Datasheet

MIC23254
4MHz Dual 400mA Synchronous Buck
Regulator with Low Input Voltage and
HyperLight Load™
General Description
Features
The MIC23254 is a low-input voltage, high-efficiency 4MHz
• Low input voltage range: 2.5V to 5.5V
dual 400mA synchronous buck regulator with HyperLight
• Dual output current 400mA/400mA
Load™ mode. HyperLight Load™ provides very-high
• Up to 94% peak efficiency and 85% efficiency at 1mA
efficiency at light loads and ultra-fast transient response
• 33µA dual quiescent current
which is perfectly suited for supplying processor core
• 1µH inductor with a 4.7µF capacitor
voltages. An additional benefit of this proprietary
• 4MHz in PWM operation
architecture is very-low output ripple voltage throughout
the entire load range with the use of small output
• Ultra-fast transient response
capacitors. MIC23254 operates from an input voltage
• Low voltage output ripple
down to 2.5V for low battery states. The MIC23254 has a
• 20mVpp in HyperLight Load™ mode
®
tiny 2mm x 2mm Thin MLF package that saves precious
• 3mV output voltage ripple in full PWM mode
board space by requiring only 6 additional external
• 0.01µA shutdown current
components to drive both outputs up to 400mA each.
• Fixed output:10-pin 2mm x 2mm Thin MLF®
The device is designed for use with a 1µH inductor and a
• –40°C to +125°C junction temperature range
4.7µF output capacitor that enables a sub-1mm height.
The MIC23254 has a very-low quiescent current of 33µA
with both outputs enabled and can achieve over 85%
Applications
efficiency at 1mA. At higher loads the MIC23254 provides a
• Mobile handsets
constant switching frequency around 4MHz while providing
• Portable media players
peak efficiencies over 90%.
• Portable navigation devices (GPS)
The MIC23254 fixed output voltage option is available in a
• WiFi/WiMax/WiBro modules
10-pin 2mm x 2mm Thin MLF®. The MIC23254 is designed
• Digital cameras
to operate over the junction operating range from –40°C to
• Wireless LAN cards
+125°C.
• USB Powered Devices
Data sheets and support documentation can be found on
Micrel’s web site at: www.micrel.com.
____________________________________________________________________________________________________________
Typical Application
Efficiency
VOUT = 1.8V
100
VIN = 3.0V
90
EFFICIENCY (%)
80
70
60
VIN = 3.6V
VIN = 2.7V
50
VIN = 4.2V
40
30
20
L = 1µH
COUT = 4.7µF
10
0
1
10
100
1000
LOAD (mA)
HyperLight Load is a trademark of Micrel, Inc.
MLF and MicroLeadFrame are registered trademarks of Amkor Technology, Inc.
Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
May 2010
M9999-052510
Micrel, Inc.
MIC23254
Ordering Information
Part Number
Marking
Code
Nominal
Output
Voltage 1
Nominal
Output
Voltage 2
Junction
Temperature
Range
Package
Lead
Finish
MIC23254-GCYMT
GCW
1V
1.8V
–40° to +125°C
10-Pin 2mm x 2mm Thin MLF®
Pb-Free
Notes:
1. Thin MLF® is GREEN RoHS compliant package. Lead finish is NiPdAu. Mold compound is Halogen Free.
Pin Configuration
SNS1
1
10 SNS2
EN1
2
9
EN2
AGND
3
8
AVIN
SW1
4
7
SW2
PGND
5
6
VIN
®
10-Pin 2mm x 2mm Thin MLF (MT) Fixed Output
(Top View)
Pin Description
Pin Number
(Fixed)
Pin Name
1
SNS1
2
EN1
3
AGND
4
SW1
5
PGND
6
VIN
Pin Function
Sense 1 (Input): Connect to VOUT1 as close to output capacitor as possible to sense output 1
voltage.
Enable 1 (Input): Logic low will shut down output 1. Logic high powers up output 1. Do not leave
unconnected.
Analog Ground. Must be connected externally to PGND.
Switch Node 1 (Output): Internal power MOSFET output.
Power Ground.
