MIC23303YML Evaluation Board User Guide

MIC23303 Evaluation Board
4MHz PWM 3A Buck Regulator with
Hyper Light Load® and Power Good
General Description
Getting Started
This board allows the customer to evaluate the
MIC23303, a fully integrated 3A, 4MHz switching
regulator that features Hyper Light Load® mode, a Power
Good output indicator, and programmable soft-start. The
MIC23303 is highly efficient throughout the output
current range, drawing just 24µA of quiescent current in
operation. The tiny 3mm x 3mm DFN package, in
combination with the 4MHz switching frequency, creates
a compact sub-1mm height solution with only six
external components. The MIC23303 provides accurate
output voltage regulation under the most demanding
conditions and responds extremely quickly to a load
transient with exceptionally small output voltage ripple.
1. Connect an external supply to the VIN (J1)
terminal and GND (J6). With the output of the
power supply disabled, set its voltage to the desired
input test voltage (2.9V ≤ VIN ≤ 5.5V). The user can
place an ammeter between the input supply and the
VIN (J1) terminal. Be sure to monitor the supply
voltage at the VIN (J1) terminal, as the ammeter
and/or power lead resistance can reduce the voltage
supplied to the device.
2. Connect a load to the VOUT (J5) and ground (J2)
terminals. The load can be either active passive
(resistive) or active (electronic load). The user can
place an ammeter between the load and the output
terminal. Make sure the output voltage is monitored
at the VOUT (J5) terminal. The board has a 2-pin
connector (JP1) to allow for output voltage
monitoring.
3. Enable the MIC23303. The MIC23303 evaluation
board has a pull-up resistor to VIN. By default, the
output voltage is enabled when the input supply of
>2.9V is applied. To disable the device, apply a
voltage below 0.5V to the EN (J3) terminal.
4. Power Good. The board provides a Power Good
test point (J4) to monitor the Power Good function.
The Power Good output goes high (VOUT)
approximately 160µs after the output voltage
reaches 90% of its nominal voltage.
Requirements
This board needs a single 10W bench power source
adjustable from 2.9V to 5.5V. The loads can be either
active (electronic load) or passive (resistor), and must be
able to dissipate 10W. It is ideal, but not essential, to
have an oscilloscope available to view the circuit
waveforms. The simplest tests require two voltage
meters to measure input and output voltage. Efficiency
measurements require two voltage meters and two
ammeters to prevent errors caused by measurement
inaccuracies.
Precautions
There is no reverse input protection on this board. Be
careful when connecting the input source to make sure
correct polarity is observed.
Data sheets and support documentation can be found on
Micrel’s web site at www.micrel.com.
Ordering Information
Part Number
Description
MIC23303YML EV
Adjustable Output Evaluation Board
Hyper Light Load is a registered 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) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
October 2012
M9999-100912-A
Micrel, Inc.
MIC23303 Evaluation Board
The feed-forward capacitor, C4, can be fitted to improve
transient performance. This improves transients by
injecting fast output voltage deviations directly into the
feedback comparator. This improved load regulation is at
the expense of slightly increasing the amount of noise on
the output at higher loads. A typical value range of 22pF
to 68pF is recommended.
Evaluation Board
Power Good (PG)
The evaluation board provides a test point above EN for
testing PG. This is an open-drain connection to the
output voltage with an on-board pull-up resistor of 10kΩ.
This is asserted high approximately 160µs after the
output voltage passes 90% of the nominal set voltage.
Hyper Light Load® Mode
MIC23303 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, the
error comparator turns the PMOS off for a minimum-offtime until the output drops below the threshold. The
NMOS acts as an ideal rectifier that conducts when the
PMOS is off. Using an 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 MIC23303 works
in pulse frequency modulation (PFM) to regulate the
output. As the output current increases, the off-time
decreases, which provides more energy to the output.
This switching scheme improves the efficiency of
MIC23303 during light load currents by switching only
when it is needed. As the load current increases, the
MIC23303 goes into continuous conduction mode (CCM)
and switches at a frequency centered at 4MHz. The
equation to calculate the load when the MIC23303 goes
into continuous conduction mode is approximated by the
following formula:
Other Features
Soft-Start Capacitor (C2)
The soft-start (SS) pin is used to control the output
voltage ramp-up time. Setting C2 to 2.2nF sets the startup time to the minimum. The start-up time can be
determined by:
TSS = 250x103 x ln(10) x CSS
The soft-start capacitor controls the rise time of the
internal reference voltage between 0% and 100% of its
nominal steady state value.
Feedback Resistors (R3, R4) for Adjustable Output
The output voltage is set nominally to 1.8V. This output
can be changed by adjusting the upper resistor, R3, in
the feedback potential divider. Therefore:
R3 = R4 x VREF/(VO-VREF)
⎛ (V − VOUT ) × D ⎞
⎟⎟
ILOAD > ⎜⎜ IN
2L × f
⎠
⎝
The previous equation shows that the load at which
MIC23303 transitions from Hyper Light Load mode to
PWM mode is a function of the input voltage (VIN), output
voltage (VOUT), duty cycle (D), inductance (L), and
frequency (f). The “Switching Frequency vs. Load” graph
on page 3 shows that, as the output current increases,
the switching frequency also increases until the
MIC23303 goes from Hyper Light Load mode to PWM
mode at approximately 300mA. The MIC23303 will
switch at a relatively constant frequency around 4MHz
after the output current is over 300mA.
