MIC2203
High Efficiency 1MHz Synchronous
Buck Regulator
General Description
The Micrel MIC2203 is a high efficiency 1MHz PWM
synchronous buck switching regulator. The MIC2203
features low noise constant frequency PWM
operation with a low dynamic supply current of
<1mA. The low noise and efficient operation both
make the MIC2203 well suited for sensitive RF, and
audio power applications.
The MIC2203 operates from 2.3V to 5.5V input and
can supply over 300mA of output current with output
voltages down to 0.5V. Additionally, the MIC2203
can be synchronized to an external clock, or multiple
MIC2203s can easily be daisy-chained with the
SYNCLOCK feature.
The MIC2203 has a high loop bandwidth with
corresponding ultra fast transient response times.
This reduces the output capacitor size, and is very
useful when powering applications that require fast
dynamic response such as CPU cores and RF
circuitry in high performance cellular phones and
PDAs.
The MIC2203 is available in 10-pin MSOP and
3mm x 3mm MLFTM-10L package options with an
operating junction temperature range from 40C to
125C.
Features
Input voltage range: 2.3V to 5.5V
Output voltage adjustable down to 0.5V
300mA output current
Constant 1MHz PWM switching frequency
> 95% efficiency
< 1mA switching supply current
< 350A static quiescent current
< 1A shutdown current
All-ceramic capacitors
Easily synchronized to external clock
SYNCLOCK feature to daisy chain multiple
devices
Thermal shutdown and current limit protection
10 pin MSOP, and 3mm x 3mm MLF-10L package
options
40C to +125C junction temperature range
Applications
802.11 WLAN modules
MD players
MP3 players
_____________________________________________________________________
Typical Application
10nF
10H
1F
R2
3.83k
R1
10k
2.2F
SYNC_IN
SYNC_OUT
2.3V to 5.5V
1.8V
300mA
EN
MIC2203BMM
1
2
3
4
5
10
9
8
7
6
High Efficiency Buck Regulator
MicroLead Frame and MLF are trademarks of Amkor Technologies.
Micrel, Inc. 2180 Fortune Drive San Jose, CA 95131 USA tel +1 (408) 944-0800 fax +1 (408) 474-1000 http://www.micrel.com
December 2004
M9999-120604
(408) 955-1690
Micrel, Inc.
MIC2203
Ordering Information
Part Number
Standard Pb-Free
Output Voltage
Junction Temperature
Range
Package
MIC2203BMM MIC2203YMM
Adjustable
-40C to +125C
MSOP-10L
MIC2203BML MIC2203YML
Adjustable
-40C to +125C
3mm x 3mm MLF-10L
Pin Configuration
MSOP-10 (MM)
MLF-10 (ML)
Top View
Pin Description
Pin Number
Pin Name
Pin Function
1
SW
Switch (Output): Internal power MOSFET output switches.
2
VIN
Supply Voltage (Input): Requires a bypass capacitor to GND.
3 SYNC_IN
SYNC_IN for the MIC2203, Sync the main switching frequency to a external
clock. Should be tied to ground when not in use.
4
SYNC_OUT
SYNC_OUT a 50ns wide sync pulse to feed into SYNC_IN on MIC2203.
Can be left open or tied to ground when not used.
5 EN
A low level EN will power down the device, reducing the quiescent current to
under 1
A.
6 FB
Input to the error amplifier, connect to the external resistor divider network to set
the output voltage.
7 BIAS
Internal circuit bias supply, nominally 2.3V. Must be de-coupled to signal ground
and can have a minimum of external DC loading.
8,9,10 GND
Ground
EP
GND
Exposed backside pad, connect to Ground (MLF option only)
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Micrel, Inc.
