MIC28512-2YFL-EV [MICROCHIP]
EVAL BOARD FOR MIC28512-2;
| 型号： | MIC28512-2YFL-EV |
| 厂家： | 
MICROCHIP |
| 描述： | EVAL BOARD FOR MIC28512-2 |
| 文件： | 总10页 (文件大小：525K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
MIC28512 Evaluation Board
70V/2A Synchronous Buck Regulator
General Description
Requirements
Micrel’s MIC28512 is a synchronous step-down regulator
featuring unique adaptive on-time control architecture with
integrated power MOSFETs. The MIC28512 operates over
an input supply range of 4.6V to 70V, and can be used to
supply up to 2A of output current. The output voltage is
adjustable down to 0.8V with a guaranteed accuracy of
±1% from 0°C to 85°C. The device operates with a
programmable switching frequency from 200kHz to
680kHz (nominal).
The MIC28512-1 uses the HyperLight Load® architecture
to operate in pulse-skipping mode at light load while
functioning in fixed-frequency CCM mode from medium
load to heavy load. The MIC28512-2 utilizes Hyper Speed
ControlTM architecture, operating in fixed-frequency CCM
mode under all load conditions.
The MIC28512 evaluation board requires only a single
power supply with at least 5A current capability. For
applications where VIN is less than +5.5V, the internal LDO
can be bypassed by tying VDD to VIN.
Precautions
The MIC28512 evaluation board does not have reverse
polarity protection. Applying a negative voltage to the VIN
and GND terminals can damage the device. The maximum
VIN of the board is rated at 70V; exceeding 70V can
damage the device.
Ordering Information
Part Number
Description
MIC28512-1YML EV
MIC28512-2YML EV
MIC28512 Evaluation Board
Datasheets and support documentation are available on
Micrel’s web site at: www.micrel.com.
Evaluation Board
Hyper Speed Control is a trademark and HyperLight 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
April 9, 2015 Revision 1.0
Micrel, Inc.
MIC28512 Evaluation Board
Where:
REF = 0.8V, and R1 is 10.0kΩ.
Getting Started
V
1. Connect VIN Supply
With jumpers J11, J8, and J7 removed, the output
regulates at the 0.8V reference voltage. All other voltages
not listed can be set by modifying R9 with Jumper J7
installed according to Equation 2:
Connect a supply to the VIN and GND terminals,
paying careful attention to the polarity and the supply
range (4.6V < VIN < 70V). 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.
R1× V
REF
2. Connect Load and Monitor Input
R9 =
Eq. 2
V
- V
REF
OUT
Connect a load to the VOUT and GND terminals. The
load can be either a passive or an active electronic
load. A current meter can be placed between the
VOUT terminal and load to monitor the output current.
Ensure the output voltage is monitored at the VOUT
terminal.
Jumper J12 shorts out the feedback and forces the
converter to operate open loop and approach 100% duty
cycle.
SW Node
3. Enable Input
Use test point J1 (VSW) for monitoring the power MOSFET
switching waveform.
The EN terminal 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 (J16) connector is provided on the evaluation
board for ease-of-access to the enable feature.
Applying an external logic signal on the EN terminal to
pull it low or using a jumper to short the EN terminal to
the GND terminal will disable the MIC28512 evaluation
board.
Current Limit
The MIC28512 uses the RDS(ON) and external resistor
connected from ILIM to the SW node to decide the current
limit (see Figure 1).
4. Apply Power
Apply VIN and verify that the output voltage regulates
to the set voltage.
Evaluation Board Description
The basic parameters of the evaluation board are:
• Input range: 4.6V to 70V
• Output range: 0.8V to 0.85V × VIN at 2A.
Figure 1. MIC28512 Current-Limiting Circuit
(For more detailed information, refer to Typical
Characteristics section. Note that 0.85V is the maximum
duty cycle of the MIC28512 controller)
In each switching cycle of the MIC28512 converter 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 R22 (VCL) is compared with the drop over the
bottom FET generating the short current limit. The small
capacitor (C18) connected from ILIM to PGND filters the
switching node ringing during the off time which allows a
better short-limit measurement. The time constant created
by R22 and C18 should be much less than the minimum
off time.
• 300kHz switching frequency
(Adjustable 200kHz to 680kHz)
Feedback Resistors
With Jumper J11 in place, the output voltage is set to 5.0V
as determined by the feedback dividers R1 and R11.
Jumper J8 sets the output voltage to 3.3V. With jumper J7
in place the output is set by modifying R9, as illustrated in
Equation 1:
The VCL drop allows programming of short limit through the
value of the resistor (R22). If the absolute value of the
voltage drop on the bottom FET is greater than VCL, V(ILIM)
is lower than PGND and a short-circuit event is triggered.
