MIC28304 [MICREL]
70V 3A Power Module;
| 型号： | MIC28304 |
| 厂家： | 
MICREL SEMICONDUCTOR |
| 描述： | 70V 3A Power Module |
| 文件： | 总39页 (文件大小：2843K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
MIC28304
70V 3A Power Module
Hyper Speed Control™ Family
General Description
Features
Micrel’s MIC28304 is synchronous step-down regulator
module, featuring a unique adaptive ON-time control
• Easy to use
− Stable with low-ESR ceramic output capacitor
− No compensation and no inductor to choose
• 4.5V to 70V input voltage
• Single-supply operation
• Power Good (PG) output
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 from 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
programmable switching frequency from 200kHz to
600kHz.
• Low radiated emission (EMI) per EN55022, Class B
• Adjustable current limit
• Adjustable output voltage from 0.9V to 24V
(also limited by duty cycle)
Micrel’s HyperLight Load™ architecture provides the same
high-efficiency and ultra-fast transient response as the
Hyper Speed Control™ architecture under the medium to
heavy loads, but also maintains high efficiency under light
load conditions by transitioning to variable frequency,
discontinuous-mode operation.
• 200kHz to 600kHz, programmable switching frequency
• Supports safe start-up into a pre-biased output
• –40°C to +125°C junction temperature range
• Available in 64-pin, 12mm × 12mm × 3mm QFN
package
The MIC28304 offers a full suite of protection features.
These include undervoltage lockout, internal soft-start,
foldback current limit, “hiccup” mode short-circuit
protection, and thermal shutdown.
Applications
• Distributed power systems
• Industrial, medical, telecom, and automotive
Datasheets and support documentation are available on
Micrel’s web site at: www.micrel.com.
Typical Application
Hyper Speed Control, HyperLight Load, and Any Capacitor are trademarks 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
Revision 1.1
March 25, 2014
Micrel, Inc.
MIC28304
Ordering Information
Junction
Temperature
Range
Switching
Frequency
Lead
Finish
Part Number
Features
Package
MIC28304-1YMP
MIC28304-2YMP
200kHz to 600kHz
200kHz to 600kHz
HyperLight Load
64-pin 12mm × 12mm QFN
64-pin 12mm × 12mm QFN
–40°C to +125°C
–40°C to +125°C
Pb-Free
Pb-Free
Hyper Speed Control
Pin Configuration
64-Pin 12mm × 12mm QFN (MP)
(Top View)
Pin Description
Pin Number
Pin Name Pin Function
Analog Ground. Ground for internal controller and feedback resistor network. The analog ground
return path should be separate from the power ground (PGND) return path.
1, 2, 3, 54, 64
GND
ILIM
Current Limit Setting. Connect a resistor from SW (pin #4) to ILIM to set the over-current threshold
for the converter.
4
Supply Voltage for Controller. The VIN operating voltage range is from 4.5V to 70V. A 0.47μF
ceramic capacitor from VIN (pin # 60) to AGND is required for decoupling. The pin # 5 should be
externally connected to either PVIN or pin # 60 on PCB.
5, 60
VIN
SW
Switch Node and Current-Sense Input. High current output driver return. The SW pin connects
directly to the switch node. Due to the high-speed switching on this pin, the SW pin should be routed
away from sensitive nodes. The SW pin also senses the current by monitoring the voltage across
the low-side MOSFET during OFF time.
6, 40 to 48, 51
Revision 1.1
March 25, 2014
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Micrel, Inc.
MIC28304
Pin Description (Continued)
Pin Number
Pin Name Pin Function
Switching Frequency Adjust Input. Leaving this pin open will set the switching frequency to 600kHz.
Alternatively a resistor from this pin to ground can be used to lower the switching frequency.
7, 8
FREQ
PGND
Power Ground. PGND is the return path for the buck converter power stage. The PGND pin
connects to the sources of low-side N-Channel external MOSFET, the negative terminals of input
capacitors, and the negative terminals of output capacitors. The return path for the power ground
should be as small as possible and separate from the analog ground (GND) return path.
9 to 13
14 to 22
23 to 38
39
PVIN
VOUT
NC
Power Input Voltage. Connection to the drain of the internal high-side power MOSFET.
Output Voltage. Connection with the internal inductor, the output capacitor should be connected
from this pin to PGND as close to the module as possible.
No Connection. Leave it floating.
Anode Bootstrap Diode Input. Anode connection of internal bootstrap diode, this pin should be
connected to the PVDD pin.
49, 50
52, 53
55, 56
ANODE
BSTC
BSTR
Bootstrap Capacitor. Connection to the internal bootstrap capacitor. Leave floating, no connect.
Bootstrap Resistor. Connection to the internal bootstrap resistor and high-side power MOSFET
drive circuitry. Leave floating, no connect.
Feedback Input. Input to the transconductance amplifier of the control loop. The FB pin is regulated
to 0.8V. A resistor divider connecting the feedback to the output is used to set the desired output
voltage.
57
58
59
FB
PGOOD
EN
Power Good Output. Open drain output, an external pull-up resistor to external power rails is
required.
Enable Input. A logic signal to enable or disable the buck converter operation. The EN pin is CMOS
compatible. Logic high enables the device, logic low shutdowns the regulator. In the disable mode,
the input supply current for the device is minimized to 4µA typically. Do not pull EN to PVDD.
Internal +5V Linear Regulator Output. PVDD is the internal supply bus for the device. In the
applications with VIN < +5.5V, PVDD should be tied to VIN to by-pass the linear regulator.
61, 62
63
PVDD
NC
No Connection. Leave it floating.
Revision 1.1
March 25, 2014
3
Micrel, Inc.
MIC28304
Operating Ratings(2)
Absolute Maximum Ratings(1)
Supply Voltage (PVIN, VIN) .............................. 4.5V to 70V
Enable Input (VEN).................................................0V to VIN
VSW, VFEQ, VILIM, VEN ..............................................0V to VIN
Power Good (VPGOOD)..………………..………...0V to PVDD
Junction Temperature (TJ) ........................−40°C to +125°C
Junction Thermal Resistance
PVIN, VIN to PGND ...................................... –0.3V to +76V
PVDD, VANODE to PGND .................................. –0.3V to +6V
VSW, VFREQ, VILIM, VEN........................ −0.3V to (PVIN +0.3V)
VBSTC/BSTR to VSW ................................................ −0.3V to 6V
VBSTC/BSTR to PGND.......................................... −0.3V to 82V
VFB, VPG to PGND .........................−0.3V to (PVDD + 0.3V)
PGND to AGND............................................ −0.3V to +0.3V
Junction Temperature ..............................................+150°C
Storage Temperature (TS).........................−65°C to +150°C
Lead Temperature (soldering, 10s)............................ 260°C
ESD Rating(3)................................................. ESD Sensitive
12mm × 12mm QFN-64 (θJA) ............................20°C/W
12mm × 12mm QFN-64 (θJC)...............................5°C/W
Electrical Characteristics(4)
PVIN = VIN = 12V, VOUT = 5V, VBST – VSW = 5V; TA = 25°C, unless noted. Bold values indicate −40°C ≤ TJ ≤ +125°C.
Parameter
Condition
Min.
Typ.
Max.