Supply Voltage (Power Input): Requires close bypass capacitor to PGND.
7
SW2
Switch Node 2 (Output): Internal power MOSFET output.
8
AVIN
Supply Voltage (Power Input): Analog control circuitry. Connect to VIN.
9
EN2
Enable 2 (Input): Logic low will shut down output 2. Logic high powers up output 2. Do not leave
unconnected.
10
SNS2
May 2010
Sense 2 (Input): Connect to VOUT2 as close to output capacitor as possible to sense output 2
voltage.
2
M9999-052510
Micrel, Inc.
MIC23254
Absolute Maximum Ratings(1)
Operating Ratings(2)
Supply Voltage (VIN) ........................................ −0.3V to +6V
Output Switch Voltage (VSW) ............................. −0.3V to 6V
Sense Input Voltage (VSNS1, VSNS2) ................... −0.3V to VIN
Logic Input Voltage (VEN1, VEN2) ........................ −0.3V to VIN
Storage Temperature Range (Ts)..............–65°C to +150°C
ESD Rating(3) ................................................. ESD Sensitive
Supply Voltage (VIN)......................................... 2.5V to 5.5V
Sense Input Voltage (VSNS1, VSNS2) ........................ 0V to VIN
Logic Input Voltage (VEN1, VEN2) ............................. 0V to VIN
Junction Temperature (TJ) ..................–40°C ≤ TJ ≤ +125°C
Thermal Resistance
2mm x 2mm Thin MLF-10 (θJA) .........................70°C/W
Electrical Characteristics(4)
TA = 25°C with VIN = VEN1 = VEN2 = 3.6V; L = 1µH; COUT = 4.7µF; IOUT = 20mA; only one channel power is enabled, unless
otherwise specified. Bold values indicate –40°C< TJ < +125°C.
Parameter
Condition
Min.
Typ.
Max.
Units
Under-Voltage Lockout Threshold
UVLO Hysteresis
(Turn-On)
2.3
2.4
60
2.485
V
mV
33
50
µA
Shutdown Current
VOUT1, 2 (Both Enabled), IOUT1, 2 = 0mA , VSNS1,2 >1.2 ×
VOUT1, 2 Nominal
VEN1, 2 = 0V; VIN = 5.5V
Output Voltage Accuracy
VIN = 3.6V, ILOAD = 20mA
–2.5
Current Limit in PWM Mode
SNS = 0.9 × VOUT NOM
0.410
Output Voltage Line Regulation
VIN = 3.6V to 5.5V, ILOAD = 20mA
0.4
%/V
Output Voltage Load Regulation
20mA < ILOAD < 400mA, VIN = 3.6V
0.5
%
ISW = 100mA PMOS
ISW = −100mA NMOS
ILOAD = 120mA
VOUT = 90%
0.6
0.8
Ω
Quiescent Current
PWM Switch ON-Resistance
Frequency
Soft-Start Time
Enable Threshold
Enable Input Current
Over-Temperature Shutdown
Over-Temperature Shutdown Hysteresis
0.01
0.5
0.62
4
260
0.9
0.1
160
20
4
µA
+2.5
%
1
A
1.2
2
MHz
µs
V
µA
°C
°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: 1.5kΩ in series with 100pF.
4. Specification for packaged product only.
May 2010
3
M9999-052510
Micrel, Inc.