MIC2203
Absolute Maximum Ratings
(1)
Supply Voltage (V
IN
) .............................................. 6V
Output Switch Voltage (V
SW
) ................................. 6V
Logic Input Voltage (V
EN
, V
SYNC_IN
) .............V
IN
to 3V
Power Dissipation ............................................Note 5
Storage Temperature (T
s
)............... 65C to +150C
ESD Rating
(3)
........................................................2kV
Operating Ratings
(2)
Supply Voltage (V
IN
)................................2.3V to 5.5V
Junction Temperature Range ......... 40C to +125C
Package Thermal Resistance
MSOP-10L
(
JA
)..................................... 115C/W
3mmX3mm
MLF-10L
(
JA
)....................... 60C/W
Electrical Characteristics
(4)
T
A
= 25C with V
IN
= V
EN
= 3.5V, unless otherwise specified. Bold values indicate 40C < T
J
< +125C
Parameter Condition
Min
Typ
Max
Units
Supply Voltage Range
2.3 5.5
V
V
FB
= 0.6V (not switching)
320
450
A
Quiescent Current
EN = 0V (shutdown)
0.01
1
A
No Load Supply Current
(switching)
870
A
MIC2203 [Adjustable]
Feedback Voltage
0.4875
0.5 0.5125
V
Output Voltage Line
Regulation
V
OUT
< 2V; V
IN
= 2.3V to 5.5V, I
LOAD
= 50mA
0.13
0.5
%
Output Voltage Load
Regulation
0mA < I
LOAD
< 300mA
0.2
0.5
%
Bias Regulator Output
Voltage
2.2
2.32
2.6
V
Maximum Duty Cycle
V
FB
0.4V
100 %
Current Limit
V
FB
= 0.4V
0.375
0.6 1.5
A
Switch ON-Resistance
I
SW
= 300mA V
FB
= 0.4V
I
SW
= -300mA V
FB
= 0.6V
1.5
1
2.2
1.6
Enable Input Current
0.01 2
A
Sync Frequency Range
0.8
1.25
MHz
SYNC_IN Threshold
0.7
1 1.7
V
Sync Minimum Pulse
Width
10
ns
SYNC_IN Input Current
1
A
Oscillator Frequency
0.8
1 1.2
MHz
Enable Threshold
0.5
0.7 1.3
V
Enable Hysteresis
20
mV
Over Temperature
Shutdown
Hysteresis
160
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.
5. Absolute maximum power dissipation is limited by maximum junction temperature where P
D(MAX)
= (T
J(MAX)
T
A
)
JA.
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M9999-120604
(408) 955-1690
Micrel, Inc.
MIC2203
Typical Characteristics
December 2004
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(408) 955-1690
Micrel, Inc.
MIC2203
Functional Diagram
Internal
Supply
Oscillator
Ramp
Generator
Driver
PWM
Comparator
MIC2203
Error
Amplifier
0.5V
FB
GND
SW
VIN
SYNC_OUT
C
IN
C
OUT
V
IN
V
OUT
SYNC_IN
BIAS
EN
R1
R2
Figure 1. MIC2203 Block Diagram
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Micrel, Inc.
MIC2203
Functional Description
V
IN
V
IN
provides power to the output and to the internal
bias supply. The supply voltage range is from 2.3V
to 5.5V. A minimum 1
F ceramic capacitor is
recommended for bypassing the input supply.
Enable
The enable pin provides a logic level control of the
output. In the off state, supply current of the device
is greatly reduced (typically <1
A). Also, in the off
state, the output drive is placed in a "tri-stated"
condition, where both the high side P-Channel
MOSFET and the low-side N-Channel are in an off
or non-conducting state. Do not drive the enable pin
above the supply voltage.
SYNC_IN
SYNC_IN pin enables the ability to change the
fundamental switching frequency. The SYNC_IN
frequency has a minimum frequency of 800KHz and
a maximum sync frequency of 1.2MHz. Careful
attention should be paid to not driving the SYNC_IN
pin greater than the supply voltage. Although this will
not damage the device, it can cause improper
operation.
SYNC_OUT
SYNC_OUT is an open collector output that
provides a signal equal to the internal oscillator
frequency. This creates the ability for multiple
MIC2203s to be connected together in a master-
slave configuration for frequency matching of the
converters. A typical 10k resistor is recommended
for the pull-up resistor.
Bias
The bias supply is an internal 2.3V linear regulator
that supplies the internal biasing voltage to the
MIC2203. A 10nF ceramic capacitor is required on
this pin for bypassing. Do not use the bias pin as a
supply. The bias pin was designed to supply internal
power only.
Feedback
The feedback pin provides the control path to control
the output. A resistor divider connecting the
feedback to the output is used to adjust the desired
output voltage. Refer to the feedback section in the
"Applications Information" for more detail.
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Micrel, Inc.
MIC2203
Application Information
Input Capacitor
A minimum 1
F ceramic capacitor is recommended
on the V
IN
pin for bypassing. X5R or X7R dielectrics
are recommended for the input capacitor. Y5V
dielectrics, aside from losing most of their
capacitance over temperature, also become resis-
tive at high frequencies. This reduces their ability to
filter out high frequency noise.
