MIC33153
4MHz PWM 1.2A Internal Inductor
Buck Regulator with HyperLight Load™
and Power Good
HyperLight Load is a trademark of Micrel, Inc.
MLF and MicroLeadFrame are registered trademark Amkor Technology Inc.
Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (408) 944-01200 • fax + 1 (408) 474-1000 • http://www.micrel.com
General Description
The MIC33153 is a high-efficiency 4MHz 1.2A
synchronous buck regulator with an internal inductor,
HyperLight Load™ mode, Power Good (PG) output
indicator, and programmable soft start. HyperLight Load™
provides very high efficiency at light loads and ultra-fast
transient response which makes the MIC33153 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 MIC33153 is designed so that only two external
capacitors as small as 2.2µF are needed for stability. This
gives the MIC33153 the ease of use of an LDO with the
efficiency of a HyperLight Load™ DC converter. The
MIC33153 achieves efficiency in HyperLight LoadTM mode
as high as 85% at 1mA, with a very low quiescent current
of 22µA. At higher loads, the MIC33153 provides a
constant switching frequency up to 4MHz.
The MIC33153 is available in 14-pin 3.0mm x 3.5mm
MLF® 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
• Internal inductor
Simplifies design to two external capacitors
• Input voltage: 2.7V to 5.5V
• Output voltage: fixed or adjustable (0.62V to 3.6V)
• Up to 1.2 A output current
• Up to 93% peak efficiency
• 85% typical efficiency at 1mA
• Power Good (PG) output
• Programmable soft start
• 22µA typical quiescent current
• 4MHz PWM operation in continuous mode
• Ultra-fast transient response
• Low ripple output voltage
35mVpp ripple in HyperLight Load™ mode
7mV output voltage ripple in full PWM mode
• 0.01µA shutdown current
• Thermal shutdown and current limit protection
• 14-pin 3.0 x 3.5 x 1.1mm MLF® package
• –40°C to +125°C junction temperature range
Applications
• Solid State Drives (SSD)
• Mobile handsets
• Portable media/MP3 players
• Portable navigation devices (GPS)
• WiFi/WiMax/WiBro modules
• Wireless LAN cards
• Portable applications
____________________________________________________________________________________________________________
Typical Application
Fixed Output Voltage Adjustable Output Voltage
September 2010 M9999-092910-A
Micrel Inc. MIC33153
September 2010 2 M9999-092910-A
Ordering Information
Part Number1 Marking Code Nominal Output
Voltage Junction Temperature
Range Package2
MIC33153-4YHJ −4
33153 1.2V –40°C to +125°C 14-pin 3.0 x 3.5 x 1.1mm MLF®
MIC33153YHJ MIC
33153 Adjustable –40°C to +125°C 14-pin 3.0 x 3.5 x 1.1mm MLF®
Notes:
1. Other options available (1V - 3.3V). Contact Micrel Marketing for details.
2. MLF® is GREEN RoHS compliant package. Lead finish is NiPdAu. Mold compound is Halogen Free.
Pin Configur ation
14- Pin 3.0mm x 3.5mm MLF® (HJ)
Fixed Output Voltage
(Top View)
14- Pin 3.0mm x 3.5mm MLF® (HJ)
Adjustable Output Voltage
(Top View)
Pin Description
Pin
Number
(Fixed)
Pin
Number
(Adjustable)
Pin
Name Pin Function
1 1 SS
Soft Start: Place a capacitor from this pin to ground to program the soft start time.
Do not leave floating, 100pF minimum CSS is required.
2 2 AGND
Analog Ground: Connect to central ground point where all high current paths meet
(CIN, COUT, PGND) for best operation.
3 3 VIN Input Voltage: Connect a capacitor to ground to decouple the noise.
4 4 PGND Power Ground.
5,6,7 5,6,7 OUT
Output Voltage: The output of the regulator. Connect to SNS pin. For adjustable option,
connect to feedback resistor network.
8,9,10 8,9,10 SW Switch: Internal power MOSFET output switches before Inductor
11 11 EN
Enable: Logic high enables operation of the regulator. Logic low will shut down the device.
Do not leave floating.
12 12 SNS Sense: Connect to VOUT as close to output capacitor as possible to sense output voltage.
13 13 PG
Power Good: Open drain output for the Power Good (PG) indicator. Use a pull up resistor
from this pin to a voltage source to detect a power good condition.
14 − NC Not Internally Connected.
− 14 FB Feedback: Connect a resistor divider from the output to ground to set the output voltage.