MIC23254
Typical Characteristics
Switching Frequency
vs. Output Current
Quiescent Current
vs. Input Voltage
10.00
10
45
40
35
30
25
20
15
10
L = 1µH
COUT = 4.7µF
5
0
2.5
3
3.5
4
4.5
5
L = 4.7µH
VIN = 2.5V
1.00
VIN = 3V
VIN = 5V
0.10
VIN = 4.2V
5.5
0.01
INPUT VOLTAGE (V)
0.1
L = 1µH
0.1
0.01
1
1
Output Voltage
vs. Input Voltage
1.88
1.86
1.84
VIN = 4.2V
1.82
1.8
1.78
1.76
VIN = 3.6V
VIN = 2.5V
1.74
1.72
TA = 25oC
20
40
60
80
0.1
VIN = 5V
VIN = 4.2V
1.82
1.8
1.78
VIN = 2.5V
1.74
L = 1µH
COUT = 4.7uF
IOUT = 20mA
1.72
1.7
-40
-20
0
20
40
60
80
TEMPERATURE (°C)
May 2010
100 120
ENABLE THRESHOLD (V)
1.88
VIN = 3.6V
1.78
1.76
1.74
1000
IOUT = 400mA
L = 1µH
COUT = 4.7µF
TA = 25°C
1.70
2.5
3
3.5
4
4.5
5
5.5
INPUT VOLTAGE (V)
Enable Threshold
vs. Input Voltage
1.2
1.9
1.76
100
1.80
Enable Threshold
vs. Temperature
Output Voltage
vs. Temperature
1.84
10
IOUT = 20mA
1.82
OUTPUT CURRENT (mA)
TEMPERATURE (°C)
1.86
1
IOUT = 200mA
1.84
1.72
1.7
100 120
1.86
1.05
1
ENon
ENABLE THRESHOLD (V)
0
1000
1.90
3
-20
100
OUTPUT CURRENT (mA)
OUTPUT VOLTAGE (V)
L = 1µH
COUT = 4.7µF
IOUT = 120mA
OUTPUT VOLTAGE (V)
4
-40
10
Output Voltage
vs. Output Current
1.9
4.5
3.5
L = 2.2µH
VIN = 3.6V
VOUT = 1.8V
COUT = 4.7µF
1.88
5
OUTPUT VOLTAGE (V)
1
LOAD CURRENT (A)
Frequency
vs. Temperature
FREQUENCY (MHz)
VOUT = 1.8V
L = 1µH
COUT = 4.7µF
VIN = 3.6V
0.01
0.001
4MHz
SWITCHING FREQUENCY (MHz)
SWITCHING FREQUENCY (MHz)
QUIESCENT CURRENT (µA)
50
Switching Frequency
vs. Output Current
0.8
ENoff
0.6
0.4
VIN = 3.6V
L = 1µH
COUT = 4.7µF
0.2
0
1
ENon
0.95
ENoff
0.9
0.85
TA = 25°C
L = 1µH
COUT = 4.7µF
0.8
-40
-20
0
20
40
60
80
TEMPERATURE (°C)
4
100
120
2.5
3
3.5
4
4.5
INPUT VOLTAGE (V)
5
5.5
M9999-052510
Micrel, Inc.
MIC23254
Typical Characteristics (Continued)
MOSFET RDSon
vs. Input Voltage
Start-Up Voltage
vs JunctionTemperature
0.9
1.00
0.8
MOSFET RESISTANCE (Ωs)
0.90
UVLOon
2.4
2.35
UVLOoff
2.3
2.25
2.2
-40
-20
0
20
40
60
80
100 120
N-CHANNEL
0.80
0.70
0.60
0.50
P-CHANNEL
0.40
0.30
0.20
TA = 25°C
0.10
2.5
3
Efficiency VOUT = 1V
V IN = 2.7V
3.5
4
4.5
V IN = 3V
70%
EFFICIENCY (%)
VIN = 4.2V
VIN = 3.6V
30%
20%
60
VIN = 3.6V
VIN = 2.7V
50
VIN = 4.2V
40
30
OUTPUT CURRENT (mA)
May 2010
1000
4.5
5
5.5
70
60
L = 0.47µH
50
40
L = 1.0µH
30
20
L = 1µH
COUT = 4.7µF
VIN = 3.6V
COUT = 4.7µF
10
0
1
100
4
80
70
0
0%
3.5
L = 1.5µH
90
10
L = 1µH
COUT = 4.7µF
3
100
20
10
TA = 25°C
L = 1µH
COUT = 4.7µF
Efficiency VOUT = 1.8V
(With Various Inductors)
80
60%
1
0.2
INPUT VOLTAGE (V)
VIN = 3.0V
90
10%
0.3
2.5
5
100
40%
0.4
Efficiency
VOUT = 1.8V
80%
50%
0.5
INPUT VOLTAGE (V)
100%
90%
0.6
0
0.00
TEMPERTURE (° C)
0.7
0.1
EFFICIENCY (%)
INPUT VOLTAGE (V)
2.45
CURRENT LIMIT (A)
2.5
EFFICIENCY (%)
Current Limit
vs. Input Voltage
10
100
LOAD (mA)
5
1000
1
10
100
LOAD (mA)
M9999-052510
1000
Micrel, Inc.
