MIC45205 Evaluation Board
26V/6A DC-to-DC Power Module
General Description
Micrel’s MIC45205 is a synchronous step-down regulator
module, featuring a unique adaptive ON-time control
architecture. The module incorporates a DC-to-DC
controller, power MOSFETs, bootstrap diode, bootstrap
capacitor, and an inductor in a single package; simplifying
the design and layout process for the end user.
This highly integrated solution expedites system design
and improves product time-to-market. The internal
MOSFETs and inductor are optimized to achieve high
efficiency at a low output voltage. The fully optimized
design can deliver up to 6A current under a wide input
voltage range of 4.5V to 26V, without requiring additional
cooling.
The MIC45205-1 uses Micrel’s HyperLight Load (HLL)
MIC45205-2 uses Micrel’s Hyper Speed Control™
architecture which enables ultra-fast load transient
response, allowing for a reduction of output capacitance.
The MIC45205 offers 1% output accuracy that can be
adjusted from 0.8V to 5.5V with two external resistors.
The basic parameters of the evaluation board are:
•
Input: 4.5V to 26V
•
Output 0.8V to 5V at 6A
•
600kHz Switching Frequency
−
Adjustable 200kHz to 600kHz
Datasheets and support documentation are available on
Micrel’s web site at:
www.micrel.com.
Requirements
The MIC45205-1 and MIC45205-2 evaluation board
requires only a single power supply with at least 10A
current capability. No external linear regulator is required
to power the internal biasing of the IC because the
MIC45205 has an internal PVDD LDO. In the applications
with VIN < +5.5V, PVDD should be tied to VIN to bypass
the internal linear regulator. The output load can either be
a passive or an active load.
Precautions
The MIC45205 evaluation board does not have reverse
polarity protection. Applying a negative voltage to the VIN
and GND terminals may damage the device. The
maximum VIN of the board is rated at 26V. Exceeding 30V
on the VIN could damage the device.
®
Getting Started
1. VIN Supply
Connect a supply to the VIN and GND terminals,
paying careful attention to the polarity and the supply
range (4.5V < VIN < 26V). Monitor IIN with a current
meter and monitor input voltage at VIN and GND
terminals with a voltmeter. Do not apply power until
Step 4.
2. Connect Load and Monitor Output
Connect a load to the VOUT and GND terminals. The
load can be either a passive (resistive) or an active (as
in an electronic load) type. A current meter may be
placed between the VOUT terminal and load to
monitor the output current. Ensure the output voltage
is monitored at the VOUT terminal.
3. Enable Input
The EN pin has an on board 100kΩ pull-up resistor
(R10) to VIN, which allows the output to be turned on
when PVDD exceeds its UVLO threshold. An EN
connector is provided on the evaluation board for
users to easily access the enable feature. Applying an
external logic signal on the EN pin to pull it low or
using a jumper to short the EN pin to GND will shut off
the output of the MIC45205 evaluation board.
4. Turn Power
Turn on the VIN supply and verify that the output
voltage is regulated to 5V.
Ordering Information
Part Number
MIC45205-1YMP EV
MIC45205-2YMP EV
Description
MIC45205-1 Evaluation Board
MIC45205-2 Evaluation Board
Hyper LightLoad is a registered trademark and Hyper Speed Control 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
February 9, 2015
Revision 2.0
Micrel, Inc.
MIC45205 Evaluation Board
Features
Feedback Resistors
The output voltage on the MIC45205 evaluation board,
which is preset to 5.0V, is determined by the feedback
divider, as illustrated in Equation 1:
where V
REF
= 0.8V, and R
BOTTOM
is one of R3 thru R9.
Leaving the R
BOTTOM
open by removing all jumpers on the
feedback headers gives a 0.8V output voltage. All other
voltages not listed above can be set by modifying R
BOTTOM
value according to Equation 2:
R14
V
OUT
=
V
REF
×
1
+
R
BOTTOM
Eq. 1
R
BOTTOM
=
R1
×
V
REF
V
OUT
−
V
REF
Eq. 2
Note that the output voltage should not be set to exceed
5V.
Table 1. Typical Values of Some Components
V
OUT
1.0V
1.2V
1.5V
1.8V
2.5V
3.3V
5V
VIN
5V to 26V
5V to 26V
5V to 26V
5V to 26V
5V to 26V
5V to 26V
7V to 26V
R14
(Top Feedback Resistor)
10kΩ
10kΩ
10kΩ
10kΩ
10kΩ
10kΩ
10kΩ
R
(Bottom Feedback Resistor)
40.2kΩ
20.0kΩ
11.5kΩ
8.06kΩ
4.75kΩ
3.24kΩ
1.91kΩ
C14
(C
ff
)
2.2nF
2.2nF
2.2nF
2.2nF
2.2nF
2.2nF
2.2nF
C
OUT
100µF/6.3V
100µF/6.3V
100µF/6.3V
100µF/6.3V
100µF/6.3V
100µF/6.3V
100µF/6.3V
February 9, 2015
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Revision 2.0
Micrel, Inc.