Output Capacitor
The MIC2203 was designed specifically for the use
of a 2.2
F ceramic output capacitor. Since the
MIC2203 is voltage mode regulator, the control loop
relies on the inductor and output capacitor for
compensation. For this reason, do not use
excessively large output capacitors. The output
capacitor requires either an X7R or X5R dielectric.
Y5V and Z5U dielectric capacitors, aside from the
undesirable effect of their wide variation in
capacitance over temperature, become resistive at
high frequencies. Using Y5V or Z5U capacitors will
cause instability in the MIC2203.
Total output capacitance should not exceed 3
F.
Inductor Selection
Inductor selection will be determined by the following
(not necessarily in the order of importance):
Inductance
Rated current value
Size requirements
DC resistance (DCR)
The MIC2203 is designed for use with a 10
H
inductor.
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 40C temperature
rise or a 10% 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 that the peak current will not
saturate the inductor.
The size requirements refer to the area and height
requirements that are necessary to fit a particular
design. Please refer to the inductor dimensions on
their datasheet.
DC resistance is also important. While DCR is
inversely proportional to size, DCR can represent a
significant efficiency loss. Refer to the "Efficiency
Considerations" below for a more detailed
description.
Bias Capacitor
A small 10nF ceramic capacitor is required to
bypass the bias pin. The use of low ESR ceramics
provides improved filtering for the bias supply.
Efficiency Considerations
Efficiency is defined as the amount of useful output
power, divided by the amount of power consumed.
Efficiency%
=
V
OUT
I
OUT
V
IN
I
IN
100
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 drawn from a battery increases the device's
operating time, which is critical in hand held devices.
There are two loss terms in switching converters: DC
losses and switching losses. DC losses are simply
the power dissipation of I
2
R. Power is dissipated in
the high side switch during the on cycle. Power loss
is equal to the high side MOSFET R
DS(ON)
multiplied
by the (Switch Current)
2
. 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 to drive the gates on
and off at a constant 1MHz frequency and the
switching transitions make up the switching losses.
Figure 2 shows an efficiency curve. The non-shaded
portion, from 0mA to 100mA, efficiency losses are
dominated by quiescent current losses, gate drive
and transition losses. In this case, lower supply
voltages yield greater efficiency in that they require
less current to drive the MOSFETs and have
reduced input power consumption.
Figure 2. Efficiency Curve
The shaded region, 100mA to 300mA, efficiency
loss is dominated by MOSFET R
DS(ON)
and inductor
DC losses. Higher input supply voltages will increase
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Micrel, Inc.
MIC2203
the Gate-to-Source threshold on the internal
MOSFETs, reducing the internal R
DS(ON)
. 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
L
= I
OUT
2
DCR
From that, the loss in efficiency due to inductor
resistance can be calculated as follows:
Efficiency Loss = -1
V
OUT
I
OUT
V
OUT
I
OUT
P
L
100
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.
Compensation
The MIC2203 is an internally compensated, voltage
mode buck regulator. Voltage mode is achieved by
creating an internal 1MHz ramp signal and using the
output of the error amplifier to pulse width modulate
the switch node, maintaining output voltage
regulation. With a typical gain bandwidth of 100kHz,
the MIC2203 is capable of extremely fast transient
responses.
The MIC2203 is designed to be stable with a 10
H
inductor and a 2.2
F ceramic (X5R) output
capacitor.
Feedback
The MIC2203 provides a feedback pin to adjust the
output voltage to the desired level. This pin connects
internally to an error amplifier. The error amplifier
then compares the voltage at the feedback to the
internal 0.5V reference voltage and adjusts the
output voltage to maintain regulation. To calculate
the resistor divider network for the desired output is
as follows:
R2
=
R1
V
OUT
V
REF
-1
Where V
REF
is 0.5V and V
OUT
is the desired output
voltage. A 10k or lower resistor value from the
output to the feedback is recommended. Larger
resistor values require an additional capacitor (feed-
forward) from the output to the feedback. The large
high side resistor value and the parasitic
capacitance on the feedback pin (~10pF) can cause
an additional pole in the loop. The additional pole
can create a phase loss at high frequency. This
phase loss degrades transient response by reducing
phase margin. Adding feed-forward capacitance
negates the parasitic capacitive effects of the
feedback pin.
Also, large feedback resistor values increase the
impedance, making the feedback node more
susceptible to noise pick-up. A feed-forward
capacitor would also reduce noise pick-up by
providing a low impedance path to the output.
