MIC33153 Evaluation Board
4MHz 1.2A PWM Buck Regulator with
HyperLight Load™ and Power Good
General Description
This board enables the evaluation of the MIC33153, a
fully integrated 1.2A, 4MHz switching regulator featuring
HyperLight Load™ mode, Power Good (PG) output
indicator, and programmable soft start. The MIC33153 is
highly efficient throughout the entire output current
range, drawing just 22µA of quiescent current in
operation. The tiny 3.5mm x 3.0mm x 0.9mm MLF
®
package, in combination with the 4MHz switching
frequency, enables a compact sub 1mm height solution
with only two external input and output capacitors. The
MIC33153 provides accurate output voltage regulation
under the most demanding conditions and responds
extremely quickly to a load transient with exceptionally
small output voltage ripple.
Datasheets and support documentation can be found on
Micrel’s web site at:
www.micrel.com.
Requirements
This board needs a single 5W bench power source
adjustable from 2.7V to 5.5V. The loads can either be
active (electronic load) or passive (resistor) with the
capability to dissipate 5W. It is ideal to have an
oscilloscope available to view the circuit waveforms, but
not essential. For the simplest tests two voltage meters
are required to measure input and output voltage. For
efficiency measurements two voltage meters and two
ammeters are required to prevent errors due to
measurement inaccuracies.
Precautions
There is no reverse input protection on this board. Be
cautious when connecting the input source to ensure
correct polarity is observed.
Getting Started
1.
Connect an external supply to the V
IN
(TP4)
terminal and GND (TP3).
With the output of the
power supply disabled, set its voltage to the desired
input test voltage (2.7V
≤
V
IN
≤
5.5V). An ammeter
may be placed between the input supply and the V
IN
(TP4) terminal. Be sure to monitor the supply
voltage at the V
IN
(TP4) terminal, as the ammeter
and/or power lead resistance can reduce the
voltage supplied to the device.
2.
Connect a load to the V
OUT
(TP1) and ground (TP
2) terminals.
The load can be either active passive
(resistive) or active (electronic load). An ammeter
may be placed between the load and the output
terminal. Ensure the output voltage is monitored at
the V
OUT
(TP1) terminal.
3.
Enable the MIC33153.
The MIC33153 evaluation
board has a pull up resistor (R4) to V
IN
. By default,
the output voltage will be enabled when the input
supply of >2.7V is applied. To disable the device,
apply a voltage below 0.5V to the EN (TP6)
terminal.
4.
Power Good (PG).
A PG test point (TP5) is
provided to monitor the Power Good function. The
PG output will go high (V
OUT
) approximately 70µs
after the output voltage reaches 92% of its nominal
voltage.
Ordering Information
Part Number
MIC33153-4YHJ
MIC33153YHJ
Description
1.2V Fixed Output Evaluation Board
Adjustable Output Evaluation Board
HyperLight Load is a trademark of Micrel, Inc.
MLF and
MicroLeadFrame
are 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
December 2010
M9999-121710-A
Micrel, Inc.
Soft start Capacitor
The MIC33153 has a nominal 270kΩ resistor charging
the capacitor on the SS pin. This enables the output to
follow a controlled soft start characteristic. Setting C3 to
100pF sets the startup time to the minimum. The startup
time can be determined by:
T
SS
= 270 x 10
3
x ln(10) x C
SS
The action of the soft start capacitor is to control the rise
time of the internal reference voltage between 0% and
100% of its nominal steady state value.
Feedback Resistors (R1, R2) for Adjustable Output
The output voltage is set nominally to 1.8V. This output
can be changed by adjusting the upper resistor, R1, in
the feedback potential divider. Therefore:
R1 = R2
×
V
REF
/(V
O
−
V
REF
)
where V
REF
= 0.62V.