SW Node
A test pad is placed for monitoring the switching waveform,
which is one of the most critical waveforms for the
converter.
Current Limit
The MIC45205 uses the R
DS(ON)
of the low-side MOSFET
and external resistor connected from the ILIM pin to the
SW node to decide the current limit.
MIC45205 Evaluation Board
The short-circuit current limit can be programmed by using
Equation 3:
R15
=
where:
(I
CLIM
− D
I
L
(
PP
)
×
0.5)
×
R
DS(ON)
+
V
CL
I
CL
Eq. 3
I
CLIM
= Desired current limit
R
DS(ON)
= On-resistance of low-side power MOSFET, 16mΩ
typically
V
CL
= Current-limit threshold (typical absolute value is
14mV per Electrical Characteristics in the MIC45205 data
sheet)
I
CL
= Current-limit source current (typical value is 80µA,
per Electrical Characteristics in the MIC45205 data sheet).
ΔI
L(PP)
= Inductor current peak-to-peak, since the inductor
is integrated, use Equation 4 to calculate the inductor
ripple current.
The peak-to-peak inductor current ripple is:
Figure 1. MIC45205 Current-Limiting Circuit
In each switching cycle of the MIC45205, the inductor
current is sensed by monitoring the low-side MOSFET in
the OFF period. The sensed voltage V
(ILIM)
is compared
with the power ground (PGND) after a blanking time of
150ns. In this way the drop voltage over the resistor R15
(V
CL
) is compared with the drop over the bottom FET
generating the short current limit. The small capacitor
(C15) connected from ILIM pin to PGND filters the
switching node ringing during the off-time allowing a better
short-limit measurement. The time constant created by
R15 and C15 should be much less than the minimum off
time.
The V
CL
drop allows programming of short limit through the
value of the resistor (R15) if the absolute value of the
voltage drop on the bottom FET is greater than V
CL
. In that
case the V
(ILIM)
is lower than PGND and a short circuit
event is triggered. A hiccup cycle to treat the short event is
generated. The hiccup sequence including the soft-start
reduces the stress on the switching FETs and protects the
load and supply for severe short conditions.
D
I
L(PP)
=
V
OUT
×
(V
IN(MAX)
−
V
OUT
)
V
IN(MAX)
×
f
sw
×
L
Eq. 4
The MIC45205 has 1.0µH inductor integrated into the
module. In case of hard short, the short limit is folded
down to allow an indefinite hard short on the output without
any destructive effect. It is mandatory to make sure that
the inductor current used to charge the output capacitance
during soft start is under the folded short limit; otherwise
the supply will go in hiccup mode and may not be finishing
the soft start successfully.
The MOSFET R
DS(ON)
varies 30 to 40% with temperature.
Therefore, it is recommended to add a 50% margin to I
CLIM
in the above equation to avoid false current limiting due to
increased MOSFET junction temperature rise. With R15 =
1.37kΩ and C15 = 15pF, the typical output current limit is
8A.
February 9, 2015
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Revision 2.0
Micrel, Inc.
Setting the Switching Frequency
The MIC45205 switching frequency can be adjusted by
changing the value of resistors R1 and R2. The switching
frequency also depends on VIN, V
OUT
and load conditions.
MIC45205 Evaluation Board
Figure 2. Switching Frequency Adjustment
Equation 5 gives the estimated switching frequency:
f
SW
=
f
O
×
R2
R1
+
R2
Eq. 5
where:
f
O
= 600kHz
R1 = 100kΩ (recommended)
R2 is selected to set the required switching frequency as
shown in
Figure 3:
Switching Frequency
800
700
600
V
OUT
= 5V
V
IN
= 12V
SW FREQ (kHz)
500
400
300
200
100
0
10.00
R1 = 100kΩ
100.00
1000.00
10000.00
R2 (kΩ)
Figure 3. Switching Frequency vs. R2
February 9, 2015
4
Revision 2.0
Micrel, Inc.
MIC45205 Evaluation Board
MIC45205 Evaluation Board Schematic
Figure 4. Schematic of MIC45205 Evaluation Board
February 9, 2015
5
Revision 2.0
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