April 2005 1 M9999-042205
MIC2204 Micrel, Inc.
Typical Application
MIC2204
High-Efficiency 2MHz Synchronous Buck Converter
General Description
The Micrel MIC2204 is a high-efficiency, 2MHz PWM syn-
chronous buck switching regulator. Power conversion effi-
ciency of above 95% is easily obtainable over a wide range
of applications. A proprietary internal compensation tech-
nique ensures stability with the smallest possible inductor
and ceramic output capacitor.
The MIC2204 operates from 2.3V to 5.5V input and features
internal power MOSFETs that can supply over 600mA of
output current with output voltages down to 1V. The MIC2204
implements a constant 2MHz pulse-width-modulation (PWM)
control scheme which reduces spurious noise in sensitive RF
and communication applications. Additionally, the MIC2204
can be synchronized to an external clock, or multiple MIC2204s
can easily be daisy-chained with the SYNCLOCK feature.
The MIC2204 has a high bandwidth loop (typ. 200kHz) which
allows ultra-fast transient response times. This is very useful
when powering applications that require fast dynamic re-
sponses, such as the CPU cores and RF circuitry in high-
performance cellular phones and PDAs.
The MIC2204 is available in 10-pin MSOP and 3mm × 3mm
MLF™-10L package options with an operating junction tem-
perature range from –40°C to 125°C .
Features
•Input voltage range: 2.3V to 5.5V
•Output down to 1V/ 600mA
•2MHz PWM operation
•Ultra-fast transient response (typical 200kHz GBW)
•Internal compensation
•All ceramic capacitors
•>95% efficiency
•Fully integrated MOSFET switches
•Easily synchronized to external clock
•SYNCLOCK feature to daisy-chain multiple 2204s
•<340µA quiescent current
•Logic controlled micropower shutdown
•Thermal shutdown and current limit protection
•10-pin MSOP and 3mm×3mm MLF™-10L
•–40°C to +125°C junction temperature range
Applications
•High-efficiency portable power
•Cellular phones
•PDAs
•802.11 WLAN power supplies
•RF power supplies
•Li Ion battery powered applications
10nF
4.7µH3.3V
500mA
2.3V to 6V
4.7µF
EN 65
1
SYNC_IN
SYNC_OUT
10
9
8
7
2
3
4
MIC2204BMM
Adjustable Output Synchronous Buck Converter
Micrel, Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
MLF and MicroLeadFrame are trademarks of Amkor Technology, Inc.
50
55
60
65
70
75
80
85
90
95
100
0100 200 300 400 500
EFFICIENCY (%)
OUTPUT CURRENT (mA)
Efficiency
vs. Output Current
3.6V
IN
4.2V
IN
3.3V
OUT
5V
IN
MIC2204 Micrel, Inc.
M9999-042205 2April 2005
Ordering Information
Part Number Voltage Junction Temp. Range Package Lead Finish
MIC2204BMM Adjustable –40°C to +125°C10-pin MSOP Standard
MIC2204YMM Adjustable –40°C to +125°C10-pin MSOP Lead-Free
MIC2204BML Adjustable –40°C to +125°C10-pin MLF™ Standard
MIC2204YML Adjustable –40°C to +125°C10-pin MLF™ Lead-Free
EN FB65
1SW
VIN
SYNC_IN
SYNC_OUT
10 GND
GND
GND
BIAS
9
8
7
2
3
4
MSOP-10 (MM)
Pin Configuration
Pin Description
Pin Number Pin Name Pin Function
1SWSwitch (Output): Internal power MOSFET output switches.
2VIN Supply Voltage (Input): Requires bypass capacitor to GND.
3SYNC_IN SYNC_IN for the MIC2204: Sync the main switching frequency to an
external clock. Tie pin to ground if not using this function. Tying SYNC_IN
high reduces the switching frequency to 1.6MHz (See “Applications Informa-
tion” section).
4SYNC_OUT SYNC_OUT an open collector output to feed into SYNC_IN. Float or ground
the SYNC_OUT pin if not using sync out function.
5ENA low level EN will power down the device, reducing the quiescent current to
under 15µA (typ. 6.5µA).
