Micrel MIC28511 60v/3a synchronous buck regulator Datasheet

MIC28511 Evaluation Board
60V/3A Synchronous Buck Regulator
General Description
Requirements
Micrel’s MIC28511 is a synchronous step-down regulator
featuring unique adaptive on-time control architecture with
integrated power MOSFETs. The MIC28511 operates over
an input supply range of 4.6V to 60V, 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% from 0°C to 85°C. The device operates with a
programmable switching frequency from 200kHz to
680kHz (nominal).
The MIC28511 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.
®
The MIC28511-1 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 MIC28511-2 utilizes Hyper Speed
TM
Control architecture, operating in fixed-frequency CCM
mode under all load conditions.
Datasheets and support documentation are available on
Micrel’s web site at: www.micrel.com.
Precautions
The MIC28511 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 60V; exceeding 60V can
damage the device.
Ordering Information
Part Number
MIC28511-1YML EV
MIC28511-2YML EV
Description
MIC28511 Evaluation Board
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.
MIC28511 Evaluation Board
Where:
Getting Started
VREF = 0.8V, and R1 is 10.0kΩ.
1. Connect VIN Supply
Connect a supply to the VIN and GND terminals,
paying careful attention to the polarity and the supply
range (4.6V < VIN < 60V). 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.
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 the R9 with Jumper J7
installed according to Equation 2:
R9 =
2. Connect Load and Monitor Input
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.
R1× VREF
VOUT - VREF
Eq. 2
Jumper J12 shorts out the feedback and forces the
converter to operate open loop and approach 100% duty
cycle.
SW Node
Use test point J1 (VSW) for monitoring the power MOSFET
switching waveform.
3. Enable Input
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 MIC28511 evaluation
board.
Current Limit
The MIC28511 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 60V
• Output range: 0.8V to 0.85V × VIN at 3A.
(For more detailed information, refer to Typical
Characteristics section. Note that 0.85V is the maximum
duty cycle of the MIC28511 controller)
Figure 1. MIC28511 Current Limiting Circuit
In each switching cycle of the MIC28511 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 pin 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:
R1 

VOUT = VREF ×  1 +

R9 

April 9, 2015
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.
Eq. 1
2
Revision 1.0
Micrel, Inc.
MIC28511 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 MIC28511 evaluation board was designed with a
6.8µH inductor for operation at 300kHz at 5V output. The
typical value of RWINDING(DCR) of this particular inductor is
39mΩ.
The short circuit current limit can be programmed by using
Equation 3:
R 22 =
(ICLIM - ΔIL (PP) × 0.5) × R DS(ON) + VCL
Setting the Switching Frequency
The MIC28511 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.
R17 is connected from the FREQ input to PGND and sets
the switching frequency according to Equation 4.
Eq. 3
ICL
Where:
ICLIM = Desired current limit
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
MIC28511 datasheet)
ICL = Current-limit source current (typical value is 70µA,
per the Electrical Characteristics section in the MIC28511
datasheet).
Figure 2. Switching Frequency Adjustment
ΔIL(PP) = Inductor current peak-to-peak
fSW _ ADJ = fO ×
The peak-to-peak inductor current ripple is:
∆IL(PP) =
VOUT × (VIN(MAX) - VOUT )
VIN(MAX) × fsw × L
R17
R19 + R17
Eq. 4
Where:
Eq. 4
fO = Switching frequency when R17 is open, per the
Electrical Characteristics section in the MIC28511
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 may 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
R22
Typical Output Current Limit
(VIN = 12V, VOUT = 5V, L = 6.8µH)
1.74kΩ
4.4 A
1.24kΩ
3.1 A
April 9, 2015
Figure 3. Switching Frequency vs. R17
3
Revision 1.0
Micrel, Inc.