Micrel Inc. MIC33153
September 2010 3 M9999-092910-A
Absolute Maximum Ratings(1)
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 (PG) Voltage (VPG) .......................−0.3V to VIN
Storage Temperature Range ..……………−65°C to +150°C
Lead Temperature (soldering, 10 sec.)...................... 260°C
ESD Rating(3)................................................. ESD Sensitive
Operating Ratings(2)
Supply Voltage (VIN)... …………………………..2.7V to 5.5V
Enable Input Voltage (VEN) .. ……………………….0V to VIN
Sense Voltage (VSNS) ..................................... 0.62V to 3.6V
Junction Temperature Range (TJ).. ….−40°C ≤ TJ ≤ +125°C
Thermal Resistance
3.0mm x 3.5mm MLF®-14 (θJA)..........................55°C/W
Electrical Characteristics(4)
TA = 25°C; VIN = VEN = 3.6V; COUT = 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
Under-Voltage Lockout Threshold (Turn-On) 2.45 2.55 2.65 V
Under-Voltage Lockout Hysteresis 75 mV
Quiescent Current IOUT = 0mA , SNS > 1.2 * VOUT Nominal 22 45 µA
Shutdown Current VEN = 0V; VIN = 5.5V 0.01 5 µA
VIN = 3.6V if VOUTNOM < 2.5V, ILOAD = 20mA
Output Voltage Accuracy VIN = 4.5V if VOUTNOM 2.5V, ILOAD = 20mA −2.5 +2.5 %
Feedback Regulation Voltage ILOAD = 20mA 0.6045 0.62 0.6355 V
Current Limit SNS = 0.9*VOUTNOM 2.2 3.3 A
VIN = 3.6V to 5.5V if VOUTNOM < 2.5V, ILOAD = 20mA
Output Voltage Line Regulation VIN = 4.5V to 5.5V if VOUTNOM 2.5V, ILOAD = 20mA 0.3 %/V
1mA < ILOAD < 1A, VIN = 3.6V if VOUTNOM < 2.5V 0.8
Output Voltage Load Regulation 1mA < ILOAD < 1A, VIN = 5.0V if VOUTNOM 2.5V 0.85 %/A
PWM Switch ON-Resistance ISW = 100mA PMOS
ISW = −100mA NMOS 0.2
0.19 Ω
Maximum Switching Frequency IOUT = 300mA 4 MHz
Soft Start Time VOUT = 90%, CSS = 470pF 320 µs
Soft Start Current VSS = 0V 2.7 µA
PG Threshold (Rising) 86 92 96 %
PG Threshold Hysteresis 7 %
PG Delay Time Rising 68 µs
Enable Threshold Turn-On 0.5 0.9 1.2 V
Enable Input Current 0.1 2 µA
Over-Temperature Shutdown 160 °C
Over-Temperature Shutdown
Hysteresis 20 °C
Notes:
1. Exceeding the absolute maximum rating may damage the device.
2. The device is not guaranteed to function outside its operating rating.
3. Devices are ESD sensitive. Handling precautions recommended. Human body model, 1.5k in series with 100pF.
4. Specification for packaged product only.
Micrel Inc. MIC33153
September 2010 4 M9999-092910-A
Typical Characteristics
Efficiency (VOUT = 3.3V)
0
10
20
30
40
50
60
70
80
90
100
1 10 100 1000 10000
OUTPUT CURRENT (mA)
EFFI CI E NCY (%)
COUT = 4.7µF
VIN = 4.2V VIN = 5.0V VIN = 5.5V
Efficiency (VOUT = 2.5V)
0
10
20
30
40
50
60
70
80
90
100
1 10 100 1000 10000
OUTPUT CURRENT (mA)
EFFI CI E NCY (%)
COUT = 4.7µF
VIN = 3.6V VIN = 4.2V
VIN = 5.5V
Efficiency (VOUT = 1.8V)
0
10
20
30
40
50
60
70
80
90
100
1 10 100 1000 10000
OUTPUT CURRENT (mA)
EFFI CI E NCY (%)
COUT = 4.7µF
VIN = 3.0V VIN = 3.6V VIN = 4.2V
Efficiency (VOUT = 1.5V)
0
10
20
30
40
50
60
70
80
90
100
1 10 100 1000 10000
OUTPUT CURRENT (mA)
EFFI CI E NCY (%)
COUT = 4.7µF
VIN = 3.0V
VIN = 3.6V VIN = 4.2V
Efficiency (VOUT = 1.2V)
0
10
20
30
40
50
60
70
80
90
100
1 10 100 1000 10000
OUTPUT CURRENT (mA)
EFFI CI E NCY (%)
COUT = 4.7µF
VIN = 3.0V
VIN = 3.6V VIN = 4.2V
Efficiency (VOUT = 1.0V)
0
10
20
30
40
50
60
70
80
90
100
1 10 100 1000 10000
OUTPUT CURRENT (mA)
EFFI CI E NCY (%)
COUT = 4.7µF
VIN = 3.0V
VIN = 3.6V VIN = 4.2V
Curre nt Limit
vs . Input Voltage
0.00
0.50
1.00
1.50
2.00
2.50
3.00
3.50
4.00
4.50
5.00
2.7 3.2 3.7 4.2 4.7 5.2 5.7
INPUT VOLTAGE (V)
CURRENT LIMIT (A)