6FBInput to the error amplifier, connect to the external resistor divider network to
set the output voltage.
7BIAS Internal circuit bias supply, nominally 2.3V. Must be de-coupled to signal
ground with a 0.01µF capacitor.
8, 9, 10 GND Ground.
SW
VIN
SYNC_IN
SYNC_OUT
GND
GND
GND
BIAS
1
2
3
4
10
9
8
7
56
EN FB
MLF-10 (ML)
April 2005 3 M9999-042205
MIC2204 Micrel, Inc.
Absolute Maximum Ratings(1)
Supply Voltage (VIN)....................................................... 6V
Output Switch Voltage (VSW).......................................... 6V
Logic Input Voltage (VEN, VSYNC_IN) ............... VIN to –0.3V
Power Dissipation(2)
Storage Temperature (TS) ....................... –65°C to +150°C
Operating Ratings(3)
Supply Voltage (VIN)................................... +2.3V to +5.5V
Junction Temperature (TJ) ................ –40°C ≤ TJ ≤ +125°C
Package Thermal Resistance
MSOP (θJA) ....................................................... 115°C/W
3mm×3mm MLF™-10L (θJA) ............................... 60°C/W
Electrical Characteristics(4)
TA = 25°C with VIN =VEN = 3.5V, unless otherwise noted. Bold values indicate –40°C < TJ < +125°C
Parameter Condition Min Typ Max Units
Supply Voltage Range 2.3 5.5 V
Current Limit VFB = 0.7V 0.6 1.2 2 A
Quiescent Current VFB = 1.1V 320 450 µA
EN = 0V 6.0 15 µA
Feedback Voltage 0.98 1.0 1.02 V
Output Voltage Line Regulation VOUT = 1V, VIN = 2.3V to 5.5V, ILOAD= 100mA 0.2 %
Output Voltage Load Regulation 0mA < ILOAD < 500mA 0.2 %
Maximum Duty Cycle VFB = 0.7V 100 %
Switch On-Resistance ISW = 300mA, VFB = 0.7V 0.72 Ω
ISW = –300mA, VFB = 1.1V 0.55 Ω
Oscillator Frequency 1.8 2 2.2 MHz
Sync Frequency Range 1.8 2.5 MHz
SYNC_IN Threshold 1.2 V
Sync Minimum Pulse Width 10 ns
SYNC_IN Input Current 12µA
Enable Threshold 0.52 0.72 0.96 V
Enable Hysteresis 20 mV
Enable Input Current 12µA
Overtemperature Shutdown 160 °C
Overtemperature Shutdown 20 °C
Hysteresis
Notes:
1. Exceeding the ABSOLUTE MAXIMUM RATINGS may damage device.
2. Absolute maximum power dissipation is limited by maximum junction temperature where PD(MAX) = (TJ(MAX)–TA) ÷ θJA.
3. The device is not guaranteed to function outside its operating rating.
4. Specification for packaged product only.
MIC2204 Micrel, Inc.
