 3 ≥ 2.5V, ILOAD = 20mA
Output Voltage Load Regulation
(VOUT1, VOUT2, VOUT3)
DCM: 20mA < ILOAD < 130mA, VIN = 3.6V if VOUTNOM < 2.5V 0.2
%
DCM: 20mA < ILOAD < 130mA, VIN = 5.0V if VOUTNOM > 2.5V 0.4
CCM: 200mA < ILOAD < 500mA, VIN = 3.6V if VOUTNOM < 2.5V 0.6
CCM: 200mA < ILOAD < 1A, VIN = 5.0V if VOUTNOM > 2.5V 0.3
PWM Switch ON-Resistance
(RSW1, RSW2, RSW3)
ISW1, ISW2, ISW3 = +100mA (PMOS) 0.2 Ω
ISW1, ISW2, ISW3 = −100mA (NMOS)
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, 1.5kΩ in series with 100pF.
4. Specification for packaged product only.
Micrel, Inc.
MIC23450
November
5, 2013 4 110513-1.1
Electrical Characteristics(4) (Continued)
TA = +25°C; VIN = VEN1, VEN2, VEN3 = 3.6V; L1 = L2 = L3 = 1µH; COUT1, COUT2, COUT3 = 4.7µF, unless otherwise specified.
Bold values indicate –40°C ≤ TJ ≤ +125°C, unless noted.
Parameter Condition Min. Typ. Max. Units
Maximum Frequency IOUT1, IOUT2, IOUT3 = 120mA 3 MHz
Soft-Start Time VOUT1, VOUT2, VOUT3 = 90% 115 µs
Power Good Threshold % of VNOM 83 90 96 %
Power Good Hysteresis 10 %
Power Good Pull Down VSNS = 90% VNOM, IPG = 1mA 200 mV
Enable Threshold Turn-On 0.5 0.8 1.2 V
Enable Input Current 0.1 1 µA
Overtemperature Shutdown 160 °C
Overtemperature Shutdown
Hysteresis 20 °C
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MIC23450
November
5, 2013 5 110513-1.1
Typical Characteristics
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
0.001 0.01 0.1 110
EFFICIENCY (%)
OUTPUT CURRENT (A)
Efficiency vs. Output Current
V
OUT
= 1.8V
V
IN
= 3V
V
IN
= 3.6V
V
IN
= 5V
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
0.001 0.01 0.1 110
EFFICIENCY (%)
OUTPUT CURRENT (A)
Efficiency vs. Output Current
V
OUT
= 2.5V
V
IN
= 3V
V
IN
= 3.6V V
IN
= 5V
0
1
2
3
4
5
6
7
8
23456
CURRENT LIMIT (A)
INPUT VOLTAGE (V)
Current Limit
vs. Input Voltage
CH3 = 1.2V
CH2 = 1.8V
CH1 = 2.5V
0
20
40
60
80
100
120
140
160
180
2 3 4 5 6
SUPPLY CURRENT (nA)
INPUT VOLTAGE (V)
Shutdown Current
vs. Input Voltage
1.7
1.75
1.8
1.85
1.9
22.5 33.5 44.5 55.5 6
OUTPUT VOLTAGE (V)
INPUT VOLTAGE (V)
Line Regulation
(Low Loads)
I
OUT
= 1mA
I
OUT
= 20mA
I
OUT
= 120mA
1.65
1.7
1.75
1.8
1.85
1.9
22.5 33.5 44.5 55.5 6
OUTPUT VOLTAGE (V)
INPUT VOLTAGE (V)
Line Regulation
(High Loads)
I
OUT
= 1A
I
OUT
= 2A
1.7
1.72
1.74
1.76
1.78
1.8
1.82
1.84
1.86
1.88
1.9
00.03 0.06 0.09 0.12 0.15 0.18
OUTPUT VOLTAGE (V)
LOAD CURRENT (A)
Output Voltage
vs. Output Current (HLL)
V
OUT
= 1.8V
V
IN
= 3V
V
IN
= 3.6VV
IN
= 5V
1.7
1.72
1.74
1.76
1.78
1.8
1.82
1.84
1.86
1.88
1.9
0.2 0.4 0.6 0.8 11.2 1.4 1.6 1.8 2
OUTPUT VOLTAGE (V)
LOAD CURRENT (A)
Output Voltage
vs. Output Current (CCM)
V
OUT
= 1.8V V
IN
= 3V
V
IN
= 5V
V
IN
= 3.6V
1.74
1.76
1.78
1.80
1.82
1.84
-60 -40 -20 020 40 60 80 100 120 140
OUTPUT VOLTAGE (V)
TEMPERATURE (°C)
Output Voltage
vs. Temperature
V
IN
= 5.5V
V
IN
= 3.6V
V
IN
= 2.7V