MIC23254
Functional Characteristics
May 2010
6
M9999-052510
Micrel, Inc.
MIC23254
Functional Characteristics (Continued)
May 2010
7
M9999-052510
Micrel, Inc.
MIC23254
Functional Characteristics (Continued)
May 2010
8
M9999-052510
Micrel, Inc.
MIC23254
Functional Diagram
MIC23254 Simplified Fixed Output Block Diagram
May 2010
9
M9999-052510
Micrel, Inc.
MIC23254
Functional Description
VIN
The VIN provides power to the internal MOSFETs for the
switch mode regulator along with the current limit sensing.
The VIN operating range is 2.5V to 5.5V so an input
capacitor with a minimum of 6.3V voltage rating is
recommended. Due to the high switching speed, a
minimum of 2.2µF bypass capacitor placed close to VIN
and the power ground (PGND) pin is required. Based upon
size, performance and cost, a TDK C1608X5R0J475K,
size 0603, 4.7µF ceramic capacitor is highly recommended
for
most
applications.
Refer
to
the
layout
recommendations for details.
SNS1/SNS2
The SNS pin (SNS1 or SNS2) is connected to the output
of the device to provide feedback to the control circuitry. A
minimum of 2.2µF bypass capacitor should be connected
in shunt with each output. Based upon size, performance
and cost, a TDK C1608X5R0J475K, size 0603, 4.7µF
ceramic capacitor is highly recommended for most
applications. In order to reduce parasitic inductance, it is
good practice to place the output bypass capacitor as
close to the inductor as possible. The SNS connection
should be placed close to the output bypass capacitor.
Refer to the layout recommendations for more details.
AVIN
The analog VIN (AVIN) provides power to the analog
supply circuitry. AVIN and VIN must be tied together.
Careful layout should be considered to ensure high
frequency switching noise caused by VIN is reduced
before reaching AVIN. A 0.01µF bypass capacitor placed
as close to AVIN as possible is recommended. See layout
recommendations for details.
PGND
The power ground (PGND) is the ground path for the high
current in PWM mode. The current loop for the power
ground should be as small as possible and separate from
the Analog ground (AGND) loop. Refer to the layout
recommendations for more details.
EN1/EN2
The enable pins (EN1 and EN2) control the on and off
states of outputs 1 and 2, respectively. A logic high signal
on the enable pin activates the output voltage of the
device. A logic low signal on each enable pin deactivates
the output. MIC23254 features built-in soft-start circuitry
that reduces in-rush current and prevents the output
voltage from overshooting at start up.
AGND
The signal ground (AGND) is the ground path for the
biasing and control circuitry. The current loop for the signal
ground should be separate from the Power Ground
(PGND) loop. Refer to the layout recommendations for
more details.
SW1/SW2
The switching pin (SW1 or SW2) connects directly to one
end of the inductor (L1 or L2) and provides the current
path during switching cycles. The other end of the inductor
is connected to the load and SNS pin. Due to the high
speed switching on this pin, the switch node should be
routed away from sensitive nodes.
May 2010
10
M9999-052510
Micrel, Inc.
Applications Information
The MIC23254 is designed for high performance with a
small solution size. With a dual 400mA output inside a tiny
2mm x 2mm Thin MLF® package and requiring only six
external components, the MIC23254 meets today’s
miniature portable electronic device needs. While small
solution size is one of its advantages, the MIC23254 is big
in performance. Using the HyperLight Load™ switching
scheme, the MIC23254 is able to maintain high efficiency
throughout the entire load range while providing ultra-fast
load transient response. Even with all the given benefits,
the MIC23254 can be as easy to use as linear regulators.