Units
Power Supply Input
Input Voltage Range (PVIN, VIN)
4.5
70
0.75
3
V
Current into Pin 60; VFB = 1.5V (MIC28304-1)
Current into Pin 60;VFB = 1.5V (MIC28304-2)
Current into Pin 60;VEN = 0V
0.4
2.1
0.1
0.7
27
4
mA
µA
mA
µA
Controller Supply Current(5)
10
IOUT = 0A (MIC28304-1)
Operating Current
IOUT = 0A (MIC28304-2)
Shutdown Supply Current
PVDD Supply(5)
PVIN = VIN = 12V, VEN = 0V
4.8
3.8
5.4
4.7
PVDD Output Voltage
PVDD UVLO Threshold
PVDD UVLO Hysteresis
Load Regulation
VIN = 7V to 70V, IPVDD = 10mA
PVDD rising
5.2
4.2
400
2
V
V
mV
%
IPVDD = 0 to 40mA
0.6
3.6
Reference(5)
TJ = 25°C (±1.0%)
−40°C ≤ TJ ≤ 125°C (±2%)
VFB = 0.8V
0.792
0.8
0.8
5
0.808
0.816
500
Feedback Reference Voltage
V
0.784
FB Bias Current
nA
Notes:
1. Exceeding the absolute maximum ratings may damage the device.
2. The device is not guaranteed to function outside its operating ratings.
3. Devices are ESD sensitive. Handling precautions are recommended. Human body model, 1.5kΩ in series with 100pF.
4. Specification for packaged product only.
5. IC tested prior to assembly.
Revision 1.1
March 25, 2014
4
Micrel, Inc.
MIC28304
Electrical Characteristics(4) (Continued)
PVIN = VIN = 12V, VOUT = 5V, VBST – VSW = 5V; TA = 25°C, unless noted. Bold values indicate −40°C ≤ TJ ≤ +125°C.
Parameter
Condition
Min.
Typ.
Max.
Units
Enable Control
EN Logic Level High
EN Logic Level Low
EN Hysteresis
EN Bias Current
Oscillator
1.8
V
V
0.6
20
200
5
mV
µA
VEN = 12V
400
750
FREQ pin = open
600
300
85
Switching Frequency
kHz
RFREQ = 100kΩ (FREQ pin-to-GND)
Maximum Duty Cycle
%
%
ns
Minimum Duty Cycle
VFB > 0.8V
0
Minimum Off-Time
140
200
260
Soft-Start(5)
Soft-Start Time
5
ms
Short-Circuit Protection(5)
Current-Limit Threshold (VCL)
Short-Circuit Threshold
Current-Limit Source Current
Short-Circuit Source Current
Leakage
VFB = 0.79V
VFB = 0V
0
9
mV
mV
µA
−30
−23
60
−14
−7
VFB = 0.79V
VFB = 0V
80
100
47
27
36
µA
SW, BSTR Leakage Current
Power Good(5)
50
µA
85
95
Power Good Threshold Voltage
Power Good Hysteresis
Power Good Delay Time
Power Good Low Voltage
Thermal Protection
Sweep VFB from low-to-high
Sweep VFB from high-to-low
Sweep VFB from low-to-high
VFB < 90% x VNOM, IPG = 1mA
90
6
%VOUT
%VOUT
µs
100
70
200
mV
Overtemperature Shutdown
Overtemperature Shutdown Hysteresis
TJ Rising
160
4
°C
°C
Revision 1.1
March 25, 2014
5
Micrel, Inc.
MIC28304
Electrical Characteristics(4) (Continued)
PVIN = VIN = 12V, VOUT = 5V, VBST – VSW = 5V; TA = 25°C, unless noted. Bold values indicate −40°C ≤ TJ ≤ +125°C.
Parameter
Condition
Min.
Typ.
Max.
Units
Output Characteristic
Output Voltage Ripple
Line Regulation
IOUT = 3A
16
mV
%
PVIN = VIN = 7V to 70V, IOUT = 3A
IOUT = 0A to 3A PVIN= VIN =12V (MIC28304-1)
IOUT = 0A to 3A PVIN= VIN =12V (MIC28304-2)
0.36
0.75
0.05
400
500
Load Regulation
%
I
OUT from 0A to 3A at 5A/µs (MIC28304-1)
IOUT from 3A to 0A at 5A/µs (MIC28304-1)
Output Voltage Deviation from Load Step
mV
IOUT from 0A to 3A at 5A/µs (MIC28304-2)
IOUT from 3A to 0A at 5A/µs (MIC28304-2)
400
500
Revision 1.1
March 25, 2014
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Micrel, Inc.
MIC28304
Typical Characteristics − 275kHz Switching Frequency
Efficiency vs. Output Current
(MIC28304-1)
Efficiency vs. Output Current
(MIC28304-2)
Thermal Derating
3
2
1
0
100
95
90
85
80
75
70
65
60
55
50
100
90
80
70
60
50
40
30
VOUT = 5V
FSW = 275kHz
j_MAX =125°C
12VIN
12VIN
24VIN
T
24VIN
MIC28304-2
VIN = 12V
VIN = 24V
36VIN
36VIN
48VIN
48VIN
VIN = 48V
VOUT = 5V
FSW = 275kHz
VOUT = 5V
FSW = 275kHz
25
40
55
70
85
100
115
0
0.5
1
1.5
2
2.5
3
0
0.5
1
1.5
2
2.5
3
MAXIMUM AMBIENT TEMPERATURE
(°C)
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
Table 1. Recommended Component Values for 275kHz Switching Frequency
R1
R11
R3
(Rinj)
C10
(Cinj)
C12
(Cff)
VOUT
VIN
R19
R15
COUT
(Top Feedback
Resistor)
(Bottom Feedback
Resistor)
5V
5V
7V to 18V
18V to 70V
5V to 18V
18V to 70V
16.5kΩ
39.2kΩ
16.5kΩ
39.2kΩ
10kΩ
10kΩ
10kΩ
10kΩ
1.9kΩ
1.9kΩ
0.1µF
0.1µF
0.1µF
0.1µF
2.2nF
2.2nF
2.2nF
2.2nF
2x47µF/6.3V
2x 47µF/6.3V
2x 47µF/6.3V
2x 47µF/6.3V
75kΩ
75kΩ
3.57k
3.57k
3.3V
3.3V
3.24kΩ
3.24kΩ
75kΩ
75kΩ
3.57k
3.57k
Revision 1.1
March 25, 2014
7
Micrel, Inc.
MIC28304
Typical Characteristics
VIN Operating Supply Current
vs. Input Voltage (MIC28304-1)
Output Regulation
vs. Input Voltage (MIC28304-1)
Feedback Voltage
vs. Input Voltage (MIC28304-1)
2.00
5.0%
4.0%
3.0%
2.0%
1.0%
0.0%
-1.0%
0.817
0.812
0.807
0.802
0.797
0.792
VOUT = 5.0V
IOUT = 0A to 3A
FSW = 600kHz
VOUT = 5V
IOUT = 0A
FSW = 600kHz
1.60
1.20
0.80
0.40
0.00
V
OUT = 5.0V
IOUT = 0A
SW = 600kHz
F
5
10 15 20 25 30 35 40 45 50 55 60 65 70
7
12 17 22 27 32 37 42 47 52 57 62 67
5
10 15 20 25 30 35 40 45 50 55 60 65 70
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
VIN Operating Supply Current
vs. Temperature (MIC28304-1)
Feedback Voltage
vs. Temperature (MIC28304-1)
Output Voltage
vs. Input Voltage (MIC28304-1)
2.00
1.60
1.20
0.80
0.40
0.00
0.808
0.804
0.800
0.796
0.792
5.08
5.06
5.04
5.02
5.00
4.98
4.96
4.94
4.92
4.90
VIN = 12V
VOUT = 5.0V
IOUT = 0A
FSW = 600kHz
VOUT = 5V
IOUT = 0A
FSW = 600kHz
VIN= 12V
VOUT = 5.0V
IOUT = 0A
FSW = 600kHz
5
10 15 20 25 30 35 40 45 50 55 60 65 70
-50
-25
0
25
50
75
100
125
-50
-25
0
25
50
75
100 125
INPUT VOLTAGE (V)
TEMPERATURE (°C)
TEMPERATURE (°C)
Load Regulation
vs. Temperature (MIC28304-1)
Line Regulation
vs. Temperature (MIC28304-1)
Line Regulation
vs. Temperature (MIC28304-1)
1.2%
1.0%
0.8%
0.6%
0.4%
0.2%
0.0%
0.8%
0.7%
0.6%
0.5%
0.4%
0.3%
0.2%
0.1%
0.0%
-0.1%
-0.2%
-0.3%
-0.4%
-0.5%
-0.6%
0.8%
VIN = 12V
0.7%
0.6%
0.5%
0.4%
0.3%
0.2%
0.1%
0.0%
-0.1%
-0.2%
-0.3%
-0.4%
-0.5%
-0.6%
VOUT = 5.0V
IOUT = 0A to 3A
FSW = 600kHz
VIN = 7V to 70V
VOUT = 5.0V
IOUT = 3A
VIN = 7V to 70V
VOUT = 5.0V
IOUT = 0A
FSW = 600kHz
FSW = 600kHz
-50
-25
0
25
50
75
100 125
-50
-25
0
25
50
75
100 125
-50
-25
0
25
50
75
100 125
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
Revision 1.1
March 25, 2014
8
Micrel, Inc.