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MIC23450
November
5, 2013 6 110513-1.1
Typical Characteristics (Continued)
0
20
40
60
80
100
23456
PG DELAY (µs)
INPUT VOLTAGE (V)
PG Delay Time
vs. Input Voltage
PG RISING
PG FALLING
0.83
0.84
0.85
0.86
0.87
0.88
0.89
0.9
0.91
22.5 33.5 44.5 55.5 6
PG THRESHOLD (% of VREF)
INPUT VOLTAGE (V)
PG Thresholds
vs. Input Voltage
PG RISING
PG FALLING
2.47
2.49
2.51
2.53
2.55
2.57
-60 -40 -20 020 40 60 80 100 120 140
UVLO THRESHOLD (V)
TEMPERATURE (°C)
UVLO Threshold
vs. Temperature
UVLO RISING
UVLO FALLING
0.5
0.6
0.7
0.8
0.9
1
1.1
1.2
22.5 33.5 44.5 55.5 6
ENABLE THRESHOLD (V)
INPUT VOLTAGE (V)
Enable Threshold
vs. Input Voltage
T
AMB
= 25°C
0.5
0.6
0.7
0.8
0.9
1
1.1
-60 -40 -20 020 40 60 80 100 120 140
ENABLE THRESHOLD (V)
TEMPERATURE (°C)
Enable Threshold
vs. Temperature
V
IN
= 5.5V
V
IN
= 3.6V
V
IN
= 2.7V
0.1
1
10
100
1000
10000
0.0001 0.001 0.01 0.1 110
FREQUENCY (kHz)
OUTPUT CURRENT (A)
Switching Frequency
vs. Load Current
V
OUT
= 1.8V
V
IN
= 5V
V
IN
= 3V
V
IN
= 3.6V
0.600
0.605
0.610
0.615
0.620
0.625
0.630
0.635
0.640
-60 -40 -20 020 40 60 80 100 120 140
VFB (V)
TEMPERATURE (°C)
VFB
vs. Temperature
V
IN
= 2.7V
V
IN
= 5.5V
V
IN
= 3.6V
0.0
0.5
1.0
1.5
2.0
2.5
20 40 60 80 100 120 140
CURRENT PER OUTPUT (A)
AMBIENT TEMPERATURE (°C)
Maximum Output Current
per O/P vs. Temperature (1 O/P)
V
IN
= 3.6V
V
OUT
= 1V
V
OUT
= 2.8V
0.0
0.5
1.0
1.5
2.0
2.5
20 40 60 80 100 120 140
CURRENT PER OUTPUT (A)
AMBIENT TEMPERATURE (°C)
Maximum Output Current
per O/P vs. Temperature (2 O/Ps)
V
IN
= 3.6V
V
OUT
= 1V
V
OUT
= 2.8V
Micrel, Inc.
MIC23450
November
5, 2013 7 110513-1.1
Typical Characteristics (Continued)
0.0
0.5
1.0
1.5
2.0
2.5
20 40 60 80 100 120 140
MAX OUTPUT CURRENT (A)
AMBIENT TEMPERATURE (°C)
Maximum Output Current
per O/P vs. Temperature (3 O/Ps)
V
IN
= 3.6V
V
OUT
= 1V
V
OUT
= 2.8V
0.00
0.20
0.40
0.60
0.80
1.00
1.20
1.40
00.5 11.5 22.5
POWER DISSIPATION (W)
OUTPUT CURRENT (A)
Power Dissipation
vs. Load Current (per Channel)
VOUT = 1.8V
VOUT = 2.5V
0.00
0.50
1.00
1.50
2.00
2.50
3.00
3.50
4.00
4.50
020 40 60 80 100 120 140
POWER DISSIPATION (W)
AMBIENT TEMPERATURE (°C)
Maximum Package Dissipation
vs. Ambient Temperature
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MIC23450
November
5, 2013 8 110513-1.1
Functional Characteristics
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MIC23450
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5, 2013 9 110513-1.1
Functional Characteristics (Continued)
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MIC23450
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5, 2013 10 110513-1.1
Functional Characteristics (Continued)
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MIC23450
November
5, 2013 11 110513-1.1
Functional Diagram
Figure 1. Simplified MIC23450 Adjustable Functional Block Diagram
Micrel, Inc.