M9999-042205 4April 2005
Typical Characteristics
50
55
60
65
70
75
80
85
90
95
100
0
50
100
150
200
250
300
350
400
450
500
EFFI
C
IEN
C
Y (%)
OUTPUT CURRENT (mA)
Efficiency
vs. Output Current
3V
IN
3.5V
IN
4V
IN
1.8V
OUT
50
55
60
65
70
75
80
85
90
95
100
0100 200 300 400 500
EFFI
C
IEN
C
Y (%)
OUTPUT CURRENT (mA)
Efficiency
vs. Output Current
4.2V
IN
3.6V
IN
3.3V
IN
2.5V
OUT
50
55
60
65
70
75
80
85
90
95
100
0100 200 300 400 500
EFFICIENCY (%)
OUTPUT CURRENT (mA)
Efficiency
vs. Output Current
3.6V
IN
4.2V
IN
3.3V
OUT
5V
IN
0.99
0.9925
0.995
0.9975
1
1.0025
1.005
1.0075
1.01
00.10.20.3 0.4 0.5
OUTPUT VOLTAGE (V)
OUTPUT CURRENT
(
A
)
Output Voltage
vs. Output Current
0.99
0.995
1
1.005
1.01
-40 -20 0 20 40 60 80 100 120
OUTPUT VOLTAGE (V)
TEMPERATURE
(
°C
)
Output Voltage
vs. Temperature
0
0.5
1.0
1.5
2.0
2.5
0246
VBIAS
(V)
SUPPLY VOLTAGE (V)
V
BIAS
vs. Supply Voltage
V
FB
= 0V
2.302
2.304
2.306
2.308
2.31
2.312
2.314
2.316
2.318
2.32
-40 -20 0 20 40 60 80 100 120
BIAS SUPPLY (V)
TEMPERATURE
(
°C
)
Bias Supply
vs. Temperature
0
50
100
150
200
250
300
350
0123456
I
Q
(µA)
SUPPLY VOLTAGE
(
V
)
Quiescent Current
vs. Supply Voltage
V
FB
= 0V
298
300
302
304
306
308
310
312
314
316
318
-40 -20 0 20 40 60 80 100 120
I
Q
(µA)
TEMPERATURE
(
°C
)
Quiescent Current
vs. Temperature
V
IN
= 3.6V
1.60
1.70
1.80
1.90
2.00
2.10
2.20
2.30
2.40
-40 -20 0 20 40 60 80 100 120
FREQUENCY (MHz)
TEMPERATURE
(
°C
)
Frequency
vs. Temperature
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
2.3 2.8 3.3 3.8 4.3 4.8 5.3
ENABLE THRESHOLD (V)
SUPPLY VOLTAGE (V)
Enable Threshold
vs. Supply Voltage
Enable On
Enable Off
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
-40 -20 0 20 40 60 80 100 120
ENABLE THRESHOLD (V)
TEMPERATURE
(
°C
)
Enable Threshold
vs. Temperature
V
IN
= 3.6V
April 2005 5 M9999-042205
MIC2204 Micrel, Inc.
Functional Characteristics
Enable Transient
TIME (40µs/div.)
ENABLE
2V/div
V
OUT
500mV/div
V
IN
= 3.6V
V
OUT
= 1V
L = 4.7µH
C = 10µF
Disable Transient
TIME (40µs/div.)
ENABLE
2V/div
V
OUT
500mV/div
V
IN
= 3.6V
V
OUT
= 1V
L = 4.7µH
C = 10µF
I
OUT
= 500mA
Line Transient
TIME (200µs/div.)
V
IN
2V/div
V
OUT
20mV/div
V
OUT
= 1V
L = 4.7µH
C = 10µF
I
OUT
= 500mA
Load Transient
TIME (20µs/div.)
V
IN
200mA/div
V
OUT
50mV/div
V
IN
= 3.6V
V
OUT
= 2V
L = 4.7µH
C = 4.7µF
Switch Node Output Ripple
TIME (400ns/div.)
I
OUT
= 500mA
L = 4.7µHC = 10µF X5R
V
SW
2V/div
OUTPUT RIPPLE
10mV/div
V
IN
= 3.6V
V
OUT
= 1V
MIC2204 Micrel, Inc.
M9999-042205 6April 2005
Block Diagram
Error
Amplifier SW
C
OUT
V
OUT
FB
EN
BIAS
SYNC_IN
SYNC_OUT
PGND
PWM
Comparator
1.0V
MIC2204
Internal
Supply
Oscillator
Ramp
Generator
V
IN
C
IN
VIN
Driver
MIC2204 Block Diagram
April 2005 7 M9999-042205
MIC2204 Micrel, Inc.
Functional Description
VIN
VIN provides power to the output and to the internal bias
supply. The supply voltage range is from 2.3V to 5.5V. A
minimum 1µF ceramic 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 6.5µA). 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 enables the ability to change the fundamental
switching frequency. The SYNC_IN frequency has a mini-
mum frequency of 1.8MHz and a maximum sync frequency
of 2.5MHz.
Careful attention should be paid to not driving the SYNC_IN
pin greater than the supply voltage. While this will not damage
the device, it will cause improper operation.