R1
R9
Eq. 1
VOUT = VREF × 1+
April 8, 2015
Revision 1.0
2
Micrel, Inc.
MIC28512 Evaluation Board
A “hiccup” soft-start cycle is generated, reducing the stress
on the power switching FETs while protecting the load and
supply during severe short conditions.
The MIC28512 evaluation board was designed with a
8.2µH inductor for operation at 300kHz at 5V output. The
typical value of RWINDING(DCR) of this particular inductor is
44mΩ.
The short circuit current limit can be programmed by using
Equation 3:
Setting the Switching Frequency
The MIC28512 switching frequency can be adjusted by
changing the value of resistor R17. The top resistor (R19)
is set at 100kΩ and is connected between VIN and FREQ.
R4 is connected from the FREQ input to PGND and sets
the switching frequency according to Equation 4.
(ICLIM - ΔIL ) × 0.5)×RDS(ON) + VCL
(
PP
Eq. 3
R22 =
ICL
Where:
CLIM = Desired current limit
I
RDS(ON) = On-resistance of low-side power MOSFET,
28mΩ typically
VCL = Current-limit threshold (typical absolute value is
14mV, per the Electrical Characteristics section in the
MIC28512 datasheet)
ICL = Current-limit source current (typical value is 70µA,
per the Electrical Characteristics section in the MIC28512
datasheet).
Figure 2. Switching Frequency Adjustment
ΔIL(PP) = Inductor current peak-to-peak
R17
Eq. 4
f
= f ×
O
The peak-to-peak inductor current ripple is:
SW _ ADJ
R19 + R17
V
×(V
- V
)
OUT
IN(MAX)
OUT
Eq. 4
Where:
∆I
=
L(PP)
V
× f ×L
sw
IN(MAX)
fO = Switching frequency when R17 is open, per the
Electrical Characteristics section in the MIC28512
datasheet.
In case of hard short, the short current-limit threshold (VCL)
is reduced by half to the short-circuit threshold. This allows
an indefinite hard short on the output without any
destructive effect. It is critical to make sure that the
inductor current used to charge the output capacitance
during soft start is below the foldback short-circuit level;
otherwise the supply can go into hiccup mode and latch up
at start up. This should be verified over the operating
temperature range as well.
For a more precise setting, it is recommended to use the
Figure 3:
The MOSFET RDS(ON) varies 30% to 40% with temperature.
Therefore, it is recommended to add a 50% margin to ICL
in Equation 4 to avoid false current limiting due to
increased MOSFET junction temperature rise. Table 1
shows typical output current limit value for a given R22.
Table 1. R22 Typical Output Current-Limit Value
Typical Output Current Limit
R22
(VIN = 12V, VOUT = 5V, L = 8.2µH)
2.21kΩ
1.82kΩ
4.3A
3.0A
Figure 3. Switching Frequency vs. R17
April 8, 2015
Revision 1.0
3
Micrel, Inc.
MIC28512 Evaluation Board
Typical Characteristics
Efficiency (VIN = 24V)
Efficiency (VIN = 48V)
Efficiency (VIN = 12V)
vs. Output Current MIC28512-1
vs. Output Current MIC28512-1
vs. Output Current MIC28512-1
100
100
90
80
70
60
50
40
30
20
10
100
90
80
70
60
50
40
30
20
10
5.0V
90
3.3V
5.0V
3.3V
5.0V
3.3V
80
70
60
50
40
30
fSW = 300kHz
fSW = 300kHz
fSW = 300kHz
20
10
0.01
0.1
1
10
0.01
0.1
1
10
0.01
0.1
1
10
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
12V Input Thermal Derating
MIC28512-1
24V Input Thermal Derating
MIC28512-1
48V Input Thermal Derating
MIC28512-1
2.5
2.5
2.5
2.0
1.5
1.0
0.5
0.0
2.0
1.5
1.0
0.5
0.0
2.0
1.5
1.0
0.5
0.0
5.0V
3.3V
5.0V
3.3V
5.0V
3.3V
VIN = 24V
fSW = 300kHz
TJ(MAX) =125°C
VIN = 48V
fSW = 300kHz
TJ(MAX) =125°C
VIN = 12V
fSW = 300kHz
TJ(MAX) =125°C
θJA = 30°C/W
θJA = 30°C/W
θJA = 30°C/W
25
40
55
70
85
100
25
40
55
70
85
100
25
40
55
70
85
100
AMBIENT TEMPERATURE (°C)
AMBIENT TEMPERATURE (°C)
AMBIENT TEMPERATURE (°C)
IC Power Dissipation
IC Power Dissipation
IC Power Dissipation
vs. Output Current MIC28512-1
vs. Output Current MIC28512-1
vs. Output Current MIC28512-1
1.0
1.2
1.0
0.8
0.6
0.4
0.2
0.0
2.4
2.0
1.6
1.2
0.8
0.4
0.0
VIN =12V
fSW = 300kHz
=
2
4
V
= 48V
IN
IN
f= 300kHz
f= 300kHz
SW
SW
0.8
0.6
0.4
0.2
0.0
5.0V
3.3V
5.0V
3.3V
5.0V
3.3V
0
0.5
1
1.5
2
0
0.5
1
1.5
2
0
0.5
1
1.5
2
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
April 8, 2015
Revision 1.0
4
Micrel, Inc.