The following sections provide an over view of
implementing MIC23254 into related applications
Input Capacitor
A minimum of 2.2µF ceramic capacitor should be placed
close to the VIN pin and PGND pin for bypassing. A TDK
C1608X5R0J475K, size 0603, 4.7µF ceramic capacitor is
recommended based upon performance, size and cost. A
X5R or X7R temperature rating is recommended for the
input capacitor. Y5V temperature rating capacitors, aside
from losing most of their capacitance over temperature,
can also become resistive at high frequencies. This
reduces their ability to filter out high-frequency noise.
Output Capacitor
The MIC23254 was designed for use with a 2.2µF or
greater ceramic output capacitor. Increasing the output
capacitance will lower output ripple and improve load
transient response but could increase solution size or cost.
A low equivalent series resistance (ESR) ceramic output
capacitor such as the TDK C1608X5R0J475K, size 0603,
4.7µF ceramic capacitor is recommended based upon
performance, size and cost. Either the X7R or X5R
temperature rating capacitors are recommended. The Y5V
and Z5U temperature rating capacitors, aside from the
undesirable effect of their wide variation in capacitance
over temperature, become resistive at high frequencies.
Inductor Selection
Inductor selection will be determined by the following (not
necessarily in the order of importance):
1.
2.
3.
4.
Inductance
Rated current value
Size requirements
DC resistance (DCR)
May 2010
MIC23254
The MIC23254 was designed for use with an inductance
range from 0.47µH to 4.7µH. Typically, a 1µH inductor is
recommended for a balance of transient response,
efficiency and output ripple. For faster transient response a
0.47µH inductor may be used. For lower output ripple, a
4.7µH is recommended.
Maximum current ratings of the inductor are generally
given in two methods; permissible DC current and
saturation current. Permissible DC current can be rated
either for a 40°C temperature rise or a 10% to 20% loss in
inductance. Ensure the inductor selected can handle the
maximum operating current. When saturation current is
specified, make sure that there is enough margin so that
the peak current of the inductor does not cause it to
saturate. Peak current can be calculated as follows:
⎡
⎛ 1 - VOUT / VIN ⎞⎤
IPEAK = ⎢IOUT + VOUT ⎜
⎟⎥
⎝ 2 × f × L ⎠⎦
⎣
As shown by the previous calculation, the peak inductor
current is inversely proportional to the switching frequency
and the inductance; the lower the switching frequency or
the inductance the higher the peak current. As input
voltage increases the peak current also increases.
The size of the inductor depends on the requirements of
the application. Refer to the Application Circuit and Bill of
Material for details.
DC resistance (DCR) is also important. While DCR is
inversely proportional to size, DCR can represent a
significant efficiency loss. Refer to the Efficiency
Considerations.
Compensation
The MIC23254 is designed to be stable with a 0.47µH to
4.7µH inductor with a minimum of 2.2µF ceramic (X5R)
output capacitor.
Efficiency Considerations
Efficiency is defined as the amount of useful output power,
divided by the amount of power supplied:
⎡ ⎛
⎞⎤
VOUT × IOUT
⎟⎟⎥ × 100
Efficiency Loss = ⎢1 - ⎜⎜
⎣ ⎝ VOUT × IOUT + L_PD ⎠⎦
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.
11
M9999-052510
Micrel, Inc.
MIC23254
There are two types of losses in switching converters; DC
losses and switching losses. DC losses are simply the
power dissipation of I2R. Power is dissipated in the high
side switch during the on cycle. Power loss is equal to the
high-side MOSFET RDSON multiplied by the Switch Current
squared. During the off cycle, the low side N-channel
MOSFET conducts, also dissipating power. Device
operating current also reduces efficiency. The product of
the quiescent (operating) current and the supply voltage is
another DC loss. The current required driving the gates on
and off at a constant 4MHz frequency and the switching
transitions make up the switching losses.