Some example values are:
V
OUT
1.2V
1.5V
1.8V
2.5V
3.3V
R1
274k
316k
301k
324k
309k
R2
294k
221k
158k
107k
71.5k
MIC33153 Evaluation Board
Power Good (PG)
The evaluation board has a test point provided to the
right of EN for testing PG. This is an open drain
connection with an on board pull up resistor of 10k to
the output voltage. This is asserted high approximately
70µs after the output voltage passes 92% of the nominal
set voltage.
HyperLight Load™ Mode
The 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:
V
OUT
)
× D
2L × f
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 (V
IN
),
output voltage (V
OUT
), duty cycle (D), inductance (L) and
frequency (f). For example, if V
IN
= 3.6V, V
OUT
= 1.8V, D
= 0.5, f = 4MHz and the internal inductance of
MIC33153 is 0.47μH, then the device will enter
HyperLight Load™ mode or PWM mode at
approximately 200mA.
The feed forward capacitor, C4, is typically not fitted
given that transient load regulation is already very good.
However, it can be improved slightly by fitting a
capacitor at C4 to inject fast output voltage deviations
directly into the feedback comparator. This improved
load regulation occurs at the expense of slightly
increasing the amount of noise on the output at higher
loads. Values between 100pF and 1nF are
recommended to prevent instability.
I
LOAD
>
(
V
IN
December 2010
2
M9999-121710-A
Micrel, Inc.
MIC33153 Evaluation Board
MIC33153-xYMT Evaluation Board Schematic (Fixed Output)
Bill of Materials
Item
C1, C2
C3
R3, R4
U1
Notes:
1.
2.
3.
4.
TDK:
www.tdk.com.
Murata:
www.murata.com.
Vishay:
www.vishay.com.
Micrel, Inc.:
www.micrel.com.
Part Number
C1608X5R0J475K
GRM188R60J475KE19D
C1608NPO0J471K
CRCW06031002FKEA
MIC33153-xYHJ
Manufacturer
TDK
(2)
Murata
TDK
(1)
Vishay
(3)
Micrel, Inc.
(4)
(1)
Description
Ceramic Capacitor, 4.7µF, 6.3V, X5R, Size 0603
Ceramic Capacitor, 470pF, 6.3V, NPO, Size 0603
Resistor, 10k, Size 0603
4MHz 1.2A Buck Regulator with HyperLight Load™
Mode and Fixed Output Voltage
Qty.
2
1
2
1
December 2010
3
M9999-121710-A
Micrel, Inc.
MIC33153 Evaluation Board
MIC33153 Evaluation Board Schematic (Adjustable Output)
Bill of Materials
Item
C1, C2
C3
C4
R1
R2
R3, R4
U1
Notes:
1.
2.
3.
4.
TDK:
www.tdk.com.
Murata:
www.murata.com.
Vishay:
www.vishay.com.
Micrel, Inc.:
www.micrel.com.
Part Number
C1608X5R0J475K
GRM188R60J475KE19D
C1608NPO0J471K
−
CRCW06033013FKEA
CRCW06031583FKEA
CRCW06031002FKEA
MIC33153-YHJ
Manufacturer
TDK
(2)
Murata
TDK
(1)
−
Vishay
(3)
Vishay
(3)
Vishay
(3)
Micrel, Inc.
(4)
(1)
Description
Ceramic Capacitor, 4.7µF, 6.3V, X5R, Size 0603
Ceramic Capacitor, 470pF, 6.3V, NPO, Size 0603
Not Fitted (NF)
Resistor, 301k, Size 0603
Resistor, 158k, Size 0603
Resistor, 10k, Size 0603
4MHz 1.2A Buck Regulator with HyperLight Load™
Mode and Adjustable Output Voltage
Qty.
2
1
0
1
1
2
1
December 2010
4
M9999-121710-A
Micrel, Inc.
MIC33153 Evaluation Board
PCB Layout Recommendations
Top Layer
Bottom Layer
December 2010
5
M9999-121710-A
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