MIC28512 Evaluation Board
Typical Characteristics (Continued)
Efficiency (VIN = 12V)
Efficiency (VIN = 24V)
Efficiency (VIN = 48V)
vs. Output Current MIC28512-2
vs. Output Current MIC28512-2
vs. Output Current MIC28512-2
100
90
80
70
60
50
40
30
20
10
100
90
80
70
60
50
40
30
20
10
100
90
80
70
60
50
40
30
20
10
5.0V
3.3V
5.0V
3.3V
5.0V
3.3V
fSW = 300kHz
fSW = 300kHz
fSW = 300kHz
0.01
0.1
1
10
0.01
0.1
1
10
100
2
0.01
0.1
1
10
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
12V Input Thermal Derating
MIC28512-2
48V Input Thermal Derating
MIC28512-2
24V Input Thermal Derating
MIC28512-2
2.5
2.5
2.5
2.0
1.5
1.0
0.5
0.0
5.0V
3.3V
2.0
1.5
1.0
0.5
0.0
2.0
1.5
1.0
0.5
0.0
5.0V
3.3V
5.0V
3.3V
VIN = 48V
fSW = 300kHz
TJ(MAX) =125°C
VIN = 24V
VIN = 12V
fSW = 300kHz
TJ(MAX) =125°C
fSW = 300kHz
TJ(MAX) =125°C
JA = 30°C/W
θ
JA = 30°C/W
θ
θ
JA = 30°C/W
25
40
55
70
85
25
40
55
70
85
100
25
40
55
70
85
100
AMBIENT TEMPERATURE (°C)
AMBIENT TEMPERATURE (°C)
AMBIENT TEMPERATURE (°C)
IC Power Dissipation
vs. Output Current MIC28512-2
IC Power Dissipation
vs. Output Current MIC28512-2
IC Power Dissipation
vs. Output Current MIC28512-2
1.0
1.2
1.0
0.8
0.6
0.4
0.2
0.0
2.4
VIN = 12V
VIN=24V
VIN=48V
2.0
1.6
1.2
0.8
0.4
0.0
fSW = 300kHz
fSW = 300kHz
fSW = 300kHz
0.8
0.6
0.4
0.2
0.0
5.0V
3.3V
5.0V
3.3V
5.0V
3.3V
0
0.5
1
1.5
2
0
0.5
1
1.5
0
0.5
1
1.5
2
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
April 8, 2015
Revision 1.0
5
Micrel, Inc.
MIC28512 Evaluation Board
Evaluation Board Schematic
Bill of Materials
Item
Part Number
Manufacturer Description
Qty.
C1
UVZ2A330MPD
Nichicon(1)
AVX(2)
TDK(3)
33µF/100V 20% Radial Aluminum Capacitor
4.7µF/100V, X7S, Size 1206 Ceramic Capacitor
1
2
2
C2, C3
C4, C7
12061Z475KAT2A
C1608X7R1A225K080AC
2.2µF/10V, X7R, Size 0603 Ceramic Capacitor
C5, C11, C13,
C18, C19, C20,
C21
Open
NA
C6, C16
C0603C104K8RACTU
GRM21BR72A474KA73
08051C474KAT2A
Kemet(4)
Murata(5)
AVX
0.1µF/10V, X7R, Size 0603 Ceramic Capacitor
0.47µF/100V, X7R, Size 0805 Ceramic Capacitor
2
1
C9
C10, C17
C12
GRM188R72A104KA35D
CGA3E2X7R1H102K
Murata
TDK
0.1µF/100V, X7R, Size 0603 Ceramic Capacitor
1nF/50V, X7R, Size 0603 Ceramic Capacitor
2
1
Notes:
1. Nichicon: www.nichicon.co.jp/english.
2. AVX: www.avx.com.
3. TDK: www.tdk.com.
4. Kemet.: www.kemet.com.
5. Murata: www.murata.com.
April 8, 2015
Revision 1.0
6
Micrel, Inc.
MIC28512 Evaluation Board
Bill of Materials (Continued)
Item
C14, C15
D1
Part Number
Manufacturer
Murata
Description
Qty.
