MIC23603 Evaluation Board
4MHz PWM 6A Buck Regulator with
Hyper Light Load
®
General Description
The MIC23603 evaluation board allows the customer to
evaluate the MIC23603, a fully-integrated 6A, 4MHz
®
switching regulator that features Hyper Light Load mode,
a power good output indicator, and programmable soft-
start. The MIC23603 is highly efficient throughout the
output current range, drawing just 24µA of quiescent
current in operation. The tiny 4mm × 5mm DFN package
saves precious board space and requires few external
components. The MIC23603 provides accurate output
voltage regulation under the most demanding conditions
and responds extremely quickly to a load transient with
exceptionally small output voltage ripple.
Requirements
The MIC23603 evaluation board requires a single 40W
bench power source adjustable from 2.7V to 5.5V. The
loads can be either active (electronic load) or passive
(resistor), and must be able to dissipate 30W. 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.
Datasheets and support documentation are available on
Micrel’s web site at:
www.micrel.com.
Getting Started
1.
Connect an external supply to the V
IN
(J1) terminal
and GND (J2).
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
(J1) terminal. 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 device.
2.
Connect a load to the V
OUT
(J4) and ground (J3)
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. Make sure
the output voltage is monitored at the V
OUT
(J4)
terminal. The board has a 2-pin connector (TP1) to
allow for output voltage monitoring.
3.
Enable the MIC23603.
The MIC23603 evaluation board has a pull-up resistor
to V
IN
. By default, the output voltage is enabled when
the input supply of >2.7V is applied. To disable the
device, apply a voltage below 0.4V to the EN (J6)
terminal.
4.
Power Good.
The board provides a power good test point (J5) to
monitor the power good function. The power good
output goes high (V
OUT
) approximately 40µs after the
output voltage reaches 90% of its nominal voltage.
Ordering Information
Part Number
MIC23603YML EV
Description
Adjustable Output Evaluation Board
Hyper Light Load 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
June 24, 2013
062413-1.0
Micrel, Inc.
MIC23603 Evaluation Board
Evaluation Board
Examples of values are illustrated in Table 1.
Table 1. Example Values for V
OUT
, R3, and R4
V
OUT
1.2V
1.5V
1.8V
2.5V
3.3V
R3
274kΩ
316kΩ
560kΩ
324kΩ
464kΩ
R4
294kΩ
221kΩ
294kΩ
107kΩ
107kΩ
The feed-forward capacitor, C10, 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 33pF to
68pF is recommended.
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 to
the output voltage with an on-board pull-up resistor of
100kΩ. This is asserted high approximately 40µs after the
output voltage passes 90% of the nominal set voltage.
Hyper Light Load Mode
MIC23603 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 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 MIC23603 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 MIC23603 during light
load currents by switching only when it is needed. As the
load current increases, the MIC23603 goes into
continuous conduction mode (CCM) and switches at a
frequency centered at 4MHz.
Figure 1. MIC23603 Evaluation Board – Top Layer
Other Features
Soft-Start Capacitor
The soft-start (SS) pin is used to control the output voltage
ramp-up time. Setting C4 to 2.2nF sets the start-up time to
the minimum. The start-up time can be determined by:
3
T
SS
= 250 × 10 × In(10) × C
SS
Eq.1
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 × (V
O
−
V
REF
)/V
REF
where V
REF
= 0.62V.
Eq. 2
June 24, 2013
2
062413-1.0
Micrel, Inc.
Refer to Equation 3 to calculate the load when the
MIC23603 goes into continuous conduction mode:
MIC23603 Evaluation Board
I
LOAD
>
V
IN
−
V
OUT
×
D
2L
×
f
Eq. 3
Equation 3 illustrates that the load at which MIC23603
transitions from Hyper Light 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). The
“Switching Frequency vs. Load” graph (see
Evaluation
Board Performance
section) shows that, as the output
current increases, the switching frequency also increases
until the MIC23603 goes from Hyper Light Load mode to
PWM mode at approximately 300mA. The MIC23603 will
switch at a relatively constant frequency around 4MHz
after the output current is over 300mA.
June 24, 2013
3
062413-1.0
Micrel, Inc.
MIC23603 Evaluation Board
Evaluation Board Performance
Switching Frequency Vs
Load Current
10000
V
IN
=2.9V
100
90
1000
80
Efficiency Vs.
Output Current
100
V
OUT
=3.3V
90
80
V
OUT
=2.5V
Efficiency vs. Load
1.8vout
FREQUENCY (kHz)
EFFICIENCY (%)
Efficiency (%)
70
60
50
40
30
20
10
70
60
50
40
30
20
10
V
IN
=3.6V
V
IN
=2.9V
V
IN
=5V
100
10
V
IN
=3.6V
1
V
IN
=5V
0.1
0.0001
0.001
0.01
V
OUT
=1.8V
L=0.33µH
C
OUT
=2x47µF
0.1
1
10
V
IN
=5V
L=0.33µH
C
OUT
=2x47µF
0.001
0.01
0.1
1
10
L=0.33µF
C
OUT
=2x47µF
0.001
0.01
0.1
1
10
0
0.0001
0
0.0001
LOAD CURRENT (A)
OUTPUT CURRENT (A)
LOAD CURRENT(A)
VOUT Rise Time
vs Css
1000000
1.10
1.05
Enable Thresholds Vs.
Input Voltage
100000
ENABLE THRESHOLD (V)
ENABLE ON
1.00
0.95
0.90
0.85
0.80
2.5
3
3.5
4
4.5
5
5.5
10000
Rise Time (us)
1000
ENABLE OFF
100
10
V
IN
=3.6V
V
OUT
=1.8V
LOAD=150mA
1
1000
10000
100000
1000000
INPUT VOLTAGE (V)
Css (pF)
June 24, 2013
4
062413-1.0
Micrel, Inc.
MIC23603 Evaluation Board
Evaluation Board Schematic
June 24, 2013
5
062413-1.0
京公网安备 11010802033920号
Copyright © 2005-2026 EEWORLD.com.cn, Inc. All rights reserved
电子工程世界