MIC28511 Evaluation Board
Typical Characteristics
100
100
90
90
5.0V
90
80
3.3V
80
70
3.3V
60
2.5V
EFFICIENCY (%)
5.0V
50
40
100
5.0V
EFFICIENCY (%)
80
EFFICIENCY (%)
Efficiency (VIN = 48V)
vs. Output Current MIC28511-1
Efficiency (VIN = 24V)
vs. Output Current MIC28511-1
Efficiency (VIN =12V)
vs. Output Current MIC28511-1
2.5V
70
60
50
40
20
20
fSW = 300kHz
10
0.01
0.1
1
50
40
0.1
1
fSW = 300kHz
20
fSW = 300kHz
10
0.01
10
2.5V
60
30
30
30
3.3V
70
10
0.01
10
0.1
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
24V Input Thermal Derating
MIC28511-1
12V Input Thermal Derating
MIC28511-1
3.5
1
10
OUTPUT CURRENT (A)
48V Input Thermal Derating
MIC28511-1
3.5
3.5
3.0
3.0
OUTPUT CURRENT (A)
5.0V
3.3V
2.5
2.0
1.5
VIN =12V
fSW = 300kHz
TJMAX =125°C
θJA = 30°C/W
1.0
0.5
5.0V
3.3V
2.5V
2.5
2.0
1.5
VIN =24V
fSW = 300kHz
TJMAX =125°C
θJA = 30°C/W
1.0
0.5
0.0
40
55
70
85
25
100
IC Power Dissipation
vs. Output Current MIC28511-1
IC POWER DISSIPATION (W)
IC POWER DISSIPATION (W)
40
55
70
85
0.8
0.6
5.0V
3.3V
0.2
25
1
1.5
2
OUTPUT CURRENT (A)
April 9, 2015
2.5
3
55
70
85
100
IC Power Dissipation
vs. Output Current MIC28511-1
3.0
1.5
1.0
5.0V
0.5
3.3V
2.5V
0.0
0.0
40
AMBIENT TEMPERATURE (°C)
VIN ==24V
Vin
24V
fSW = 300kHz
2.5V
0.5
VIN = 48V
fSW = 300kHz
TJMAX = 125°C
θJA = 30°C/W
1.0
100
2.0
VIN = 12V
fSW = 300kHz
0
1.5
IC Power Dissipation
vs. Output Current MIC28511-1
1.2
0.4
2.0
AMBIENT TEMPERATURE (°C)
AMBIENT TEMPERATURE (°C)
1.0
5.0V
2.5
0.0
0.0
25
3.3V
2.5V
0.5
IC POWER DISSIPATION (W)
OUTPUT CURRENT (A)
3.0
OUTPUT CURRENT (A)
2.5V
VIN ==24V
Vin
48V
fSW = 300kHz
2.5
2.0
1.5
5.0V
3.3V
1.0
2.5V
0.5
0.0
0
0.5
1
1.5
2
OUTPUT CURRENT (A)
4
2.5
3
0
0.5
1
1.5
2
2.5
3
OUTPUT CURRENT (A)
Revision 1.0
Micrel, Inc.
MIC28511 Evaluation Board
Typical Characteristics (Continued)
100
90
90
90
80
80
80
5.0V
3.3V
2.5V
70
60
50
40
70
5.0V
3.3V
2.5V
60
50
40
fSW = 300kHz
0.1
1
fSW = 300kHz
20
10
0.01
10
0.1
12V Input Thermal Derating
MIC28511-2
OUTPUT CURRENT (A)
10
0.01
10
1.5
VIN = 12V
fSW = 300kHz
TJMAX =125°C
θJA = 30°C/W
55
70
3.0
2.5
3.3V
2.0
1.5
2.5V
VIN = 24V
fSW = 300kHz
TJMAX =125°C
θJA = 30°C/W
1.0
85
40
2.0
1.5
VIN = 48V
fSW = 300kHz
TJMAX = 125°C
θJA = 30°C/W
1.0
0.5
55
70
85
25
100
IC POWER DISSIPATION (W)
1.2
1.0
0.8
5.0V
3.3V
70
85
100
3.0
VIN ==24V
Vin
24V
fSW = 300kHz
1.5
1.0
5.0V
0.5
55
IC Power Dissipation
vs. Output Current MIC28511-2
2.0
VIN =12V
fSW = 300kHz
40
AMBIENT TEMPERATURE (°C)
IC Power Dissipation
vs. Output Current MIC28511-2
1.8
0.6
2.5
AMBIENT TEMPERATURE (°C)
IC Power Dissipation
vs. Output Current MIC28511-2
1.4
5.0V
3.3V
2.5V
3.0
0.0
25
100
AMBIENT TEMPERATURE (°C)
1.6
10
48V Input Thermal Derating
MIC28511-2
0.0
40
1
3.5
0.5
0.0
25
0.1
OUTPUT CURRENT (A)
IC POWER DISSIPATION (W)
OUTPUT CURRENT (A)
2.5V
0.5
fSW = 300kHz
5.0V
3.3V
1.0
1
3.5
3.0
2.0
40
24V Input Thermal Derating
MIC28511-2
5.0V
2.5
50
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
3.5
5.0V
3.3V
2.5V
60
20
OUTPUT CURRENT (A)
10
0.01
70
30
30
20
0.4
EFFICIENCY (%)
100
EFFICIENCY (%)
EFFICIENCY (%)
100
30
IC POWER DISSIPATION (W)
Efficiency (VIN = 48V)
vs. Output Current MIC28511-2
Efficiency (VIN = 24V)
vs. Output Current MIC28511-2
Efficiency (VIN = 12V)
vs. Output Current MIC28511-2
3.3V
2.5V
0.2
VIN = 48V
fSW = 300kHz
2.5
2.0
1.5
5.0V
1.0
3.3V
2.5V
0.5
2.5V
0.0
0.0
0.0
0.0
0.5
1.0
1.5
2.0
OUTPUT CURRENT (A)
April 9, 2015
2.5
3.0
0.0
0.5
1.0
1.5
2.0
OUTPUT CURRENT (A)
5
2.5
3.0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
OUTPUT CURRENT (A)
Revision 1.0
Micrel, Inc.