MIC28304
Typical Characteristics (Continued)
Efficiency (VIN = 12V)
Feedback Voltage
Line Regulation
vs. Output Current (MIC28304-1)
vs. Output Current (MIC28304-1)
vs. Output Current (MIC28304-1)
0.808
0.804
0.800
0.796
0.792
1.0%
0.5%
100
90
80
70
60
50
40
30
20
10
VIN = 12V
VOUT = 5.0V
FSW = 600kHz
5.0V
3.3V
2.5V
1.8V
1.2V
0.8V
0.0%
-0.5%
-1.0%
-1.5%
-2.0%
-2.5%
-3.0%
VIN = 12V to 75V
VOUT = 5.0V
FSW = 600kHz
F
CCM
SW = 600kHz
0.0
0.5
1.0
1.5
2.0
2.5
3.0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
0.01
0.1
1
10
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
Efficiency (VIN = 18V)
vs. Output Current (MIC28304-1)
Efficiency (VIN = 24V)
vs. Output Current (MIC28304-1)
Efficiency (VIN = 38V)
vs. Output Current (MIC28304-1)
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
2.5V
1.8V
1.2V
0.8V
5.0V
5.0V
3.3V
2.5V
3.3V
2.5V
1.8V
1.8V
1.2V
0.8V
1.2V
0.8V
FSW = 600kHz
CCM
FSW = 600kHz
FSW = 600kHz
CCM
CCM
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)
Efficiency (VIN = 48V)
Efficiency (VIN = 70V)
Efficiency
vs. Output Current (MIC28304-1)
vs. Output Current (MIC28304-1)
vs. Output Current (MIC28304-1)
100
90
80
70
60
50
40
30
20
10
100
90
80
70
60
50
40
30
20
10
100
95
90
85
80
75
70
65
60
55
50
18VIN
24VIN
36VIN
48VIN
70VIN
5.0V
3.3V
5.0V
3.3V
2.5V
1.8V
1.2V
2.5V
1.8V
1.2V
0.8V
0.8V
VOUT = 12V
FSW = 600kHz
CCM
FSW = 600kHz
FSW = 600kHz
CCM
R3 = 23.2kΩ
CCM
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)
Revision 1.1
March 25, 2014
9
Micrel, Inc.
MIC28304
Typical Characteristics (Continued)
Output Regulation
vs. Input Voltage (MIC28304-2)
VIN Operating Supply Current
vs. Input Voltage (MIC28304-2)
Feedback Voltage
vs. Input Voltage (MIC28304-2)
50
40
30
20
10
0
0.812
0.808
0.804
0.800
0.796
0.792
1.0%
0.8%
0.6%
0.4%
0.2%
0.0%
-0.2%
-0.4%
-0.6%
-0.8%
-1.0%
VOUT = 5.0V
IOUT = 0A
FSW = 600kHz
VOUT = 5.0V
IOUT = 0A TO 3A
FSW = 600kHz
VOUT = 5V
IOUT = 0A
FSW = 600kHz
5
10 15 20 25 30 35 40 45 50 55 60 65 70
7
12 17 22 27 32 37 42 47 52 57 62 67
7
12 17 22 27 32 37 42 47 52 57 62 67
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
PVDD Voltage
vs. Input Voltage
Output Peak Current Limit
vs. Input Voltage
VIN Shutdown Current
vs. Input Voltage
50
10
10
8
45
40
35
30
25
20
15
10
5
8
6
4
2
0
IPVDD = 10mA
6
4
IPVDD = 40mA
VOUT = 5.0V
FSW = 600kHz
VOUT = 5.0V
FSW = 600kHz
2
VEN = 0V
R16 = OPEN
FSW = 600kHz
0
0
7
5
10 15 20 25 30 35 40 45 50 55 60 65 70
7
12 17 22 27 32 37 42 47 52 57 62 67
12 17 22 27 32 37 42 47 52 57 62 67
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
Switching Frequency
vs. Input Voltage
VIN Shutdown Current
vs. Temperature
Enable Threshold
vs. Input Voltage
800
750
700
650
600
550
500
450
400
1.50
1.20
0.90
0.60
0.30
0.00
10
9
8
7
6
5
4
3
2
1
RISING
VOUT = 5.0V
IOUT = 2A
FALLING
VIN = 12V
VEN = 0V
IOUT = 0A
FSW = 600kHz
FSW = 600kHz
0
5
10 15 20 25 30 35 40 45 50 55 60 65 70
-50
-25
0
25
50
75
100
125
7
12 17 22 27 32 37 42 47 52 57 62 67
INPUT VOLTAGE (V)
TEMPERATURE (°C)
INPUT VOLTAGE (V)
Revision 1.1
March 25, 2014
10
Micrel, Inc.
MIC28304
Typical Characteristics (Continued)
Output Peak Current Limit
vs. Temperature
PVDD Voltage
vs. Temperature
PVDD UVLO Threshold
vs. Temperature
6.0
5.5
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
4.4
4.3
4.2
4.1
4.0
3.9
3.8
3.7
3.6
3.5
3.4
3.3
10
8
IPVDD = 10mA
RISING
IPVDD = 40mA
6
FALLING
4
VIN = 12V
VOUT = 5.0V
FSW = 600kHz
VIN = 12V
IOUT = 0A
FSW = 600kHz
2
VIN = 12V
IOUT = 0A
FSW = 600kHz
0
-50
-25
0
25
50
75
100
125
-50
-25
0
25
50
75 100 125
-50
-25
0
25
50
75
100
125
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
EN Bias Current
vs. Temperature
Enable Threshold
vs. Temperature
VIN Operating Supply Current
vs. Temperature (MIC28304-2)
100
80
60
40
20
0
1.5
1.4
1.3
1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
40
VIN = 12V
VOUT = 5V
FSW = 600kHz
36
32
28
24
20
16
12
8
VIN = 12V
VEN = 0V
FSW = 600kHz
RISING
FALLING
VIN = 12V
VOUT = 5.0V
IOUT = 0A
FSW = 600kHz
4
0
-50
-25
0
25
50
75
100
125
-50
-25
0
25
50
75
100
125
-50
-25
0
25
50
75
100
125
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
Feedback Voltage
Load Regulation
Line Regulation
vs. Temperature (MIC28304-2)
vs. Temperature (MIC28304-2)
vs. Temperature (MIC28304-2)
0.812
0.808
0.804
0.800
0.796
0.792
0.4%
0.3%
0.2%
0.1%
0.0%
-0.1%
-0.2%
-0.3%
1.00%
0.50%
0.00%
-0.50%
-1.00%
VIN = 12V
VOUT = 5.0V
IOUT = 0A TO 3A
FSW = 600kHz
VIN = 7V TO 70V
VOUT = 5.0V
IOUT = 0A
FSW = 600kHz
VIN = 12V
VOUT = 5.0V
IOUT = 0A
FSW = 600kHz
-50
-25
0
25
50
75
100
125
-50
-25
0
25
50
75
100 125
-50
-25
0
25
50
75
100 125
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
Revision 1.1
March 25, 2014
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Micrel, Inc.
