MIC23250 Evaluation Board
4MHz Dual 400mA
Synchronous Buck Regulator
with HyperLight Load™
General Description
The MIC23250 is a dual 400mA 4MHz switching regulator
with HyperLight Load™ mode. The MIC23250 is highly
efficient, consuming 33µA of quiescent current to operate
both of its outputs. A Sub-1mm height solution is easily
attainable using the tiny package (2mm x 2mm x 0.55mm)
and only six external components. Small and fast, the
MIC23250 can respond to a load transient at ultra-fast
speed while reducing output peak-to-peak voltage.
The MIC23250 has two modes of operation that is
automatically selected by the internal circuitry. Under light
load conditions, the MIC23250 goes into HyperLight
Load™ mode. The MIC23250 HyperLight Load™ uses a
Pulse-Frequency Modulation (PFM) control scheme that
controls the off time at light load. This allows the device to
reduce the amount of switching needed at light load, thus
reducing the switching losses. The MIC23250 can attain
up to 85% efficiency at 1mA output load. At higher output
currents of approximately 100mA, HyperLight Load™
mode automatically switches back to Pulse-Width
Modulation (PWM) mode to ensure high efficiency up to
94% at higher load. The two modes of operation ensure
that the MIC23250 maintains the highest efficiency
throughout the entire load range.
The MIC23250 operates from a 2.7V to 5.5V input and
features internal power MOSFETs that can supply up to
400mA of output current on each channel. It can operate
with a maximum duty cycle of 90%.
Requirements
The MIC23250 evaluation board requires an input power
source that is able to deliver greater than 800mA at 2.7V.
The output loads can either be an active (electronic) or
passive (resistive) load.
Getting Started
1.
Connect an external supply to the V
IN
(J1)
terminal.
Apply desired input voltage to the V
IN
(J1) and ground (J2) terminal 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
(J1) terminal to the evaluation board. Be sure
to monitor the supply voltage at the V
IN
(J1)
terminal, as the ammeter and/or power lead
resistance can reduce the voltage supplied to the
input.
2.
Connect a load to the V
O
1 (J4) and V
O
2 (J6)
outputs and ground terminal (J7).
The loads
can be either passive (resistive) or active
(electronic load). An ammeter can be placed
between the load and the output terminal. Ensure
that the output voltages are monitored at the V
O
1
(J4) and V
O
2 (J6) terminals.
3.
Enable the MIC23250 outputs.
The MIC23250
evaluation board has pre-installed pull-up resistors
(R1 and R2) that enable the device as soon as
input voltage is applied. These resistors are
optional. To disable the device, apply a voltage
below 0.5V to EN1 (J3) or EN2 (J5) terminals.
Similarly, if the pull up resistors (R1 and R2) are
not used the device may be enabled by applying a
voltage greater than 1.2V to the EN1 (J3) or EN2
(J5) terminals. Be sure that the enable voltage
never exceeds the input voltage.
Output Voltage
The MIC23250 evaluation board has fixed output voltage
options available per the table below.
Ordering Information
Part Number
MIC23250-C4YMT EV
MIC23250-G4YMT EV
MIC23250-S4YMT EV
MIC23250-AAYMT EV
Description
1.2V / 1.0V Output Evaluation Board
1.2V / 1.8V Output Evaluation Board
1.2V / 3.3V Output Evaluation Board
Adjustable Output Evaluation Board
Note:
Other voltage options available upon request. Contact Micrel.
HyperLight Load is a 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
July 2009
M9999-070909-C
Micrel, Inc.
Feedback Resistor Selection (Adjustable Only)
The feedback pins (FB1/FB2) are two extra pins that can
only be found on the MIC23250-AAYMT devices. It
allows the regulated output voltage to be set by applying
an external resistor network. The internal reference
voltage is 0.72V and the recommended value of R
BOTTOM
is within 10% of 442kΩ. The R
TOP
resistor is the resistor
from the FB pin to the output of the device and R
BOTTOM
is the resistor from the FB pin to ground. The output
voltage is calculated from the equation below.