MIC23450
November
5, 2013 12 110513-1.1
Functional Description
PVIN
The input supply (PVIN) provides power to the internal
MOSFETs for the switch mode regulator. 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 di/dt switching speeds, a minimum 2.2µF
or 4.7µF recommended bypass capacitor placed close to
PVIN and the power ground (PGND) pin is required.
Refer to the layout recommendations for details.
AVIN
The input supply (AVIN) provides power to the internal
control circuitry. As the high di/dt switching speeds on
PVIN cause small voltage spikes, an RC filter comprising
50Ω and a minimum 100nF decoupling capacitor placed
close to the AVIN and signal ground (AGND) pin is
required.
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
0.01µA. MIC23450 features internal soft-start circuitry
that reduces in-rush current and prevents the output
voltage from overshooting at start up. 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.
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 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 layout recommendations for
more 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 short and wide as possible and
separate from the analog ground (AGND) loop as
applicable. Refer to the layout recommendations for
more details.
PG
The power good (PG) pin is an open drain output which
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.
FB
The feedback (FB) pin 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 1V and
3.3V using Equation 1:
+
⋅= R2
R1
1VV
REF
OUT
Eq. 1
Where: R1 is the top, VOUT connected resistor, R2 is the
bottom, AGND connected resistor.
Table 1 illustrates example feedback resistor values.
VOUT R1 R2
1.2V 274k 294k
1.5V 316k 221k
1.8V 301k 158k
2.5V 324k 107k
3.3V 309k 71.5k
Table 1. Feedback Resistor Values
Micrel, Inc.
MIC23450
November
5, 2013 13 110513-1.1
Application Information
The MIC23450 is a triple high performance DC-to-DC
step down regulator offering a small solution size.
Supporting 3 outputs with currents up to 2A inside a
5mm x 5mm QFN package, the IC requires only five
external components per channel while meeting today’s
miniature portable electronic device needs. Using the
HyperLight Load® switching scheme, the MIC23450 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 2.2µF ceramic capacitor or greater should be placed
close to the PVIN pin for each channel and it’s
corresponding PGND pin for bypassing. For example,
Murata GRM188R60J475ME19D, size 0603, 4.7µF
ceramic capacitor is ideal, 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 MIC23450 is 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 also increase solution size
or cost. A low equivalent series resistance (ESR)
ceramic output capacitor such as the Murata
GRM188R60J475ME84D, size 0603, 4.7µF ceramic
capacitor is recommended based upon performance,
size and cost. 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)
The MIC23450 is designed for use with a 0.47µH to
2.2µH inductor. For faster transient response, a 0.47µH
inductor will yield the best result. On the other hand, a
2.2µH inductor will yield lower output voltage ripple. For
the best compromise of these, generally, a 1µH 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 does not cause the inductor to
saturate. Peak current can be calculated as shown in
Equation 2:
××
−
+= Lf2
/VV1
VII INOUT
OUTOUTPEAK
Eq. 2
As shown in Equation 2, 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 Typical Application Circuit
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 as illustrated in Figure 2.
Figure 2. Transition between CCM Mode and HLL Mode
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5, 2013 14 110513-1.1
The diagram 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 -50mA. When
the LSD (or TOFF) time reaches its minimum and the
inductor falling current is no longer able to reach this -
50mA threshold, the part is in CCM mode and switching
at a virtually constant frequency.
Once in CCM mode, the TOFF time will not vary.
Therefore, it is important to note that if L is large enough,
the HLL transition level will not be triggered.
That inductor is:
50mA2
135nsV
L
OUT
MAX
×
×
=
Eq. 3
Compensation
The MIC23450 is designed to be stable with a 0.47µH to
2.2µH inductor with a 4.7µF ceramic (X5R) output
capacitor.
Duty Cycle
The typical maximum duty cycle of the MIC23450 is
80%.
Efficiency Considerations
Efficiency is defined as the amount of useful output
power, divided by the amount of power supplied.
