MIC4684 [MICREL]
2A High-Efficiency SuperSwitcher Buck Regulator; 2A高效SuperSwitcher降压稳压器
| 型号： | MIC4684 |
| 厂家： | 
MICREL SEMICONDUCTOR |
| 描述： | 2A High-Efficiency SuperSwitcher Buck Regulator |
| 文件： | 总16页 (文件大小：215K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
MIC4684
2A High-Efficiency SuperSwitcher™ Buck Regulator
Final Information
General Description
Features
The MIC4684 is a high-efficiency 200kHz stepdown (buck)
switching regulator. Power conversion efficiency of above
85% is easily obtainable for a wide variety of applications.
The MIC4684 achieves 2A of continuous current in an 8-lead
SO (small outline) package at 60°C ambient temperature.
• SO-8 package with 2A continuous output current
• Over 85% efficiency
• Fixed 200kHz PWM operation
• Wide 4V to 30V input voltage range
• Output voltage adjustable to 1.235V
• All surface mount solution
• Internally compensated with fast transient response
• Over-current protection
• Frequency foldback short-circuit protection
• Thermal shutdown
Highefficiencyismaintainedoverawideoutputcurrentrange
byutilizingaboostcapacitortoincreasethevoltageavailable
to saturate the internal power switch. As a result of this high
efficiency, no external heat sink is required. The MIC4684,
housed in an SO-8, can replace larger TO-220 and TO-263
packages in many applications.
Applications
The MIC4684 allows for a high degree of safety. It has a wide
input voltage range of 4V to 30V (34V transient), allowing it to
beusedinapplicationswhereinputvoltagetransientsmaybe
present. Built-in safety features include over-current protec-
tion, frequency-foldback short-circuit protection, and thermal
shutdown.
• Simple high-efficiency step-down regulator
• 5V to 3.3V/1.7A converter (60°C ambient)
• 12V to 1.8V/2A converter (60°C ambient)
• On-card switching regulator
• Dual-output ±5V converter
• Battery charger
The MIC4684 is available in an 8-lead SO package with a
junction temperature range of –40°C to +125°C.
Ordering Information
Part Number
Voltage
Junction Temperature Range
Package
MIC4684BM
Adj
–40°C to +125°C
SOP-8
Typical Application
VIN
6.5V to 25V
MIC4684BM
CBS
3
4
1
5
0.33µF/50V
VIN
BS
SW
FB
VOUT
2.5V/1.5A
8
EN
Efficiency
68µH
R1
CIN
33µF
35V
vs. Output Current
3.01k
330µF
6.3V
100
R2
3.01k
VOUT = 3.3V
GND
2, 6, 7
3A
40V
80
60
40
20
0
VOUT = 1.8V
VOUT = 2.5V
Adjustable Buck Converter
1A, 20V Feed forward diode
MIC4684BM
VIN = 5.0V
0.5
VIN
5V
±10%
0
1
1.5
2
CBS
3
8
4
OUTPUT CURRENT (A)
VIN
BS
SW
FB
VOUT
3.3V/1.7A
0.33µF/50V
1
5
EN
47µH
CIN
68µF
10V
Efficiency vs. Output Current
220µF
10V
GND
2, 6, 7
2A
20V
5V to 3.3V Converter
Micrel, Inc. • 1849 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 944-0970 • http://www.micrel.com
July 2001
1
MIC4684
MIC4684
Micrel
Pin Configuration
SW
GND
VIN
1
2
3
4
8
7
6
5
EN
GND
GND
FB
BS
8-Pin SOP (M)
Pin Description
Pin Number
Pin Name
Pin Function
1
SW
Switch (Output): Emitter of NPN output switch. Connect to external storage
inductor and Shottky diode.
2, 6, 7
GND
IN
Ground
3
4
Supply (Input): Unregulated +4V to 30V supply voltage (34V transient)
BS
Booststrap Voltage Node (External Component): Connect to external boost
capacitor.