Quiescent Current
vs. Input Voltage
0
5
10
15
20
25
30
35
40
2.7 3.2 3.7 4.2 4.7 5.2 5.7
INPUT V OLTAGE (V)
QUIESCENT CURRENT (µA)
No Switching
SNS > 1.2 * V
OUTNOM
C
OUT
= 4.7µF
T = 125°C T = 20°C
T = - 45°C
Shutdown Current
vs. Input Voltage
0
5
10
15
20
25
30
2.5 3.0 3.5 4.0 4.5 5.0 5.5
INPUT VOLTAGE (V)
SHUTDOW N CURRENT (nA)
Line Regulation
(Light Load)
1.700
1.720
1.740
1.760
1.780
1.800
1.820
1.840
1.860
1.880
1.900
2.533.544.555.5
INPUT V OLTAGE (V)
OUTPUT VOLTAGE ( V)
V
OUTNOM
= 1.8V
C
OUT
= 4.7µF
I
OUT
= 160mA
I
OUT
= 40mA
I
OUT
= 1mA
Line Regulation
(Heav y Load)
1.700
1.720
1.740
1.760
1.780
1.800
1.820
1.840
1.860
1.880
1.900
2.5 3 3.5 4 4.5 5 5.5
INPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
V
OUTNOM
= 1.8V
C
OUT
= 4.7µF
I
OUT
= 500mA
I
OUT
= 300mA
I
OUT
= 1000mA
Load Regulation
1.100
1.150
1.200
1.250
1.300
0 200 400 600 800 1000 1200
OUTPUT CURRENT (mA)
OUTPUT VOLTAGE (V)
V
OUTNOM
= 1.2V
C
OUT
= 4.7µF
V
IN
= 4.2V
V
IN
= 3.6V
V
IN
= 3.0V
Micrel Inc. MIC33153
September 2010 5 M9999-092910-A
Typical Characteristics
Feedback Voltage
vs. Temperature
0.59
0.60
0.61
0.62
0.63
0.64
0.65
-40 -20 0 20 40 60 80 100 120
TEMPERATURE (°C)
FB VOLTAGE (V
)
V
IN
= 3.6V
UVLO Thre s hold
vs. Temperature
2.46
2.47
2.48
2.49
2.50
2.51
2.52
2.53
2.54
2.55
2.56
-40 -20 0 20 40 60 80 100 120
TEMPERATURE (°C)
UVLO THRESHOLD (V)
ON
OFF
Enable Threshold
vs. Temperature
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
-40 -20 0 20 40 60 80 100 120
TEMPERATURE (%)
VEN THRE S HOL D (V )
VOUT = 3.6V
Turn ON
Turn OFF
Enable Voltage
vs. Input Voltage
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
2.7 3.2 3.7 4.2 4.7 5.2 5.7
INPUT VOLTAGE (V )
ENABL E VOLTAGE (V
)
C
OUT
= 4.7µF
I
OUT
= 150mA
Enable ON
Enable OFF
V
OUT
Rise Time
vs. C
SS
1
10
100
1000
10000
100000
1000000
100 1000 10000 100000 1000000
CSS (pF)
RISE TIME (µs)
SW Frequency
vs. Temperature
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
5.5
6
-40 -20 0 20 40 60 80 100 120
TEMPERATURE (°C)
SW FREQUENCY (MHz)
VIN = 3.6V
COUT = 4.7µF
Load = 400mA
Switching Freque nc y
vs . Output Current
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
0.1 1 10 100 1000 10000
OUTPUT CURRENT (mA)
SW F REQUENCY (MHz)
V
IN
= 3.6V
V
IN
= 4.2V
Micrel Inc. MIC33153
September 2010 6 M9999-092910-A
Functional Characteristics
Micrel Inc. MIC33153
September 2010 7 M9999-092910-A
Functional Characteristics (Continued)
Micrel Inc. MIC33153
September 2010 8 M9999-092910-A
Functional Characteristics (Continued)
Micrel Inc. MIC33153
September 2010 9 M9999-092910-A
Functional Diagram
Figure 1. Simplified MIC331 53 Functional Block Diagram – Fixed Output Voltage
Figure 2. Simplified MIC33153 Functional Block Diagram – Adjustable Output Voltage
Micrel Inc. MIC33153
September 2010 10 M9999-092910-A
Functional Description
VIN
The input supply (VIN) provides power to the internal
MOSFETs for the switch mode regulator along with the
internal control circuitry. 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 2.2µF bypass capacitor
placed close to VIN and the power ground (PGND) pin is
required. Refer to the 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
0.01µA. MIC33153 features external soft start circuitry
via the soft start (SS) pin 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 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 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 small as possible and separate
from the analog ground (AGND) loop as applicable.
