Microchip MIC28304-2-12V Handleiding

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MIC28304 Evaluation Board
70V 3A Power Module
Hyper Speed Controlâ„¢ Family
General Description
The Micrel MIC28304 is 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. The
MIC28304 operates over an input supply range of 4.5V to
70V and can be used to supply up to 3A of output current.
The output voltage is adjustable down to 0.8V with a
guaranteed accuracy of ±1%. The device operates with a
programmable switching frequency from 200kHz to
600kHz.
The MIC28304-1 has the HyperLight Load® architecture,
so it can operate in pulse skipping mode at light load.
However, it operates in fixed frequency CCM mode from
medium load to heavy load. The MIC28304-2 has Hyper
Speed Control which operates in fixed â„¢ architecture,
frequency CCM mode under all load conditions.
The basic parameters of the evaluation board are:
• Input: 7V to 70V
• Output: 0.8V to 5V at 3A(1)
• 600kHz Switching Frequency (Adjustable 200kHz
to 600kHz)
Note:
1. Refer to temperature curves shown in the MIC28304 0.8V to 5V/3A
Evaluation Board Typical Characteristics section.
Datasheets and support documentation are available on
Micrel’s web site at: www.micrel.com.
Requirements
The MIC28304-1 and MIC28304-2 evaluation board
requires only a single power supply with at least 10A
current capability. o external linear regulator is required N
to power the internal biasing of the IC because the
MIC28304 has 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 MIC28304 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 70V. Exceeding 70V
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 (7V < VIN < 70V). Monitor with a current IIN
meter and input voltage at VIN and GND monitor
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
(R16) 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 28304 evaluation boardMIC .
4. Turn Power
Turn on the VIN supply and verify that the output
voltage is regulated to 5V.
Ordering Information
Part Number Description
MIC28304- 1 5V EV MIC28304 Evaluation -1
Board up to 5V Output
MIC28304- 2 5V EV MIC28304 2 Evaluation -
Board up to 5V Output
MIC28304-1 12V EV MIC28304 Evaluation -1
Board 12V Output
MIC28304-2 12V EV MIC28304 Evaluation -2
Board 12V Output
Hyper LightLoad is a registered trademark and Hyper Speed Control trademark of Micrel, Inc. is a
Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
April 29, 2014 Revision 1.0
Micrel, Inc.
MIC28304 Evaluation Board
Features
Feedback Resistors
The output voltage on the MIC28304 evaluation board,
which is preset to 5.0V, is determined by the feedback
divider:







+×=
BOTTOM
REFOUT R
R1
1VV
Eq. 1
where VREF = 0.8V, and RBOTTOM is one of R10, or R11,
which corresponds to 3.3V, 5V. Leaving the R BOTTOM open
gives a 0.8V output voltage. All other voltages not listed
above can be set by modifying RBOTTOM value according to:
REFOUT
REF
BOTTOM VV
VR1
R−
×
=
Eq. 2
Note that the output voltage should not be set to exceed
5V due to the 6.3V voltage rating on the output capacitors.
For higher output voltage, use the Ordering Information
table. Table 1 gives the typical values of some of the
components, for details refer to Bill of Material table.
Table 1. Typical Values of Some Components
VOUT VIN
R3
(Rinj)
R1
(Top Feedback Resistor)
R11
(Bottom Feedback Resistor)
C10
(Cinj)
C12
(Cff) COUT
0.9V 5V to 70V 16.5kΩ 10kΩ 80.6kΩ 0.1µF 2.2nF 47 µF /6.3V
or 2 x 22µF
1.2V 5V to 70V 16.5kΩ 10kΩ 20kΩ 0.1µF 2.2nF 47 µF /6.3V
or 2 x 22µF
1.8V 5V to 70V 16.5kΩ 10kΩ 8.06kΩ 0.1µF 2.2nF 47 µF /6.3V
or 2 x 22µF
2.5V 5V to 70V 16.5kΩ 10kΩ 4.75kΩ 0.1µF 2.2nF 47 µF /6.3V
or 2 x 22µF
3.3V 5V to 70V 16.5kΩ 10kΩ 3.24kΩ 0.1µF 2.2nF 47 µF /6.3V
or 2 x 22µF
5V 0.1µF 7V to 70V 16.5kΩ 10kΩ 1.9kΩ 2.2nF 47 µF/6.3V
or 2 x 22µF
12V 715 0.1µF 18V to 70V 23.2kΩ 10kΩ Ω 2.2nF 47 µF/16V
or 2 x 22µF
April 29 2 , 2014 Revision 1.0
Micrel, Inc.
MIC28304 Evaluation Board
SW Node
Test point J1 (VSW) is placed for monitoring the switching
waveform, which is one of the most critical waveforms for
the converter.
Current Limit
The MIC28304 uses the RDS(ON) -of the low side MOSFET
and external resistor connected from the ILIM pin to the
SW node to decide the current limit.
2.2µF
x2
MIC28304
PGND
VIN
VIN
SW
ILIM
R15
C6
Figure 1 . MIC28304 Current Limiting Circuit
In each switching cycle of the MIC28304, 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
(VCL) is compared with the drop over the bottom FET
generating the short current limit. The small capacitor (C6)
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 C6
should be much less than the minimum off time.
The VCL 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.
The short circuit current limit can be programmed by using
the following formula:
Eq. 3
ICLIM = Desired current limit
RDS(ON) = On- -resistance of low side power MOSFET, 57mΩ
typically
VCL -= Current limit threshold (typical absolute value is
14mV per Electrical Characteristics Table in MIC28304
data sheet)
ICL -= Current limit source current (typical value is 80µA,
per the Electrical Characteristics table).
ΔIL(PP) - -= Inductor current peak to peak, since the inductor
is integrated use Equation 4 to calculate the inductor ripple
current.
The peak peak inductor current ripple is:- -to
L f V
)V(VV
I
swIN(max)
OUTIN(max)OUT
L(PP)
××
−×
=∆
Eq. 4
The MIC28304 has 4.7µH inductor integrated into the
module. The typical value of RWINDING(DCR) of this particular
inductor is in the range of 45mΩ.
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 RDS(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. The
following table shows typical output current limit value for a
given R15 with C6 = 10pF.
R15 Typical Output Current Limit
1.81k 3AΩ
2.7k 6.3AΩ
April 29 3 , 2014 Revision 1.0

Product specificaties

Merk: Microchip
Categorie: Niet gecategoriseerd
Model: MIC28304-2-12V

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