SYNC_OUT
Since SYNC_OUT is an open collector output that provides
a signal equal to the internal oscillator frequency, multiple
MIC2204s to be connected together in a master-slave con-
figuration for frequency matching of the converters. A typical
10kΩ is recommended for a pull-up resistor.
BIAS
The bias supply is an internal 2.3V linear regulator that
supplies the internal biasing voltage to the MIC2204. 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 and not external circuitry.
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” material in the “Applications Information”
section for more detail.
10kΩ
SYNC_IN
VIN
MIC2204
“Master”
SYNC_OUT
SW
BIAS
FB
SYNC_IN
VIN
MIC2204
“Slave”
SYNC_OUT
SW
BIAS
FB
Figure 1. SYNC_OUT
MIC2204 Micrel, Inc.
M9999-042205 8April 2005
Applications Information
Input Capacitor
A minimum 1µF ceramic is recommended on the VIN pin for
bypassing. X5R or X7R dielectrics are recommended for the
input capacitor. Y5V dielectrics are not recommended: they
lose most of their capacitance over temperature and also
become resistive at high frequencies. This reduces their
ability to filter out high frequency noise.
Output Capacitor
The MIC2204 was designed specifically for the use of a 4.7µF
ceramic output capacitor. 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 MIC2204. For output voltages less than 1.6V,
a 10µF capacitor may be required for stability. See the
“Compensation” section for more detail.
Total output capacitance should not exceed 15µF. Large
values of capacitance can cause current limit to engage
during start-up. If larger than 15µF is required, a feed-forward
capacitor from the output to the feedback node should be
used to slow the start-up time.
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 MIC2204 is designed for use with a 4.7µH inductor.
Maximum current ratings of the inductor are generally given
in two methods: permissible DC current and saturation cur-
rent. Permissible DC current can be rated either for a 40°C
temperature rise or a 10% loss in inductance. Ensure the
inductor selected can handle the maximum operating cur-
rent. 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 require-
ments that are necessary to fit a particular design. Please
refer to the inductor dimensions on their data sheet.
DC resistance is also important. While DCR is inversely
proportional to size, DCR can represent a significant effi-
ciency loss. Refer to the “Efficiency Considerations ” below
for a more detailed description.
Table 1 below shows a list of recommended 4.7µH inductors
by manufacturer, part number and key specifications.
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 % VI
VI 100
OUT OUT
IN IN
=×
×
×
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, critical in handheld devices.
There are two loss terms in switching converters: DC losses
and switching losses. DC losses are simply the power dissi-
pation of I2R. For example, power is dissipated in the high-
side switch during the on cycle, where power loss is equal to
the high-side MOSFET RDSON multiplied by the Switch
Current2. 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
2MHz frequency and the switching transitions make up the
switching losses.
Manufacturer P/N H(mm) W(mm) L(mm) DCR(mΩ)
Sumida CDRH2D18-4R7 2 3.2 3.2 81
Murata LQH43CN4R7M01 2.6 3.2 4.6 150
Murata LQH32CN4R7M11 2.2 2.7 3.4 195
Coilcraft 1008PS-472M 2.74 3.8 3.8 350
Low Profile
TDK LDR5610T-4R7MR90 15.2 5.8 240
Sumida CMD4D06 0.8 6.3 5.8 216
Table 1. Component Selection Table
April 2005 9 M9999-042205
MIC2204 Micrel, Inc.
Figure 2 shows an efficiency curve. On the non-shaded
portion, from 0 to 200mA, 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.
50
55
60
65
70
75
80
85
90
95
100
0100 200 300 400 500
EFFICIENCY (%)
OUTPUT CURRENT
(
A
)
3.3V
OUT
4.2V
IN
3.6V
IN
Efficiency
vs. Output Current
5V
IN
Figure 2.
On the shaded region, 200mA to 500mA, efficiency loss is
dominated by MOSFET RDSON and inductor losses. Higher
input supply voltages will increase the Gate-to-Source thresh-
old on the internal MOSFETs, reducing the internal RDSON.
This improves efficiency by reducing DC losses in the device.