5
8
FB
EN
Feedback (Input): Outback voltage feedback to regulator. Connect to output
of supply for fixed versions. Connect to 1.23V tap of resistive divider for
adjustable versions.
Enable (Input): Logic high = enable; logic low = shutdown
Bootstrap (BS, pin 4)
Detailed Pin Description
Switch (SW, pin 1)
The bootstrap pin in conjunction with the external bootstrap
capacitor provides a bias voltage higher than the input
voltage to the MIC4684’s main NPN pass element. The
bootstrap capacitor sees the dv/dt of the switching action at
the SW pin as an AC voltage. The bootstrap capacitor then
couples the AC voltage back to the BS pin plus the dc offset
The switch pin is tied to the emitter of the main internal NPN
transistor. This pin is biased up to the input voltage minus the
V
of the main NPN pass element. The emitter is also
SAT
driven negative when the output inductor’s magnetic field
collapses at turn-off. During the OFF time the SW pin is
clamped by the output schottky diode to a –0.5V typically.
of V where it is rectified and used to provide additional drive
IN
to the main switch, in this case a NPN transistor.
Ground (GND, pins 2,6,7)
This additional drive reduces the NPN’s saturation voltage
There are two main areas of concern when it comes to the
ground pin, EMI and ground current. In a buck regulator or
any other non-isolated switching regulator the output
capacitor(s) and diode(s) ground is referenced back to the
switching regulator’s or controller’s ground pin. Any resis-
tance between these reference points causes an offset
voltage/IR drop proportional to load current and poor load
regulation. This is why its important to keep the output
groundsplacedascloseaspossibletotheswitchingregulator’s
groundpin. TokeepradiatedEMItoaminimumitsnecessary
to place the input capacitor ground lead as close as possible
to the switching regulators ground pin.
and increases efficiency, from a V
of 1.8V, and 75%
SAT
efficiency to a V
of 0.5V and 88% efficiency respectively.
SAT
Feedback (FB, pin 5)
The feedback pin is tied to the inverting side of a GM error
amplifier. The noninverting side is tied to a 1.235V bandgap
reference. Fixed voltage versions have an internal voltage
divider from the feedback pin. Adjustable versions require an
external resistor voltage divider from the output to ground,
with the center tied to the feedback pin.
Enable (EN, pin 8)
The enable (EN) input is used to turn on the regulator and is
TTL compatible. Note: connect the enable pin to the input if
unused. A logic-high enables the regulator. A logic-low shuts
downtheregulatorandreducesthestand-byquiescent input
current to typically 150µA. The enable pin has an upper
threshold of 2.0V minimum and lower threshold of 0.8V
maximum. The hysterisis provided by the upper and lower
thresholds acts as an UVLO and prevents unwanted turn on
of the regulator due to noise.
Input Voltage (V , pin 3)
IN
The V pin is the collector of the main NPN pass element.
IN
Thispinisalsoconnectedtotheinternalregulator.Theoutput
diode or clamping diode should have its cathode as close as
possible to this point to avoid voltage spikes adding to the
voltage across the collector.
MIC4684
2
July 2001
MIC4684
Micrel
Absolute Maximum Ratings (Note 1)
Operating Ratings (Note 2)
Supply Voltage (V ), Note 3 ......................................+34V
Supply Voltage (V ) Note 4 ........................... +4V to +30V
IN
IN
Enable Voltage (V ) .................................... –0.3V to +V
Ambient Temperature (T ) ......................... –40°C to +85°C
EN
IN
A
Steady-State Output Switch Voltage (V ) ....... –1V to V
Junction Temperature (T ) ....................... –40°C to +125°C
SW
IN
J
Feedback Voltage (V )..............................................+12V
Package Thermal Resistance
FB
Storage Temperature (T ) ....................... –65°C to +150°C
θ
θ
, Note 5 ..........................................................75°C/W
, Note 5 ..........................................................25°C/W
S
JA
JC
ESD Rating .............................................................. Note 3
Electrical Characteristics
VIN = VEN = 12V, VOUT = 5V; IOUT = 500mA; TA = 25°C, unless otherwise noted. Bold values indicate –40°C ≤ TJ ≤ +125°C.