Efficiency
VOUT = 1.8V
100
VIN = 3.0V
90
EFFICIENCY (%)
80
70
60
VIN = 3.6V
VIN = 2.7V
50
VIN = 4.2V
40
30
20
L = 1µH
COUT = 4.7µF
10
0
1
10
100
1000
LOAD (mA)
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 MIC23254 is able to
maintain high efficiency at low output currents.
Over 100mA, efficiency loss is dominated by MOSFET
RDSON and inductor losses. Higher input supply voltages
will increase the Gate-to-Source threshold on the internal
MOSFETs, thereby reducing the internal RDSON. This
improves efficiency by reducing DC losses in the device.
All but the inductor losses are inherent to the device. In
which case, inductor selection becomes increasingly
critical in efficiency calculations. As the inductors are
reduced in size, the DC resistance (DCR) can become
quite significant. The DCR losses can be calculated as
follows:
From that, the loss in efficiency due to inductor resistance
can be calculated as follows:
⎡ ⎛
⎞⎤
VOUT × IOUT
⎟⎟⎥ × 100
Efficiency Loss = ⎢1 - ⎜⎜
⎣ ⎝ VOUT × IOUT + L_PD ⎠⎦
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™
The MIC23254 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 minimumon-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 MIC23254 works in pulse
frequency modulation (PFM) to regulate the output. As the
output current increases, the off-time decreases, thus
providing more energy to the output. This switching
scheme improves the efficiency of MIC23254 during light
load currents by only switching when it is needed. As the
load current increases, the MIC23254 goes into
continuous conduction mode (CCM) and switches at a
frequency centered at 4MHz. The equation to calculate the
load when the MIC23254 goes into continuous conduction
mode may be approximated by the following formula:
⎛ (VIN - VOUT ) × D ⎞
ILOAD > ⎜
⎟
2L × f
⎠
⎝
DCR Loss = IOUT2 × DCR
May 2010
12
M9999-052510
Micrel, Inc.
MIC23254
As shown in the previous equation, the load at which
MIC23254 transitions from HyperLight Load™ mode to
PWM mode is a function of the input voltage (VIN), output
voltage (VOUT), duty cycle (D), inductance (L) and
frequency (f). This is illustrated in the graph below. Since
the inductance range of MIC23254 is from 0.47µH to
4.7µH, the device may then be tailored to enter HyperLight
Load™ mode or PWM mode at a specific load current by
selecting the appropriate inductance. For example, in the
graph below, when the inductance is 4.7µH the MIC23254
will transition into PWM mode at a load of approximately
5mA. Under the same condition, when the inductance is
1µH, the MIC23254 will transition into PWM mode at
approximately 70mA.
Switching Frequency
vs. Output Current
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):
10
L = 4.7µH
SWITCHING FREQUENCY (MHz)
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):
4MHz
1
TJ = PDISS ⋅ (Rθ JC + Rθ CA ) + TAMB
L = 1µH
0.1
L = 2.2µH
As can be seen in the diagram, total thermal resistance
RθJA = RθJC + RθCA. Hence this can also be written:
VIN = 3.6V
VOUT = 1.8V
COUT = 4.7µF
TJ = PDISS ⋅ (Rθ JA ) + TAMB
0.01
1
10
100
1000
OUTPUT CURRENT (mA)
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, ohms law
type relationship between thermal resistance, power
dissipation and temperature which are analogous to an
electrical circuit:
PDISS can be calculated thus:
1
PDISS = POUT ⋅ ( − 1)
η
Where η = Efficiency taken from efficiency curves
RθJC and RθJA are found in the operating ratings section of
the datasheet.
From this simple circuit we can calculate Vx if we know
Isource, Vz and the resistor values, Rxy and Ryz using the
equation:
Vx = Isource ⋅ (Rxy + Ryz) + Vz
May 2010
13
M9999-052510
Micrel, Inc.
MIC23254
Example:
The MIC23254 is intended to drive a 200mA load at 1.8V,
a 200mA load at 1.0V, 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.
Summary of variables:
IOUT1 = 0.2A, IOUT2 = 0.2A
VOUT1 = 1.0V, VOUT2 = 1.8V
VIN = 3V to 4.2V
Inductor DCR = 190mΩ
TAMB = 50ºC
PIND = 0.0076W
PDISS = 0.115 - 2*(0.0076) = 0.1W
Therefore:
TJ = 0.1W * (70 ºC/W) + 50ºC
TJ = 57ºC
This is well below the maximum 125ºC.