MIC28511 Evaluation Board
Evaluation Board Schematic
Bill of Materials
Item
C1
C2, C3
C4, C7
Part Number
UVZ2A330MPD
12061Z475KAT2A
C1608X7R1A225K080AC
Manufacturer
Description
(1)
Nichicon
33µF/100V 20% Radial Aluminum Capacitor
1
(2)
4.7µF/100V, X7S, Size 1206 Ceramic Capacitor
2
(3)
2.2µF/10V, X7R, Size 0603 Ceramic Capacitor
2
Open
NA
0.1µF/10V, X7R, Size 0603 Ceramic Capacitor
2
0.47µF/100V, X7R, Size 0805 Ceramic Capacitor
1
Murata
0.1µF/100V, X7R, Size 0603 Ceramic Capacitor
2
TDK
470pF/50V, X7R, Size 0603 Ceramic Capacitor
1
AVX
TDK
C5, C11, C13,
C18, C19, C20
C6, C16
C9
C0603C104K8RACTU
GRM21BR72A474KA73
08051C474KAT2A
C10, C17
GRM188R72A104KA35D
C12
CGA3E2X7R1H471K
Qty.
(4)
Kemet
Murata
(5)
AVX
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 9, 2015
6
Revision 1.0
Micrel, Inc.
MIC28511 Evaluation Board
Bill of Materials (Continued)
Item
Part Number
C14, C15
GRM32ER71A476KE15L
Murata
C21
C1608NP02A270J080AA
TDK
D1
BAT46W-TP
Manufacturer
(6)
MCC
D3
77311-118-02LF
L1
XAL7030-682MED
CRCW060310K0FKEA
FCI
(7)
Coilcraft
(8)
Vishay Dale
(9)
R2, R9, R25, R26
Qty.
47µF/10V, X7R, Size 1210 Ceramic Capacitor
2
27pF 100V, NPO, Size 0603 Ceramic Capacitor
1
100V Small Signal Schottky Diode, SOD123
1
Open
J1, J7, J8,
J10 − J12,
J16 − J18
R1
Description
NA
CONN HEADER 2POS VERT T/H
9
6.8µH, 10.7A Saturation Current
1
10.0kΩ, Size 0603, 1% Resistor
1
Open
NA
R10
CRCW06033K24FKEA
Vishay Dale
3.24kΩ, Size 0603, 1% Resistor
1
R11
CRCW06031K91FKEA
Vishay Dale
1.91kΩ, Size 0603, 1% Resistor
1
R14, R15
CRCW06030000FKEA
Vishay Dale
0.0 Ω, Size 0603, Resistor Jumper
2
R3, R16,
R17, R19
CRCW0603100K0FKEA
Vishay Dale
100kΩ, Size 0603, 1% Resistor
4
R18
CRCW06031K00JNEA
Vishay Dale
1.0kΩ, Size 0603, 5% Resistor
1
R20, R21
CRCW060349R9FKEA
Vishay Dale
49.9Ω, Size 0603, 1% Resistor
2
R22
CRCW06031K74FKEA
Vishay Dale
1.74kΩ, Size 0603, 1% Resistor
1
R23
CRCW08051R21FKEA
Vishay Dale
1.21Ω, Size 0805, 1% Resistor
1
R24
CRCW060310R0FKEA
Vishay Dale
10.0Ω, Size 0603, 1% Resistor
1
TP7, TP14,
TP8, TP13,
TP17, TP18
TP9 − TP12
U1
Open
1502
MIC28511-1YFL
MIC28511-2YFL
Keystone
(10)
Electronics
(11)
Micrel. Inc.
NA
Test Point Turret, .090
4
60V/3A 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 9, 2015
7
Revision 1.0
Micrel, Inc.
MIC28511 Evaluation Board
Evaluation Board Layout Recommendations
Top Layer
Mid-Layer 1 (Ground Plane)
April 9, 2015
8
Revision 1.0
Micrel, Inc.
MIC28511 Evaluation Board
Evaluation Board Layout Recommendations (Continued)
Mid-Layer 2
Bottom Layer
April 9, 2015
9
Revision 1.0
Micrel, Inc.
MIC28511 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 9, 2015
10
Revision 1.0