⎛
R
TOP
⎞
+
1
⎟
V
OUT
=
0.72
V
⎜
⎜
R
⎟
⎝
BOTTOM
⎠
MIC23250 Evaluation Board
V
OUT
(V)
0.8
0.9
1
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
1.9
2
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
2.9
3
R
TOP
(kΩ)
49
111
172
233
295
356
417
479
540
602
663
724
786
847
909
970
1031
1093
1154
1216
1277
1338
1400
1461
1522
1584
R
BOTTOM
(kΩ)
442
442
442
442
442
442
442
442
442
442
442
442
442
442
442
442
442
442
442
442
442
442
442
442
442
442
CFF (pF)
120
120
120
120
120
120
120
120
120
120
120
120
120
120
120
120
120
120
120
120
120
120
120
120
120
120
Compensation
The MIC23250 is designed to be stable with a 0.47µH to
4.7µH inductor with a minimum of 2.2µF ceramic (X5R)
output capacitor. For the adjustable MIC23250, the total
feedback resistance should be kept as high as possible
to reduce current loss down the feedback resistor
network. This helps to improve efficiency. A feed-forward
capacitor (CFF) of 120pF must be used in conjunction
with the external feedback resistors to reduce the effects
of parasitic capacitance that is inherent of most circuit
board layouts. Figure 1 and Table 1 shows the
recommended feedback resistor values along with the
recommended feed-forward capacitor for the MIC23250
adjustable device.
R
TOP
C
FF
R
BOTTOM
3.1
3.2
3.3
Figure 1. Feedback Resistor Network
Table 1. Recommended Feedback Component Values
For V
O
1 the feedback components are: R
TOP
= R3,
R
BOTTOM
= R4, C
FF
= C5. For V
O
2 the feedback
components are: R
TOP
= R5, R
BOTTOM
= R6, C
FF
= C6.
July 2009
2
M9999-070909-C
Micrel, Inc.
HyperLight Load Mode™
MIC23250 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 MIC23250 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
MIC23250 during light load currents by only switching
when it is needed. As the load current increases, the
MIC23250 goes into continuous conduction mode (CCM)
and switches at a frequency centered at 4MHz. The
equation to calculate the load when the MIC23250 goes
into continuous conduction mode may be approximated
by the following formula:
⎛
V
−
V
OUT
×
D
⎞
⎟
I
LOAD
= ⎜
IN
⎟
⎜
2
L
×
f
⎠
⎝
MIC23250 Evaluation Board
As shown in the previous equation, the load at which
MIC23250 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). This is illustrated in the graph below. Since
the inductance range of MIC23250 is from 0.47µH to
4.7µH, the device may then be tailored to enter
HyperLight Load™ mode or PWM mode at a specific
load current by selecting the appropriate inductance. For
example in the graph below, when the inductance is
4.7µH the MIC23250 will transition into PWM mode at a
load of approximately 4mA. Under the same condition,
when the inductance is 1µH, the MIC23250 will transition
into PWM mode at approximately 70mA.
Switching Frequency
vs. Output Current
L = 4.7µH
10
4MHz
1
L = 1µH
L = 2.2µH
0.1
V
IN
= 3.6V
V
OUT
= 1.8V
C
OUT
= 4.7µF
10
100
1000
OUTPUT CURRENT (mA)
0.01
1
July 2009
3
M9999-070909-C
Micrel, Inc.