All but the inductor losses are inherent to the device, making
inductor selection even more critical in efficiency calcula-
tions. As the inductors are reduced in size, the DC resistance
(DCR) can become quite significant. The DCR losses can be
calculated as follows:
LPD=IOUT2 x DCR
From that, the loss in efficiency due to inductor resistance can
be calculated as follows:
Efficiency Loss 1± VI
VIL 100
OUT OUT
OUT OUT 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.
Compensation
The MIC2204 is an internally compensated, voltage-mode
buck regulator. Voltage mode is achieved by creating an
internal 2MHz ramp signal and using the output of the error
amplifier to pulsewidth modulate the switch node, maintain-
ing output voltage regulation. With a typical gain bandwidth of
200kHz, the MIC2204 is capable of extremely fast transient
responses.
The MIC2204 is designed to be stable with a 4.7µH inductor
and a 4.7µF ceramic (X5R) output capacitor for output
voltages greater than 1.6V. For output voltages less than
1.6V, a 10µF capacitor is required. Also, when a feed forward
capacitor is used, the gain bandwidth is increased to unity
gain. This will also require increasing the output capacitor to
10µF.
Feedback
The MIC2204 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 1V 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
V±1
OUT
REF
=
Where VREF is 1.0V and VOUT is the desired output voltage.
A 10kΩ 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.
A minimum 1000pF capacitor is recommended for feed-
forward capacitance.
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.
When using a feed-forward capacitor, the gain bandwidth of
the device reaches unity gain at high-frequency. Therefore,
output capacitance will need to be increased to a minimum
10µF. For more information on output capacitor selection for
stability, see the “Compensation ” section.
MIC2204 Micrel, Inc.
M9999-042205 10 April 2005
PWM Operation
The MIC2204 is a pulsewidth modulation (PWM) controller.
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 MIC2204 will run at 100% duty
cycle.
The MIC2204 provides constant switching at 2MHz 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 main-
taining a constant switching frequency, predictable funda-
mental and harmonic frequencies are achieved. Other meth-
ods of regulation, such as burst and skip modes, have
frequency spectrums that change with load and can interfere
with sensitive communication equipment.
Synchronization
SYNC_IN allows the user to change the frequency from
2MHz up to 2.5MHz or down to 1.8MHz. This controls the
fundamental frequency and all the resultant harmonics. Main-
taining a predictable frequency creates the ability to either
shift the harmonics away from sensitive carrier and IF fre-
quency bands, or to accurately filter out specific harmonic
frequencies.
Connecting the SYNC_OUT function pin to the SYNC_IN of
other MIC2204s will synchronize multiple MIC2204s in a
daisy-chain. Synchronizing multiple MIC2204s means that
regulators will run at the same fundamental frequency, result-
ing in matched harmonic frequencies and simplifying design
for sensitive communication equipment.
April 2005 11 M9999-042205
MIC2204 Micrel, Inc.
Package Information
0.15 (0.006)
0.05 (0.002)
0.50 BSC (0.020)
6° MAX
0° MIN
3.15 (0.122)
2.85 (0.114)
3.10 (0.122)
2.90 (0.114)
0.30 (0.012)
0.15 (0.006)
0.26 (0.010)
0.10 (0.004)
1.10 (0.043)
0.94 (0.037)
DIMENSIONS:
MM (INCH)
0.70 (0.028)
0.40 (0.016)
4.90 BSC (0.193)
10-Pin MSOP (MM)
0.20 dia
0.48 typ.
3.00 BSC.
1.50 BSC.
PIN 1 ID
0.85
3.00 BSC.
TOP BOTTOM
ODD TERMINAL SIDE EVEN TERMINAL SIDE
TERMINAL TIP
TERMINAL TIP
1.50 BSC.
1
2
3
1
2
3
–0.05
+0.15
0.01
0.50 BSC.
0.50 BSC.
0.50 BSC.
–0.01
+0.04
0.23
–0.05
+0.07
0.23
–0.05
+0.07
0.01
–0.01
+0.04
0.40
–0.05
+0.15
1.60
–0.15
+0.15
0.80
–0.15
+0.15
2.30
–0.15
+0.15
1.15
–0.15
+0.15
SEATING PLANE
DIMENSIONS: mm
10-Pin MLF™ (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
This 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.