Refer to the layout recommendations for more details.
Power Good PG
The Power Good (PG) pin is an open drain output which
indicates logic high when the output voltage is typically
above 92% of its steady state voltage. When the output
voltage is below 86%, the PG pin indicates logic low. A
pull up resistor of more than 10k 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 in milliseconds is:
T(ms) = 270x103 x ln (10) x CSS
where:
T is the time in milliseconds and CSS is the external soft
start capacitance (in Farads).
For example, for a CSS = 470pF, Trise ~ 0.3ms or 300µs.
See the Typical Characteristics curve for a graphical
guide. The minimum recommended value for CSS is
100pF.
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:
⎟
⎠
⎞
⎜
⎝
⎛+×= R2
R1
1VV REFOUT
where:
R1 is the top resistor, R2 is the bottom resistor.
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
Micrel Inc. MIC33153
September 2010 11 M9999-092910-A
Application Information
The MIC33153 is a high performance DC-to-DC step
down regulator offering a small solution size. With the
HyperLight Load™ switching scheme, the MIC33153 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 VIN pin and PGND pin for bypassing. A
Murata GRM188R60J475ME84D, 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 MIC33153 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.
Compensation
The MIC33153 is designed to be stable with a 4.7µF
ceramic (X5R) output capacitor.
Duty Cycle
The typical maximum duty cycle of the MIC33153 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
ININ
OUTOUT ×
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
×
×
=
Maintaining high efficiency serves two purposes. It
reduces power dissipation in the power supply, reducing
the need for heat sinks and thermal design
considerations and it reduces consumption of current for
battery powered applications. Reduced current draw
from a battery increases the devices operating time and
is critical in hand held devices.
There are two types of losses in switching converters;
DC losses and switching losses. DC losses are simply
the power dissipation of I2R. Power is dissipated in the
high side switch during the on cycle. Power loss is equal
to the high side MOSFET RDSON multiplied by the Switch
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.
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
the HyperLight Load™ mode, the MIC33153 is able to
maintain high efficiency at low output currents.
Micrel Inc. MIC33153
September 2010 12 M9999-092910-A
Over 100mA, efficiency loss is dominated by MOSFET
RDSON and inductor losses. Higher input supply voltages
will increase the gate to source threshold on the internal
MOSFETs, thereby reducing the internal RDSON. This
improves efficiency by reducing DC losses in the device.
All but the inductor losses are inherent to the device. In
which case, inductor selection becomes increasingly
critical in efficiency calculations. As the inductors are
reduced in size, the DC resistance (DCR) can become
quite significant. The DCR losses can be calculated as
follows:
P
DCR = IOUT
2 x DCR
From that, the loss in efficiency due to inductor
resistance can be calculated as follows:
100
PIV
IV
1LossEfficiency
DCROUTOUT
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.
The effect of MOSFET voltage drops and DCR losses in
conjunction with the maximum duty cycle combine to
limit maximum output voltage for a given input voltage.
The following graph shows this relationship based on the
typical resistive losses in the MIC33153:
V
OUTMAX
vs. V
IN
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
2.5 3 3.5 4 4.5 5 5.5
INPUT VOLTAGE (V )
OUTPUT V OL TAGE (V)
1.2A
800mA
400mA
100mA
HyperLight Load™ Mode
MIC33153 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 MIC33153 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
MIC33153 during light load currents by only switching
when it is needed. As the load current increases, the
MIC33153 goes into continuous conduction mode (CCM)
and switches at a frequency centered at 4MHz. The
equation to calculate the load when the MIC33153 goes
into continuous conduction mode may be approximated
by the following formula:
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
×
×−
>f2L
D)V(V
IOUTIN
LOAD
As shown in the above equation, the load at which
MIC33153 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). For example, if VIN = 3.6V, VOUT=1.8V,
D=0.5, f=4MHz and the internal inductance of MIC33153
is 0.47H, then the device will enter HyperLight Load™
mode or PWM mode at approximately 200mA.