MIC28304
Typical Characteristics (Continued)
Switching Frequency
vs. Temperature (MIC28304-2)
Feedback Voltage
vs. Output Current (MIC28304-2)
Line Regulation
vs. Temperature (MIC28304-2)
700
0.808
0.804
0.800
0.796
0.792
1.0%
650
600
550
500
450
400
350
300
250
200
150
100
0.5%
0.0%
VIN = 12V
VOUT = 5V
IOUT = 0A
VIN = 7V TO 70V
VOUT = 5.0V
IOUT = 3A
-0.5%
-1.0%
VIN = 12V
VOUT = 5.0V
FSW = 600kHz
FSW = 600kHz
-50
-25
0
25
50
75
100 125
-50
-25
0
25
50
75
100
125
0.0
0.5
1.0
1.5
2.0
2.5
3.0
TEMPERATURE (°C)
TEMPERATURE (°C)
OUTPUT CURRENT (A)
Efficiency (VIN =12V)
Efficiency (VIN = 18V)
Line Regulation
vs. Output Current (MIC28304-2)
vs. Output Current (MIC28304-2)
vs. Output Current (MIC28304-2)
0.4%
0.4%
0.3%
0.3%
0.2%
0.2%
0.1%
0.1%
0.0%
100
100
90
80
70
60
50
40
30
5.0V
3.3V
2.5V
1.8V
1.2V
0.8V
FSW = 600kHz
90
80
70
60
50
40
30
5.0V
3.3V
2.5V
1.8V
1.2V
0.8V
VIN = 12V to 70V
VOUT = 5.0V
FSW = 600kHz
FSW = 600kHz
0.0
0.5
1.0
1.5
2.0
2.5
3.0
0
0.5
1
1.5
2
2.5
3
3.5
4
0
0.5
1
1.5
2
2.5
3
3.5
4
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
Efficiency (VIN = 24V)
Efficiency (VIN = 48V)
Efficiency (VIN = 38V)
vs. Output Current (MIC28304-2)
vs. Output Current (MIC28304-2)
vs. Output Current (MIC28304-2)
100
90
80
70
60
50
40
100
90
80
70
60
50
40
30
100
90
80
70
60
50
40
30
FSW = 600kHz
FSW = 600kHz
FSW = 600kHz
5.0V
3.3V
2.5V
1.8V
1.2V
5.0V
3.3V
2.5V
1.8V
1.2V
5.0V
3.3V
2.5V
1.8V
1.2V
0.8V
0.8V
0.8V
30
0
0.5
1
1.5
2
2.5
3
3.5
4
0
0.5
1
1.5
2
2.5
3
3.5
4
0
0.5
1
1.5
2
2.5
3
3.5
4
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
Revision 1.1
March 25, 2014
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Micrel, Inc.
MIC28304
Typical Characteristics (Continued)
Efficiency (VIN = 70V)
Die Temperature* (VIN = 12V)
Die Temperature* (VIN = 48V)
vs. Output Current (MIC28304-2)
vs. Output Current (MIC28304-2)
vs. Output Current (MIC28304-2)
100
90
80
70
60
50
40
30
140
120
100
80
140
120
100
80
VIN = 12V
VOUT = 5.0V
FSW = 600kHz
FSW = 600kHz
5.0V
`
60
60
3.3V
2.5V
1.8V
1.2V
0.8V
VIN = 48V
VOUT = 5.0V
FSW = 600kHz
40
40
20
20
0
0
0
0.5
1
1.5
2
2.5
3
3.5
4
0.0
0.5
1.0
1.5
2.0
2.5
3.0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
Die Temperature* (VIN = 70V)
IC Power Dissipation
vs. Output Current (MIC28304-2)
vs. Output Current (MIC28304-2)
Switching Frequency
800
140
120
100
80
2.5
2
VIN = 12V
VIN = 12V
FSW = 600kHz
VOUT = 5V
IOUT = 2A
700
600
500
400
300
200
100
0
VOUT = 5V, 3.3V, 2.5V, 1.8V, 1.2V, 0.8V
1.5
1
VIN =48V
60
VOUT = 5V
VIN = 70V
VOUT = 5.0V
FSW = 600kHz
40
0.5
0
20
VOUT = 0.8V
0
10.00
100.00
1000.00
10000.00
0.0
0.5
1.0
1.5
2.0
2.5
3.0
0
1
2
3
R19 (k Ohm)
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
IC Power Dissipation
IC Power Dissipation
IC Power Dissipation
vs. Output Current (MIC28304-2)
vs. Output Current (MIC28304-2)
vs. Output Current (MIC28304-2)
3.5
3
6
5
4
3
2
1
0
9
8
7
6
5
4
3
2
1
0
VIN = 48V
FSW = 600kHz
VIN = 70V
FSW = 600kHz
VIN = 24V
FSW = 600kHz
VOUT = 5V, 3.3V, 2.5V, 1.8V, 1.2V, 0.8V
VOUT = 5V, 3.3V, 2.5V, 1.8V, 1.2V, 0.8V
VOUT = 5V, 3.3V, 2.5V, 1.8V, 1.2V, 0.8V
2.5
2
VOUT = 5V
VOUT = 5V
1.5
1
VOUT = 5V
VOUT = 0.8V
VOUT = 0.8V
0.5
0
VOUT = 0.8V
0
1
2
3
0
1
2
3
0
1
2
3
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
* Case Temperature: The temperature measurement was taken at the hottest point on the MIC28304 case mounted on a 5 square inch PCB (see
Thermal Measurement section). Actual results will depend upon the size of the PCB, ambient temperature and proximity to other heat-emitting
components.
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Micrel, Inc.
MIC28304
Typical Characteristics (Continued)
Thermal Derating
Thermal Derating
Thermal Derating
3
2
1
0
3
3
VIN = 12V
VIN = 12V
VIN =18V
VIN = 12V
VIN = 18V
VIN = 18V
2
1
0
2
1
0
VIN = 48V
VOUT = 2.5V
FSW = 600kHz
MIC28304-2
Tj_MAX = 125°C
VIN = 24V
VIN = 48V
VOUT = 3.3V
FSW = 600kHz
MIC28304-2
Tj_MAX = 125°C
VIN = 48V
VIN = 24V
VIN = 24V
VOUT = 5V
FSW = 600kHz
MIC28304-2
Tj_MAX = 125°C
25
40
55
70
85
100
25
40
55
70
85
100
25
40
55
70
85
100
MAXIMUM AMBIENT TEMPERATURE
MAXIMUM AMBIENT TEMPERATURE
MAXIMUM AMBIENT TEMPERATURE
(°C)
(°C)
(°C)
Thermal Derating
Thermal Derating
Thermal Derating
3
3
3
VIN = 12V
VIN = 12V
VIN = 12V
VIN =18V
VIN = 24V
2
1
0
2
1
0
2
1
0
VIN =18V
VIN = 24V
VIN =18V
VIN = 24V
VIN = 48V
VIN = 48V
VIN = 48V
VOUT = 1.2V
FSW = 600kHz
MIC28304-2
Tj_MAX =125°C
VOUT = 1.8V
FSW = 600kHz
MIC28304-2
Tj_MAX =125°C
VOUT = 0.8V
FSW = 600kHz
MIC28304-2
Tj_MAX =125°C
25
40
55
70
85
100
25
40
55
70
85
100
25
40
55
70
85
100
MAXIMUM AMBIENT TEMPERATURE
MAXIMUM AMBIENT TEMPERATURE
MAXIMUM AMBIENT TEMPERATURE
(°C)
(°C)
(°C)
IC Power Dissipation
Efficiency
Thermal Derating
vs. Output Current (MIC28304-2)
vs. Output Current (MIC28304-2)
3
2
1
0
VOUT = 12V
FSW = 600kHz
MIC28304-2
R3 = 23.2kΩ
Tj_MAX =125°C
9
100
95
90
85
80
75
70
65
60
55
50
VOUT = 12V
8
7
6
5
4
3
2
1
0
R3 = 23.2kΩ
FSW = 600kHz
18VIN
18VIN
24VIN
36VIN
70VIN
48VIN
36VIN
24VIN
18VIN
VIN = 24V
48VIN
70VIN
VIN = 48V
VOUT = 12V
FSW = 600kHz
R3 = 23.2kΩ
25
40
55
70
85
100
0
1
2
3
4
0
0.6
1.2
1.8
2.4
3
3.6
MAXIMUM AMBIENT TEMPERATURE
(°C)
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
Revision 1.1
March 25, 2014
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Micrel, Inc.