MIC23250 Evaluation Board
MIC23250 Evaluation Board Schematic (Fixed Output)
Bill of Materials
Item
C1, C2, C3
C4
R1, R2
Part Number
C1608X5R0J475K
VJ0603Y103KXXAT
CRCW060310K0FKEA
LQM21PN1R0M00
LQH32CNR1R0M33
L1, L2
LQM31P1R0M00
GLF251812T1R0M
LQM31PNR47M00
MIPF2520D1R5
U1
MIC23250-xxYMT
Manufacturer
TDK
(1)
Vishay
(2)
(2)
Description
4.7µF Ceramic Capacitor, 6.3V, X5R, Size 0603
0.01µF Ceramic Capacitor, 25V, X7R, Size 0603
10kΩ Resistor, 1%, 1/16W, Size 0603
1µH, 0.8A, 190mΩ, L2mm x W1.25mm x H0.5mm
1µH, 1A, 60mΩ, L3.2mm x W2.5mm x H2.0mm
1µH, 1.2A, 120mΩ, L3.2mm x W1.6mm x H0.95mm
1µH, 0.8A, 100mΩ, L2.5mm x W1.8mm x H1.35mm
0.47µH, 1.4A, 80mΩ, L3.2mm x W1.6mm x H0.85mm
1.5µH, 1.5A, 70mΩ, L2.5mm x W2mm x H1.0mm
4MHz Dual 400mA Buck Regulator
with HyperLight Load™ Mode
Qty
3
1
Optional
Vishay
Murata
(3)
Murata
(3)
Murata
(3)
TDK
(1)
Murata
(3)
FDK
(4)
2
Micrel, Inc.
(5)
1
Notes:
1. TDK: www.tdk.com
2. Vishay: www.vishay.com
3. Murata: www.murata.com
4. FDK: www.fdk.co.jp
5. Micrel, Inc: www.micrel.com
July 2009
4
M9999-070909-C
Micrel, Inc.
MIC23250 Evaluation Board
MIC23250 Evaluation Board Schematic (Adjustable Output)
Bill of Materials
Item
C1, C2, C3
C4
C5, C6
R1, R2
R3, R5
R4, R6
Part Number
C1608X5R0J475K
VJ0603Y103KXXAT
VJ0603Y121KXAAT
CRCW06031002FKEA
CRCW06036653FKEA
CRCW06034423FKEA
LQM21PN1R0M00
LQH32CN1R0M33
LQM31P1R0M00
L1, L2
GLF251812T1R0M
LQM31PNR47M00
MIPF2520D1R5
EPL2010-102
U1
MIC23250-AAYMT
Manufacturer
TDK
(1)
Description
4.7µF Ceramic Capacitor, 6.3V, X5R, Size 0603
0.01µF Ceramic Capacitor, 25V, X7R, Size 0603
120pF Ceramic Capacitor, 50V, X7R, Size 0603
10kΩ, 1%, 1/16W, Size 0603
665kΩ, 1%, 1/16W, Size 0603
442kΩ, 1%, 1/16W, Size 0603
1µH, 0.8A, 190mΩ, L2mm x W1.25mm x H0.5mm
1µH, 1A, 60mΩ, L3.2mm x W2.5mm x H2.0mm
1µH, 1.2A, 120mΩ, L3.2mm x W1.6mm x H0.95mm
1µH, 0.8A, 100mΩ, L2.5mm x W1.8mm x H1.35mm
0.47µH, 1.4A, 80mΩ, L3.2mm x W1.6mm x H0.85mm
1.5µH, 1.5A, 70mΩ, L2.5mm x W2mm x H1.0mm
1.0µH, 1.0A, 86mΩ, L2.0mm x W1.8mm x H1.0mm
4MHz Dual 400mA Adjustable Output
Buck Regulator with HyperLight Load™ Mode
Qty
3
1
2
Optional
2
2
Vishay
(2)
Vishay
(2)
Vishay
(2)
Vishay
(2)
Vishay
(2)
(3)
Murata
Murata
(3)
Murata
(3)
TDK
(1)
Murata
(3)
FDK
(4)
(5)
2
Coilcraft
Micrel, Inc.
(6)
1
Notes:
1. TDK: www.tdk.com
2. Vishay: www.vishay.com
3. Murata: www.murata.com
4. FDK: www.fdk.co.jp
5. Coilcraft: www.coilcraft.com
6. Micrel, Inc: www.micrel.com
July 2009
5
M9999-070909-C
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