100
IV
IV
%Efficiency
IN
IN
OUT
OUT ×
×
×
=
Eq. 4
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 represents 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%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
0.001 0.01 0.1 110
EFFICIENCY (%)
OUTPUT CURRENT (A)
Efficiency vs. Output Current
V
OUT
= 1.8V
V
IN
= 3V
V
IN
= 3.6V
V
IN
= 5V
Figure 3. Efficiency under Load
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
MIC23450 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 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. 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:
PDCR = IOUT
2 x DCR Eq. 5
Micrel, Inc.
MIC23450
November
5, 2013 15 110513-1.1
From that, the loss in efficiency due to inductor
resistance can be calculated as follows:
100
PIV
IV
1LossEfficiency
DCROUTOUT
OUTOUT ×
+×
×
−=
Eq. 6
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.
Thermal Considerations
As most applications will not require 2A continuous
current from all outputs at all times, it is useful to know
what the thermal limits will be for various loading
profiles.
The allowable overall package dissipation is limited by
the intrinsic thermal resistance of the package (Rθ(J-C))
and the area of copper used to spread heat from the
package case to the ambient surrounding temperature
(Rθ(C-A)). The composite of these two thermal resistances
is Rθ(J-A), which represents the package thermal
resistance with at least 1 square inch of copper ground
plane. From this figure, which for the MIC23450 is
30°C/W, we can calculate maximum internal power
dissipation as shown in Equation 7:
A)(J
AMBJMAX
MAX Rθ
TT
PD
−
−
=
Eq. 7
where:
TJMAX = Maximum junction temp (125°C)
TAMB = Ambient temperature
Rθ(J-A) = 30°C/W
As can be expected, the allowable dissipation tends
towards zero as the ambient temperature increases
towards the maximum operating junction temperature.
The graph of PDMAX vs. Ambient temperature could be
drawn quite simply using this equation. However, a more
useful measure is the maximum output current per
regulator vs. ambient temperature. For this, we must first
create an ‘exchange rate’ between power dissipation per
regulator (PDISS) and its output current (IOUT).
An accurate measure of this function can utilize the
efficiency curve, as illustrated in Equation 8:
()
η
η
1P
P
P
P
P
η
OUT
LOSS
LOSSOUT
OUT
−
=
+
=
Eq. 8
where:
η = Efficiency
POUT = IOUT.VOUT
To arrive at the internal package dissipation PDISS, one
would need to remove the inductor loss PDCR which is
not dissipated within the package. This however, does
not give a worst case figure, since efficiency is typically
measured on a nominal part at nominal temperatures.
The IOUT to PDISS function we use therefore is a
synthesized PDISS which accounts for worst case values
at maximum operating temperature, as shown in
Equation 9:
−×+×=
IN
OUT
DSON_N
IN
OUT
DSON_P
2
OUTDISS V
V
1R
V
V
RIP
Eq. 9
where:
RDSON_P = Maximum RDSON of the high side, P-Channel
switch at TJMAX
RDSON_N = Maximum RDSON of the low side, N-Channel
switch at TJMAX
VOUT = Output Voltage,
VIN = Input Voltage
Since ripple current and switching losses are small with
respect to resistive losses at maximum output current,
they can be considered negligible for the purpose of this
method, but could be included if required.
Micrel, Inc.
MIC23450
November
5, 2013 16 110513-1.1
Now we have a function describing PDISS in terms of IOUT,
we can substitute PDISS with Equation 7 to form the
function of maximum output current IOUTMAX vs. ambient
temperature TAMB (Equation 10):
−×
+×
−
=−
IN
OUT
DSON_N
IN
OUT
DSON_P
A)
(J
AMBJMAX
OUTMAX
V
V
1
R
V
V
R
Rθ
T
T
I
Eq. 10
The curves shown in the characteristic curves section
are plots of this function adjusted to account for 1, 2 or 3
regulators running simultaneously.
HyperLight Load Mode
Each regulator in the MIC23450 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 MIC23450 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 MIC23450 during light load currents by
only switching when it is needed. As the load current
increases, the MIC23450 goes into continuous
conduction mode (CCM) and switches at a frequency
centered at 3MHz. The equation to calculate the load
when the MIC23450 goes into continuous conduction
mode may be approximated in Equation 11:
×
×−
>f2L
D
)V(V
I
OUTIN
LOAD
Eq. 11
As shown in Equation 11, the load at which the
MIC23450 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). As shown in Figure 4, as the Output
Current increases, the switching frequency also
increases until the MIC23450 goes from HyperLight
Load mode to PWM mode at approximately 120mA. The
MIC23450 will switch at a relatively constant frequency
around 3MHz once the output current is over 120mA.