MIC28304
Functional Characteristics − 600kHz Switching Frequency
Revision 1.1
March 25, 2014
15
Micrel, Inc.
MIC28304
Functional Characteristics − 600kHz Switching Frequency (Continued)
Revision 1.1
March 25, 2014
16
Micrel, Inc.
MIC28304
Functional Characteristics − 600kHz Switching Frequency (Continued)
Revision 1.1
March 25, 2014
17
Micrel, Inc.
MIC28304
Functional Characteristics − 600kHz Switching Frequency (Continued)
Revision 1.1
March 25, 2014
18
Micrel, Inc.
MIC28304
Functional Characteristics − 600kHz Switching Frequency (Continued)
Revision 1.1
March 25, 2014
19
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MIC28304
Functional Characteristics
Revision 1.1
March 25, 2014
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Micrel, Inc.
MIC28304
Functional Diagram
Revision 1.1
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Micrel, Inc.
MIC28304
Functional Description
The maximum duty cycle is obtained from the 200ns
The MIC28304 is an adaptive on-time synchronous buck
regulator module built for high-input voltage to low-output
voltage conversion applications. The MIC28304 is
designed to operate over a wide input voltage range,
from 4.5V to 70V, and the output is adjustable with an
external resistor divider. An adaptive on-time control
scheme is employed to obtain a constant switching
frequency and to simplify the control compensation.
Hiccup mode over-current protection is implemented by
sensing low-side MOSFET’s RDS(ON). The device features
internal soft-start, enable, UVLO, and thermal shutdown.
The module has integrated switching FETs, inductor,
bootstrap diode, resistor and capacitor.
tOFF(MIN)
:
tS − tOFF(MIN)
200ns
tS
Eq. 2
DMAX
=
= 1−
tS
Where:
tS = 1/fSW. It is not recommended to use MIC28304 with
an OFF-time close to tOFF(MIN) during steady-state
operation.
Theory of Operation
The adaptive ON-time control scheme results in a
constant switching frequency in the MIC28304. The
actual ON-time and resulting switching frequency will
vary with the different rising and falling times of the
external MOSFETs. Also, the minimum tON results in a
lower switching frequency in high VIN to VOUT applications.
During load transients, the switching frequency is
changed due to the varying OFF-time.
Per the Functional Diagram of the MIC28304 module, the
output voltage is sensed by the MIC28304 feedback pin
FB via the voltage divider R1 and R11, and compared to
a 0.8V reference voltage VREF at the error comparator
through a low-gain transconductance (gm) amplifier. If
the feedback voltage decreases and the amplifier output
is below 0.8V, then the error comparator will trigger the
control logic and generate an ON-time period. The ON-
time period length is predetermined by the “Fixed tON
Estimator” circuitry:
To illustrate the control loop operation, we will analyze
both the steady-state and load transient scenarios. For
easy analysis, the gain of the gm amplifier is assumed to
be 1. With this assumption, the inverting input of the error
comparator is the same as the feedback voltage.
VOUT
tON(ESTIMATED)
=
Eq. 1
Figure 1 shows the MIC28304 control loop timing during
steady-state operation. During steady-state, the gm
amplifier senses the feedback voltage ripple, which is
proportional to the output voltage ripple plus injected
voltage ripple, to trigger the ON-time period. The ON-time
is predetermined by the tON estimator. The termination of
the OFF-time is controlled by the feedback voltage. At the
valley of the feedback voltage ripple, which occurs when
VFB falls below VREF, the OFF period ends and the next
ON-time period is triggered through the control logic
circuitry.
VIN × fSW
where VOUT is the output voltage, VIN is the power stage
input voltage, and fSW is the switching frequency.
At the end of the ON-time period, the internal high-side
driver turns off the high-side MOSFET and the low-side
driver turns on the low-side MOSFET. The OFF-time
period length depends upon the feedback voltage in most
cases. When the feedback voltage decreases and the
output of the gm amplifier is below 0.8V, the ON-time
period is triggered and the OFF-time period ends. If the
OFF-time period determined by the feedback voltage is
less than the minimum OFF-time tOFF(MIN), which is about
200ns, the MIC28304 control logic will apply the tOFF(MIN)
instead. tOFF(MIN) is required to maintain enough energy in
the boost capacitor (CBST) to drive the high-side
MOSFET.
Revision 1.1
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Micrel, Inc.
MIC28304
Unlike true current-mode control, the MIC28304 uses the
output voltage ripple to trigger an ON-time period. The
output voltage ripple is proportional to the inductor
current ripple if the ESR of the output capacitor is large
enough.
In order to meet the stability requirements, the MIC28304
feedback voltage ripple should be in phase with the
inductor current ripple and are large enough to be sensed
by the gm amplifier and the error comparator. The
recommended feedback voltage ripple is 20mV~100mV
over full input voltage range. If a low ESR output
capacitor is selected, then the feedback voltage ripple
may be too small to be sensed by the gm amplifier and
the error comparator. Also, the output voltage ripple and
the feedback voltage ripple are not necessarily in phase
with the inductor current ripple if the ESR of the output
capacitor is very low. In these cases, ripple injection is
required to ensure proper operation. Please refer to
“Ripple Injection” subsection in Application Information for
more details about the ripple injection technique.
Figure 1. MIC28304 Control Loop Timing
Figure 2 shows the operation of the MIC28304 during a
load transient. The output voltage drops due to the
sudden load increase, which causes the VFB to be less
than VREF. This will cause the error comparator to trigger
an ON-time period. At the end of the ON-time period, a
minimum OFF-time tOFF(MIN) is generated to charge the
bootstrap capacitor (CBST) since the feedback voltage is
still below VREF. Then, the next ON-time period is
triggered due to the low feedback voltage. Therefore, the
switching frequency changes during the load transient,
but returns to the nominal fixed frequency once the
output has stabilized at the new load current level. With
the varying duty cycle and switching frequency, the
output recovery time is fast and the output voltage
deviation is small.
Discontinuous Mode (MIC28304-1 only)
In continuous mode, the inductor current is always
greater than zero; however, at light loads, the MIC28304-
1 is able to force the inductor current to operate in
discontinuous mode. Discontinuous mode is where the
inductor current falls to zero, as indicated by trace (IL)
shown in Figure 3. During this period, the efficiency is
optimized by shutting down all the non-essential circuits
and minimizing the supply current. The MIC28304-1
wakes up and turns on the high-side MOSFET when the
feedback voltage VFB drops below 0.8V.