PWM Operation
The MIC2203 is a pulse width modulation (PWM)
regulator. By controlling the ratio of on-to-off time, or
duty cycle, a regulated DC output voltage is
achieved. As load or supply voltage changes, so
does the duty cycle to maintain a constant output
voltage. In cases where the input supply runs into a
dropout condition, the MIC2203 will run at 100%
duty cycle.
The MIC2203 provides constant switching at 1MHz
with synchronous internal MOSFETs. The internal
MOSFETs include a high-side P-Channel MOSFET
from the input supply to the switch pin and an N-
Channel MOSFET from the switch pin-to-ground.
Since the low-side N-Channel MOSFET provides the
current during the off cycle, a free wheeling Schottky
diode from the switch node to ground is not required.
PWM control provides fixed frequency operation. By
maintaining a constant switching frequency,
predictable fundamental and harmonic frequencies
are achieved. Other methods of regulation, such as
burst and skip modes, have frequency spectrums
that change with load that can interfere with
sensitive communication equipment.
Synchronization
SYNC_IN allows the user to change the frequency
from 1MHz up to 1.25MHz or down to 800KHz. This
allows the ability to control the fundamental
frequency and all the resultant harmonics.
Maintaining a predictable frequency creates the
ability to either shift the harmonics away from
sensitive carrier and IF frequency bands or to
accurately filter out specific harmonic frequencies.
The SYNC_OUT function pin allows for the ability to
be able to sync up multiple MIC2203s in a "daisy-
chain", connecting SYNC_OUT to SYNC_IN of the
other MIC2203. Synchronizing multiple MIC2203s
benefits much in the same way as syncing up one
MIC2203. All regulators will run at the same funda-
mental frequency, resulting in matched harmonic
frequencies, simplifying design for sensitive
communication equipment.
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Micrel, Inc.
MIC2203
Figure 1. Master-Slave Operation
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Micrel, Inc.
MIC2203
MIC2203 with 10
H Inductor and 2.2F Output Capacitor
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Micrel, Inc.
MIC2203
December 2004
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MIC2203
MIC2203BMM Evaluation Board Schematic
Figure 2. MIC2203BMM Evaluation Board Schematic
Bill of Materials
Item Part
Number
Manufacturer Description
06036D105MAT
AVX 1
F Ceramic Capacitor X5R, 6.3V, Size 0603
C1
GRM185R60J105KE21D
Murata
1
F Ceramic Capacitor X5R, 6.3V, Size 0603
0201ZD103MAT2
AVX
10nF Ceramic Capacitor 6.3V, Size 0201
C2
GRM033R10J103KA01D
Murata
10nF Ceramic Capacitor 6.3V, Size 0202
06036D225MAT
AVX
2.2
F Ceramic Capacitor X5R, 6.3V, Size 0603
C3
GRM185R60J22SKE21D
Murata
2.2
F Ceramic Capacitor X5R, 6.3V, Size 0603
LQH32CN100M
Murata
10
H Inductor
L1
CDRH2D14-10
Sumida
10
H Inductor
R1
CRCW04021002F
Vishay-Dale
10k
1%, Size 0402
R2
CRCW04021781F
CRCW04022491F
CRCW04023831F
CRCW04024991F
CRCW04027151F
CRCW04021002F
NA
Vishay-Dale
Vishay-Dale
Vishay-Dale
Vishay-Dale
Vishay-Dale
Vishay-Dale
1.78k
1%, Size 0402 For 3.3V
OUT
2.49k
1%, Size 0402 For 2.5V
OUT
3.83k
1%, Size 0402 For 1.8V
OUT
4.99k
1%, Size 0402 For 1.5V
OUT
7.15k
1%, Size 0402 For 1.2V
OUT
10k
1%, Size 0402 For 1V
OUT
Open For 0.5V
OUT
U1
MIC2203BMM
Micrel, Inc.
1MHz High Efficiency Synchronous Buck Regulator
Notes:
1.
AVX: www.avx.com
2. Murata:
www.murata.com
3.
Sumida: www.sumida.com
4. Vishay-Dale:
www.vishay.com
5.
Micrel, Inc: www.micrel.com
December 2004
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Micrel, Inc.
MIC2203
December 2004
13
M9999-120604
(408) 955-1690
Package Information
10-Pin MSOP (MM)
10-Pin MLFTM (ML)
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.
2004 Micrel, Incorporated.
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