Micrel Inc. MIC33153
September 2010 13 M9999-092910-A
As can be seen in the diagram, total thermal resistance
RθJA = RθJC + RθCA. Hence this can also be written:
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 of relationship between thermal
resistance, power dissipation and temperature which is
analogous to an electrical circuit:
(
)
AMBJADISSJ TRPT +
×
=
Since effectively all of the power loss in the converter is
dissipated within the MIC33153 package, PDISS can be
calculated thus:
1)
1
( PP OUTDISS −×=
Where:
η
= Efficiency taken from efficiency curves
RθJC and RθJA are found in the operating ratings section
of the datasheet.
From this simple circuit, one can calculate VX if one
knows ISOURCE, VZ and the resistor values, RXY and RYZ
using the equation: Example:
A MIC33153 is intended to drive a 1A load at 1.8V and is
placed on a printed circuit board which has a ground
plane 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 50ºC.
()
ZYZXYSOURCEX VRRIV ++×=
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 ºC/W) and voltage sources
with temperature (in ºC):
Summary of variables:
IOUT = 1A
VOUT = 1.8V
VIN = 3V to 4.2V
TAMB = 50ºC
RθJA = 55ºC/W from Datasheet
η
@ 1A = 80% (worst case with VIN=4.2V from the
Typical Characteristics Efficiency vs. Load graphs)
1)
0.80
1
(11.8PDISS −×⋅= = 0.45W
The worst case switch and inductor resistance will
increase at higher temperatures, so a margin of 20% can
be added to account for this:
Now replacing the variables in the equation for VX, one
can find the junction temperature (TJ) from power
dissipation, ambient temperature and the known thermal
resistance of the PCB (RθCA) and the package (RθJC):
PDISS = 0.45 x 1.2 = .54W
()
AMBCAJCDISSJ TRRPT ++×=
Therefore:
TJ = 0.54W x (55 ºC/W) + 50ºC
TJ = 79.7ºC
This is well below the maximum 125ºC.
Micrel Inc. MIC33153
September 2010 14 M9999-092910-A
Typical Application Circuit (Fixed Out p ut)
Bill of Materials
Item Part Number Manufacturer Description Qty.
C1608X5R0J475K TDK(1)
C1, C2 GRM188R60J475KE19D Murata(2) Ceramic Capacitor, 4.7µF, 6.3V, X5R, Size 0603 2
C3 C1608NPO0J471K TDK(1) Ceramic Capacitor, 470pF, 6.3V, NPO, Size 0603 1
R3, R4 CRCW06031002FKEA Vishay(3) Resistor, 10k, Size 0603 2
U1 MIC33153-xYHJ Micrel, Inc.(4) 4MHz 1.2A Buck Regulator with HyperLight Load™ Mode
and Fixed Output Voltage 1
Notes:
1. TDK: www.tdk.com.
2. Murata: www.murata.com.
3. Vishay: www.vishay.com.
4. Micrel, Inc.: www.micrel.com.
Micrel Inc. MIC33153
September 2010 15 M9999-092910-A
Typical Application Circuit (Adjustable Output)
Bill of Materials
Item Part Number Manufacturer Description Qty.
C1608X5R0J475K TDK(1)
C1, C2 GRM188R60J475KE19D Murata(2) Ceramic Capacitor, 4.7µF, 6.3V, X5R, Size 0603 2
C3 C1608NPO0J471K TDK(1) Ceramic Capacitor, 470pF, 6.3V, NPO, Size 0603 1
C4 − − Not Fitted (NF) 0
R1 CRCW06033013FKEA Vishay(3) Resistor, 301k, Size 0603 1
R2 CRCW06031583FKEA Vishay(3) Resistor, 158k, Size 0603 1
R3, R4 CRCW06031002FKEA Vishay(3) Resistor, 10k, Size 0603 2
U1 MIC33153-YHJ Micrel, Inc.(4) 4MHz 1.2A Buck Regulator with HyperLight Load™ Mode
and Adjustable Output Voltage 1
1. TDK: www.tdk.com.
2. Murata : www.murata.com.
3. Vishay: www.vishay.com.
4. Micrel, Inc.: www.micrel.com.
Micrel Inc. MIC33153
September 2010 16 M9999-092910-A
PCB Layout Recommendations
Top Layer
Bottom Layer
Micrel Inc. MIC33153
September 2010 17 M9999-092910-A
Package Information
14-Pin 3.0mm x 3.5mm MLF® (HJ)
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