The MIC28304-1 has a zero crossing comparator (ZC)
that monitors the inductor current by sensing the voltage
drop across the low-side MOSFET during its ON-time. If
the VFB > 0.8V and the inductor current goes slightly
negative, then the MIC28304-1 automatically powers
down most of the IC circuitry and goes into a low-power
mode.
Once the MIC28304-1 goes into discontinuous mode,
both DL and DH are low, which turns off the high-side
and low-side MOSFETs. The load current is supplied by
the output capacitors and VOUT drops. If the drop of VOUT
causes VFB to go below VREF, then all the circuits will
wake up into normal continuous mode. First, the bias
currents of most circuits reduced during the
discontinuous mode are restored, and then a tON pulse is
triggered before the drivers are turned on to avoid any
possible glitches. Finally, the high-side driver is turned
on. Figure
discontinuous mode.
3
shows the control loop timing in
Figure 2. MIC28304 Load Transient Response
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Micrel, Inc.
MIC28304
Figure 4. 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.
Figure 3. MIC28302-1 Control Loop Timing
(Discontinuous Mode)
During discontinuous mode, the bias current of most
circuits is substantially reduced. As a result, the total
power supply current during discontinuous mode is only
about 400μA, allowing the MIC28304-1 to achieve high
efficiency in light load applications.
Soft-Start
Soft-start reduces the input power supply surge current at
startup by controlling the output voltage rise time. The
input surge appears while the output capacitor is charged
up. A slower output rise time will draw a lower input surge
current.
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 VCL. 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 MIC28304 implements an internal digital soft-start by
making the 0.8V reference voltage VREF ramp from 0 to
100% in about 5ms with 9.7mV steps. Therefore, the
output voltage is controlled to increase slowly by a stair-
case VFB ramp. Once the soft-start cycle ends, the related
circuitry is disabled to reduce current consumption.
PVDD must be powered up at the same time or after VIN
to make the soft-start function correctly.
Current Limit
The MIC28304 uses the RDS(ON) of the low side
MOSEFET and external resistor connected from ILIM pin
to SW node to decide the current limit.
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Micrel, Inc.
MIC28304
The short-circuit current limit can be programmed by
using Equation 3.
The MOSFET RDS(ON) varies 30% to 40% with
temperature; therefore, it is recommended to add a 50%
margin to ICLIM in Equation 3 to avoid false current limiting
due to increased MOSFET junction temperature rise.
Table 2 shows typical output current limit value for a
given R15 with C6 = 10pF.
(ICLIM − ∆IL ) × 0.5) × RDS(ON) + VCL
(
PP
R15 =
ICL
Table 2. Typical Output Current-Limit Value
Eq. 3
R15
Typical Output Current Limit
1.81kΩ
2.7kΩ
3A
Where:
CLIM = Desired current limit
6.3A
I
RDS(ON) = On-resistance of low-side power MOSFET,
57mΩ typically
VCL = Current-limit threshold (typical absolute value is
14mV per the Electrical Characteristics(4))
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-to-peak inductor current ripple is:
VOUT ×(VIN(max) − VOUT
VIN(max) × fsw ×L
)
∆IL(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.
Revision 1.1
March 25, 2014
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Micrel, Inc.
MIC28304
Application Information
Simplified Input Transient Circuitry
The 76V absolute maximum rating of MIC28304 allows
simplifying the transient voltage suppressor on the input
supply side which is very common in industrial
applications. The input supply voltage VIN Figure 5 may
be operating at 12V input rail most of the time, but can
encounter noise spike of 60V for a short duration. By
using MIC28304, which has 76V absolute maximum
voltage rating, the input transient suppressor is not
needed. Which saves on component count, form factor,
and ultimately the system becomes less expensive.
Equation 5 gives the estimated switching frequency:
R19
f
= f
×
O
Eq. 5
SW _ ADJ
R19 + 100kΩ
Where:
fO = Switching frequency when R19 is open
For more precise setting, it is recommended to use
Figure 7:
Switching Frequency
800
VIN = 12V
VOUT = 5V
IOUT = 2A
700
600
500
400
300
200
100
0
Figure 5. Simplified Input Transient Circuitry
Setting the Switching Frequency
VIN =48V
The MIC28304 switching frequency can be adjusted by
changing the value of resistor R19. The top resistor of
100kΩ is internal to module and is connected between
VIN and FREQ pin, so the value of R19 sets the
switching frequency. The switching frequency also
depends upon VIN, VOUT and load conditions.
10.00
100.00
1000.00
10000.00
R19 (k Ohm)
Figure 7. Switching Frequency vs. R19
Output Capacitor Selection
The type of the output capacitor is usually determined by
the application and its equivalent series resistance
(ESR). Voltage and RMS current capability are two other
important factors for selecting the output capacitor.
Recommended capacitor types are MLCC, tantalum, low-
ESR aluminum electrolytic, OS-CON and POSCAP. The
output capacitor’s ESR is usually the main cause of the
output ripple. The MIC28304 requires ripple injection and
the output capacitor ESR effects the control loop from a
stability point of view.
Figure 6. Switching Frequency Adjustment
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MIC28304
The maximum value of ESR is calculated as in Equation
6:
The output capacitor RMS current is calculated in
Equation 8:
ΔVOUT(pp)
ΔIL(PP)
ESRC
≤
OUT
IC
=
OUT (RMS)
ΔIL(PP)
Eq. 6
12
Eq. 8
Where:
The power dissipated in the output capacitor is:
ΔVOUT(pp) = Peak-to-peak output voltage ripple
ΔIL(PP) = Peak-to-peak inductor current ripple
2
Eq. 9
P
= I
× ESR
COUT
DISS(COUT
)
COUT (RMS)
Input Capacitor Selection
The total output ripple is a combination of the ESR and
output capacitance. The total ripple is calculated in
Equation 7:
The input capacitor for the power stage input PVIN
should be selected for ripple current rating and voltage
rating. Tantalum input capacitors may fail when subjected
to high inrush currents, caused by turning the input
supply on. A tantalum input capacitor’s voltage rating
should be at least two times the maximum input voltage
to maximize reliability. Aluminum electrolytic, OS-CON,
and multilayer polymer film capacitors can handle the
higher inrush currents without voltage de-rating. The
input voltage ripple will primarily depend on the input
capacitor’s ESR. The peak input current is equal to the
peak inductor current, so:
2
ΔIL(PP)
2
ΔVOUT(pp)
=
+
(
ΔIL(PP) × ESRC
)
OUT
COUT × fSW × 8
Eq. 7
Where:
D = Duty cycle
ΔVIN = IL(pk) × ESRCIN
Eq. 10
COUT = Output capacitance value
fsw = Switching frequency
The input capacitor must be rated for the input current
ripple. The RMS value of input capacitor current is
determined at the maximum output current. Assuming the
peak-to-peak inductor current ripple is low:
As described in the “Theory of Operation” subsection in
Functional Description, the MIC28304 requires at least
20mV peak-to-peak ripple at the FB pin to make the gm
amplifier and the error comparator behave properly. Also,
the output voltage ripple should be in phase with the
inductor current. Therefore, the output voltage ripple
caused by the output capacitors value should be much
smaller than the ripple caused by the output capacitor
ESR. If low-ESR capacitors, such as ceramic capacitors,
are selected as the output capacitors, a ripple injection
method should be applied to provide enough feedback
voltage ripple. Please refer to the “Ripple Injection”
subsection for more details.
Eq.11
ICIN(RMS) ≈ IOUT(max)
× D×(1−D)
The power dissipated in the input capacitor is:
PDISS(CIN) = ICIN(RMS)2 × ESRCIN
Eq. 12
The voltage rating of the capacitor should be twice the
output voltage for a tantalum and 20% greater for
aluminum electrolytic or OS-CON.