GRM32ER71A476KE15L
BAT46W-TP
47µF/10V, X7R, Size 1210 Ceramic Capacitor
100V Small Signal Schottky Diode, SOD123
Open
2
1
MCC(6)
D3
NA
J1, J7, J8,
J10 − J12,
J16 − J18
77311-118-02LF
FCI(7)
CONN HEADER 2POS VERT T/H
9
L1
XAL7030-822MED
Coilcraft(8)
Vishay Dale(9)
8.2µH, 10.2A Saturation Current
10.0kΩ, Size 0603, 1% Resistor
Open
1
1
R1
CRCW060310K0FKEA
R2, R9, R25, R26
R10
NA
1
CRCW06033K24FKEA
CRCW06031K91FKEA
CRCW06030000FKEA
Vishay Dale
Vishay Dale
Vishay Dale
3.24kΩ, Size 0603, 1% Resistor
1.91kΩ, Size 0603, 1% Resistor
0.0 Ω, Size 0603, Resistor Jumper
R11
1
R14, R15
2
R3, R16,
R17, R19
CRCW0603100K0FKEA
Vishay Dale
100kΩ, Size 0603, 1% Resistor
4
R18
CRCW06031K00JNEA
CRCW060349R9FKEA
CRCW06032K21FKEA
CRCW08051R21FKEA
CRCW060340R0FKEA
Vishay Dale
Vishay Dale
Vishay Dale
Vishay Dale
Vishay Dale
1.0kΩ, Size 0603, 5% Resistor
49.9Ω, Size 0603, 1% Resistor
2.21kΩ, Size 0603, 1% Resistor
1.21Ω, Size 0805, 1% Resistor
40.0Ω, Size 0603, 1% Resistor
1
2
1
1
1
R20, R21
R22
R23
R24
TP7, TP14,
TP8, TP13,
TP17, TP18
Open
NA
Keystone
1502
Test Point Turret, .090
4
TP9 − TP12
Electronics(10)
MIC28512-1YFL
MIC28512-2YFL
Micrel. Inc.(11)
U1
70V/2A Synchronous Buck Regulator
1
Notes:
6. MCC: www.mcc.com.
7. FCI: www.fciconnect.com.
8. Coilcraft: www.coilcraft.com.
9. Vishay Dale: www.vishay.com.
10. Keystone Electronics: www.keystone.com.
11. Micrel, Inc.: www.micrel.com.
April 8, 2015
Revision 1.0
7
Micrel, Inc.
MIC28512 Evaluation Board
Evaluation Board Layout Recommendations
Top Layer
Mid-Layer 1 (Ground Plane)
April 8, 2015
Revision 1.0
8
Micrel, Inc.
MIC28512 Evaluation Board
Evaluation Board Layout Recommendations (Continued)
Mid-Layer 2
Bottom Layer
April 8, 2015
Revision 1.0
9
Micrel, Inc.
MIC28512 Evaluation Board
MICREL, INC. 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA
TEL +1 (408) 944-0800 FAX +1 (408) 474-1000 WEB http://www.micrel.com
Micrel, Inc. is a leading global manufacturer of IC solutions for the worldwide high-performance linear and power, LAN, and timing & communications
markets. The Company’s products include advanced mixed-signal, analog & power semiconductors; high-performance communication, clock
management, MEMs-based clock oscillators & crystal-less clock generators, Ethernet switches, and physical layer transceiver ICs. Company
customers include leading manufacturers of enterprise, consumer, industrial, mobile, telecommunications, automotive, and computer products.
Corporation headquarters and state-of-the-art wafer fabrication facilities are located in San Jose, CA, with regional sales and support offices and
advanced technology design centers situated throughout the Americas, Europe, and Asia. Additionally, the Company maintains an extensive network
of distributors and reps worldwide.
Micrel makes no representations or warranties with respect to the accuracy or completeness of the information furnished in this datasheet. This
information is not intended as a warranty and Micrel does not assume responsibility for its use. Micrel reserves the right to change circuitry,
specifications and descriptions at any time without notice. No license, whether express, implied, arising by estoppel or otherwise, to any intellectual
property rights is granted by this document. Except as provided in Micrel’s terms and conditions of sale for such products, Micrel assumes no liability
whatsoever, and Micrel disclaims any express or implied warranty relating to the sale and/or use of Micrel products including liability or warranties
relating to fitness for a particular purpose, merchantability, or infringement of any patent, copyright, or other intellectual property right.
Micrel Products are not designed or authorized for use as components in life support appliances, devices or systems where malfunction of a product
can reasonably be expected to result in personal injury. Life support devices or systems are devices or systems that (a) are intended for surgical
implant into the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significant injury to the user. A
Purchaser’s use or sale of Micrel Products for use in life support appliances, devices or systems is a Purchaser’s own risk and Purchaser agrees to fully
indemnify Micrel for any damages resulting from such use or sale.
© 2015 Micrel, Incorporated.
April 8, 2015
Revision 1.0
10
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