0.1
1
10
100
1000
10000
0.0001 0.001 0.01 0.1 110
FREQUENCY (kHz)
OUTPUT CURRENT (A)
Switching Frequency
vs. Load Current
V
OUT
= 1.8V
V
IN
= 5V
V
IN
= 3V
V
IN
= 3.6V
Figure 4. SW Frequency vs. Output Current
Multiple Sources
The MIC23450 provides all the pins necessary to
operate the 3 regulators from independent sources. This
can be useful in partitioning power within a multi rail
system. For example, it is possible that within a system,
two supplies are available; 3.3V and 5V. The MIC23450
can be connected to use the 3.3V supply to provide two,
low voltage outputs (e.g. 1.2V and 1.8V) and use the 5V
rail to provide a higher output (e.g. 2.5V), resulting in the
power blocks shown in Figure 5.
Figure 5. Multi-Source Power Block Diagram
Micrel, Inc.
MIC23450
November
5, 2013 17 110513-1.1
Typical Application Circuit
Bill of Materials
Item Part Number Manufacturer Description Qty.
C1, C2, C3, C11,
C12, C13
C1608X5R1E104K TDK
(1)
Ceramic Capacitor, 0.1µF, 6.3V, X5R, Size 0603 6
GRM188R60J104KD Murata
(2)
C4 EEUFR1A221 Panasonic
(3)
Electrolytic Capacitor, 220µF, 10V, Size 6.3mm 1
C6, C7, C8, C5,
C9, C10
C1608X5R0J475K TDK Ceramic Capacitor, 4.7µF, 6.3V, X5R, Size 0603 6
GRM188R60J475KE19D Murata
R1, R2, R3 CRCW040251R0FKEA Vishay
(4)
Resistor, 51Ω, Size 0402 3
R4 CRCW04023013FKEA Vishay Resistor, 301kΩ , Size 0402 1
Notes:
1. TDK: www.tdk.com.
2. Murata Tel: www.murata.com.
3. Panasonic: www.panasonic.com.
4. Vishay Tel: www.vishay.com.
Micrel, Inc.
MIC23450
November
5, 2013 18 110513-1.1
Bill of Materials (Continued)
Item Part Number Manufacturer Description Qty.
R5 CRCW04021583FKEA Vishay Resistor, 158kΩ, Size 0402 1
R6 CRCW04023163FKEA Vishay Resistor, 316kΩ, Size 0402 1
R7 CRCW04022213FKEA Vishay Resistor, 221kΩ, Size 0402 1
R12 CRCW04022743FKEA Vishay Resistor, 274kΩ, Size 0402 1
R14 CRCW04022943FKEA Vishay Resistor, 294kΩ, Size 0402 1
R8, R9, R10, R11,
R13, R15 CRCW04021003FKEA Vishay Resistor, 100kΩ, Size 0402 6
R16, R17, R18 CRCW08050000FKEA Vishay Resistor, 0Ω, Size 0805 3
L1, L2, L3 VLS3012ST-1R0N1R9 TDK 1µH, 2A, 60mΩ, L3.0mm x W3.0mm x H1.0mm 3
LQH44PN1R0NJ0 Murata 1µH, 2.8A, 50mΩ, L4.0mm x W4.0mm x H1.2mm
U1
MIC23450-AAAYML
Micrel, Inc(5)
3MHz PWM 2A Buck Regulator with HyperLight Load
1
Note:
5. Micrel, Inc.: www.micrel.com.
Micrel, Inc.
MIC23450
November
5, 2013 19 110513-1.1
PCB Layout Recommendations
Top Layer
Mid-Layer 1
Micrel, Inc.
MIC23450
November
5, 2013 20 110513-1.1
PCB Layout Recommendations (Continued)
Mid-Layer 2
Bottom Layer
Micrel, Inc.
MIC23450
November
5, 2013 22 110513-1.1
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
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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 a
nd Purchaser agrees to fully
indemnify Micrel for any damages resulting from such use or sale.
© 2013 Micrel, Incorporated.