RθJA = 70ºC/W from Datasheet
η1 @ 200mA = 78%, η2 @ 200mA = 86%, (worst case
with VIN=4.2V from the Typical Characteristics Efficiency
vs. Load graphs)
PDISS = 1.0 ⋅ 0.2 ⋅ (
1
1
− 1) + 1.8 ⋅ 0.2 ⋅ (
− 1)
0.78
0.86
PDISS= 0.115W
Subtracting the power loss from the inductors:
PIND1 = PIND2 = Inductor DCR * IOUT2
PIND = 0.19*0.22
May 2010
14
M9999-052510
Micrel, Inc.
MIC23254
MIC23254 Typical Application Circuit
Bill of Materials
Item
Part Number
C1, C2, C3
C1608X5R0J475K
C4
VJ0603Y103KXXAT
R1, R2
CRCW06031002FKEA
LQM21PN1R0MC0D
L1, L2
(1)
TDK
Vishay(2)
Description
3
0.01µF Ceramic Capacitor, 25V, X7R, Size 0603
1
(2)
10kΩ, 1%, 1/16W, Size 0603
(3)
1µH, 0.8A, 190mΩ, L2mm x W1.25mm x H0.5mm
(3)
Vishay
Murata
Murata
1µH, 1A, 60mΩ, L3.2mm x W2.5mm x H2.0mm
LQM31PN1R0M00
Murata(3)
1µH, 1.2A, 120mΩ, L3.2mm x W1.6mm x H0.95mm
GLF251812T1R0M
MIPF2520D1R5
EPL2010-102
MIC23254-GCYMT
TDK
(1)
(3)
Murata
FDK(4)
Coilcraft(5)
Micrel, Inc.(6)
Qty
4.7µF Ceramic Capacitor, 6.3V, X5R, Size 0603
LQH32CN1R0M33
LQM31PNR47M00
U1
Manufacturer
1µH, 0.8A, 100mΩ, L2.5mm x W1.8mm x H1.35mm
Optional
2
0.47µH, 1.4A, 80mΩ, L3.2mm x W1.6mm x H0.85mm
1.5µH, 1.5A, 70mΩ, L2.5mm x W2mm x H1.0mm
1.0µH, 1.0A, 86mΩ, L2.0mm x W1.8mm x H1.0mm
Low-Voltage, 4MHz Dual 400mA Fixed-Output Buck
Regulator with HyperLight Load™ Mode
1
Notes:
1. TDK: www.tdk.com.
2. Vishay: www.vishay.com.
3. Murata: www.murata.com.
4. FDK: www.fdk.co.jp.
5. Coilcraft: www.coilcraft.com.
6. Micrel, Inc: www.micrel.com.
May 2010
15
M9999-052510
Micrel, Inc.
MIC23254
PCB Layout Recommendations
Top Layer
Bottom Layer
May 2010
16
M9999-052510
Micrel, Inc.
MIC23254
Package Information
®
10-Pin 2mm x 2mm Thin MLF (MT)
MICREL, INC. 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA
TEL +1 (408) 944-0800 FAX +1 (408) 474-1000 WEB http://www.micrel.com
The information furnished by Micrel in this data sheet is believed to be accurate and reliable. However, no responsibility is assumed by Micrel for its
use. Micrel reserves the right to change circuitry and specifications at any time without notification to the customer.
Micrel Products are not designed or authorized for use as components in life support appliances, devices or systems where malfunction of a product
can reasonably be expected to result in personal injury. Life support devices or systems are devices or systems that (a) are intended for surgical implant
into the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significant injury to the user. A
Purchaser’s use or sale of Micrel Products for use in life support appliances, devices or systems is a Purchaser’s own risk and Purchaser agrees to fully
indemnify Micrel for any damages resulting from such use or sale.
© 2010 Micrel, Incorporated.
May 2010
17
M9999-052510