The general rule is to pick the capacitor with a ripple
current rating equal to or greater than the calculated
worst (VIN_MAX) case RMS capacitor current. Its voltage
rating should be 20% to 50% higher than the maximum
input voltage. Typically the input ripple (dV) needs to be
kept down to less than ±10% of input voltage. The ESR
also increases the input ripple.
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Micrel, Inc.
MIC28304
Equation 13 should be used to calculate the input
capacitor. Also it is recommended to keep some margin
on the calculated value:
Ripple Injection
The VFB ripple required for proper operation of the
MIC28304 gM amplifier and error comparator is 20mV to
100mV. However, the output voltage ripple is generally
designed as 1% to 2% of the output voltage. For a low
output voltage, such as a 1V, the output voltage ripple is
only 10mV to 20mV, and the feedback voltage ripple is
less than 20mV. If the feedback voltage ripple is so small
that the gM amplifier and error comparator cannot sense
it, then the MIC28304 will lose control and the output
voltage is not regulated. In order to have some amount of
VFB ripple, a ripple injection method is applied for low
I
×(1− D)
×dV
OUT(max)
Eq. 13
C
≈
IN
F
SW
Where:
dV = The input ripple and FSW is the switching frequency
output voltage ripple applications. The table
2
summarizes the ripple injection component values for
ceramic output capacitor.
Output Voltage Setting Components
The MIC28304 requires two resistors to set the output
voltage as shown in Figure 8:
The applications are divided into three situations
according to the amount of the feedback voltage ripple:
1. Enough ripple at the feedback voltage due to the
large ESR of the output capacitors (Figure 9):
Figure 8. Voltage-Divider Configuration
Figure 9. Enough Ripple at FB
The output voltage is determined by Equation 14:
As shown in Figure 10, the converter is stable without
any ripple injection.
R1
Eq. 14
VOUT = VFB × 1+
R11
Where:
FB = 0.8V
V
A typical value of R1 used on the standard evaluation
board is 10kΩ. If R1 is too large, it may allow noise to be
introduced into the voltage feedback loop. If R1 is too
small in value, it will decrease the efficiency of the power
supply, especially at light loads. Once R1 is selected,
R11 can be calculated using Equation 15:
Figure 10. Inadequate Ripple at FB
VFB × R1
VOUT − VFB
R11 =
Eq. 15
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Micrel, Inc.
The feedback voltage ripple is:
MIC28304
VIN = Power stage input voltage
D = Duty cycle
f
SW = Switching frequency
R11
Eq. 16
ΔVFB(PP)
=
× ESR
×ΔIL(PP)
COUT
R1+ R11
τ = (R1//R11//Rinj) × Cff
Where:
In Equations 18 and 19, it is assumed that the time
constant associated with Cff must be much greater than
the switching period:
ΔIL(PP) = The peak-to-peak value of the inductor
current ripple
2. Inadequate ripple at the feedback voltage due to the
small ESR of the output capacitors, such is the case
with ceramic output capacitor.
1
T
=
<< 1
fSW ×τ
τ
Eq. 20
The output voltage ripple is fed into the FB pin
through a feed-forward capacitor Cff in this situation,
as shown in Figure 11. The typical Cff value is
between 1nF and 100nF.
If the voltage divider resistors R1 and R11 are in the kΩ
range, then a Cff of 1nF to 100nF can easily satisfy the
large time constant requirements. Also, a 100nF injection
capacitor Cinj is used in order to be considered as short
for a wide range of the frequencies.
The process of sizing the ripple injection resistor and
capacitors is:
Step 1. Select Cff to feed all output ripples into the
feedback pin and make sure the large time constant
assumption is satisfied. Typical choice of Cff is 1nF to
100nF if R1 and R11 are in kΩ range.
Step 2. Select Rinj according to the expected feedback
voltage ripple using Equation 22:
Figure 11. Invisible Ripple at FB
With the feed-forward capacitor, the feedback voltage
ripple is very close to the output voltage ripple:
ΔVFB(pp)
fSW ×τ
D×(1− D)
Kdiv
=
×
V
IN
Eq. 21
Eq. 22
ΔV
≈ ESR× ΔI
Eq. 17
FB(PP)
L(PP)
Then the value of Rinj is obtained as:
3. Virtually no ripple at the FB pin voltage due to the
very-low ESR of the output capacitors.
1
Rinj = (R1//R11)×(
−1)
Kdiv
In this situation, the output voltage ripple is less than
20mV. Therefore, additional ripple is injected into the
FB pin from the switching node SW via a resistor Rinj
and a capacitor Cinj, as shown in Figure 11. The
injected ripple is:
Step 3. Select Cinj as 100nF, which could be considered
as short for a wide range of the frequencies.
Table 3 summarizes the typical value of components for
particular input and output voltage, and 600kHz
switching frequency design, for details refer to the Bill of
Materials section.
1
ΔVFB(pp) = VIN ×Kdiv ×D×(1-D)×
fSW ×τ
Eq. 18
R1//R11
Kdiv
=
Eq. 19
Rinj + R1//R11
Where:
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Micrel, Inc.
MIC28304
Table 3. Recommended Component Values for 600kHz Switching Frequency
R1
R11
R3
(Rinj)
C10
(Cinj)
C12
(Cff)
VOUT
VIN
COUT
(Top Feedback (Bottom Feedback
R19
Resistor)
Resistor)
47µF/6.3V
or 2 x 22µF
0.9V
1.2V
1.8V
2.5V
3.3V
5V to 70V
5V to 70V
5V to 70V
5V to 70V
5V to 70V
16.5kΩ
16.5kΩ
16.5kΩ
16.5kΩ
16.5kΩ
10kΩ
80.6kΩ
0.1µF
0.1µF
0.1µF
0.1µF
0.1µF
2.2nF
2.2nF
2.2nF
2.2nF
2.2nF
DNP
DNP
DNP
DNP
DNP
DNP
47µF/6.3V
or 2 x 22µF
10kΩ
10kΩ
10kΩ
10kΩ
20kΩ
47µF/6.3V
or 2 x 22µF
8.06kΩ
4.75kΩ
3.24kΩ
47µF/6.3V
or 2 x 22µF
47µF/6.3V
or 2 x 22µF
47µF/6.3V
or 2 x 22µF
5V
7V to 70V
18V to 70V
16.5kΩ
23.2kΩ
10kΩ
10kΩ
1.9kΩ
715Ω
0.1µF
0.1µF
2.2nF
2.2nF
47µF/16V
or 2 x 22µF
12V
DNP
Thermal Measurements and Safe Operating Area
Measuring the IC’s case temperature is recommended to
ensure it is within its operating limits. Although this might
seem like a very elementary task, it is easy to get
erroneous results. The most common mistake is to use
the standard thermal couple that comes with a thermal
meter. This thermal couple wire gauge is large, typically
22 gauge, and behaves like a heatsink, resulting in a
lower case measurement.
However, an IR thermometer from Optris has a 1mm spot
size, which makes it a good choice for measuring the
hottest point on the case. An optional stand makes it
easy to hold the beam on the IC for long periods of time.
The safe operating area (SOA) of the MIC28304 is shown
in the Typical Characteristics − 275kHz Switching
Frequency section. These thermal measurements were
taken on MIC28304 evaluation board. Since the
MIC28304 is an entire system comprised of switching
regulator controller, MOSFETs and inductor, the part
needs to be considered as a system. The SOA curves
will give guidance to reasonable use of the MIC28304.
Two methods of temperature measurement are using a
smaller thermal couple wire or an infrared thermometer. If
a thermal couple wire is used, it must be constructed of
36-gauge wire or higher (smaller wire size) to minimize
the wire heat-sinking effect. In addition, the thermal
couple tip must be covered in either thermal grease or
thermal glue to make sure that the thermal couple
junction is making good contact with the case of the IC.
Omega brand thermal couple (5SC-TT-K-36-36) is
adequate for most applications.
