MIC4721 Evaluation Board
1.5A Buck Regulator
General Description
The Micrel MIC4721 is a high efficiency PWM buck
(step-down) regulator that provides up to 1.5A of
output current. The MIC4721 operates at 2MHz and
has proprietary internal compensation that allows a
closed loop bandwidth of over 200kHz. The low on-
resistance internal P-Channel MOSFET of the
MIC4721 allows efficiencies up to 94%, reduces
external component count and eliminates the need for
an expensive external current sense resistor. The
MIC4721 operates from a 2.7V to 5.5V input and its
output is adjustable down to 1V. The devices can
operate with a maximum duty cycle of 100% for use
in low-dropout applications.
Requirements
The MIC4721 evaluation board requires an input
power source that is able to deliver greater than 2.7V
at over 1.5A. The output load can either be an active
or passive load.
Precautions
The evaluation board does not have reverse polarity
protection. Applying a negative voltage to the V
IN
terminal may damage the device. In addition, the
maximum operating voltage of the MIC4721
evaluation board is 5.5V. Exceeding 6V on the input
could damage the device.
For short circuit testing,
an additional input capacitor over 22µF is
required
when using the demo board. This is
preferably an electrolytic, but may be tantalum or
ceramic. The inductance of long test leads connecting
the supply voltage to the demo board can be over
1µH.
During a short circuit condition, the high peak currents
through the test leads may cause the input voltage to
spike high and exceed the absolute maximum rating
of 6V, possibly damaging the device.
Getting Started
1.
Connect an external supply to V
IN
terminal.
Apply desired input voltage to the
V
IN
and ground terminals of the evaluation
board, paying careful attention to polarity
and supply voltage (2.7V<V
IN
<5.5V). An
ammeter may be placed between the input
supply and the V
IN
terminal to the evaluation
board. Ensure the supply voltage is
monitored at the V
IN
terminal. The ammeter
and/or power lead resistance can reduce the
voltage supplied to the input.
2.
Connect the load to the V
OUT
and ground
terminals.
The load can be either passive
(resistive) or active (as in an electronic
load). An ammeter can be placed between
the load and the V
OUT
terminal. Ensure the
output voltage is monitored at the V
OUT
terminal. The default output voltage is set to
1.8V. This can be adjusted by changing the
feedback resistors. See “Output Voltage.”
3.
Enable the MI4721.
The enable pin is
connected to a pull up resistor. The
MIC4721 turns on when V
IN
exceeds the
UVLO threshold at the V
IN
pin. The MIC4721
may be turned off by shorting the pin to
ground or bringing the enable pin below the
enable threshold. An external connection on
the board provides easy access to the
enable pin.
LOWQ is a registered trademark of Micrel, 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
September 2007
M9999-090507-B
Micrel, Inc.
MIC4721 Evaluation Board
Output Voltage
The output voltage on the MIC4721 evaluation board
is adjustable. The output voltage is controlled by the
feedback resistors (R1 and R2) and can be calculated
as follows:
Power OK
The POK pin is pulled up to V
IN
through a pull up
resistor and is asserted low when V
OUT
is within the
regulation band. An external connection on the
board provides easy access to the POK pin.
R1
⎞
⎛
V
OUT
=
V
REF
× ⎜
1
+
⎟
R2
⎠
⎝
Where V
REF
= 1V.
The evaluation board is preset at 1.8V, but can
easily be modified by removing R2 and replacing it
with the value that yields the desired output voltage.
(Removing R2 sets the output to 1V).
R2
=
R1
×
V
REF
V
OUT
−
V
REF
R1
V
OUT
−
1
Ordering Information
Part Number
MIC4721YMM
MIC4721YMM EV
Description
IC
Evaluation Board
Package
10-Pin MSOP
10-Pin MSOP
For V
REF
= 1V, this reduces to:
R2
=
September 2007
2
M9999-090507-B
Micrel, Inc.
MIC4721 Evaluation Board
U1
MIC4721YMM
J1
+VIN
R6
49.9k
J3
EN
J4
PGOOD
R5
10k
2
C1
10µF
C2
10µF
/6.3V
9
VIN
VIN
SW
SW
1
10
1
R3
6
7
R
C3
0.1µF
/10V
J2
GND
4
EN
PGOOD
BIAS
FB
5
C4
680pF
R2
12.4K
J6
GND
2
L1
1µH
D1
SSA33L
C5
82pF
R1
10k
C6
4.7µF
J5
VOUT
1.8V@1.5A
PGND
8
Bill of Materials
Item
C1, C2
Part Number
C1608 X5R0J106K
GRM188R61A106K
08056D106MAT
JMK107BJ106MA-T
VJ0402Y104KXQCW1BC
C3
C1005X7R1A104K
0402ZD104MAT
C4
C5
VJ0402A681KXXCW1BC
C1005COG1A681J
VJ0402A82KXXCW1BC
C1005COG1A820J
C1608X5R0J475K
06036D475MAT
JMK107BJ475MA-T
GRM188R60J475KE19D
SSA33L
MBRM330-13
CDRH3D23MN-1R0NC
L1
SDH3812-1R0-R
LTF5022T-1R2N4R2
IHLP2525AHER1R0M01
R1, R5
R2
R3
R4
R6
U1
CRCW04021002FKEYE3
CRCW04021242FKEYE3
CRCW04022R70FKEYE3
CRCW040210R0FKEYE3
CRCW04024992FKEYE3
MIC4721YMM
Manufacturer
TDK
(1)
Murata
(2)
AVX
(3)
Taiyo Yuden
(4)
Vishay
(5)
TDK
(1)
AVX
TDK
TDK
(3)
3
AGND
Description
10µF Ceramic Capacitor X5R 6.3V
10µF Ceramic Capacitor X5R 10V
10µF Ceramic Capacitor X5R 6.3V
10µF Ceramic Capacitor X5R 6.3V
0.1µF Ceramic Capacitor X7R 10V
0.1µF Ceramic Capacitor X7R 10V
0.1µF Ceramic Capacitor X5R 10V
680pF Ceramic Capacitor NPO 10V
680pF Ceramic Capacitor 10V
82pF Ceramic Capacitor NPO 10V
82pF Ceramic Capacitor 10V
Qty.
2
1
Vishay
(5)
(1)
1
1
Vishay
(5)
(1)
C6
TDK
(1)
AVX
(3)
Taiyo Yuden
Murata
(2)
Vishay
(5)
Diodes, Inc.
(6)
Sumida
(7)
Cooper
(8)
TDK
(1)
Vishay
(5)
(4)
4.7µF Ceramic Capacitor X5R 6V
1
D1
3A Schottky 30V
1µH Inductor 2A 3.92x3.92mm
1µH Inductor 2A
1.2µH Inductor 4.3A ±30%
1µH Inductor 7A
10k 1% 0402 1/16W
12.4k 1% 0402 1/16W
2.7Ω 1% 0402 1/16W
10Ω 1% 0402 Resistor
49.9k 1% 0402 Resistor
2MHz 1.5A Buck Regulator
1
1
Vishay Dale
(5)
Vishay Dale
(5)
2
1
1
1
1
1
Micrel, Inc.
(9)
September 2007
3
M9999-090507-B
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