Where VREF = 0.62V.
Some example values are:
VOUT
R3
R4
1.2V
274kΩ
294kΩ
1.5V
316kΩ
221kΩ
1.8V
560kΩ
294kΩ
2.5V
324kΩ
107kΩ
3.3V
464kΩ
107kΩ
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MIC23303 Evaluation Board
Evaluation Board Performance
Efficiency vs. Load
1.8VOUT @25°C
Switching Frequency
vs. Load Current
VIN = 5V
100
VIN = 3V
10
1
VOUT = 1.8V
0.1
0.0001
0.001
0.01
0.1
1
100
100
90
90
80
80
70
60
VIN = 3.6V
50
40
30
30
0.1
1
10
0
0.0001
0.001
0.01
0.1
1
10
LOAD CURRENT (A)
Enable Threshold
vs. Input Voltage
1.1
100000
1.0
VEN THRESHOLD (V)
RISE TIME (µs)
0.01
VIN = 5V
VIN = 3V
40
10
LOAD CURRENT(A)
VOUT Rise Time
vs. CSS
10000
1000
100
10
0.9
0.8
0.7
0.6
VIN = 3.6V
1
1000
50
20
0.001
VIN = 3.6V
60
10
LOAD CURRENT (A)
1000000
70
20
0
0.0001
10
VIN = 5V
EFFICIENCY (%)
1000
EFFICIENCY (%)
SW FREQUENCY (kHz)
10000
Efficiency vs. Load
1.2VOUT @25°C
TCASE = 25°C
0.5
10000
100000
CSS (pF)
1000000
2.5
3.0
3.5
4.0
4.5
5.0
5.5
INPUT VOLTAGE (V)
MIC23303-YML Evaluation Board Schematic
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MIC23303 Evaluation Board
Bill of Materials
Item
Part Number
06036D475KAT2A
C1
GRM188R60J475ME19D
C1608X5R0J475M
06035C222KAT2A
C2
GRM188R71H222MA01D
C3,C8
C4
C6
C7
06035A330KAT2A
AVX
Murata
Panasonic(4)
Murata
TDK
06035D104KAT2A
AVX
0520CDMCDSNP-R33MC
744373240033
1
22µF/6.3V, X5R, 0805
1
33pF/50V, 0603
1
CAP ALUM 220UF 10V 20% RADIAL
1
1µF/6.3V, X5R, 0603
1
0.1µF/6.3V, X5R, 0603
1
AVX
C1608X5R0J105K
C1608X5R1H104K
L1
Murata
TDK
GRM188R71H104KA930
2.2nF/50V, X7R, 0603
AVX
Murata
C2012X5R0J226M
GRM188R60J105KA01D
1
TDK
AVX
06036D105KAT2A
4.7µF/6.3V, X5R, 0603
(3)
08056D226MAT2A
ECA-1AHG221
Qty
AVX
Murata(2)
TDK
GRM21BR60J226ME39L
Description
(1)
C1608X7R1H222K
GRM1885C1H330JA01D
C5
Manufacturer
Murata
TDK
Sumida(5)
(6)
Wurth
0.33µH/5.6A, 8mΩ
1
0.33µH/8.0A, 8.6mΩ
R1,R2
CRCW060310K0FKEA
Vishay/Dale(7)
10K, 1%, 1/10W, 0603
2
R3
CRCW0603560KFKEA
Vishay/Dale
560K, 1%, 1/10W, 0603
1
R4
CRCW0603294KFKEA
Vishay/Dale
294K,1%, 1/10W, 0603
1
R5
CRCW060310R0FKEA
Vishay/Dale
10Ω, 1%, 1/10W, 0603
1
IC1
MIC23303-YML
4MHz 3A Buck Regulator with Hyper
Light Load® Mode
1
Micrel, Inc.(8)
Notes:
1. AVX: www.avx.com.
2.
TDK: www.tdk.com.
3.
Murata: www.murata.com.
4.
Panasonic: www.panasonic.com.
5.
Sumida: www.sumida.com.
6.
Wurth: www.we-online.com.
7.
Vishay: www.vishay.com.
8.
Micrel, Inc.: www.micrel.com.
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Micrel, Inc.
MIC23303 Evaluation Board
PCB Layout Recommendations
Top Layer
Bottom Layer
October 2012
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M9999-100912-A
Micrel, Inc.
MIC23303 Evaluation Board
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
property rights is granted by this document. Except as provided in Micrel’s terms and conditions of sale for such products, Micrel assumes no liability
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 and Purchaser agrees to fully
indemnify Micrel for any damages resulting from such use or sale.
© 2012 Micrel, Incorporated.
October 2012
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