Emission Characteristics of MIC28304
The MIC28304 integrates switching components in a
single package, so the MIC28304 has reduced emission
compared to standard buck regulator with external
MOSFETS and inductors. The radiated EMI scans for
MIC28304 are shown in the Typical Characteristics
section. The limit on the graph is per EN55022 Class B
standard.
Wherever possible, an infrared thermometer is
recommended. The measurement spot size of most
infrared thermometers is too large for an accurate
reading on a small form factor ICs.
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MIC28304
PCB Layout Guidelines
Warning: To minimize EMI and output noise, follow
these layout recommendations.
Input Capacitor
• Place the input capacitors on the same side of the
board and as close to the IC as possible.
PCB layout is critical to achieve reliable, stable and
efficient performance. A ground plane is required to
control EMI and minimize the inductance in power, signal
and return paths.
• Place several vias to the ground plane close to the
input capacitor ground terminal.
• Use either X7R or X5R dielectric input capacitors. Do
not use Y5V or Z5U type capacitors.
The following figures optimized from small form factor
point of view shows top and bottom layer of a four layer
PCB. It is recommended to use mid layer 1 as a
continuous ground plane.
• Do not replace the ceramic input capacitor with any
other type of capacitor. Any type of capacitor can be
placed in parallel with the input capacitor.
• If a Tantalum input capacitor is placed in parallel with
the input capacitor, it must be recommended for
switching regulator applications and the operating
voltage must be derated by 50%.
• In “Hot-Plug” applications, a Tantalum or Electrolytic
bypass capacitor must be used to limit the over-voltage
spike seen on the input supply with power is suddenly
applied.
RC Snubber
• Place the RC snubber on the same side of the board
and as close to the SW pin as possible.
SW Node
• Do not route any digital lines underneath or close to
the SW node.
• Keep the switch node (SW) away from the feedback
Figure 12. Top And Bottom Layer of a Four-Layer Board
(FB) pin.
Output Capacitor
The following guidelines should be followed to insure
proper operation of the MIC28304 converter:
• Use a wide trace to connect the output capacitor
ground terminal to the input capacitor ground terminal.
IC
• Phase margin will change as the output capacitor value
and ESR changes. Contact the factory if the output
capacitor is different from what is shown in the BOM.
• The analog ground pin (GND) must be connected
directly to the ground planes. Do not route the GND pin
to the PGND pin on the top layer.
• The feedback trace should be separate from the power
trace and connected as close as possible to the output
capacitor. Sensing a long high-current load trace can
degrade the DC load regulation.
• Place the IC close to the point of load (POL).
• Use fat traces to route the input and output power
lines.
• Analog and power grounds should be kept separate
and connected at only one location.
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MIC28304
Evaluation Board Schematics
Figure 13. Schematic of MIC28304 Evaluation Board
(J1, J8, J10, J11, J12, J13, R14, R20, and R21 are for Testing Purposes)
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MIC28304
Evaluation Board Schematics (Continued)
Figure 14. Schematic of MIC28304 Evaluation Board
(Optimized for Smallest Footprint)
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MIC28304
Bill of Materials
Item
Part Number
Manufacturer Description
Panasonic(6) 100µF Aluminum Capacitor, 100V
Murata(7)
Qty.
C1
EEU-FC2A101
1
GRM32ER72A225K
C3225X7R2A225K
12101C225KAT2A
GCM1885C2A100JA16D
06031A100JAT2A
C2, C3
C6
TDK(8)
AVX(9)
Murata
AVX
2.2µF/100V Ceramic Capacitor, X7R, Size 1210
2
1
1
10pF, 100V, 0603, NPO
GRM188R70J105KA01D
06036C105KAT2A
C1608X5R0J105K
Murata
AVX
C8
1µF/6.3V Ceramic Capacitor, X7R, Size 0603
0.47µF/100V Ceramic Capacitor, X7R, Size 0805
TDK
GRM21BR72A474KA73
08051C474KAT2A
GRM188R72A104KA35D
C1608X7S2A104K
GRM188R72A102KA01D
06031C102KAT2A
C1608X7R2A102K
GRM188R72A222KA01D
06031C222KAT2A
C1608X7R2A222K
GRM31CR60J476ME19K
12106D476MAT2A
GRM188R71H104KA93D
06035C104KAT2A
C1608X7R1H104K
Murata
AVX
C9
1
2
Murata
TDK
0.1µF/100V Ceramic Capacitor, X7R, Size 0603
0.1µF/100V, X7S, 0603
C10, C17
Murata
AVX
C11
1nF/100V Ceramic Capacitor, X7R, Size 0603
1
TDK
Murata
AVX
C12
C14
C16
2.2nF/100V Ceramic Capacitor, X7R, Size 0603
47µF/6.3V Ceramic Capacitor, X5R, Size 1210
0.1µF/6.3V Ceramic Capacitor, X7R, Size 0603
1
1
TDK
Murata
AVX
Murata
AVX
1
TDK
C4, C5, C7, C13, C15
DNP
Notes:
6. Panasonic: www.panasonic.com.
7. Murata: www.murata.com.
8. TDK: www.tdk.com.
9. AVX: www.avx.com.
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Micrel, Inc.
MIC28304
Bill of Materials (Continued)
Item
R1
Part Number
Manufacturer Description
Vishay Dale(10) 10kΩ Resistor, Size 0603, 1%
Qty.
CRCW060310K0FKEA
CRCW08051R21FKEA
CRCW06031652F
1
R2
Vishay Dale
Vishay Dale
Vishay Dale
Vishay Dale
Vishay Dale
Vishay Dale
Vishay Dale
Vishay Dale
Vishay Dale
Vishay Dale
Vishay Dale
1.21Ω Resistor, Size 0805, 5%
16.5kΩ Resistor, Size 0603, 1%
3.24kΩ Resistor, Size 0603, 1%
1.91kΩ Resistor, Size 0603, 1%
715Ω Resistor, Size 0603, 1%
0Ω Resistor, Size 0603, 5%
1
R3
1
R10
CRCW06033K24FKEA
CRCW06031K91FKEA
CRCW0603715R0FKEA
CRCW06030000FKEA
CRCW04022K70JNED
CRCW0603100KFKEAHP
CRCW060349K9FKEA
CRCW060349R9FKEA
CRCW06031R21FKEA
1
R11
1
R12
DNP
R14, R20
R15
2
1
2.7kΩ Resistor, Size 0603, 1%
100kΩ Resistor, Size 0603, 1%
49.9kΩ Resistor, Size 0603, 1%
49.9Ω Resistor, Size 0603, 1%
1.21Ω Resistor, Size 0603, 1%
R16
1
R18
1
R21
1
R23
1
R4, R19
DNP
All reference
designators ending
with “A”
Open
MIC28304-1YMP
MIC28304-2YMP
70V, 3A Power Module − Hyper Speed Control
Family
U1
Micrel, Inc.(11)
1
Notes:
10. Vishay: www.vishay.com.
11. Micrel, Inc.: www.micrel.com.
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MIC28304
PCB Layout Recommendations
Evaluation Board Top Layer
Evaluation Board Mid-Layer 1 (Ground Plane)
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Micrel, Inc.
MIC28304
PCB Layout Recommendations (Continued)
Evaluation Board Mid-Layer 2
Evaluation Board Bottom Layer
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Micrel, Inc.
MIC28304
Package Information(12)
64-Pin 12mm × 12mm QFN (MP)
Note:
12. Package information is correct as of the publication date. For updates and most current information, go to www.micrel.com.
Revision 1.1
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Micrel, Inc.
MIC28304
Recommended Land Pattern
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 makes no representations or warranties with respect to the accuracy or completeness of the information furnished in this data sheet. 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
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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.
© 2014 Micrel, Incorporated.
Revision 1.1
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