Parameter
Condition
Min
1.210 1.235 1.260
1.198 1.272
1.186 1.235 1.284
Typ
Max
Units
Feedback Voltage
(±2%)
(±3%)
V
V
8V ≤ VIN ≤ 30V, 0.1A ≤ ILOAD ≤ 1A, VOUT = 5V
V
V
1.173
1.297
Feedback Bias Current
Maximum Duty Cycle
Output Leakage Current
50
94
nA
%
VFB = 1.0V
VIN = 30V, VEN = 0V, VSW = 0V
VIN = 30V, VEN = 0V, VSW = –1V
VFB = 1.5V
5
500
20
µA
mA
mA
mA
V
1.4
6
Quiescent Current
12
Bootstrap Drive Current
Bootstrap Voltage
VFB = 1.5V, VSW = 0V
IBS = 10mA, VFB = 1.5V, VSW = 0V
VFB = 0V
250
5.5
30
380
6.2
50
Frequency Fold Back
Oscillator Frequency
Saturation Voltage
120
225
kHz
kHz
V
180
200
0.59
IOUT = 1A
Short Circuit Current Limit
Shutdown Current
VFB = 0V, See Test Circuit
VEN = 0V
2.2
2
A
150
µA
V
Enable Input Logic Level
regulator on
regulator off
0.8
50
V
Enable Pin Input Current
Thermal Shutdown @ TJ
VEN = 0V (regulator off)
VEN = 12V (regulator on)
16
µA
mA
°C
–1
–0.83
160
Note 1. Exceeding the absolute maximum rating may damage the device.
Note 2. The device is not guaranteed to function outside its operating rating.
Note 3. Devices are ESD sensitive. Handling precautions recommended.
Note 4. 2.5V of headroom is required between V and V
. The headroom can be reduced by implementing a feed-forward diode a seen on the 5V
OUT
IN
to 3.3V circuit on page 1.
Note 5. Measured on 1" square of 1 oz. copper FR4 printed circuit board connected to the device ground leads.
July 2001
3
MIC4684
MIC4684
Micrel
Test Circuit
Device Under Test
68µH
+12V
3
8
1
4
VIN
SW
EN
BS
I
GND
FB
5
SOP-8
2,6,7
Current Limit Test Circuit
Shutdown Input Behavior
ON
OFF
GUARANTEED
GUARANTEED
OFF
ON
0.8V
1.25V
2V
TYPICAL
OFF
TYPICAL
ON
0V
1.4V
VIN(max)
Enable Hysteresis
MIC4684
4
July 2001
MIC4684
Micrel
Typical Characteristics
(T = 25°C unless otherwise noted)
A
5V
Efficiency without Feed
Forward Diode
3.3V
Efficiency without
5V Efficiency with Feed
IN
OUT
OUT
Forward Diode
Feed Forward Diode
100
100
95
90
85
80
75
70
65
60
55
50
100
95
90
85
80
75
70
65
60
55
50
95
90
85
80
75
70
65
60
55
50
VIN = 8V
VOUT = 3.3V
VIN = 8V
VOUT = 2.5V
VIN = 12V
VIN = 12V
VIN = 24V
VIN = 24V
VOUT = 1.8V
VIN = 5.0V
1.5 2
VOUT = 5V
1.2 1.4 1.6
VOUT = 3.3V
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6
0
0.2 0.4 0.6 0.8
1
0
0.5
1
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
Efficiency vs. Output Current
with Feed Forward Diode
Bootstrap Voltage
vs. Input Voltage
Bootstrap Drive Current
vs. Input Voltage
100
7
6
5
4
3
2
1
0
350
300
250
200
150
100
50
90
80
70
60
50
40
30
20
10
0
5VOUT
3.3VOUT
2.5VOUT
1.8VOUT
VIN = 12V
VFB = 1.5V
VIN = 12V
VFB = 1.5V
VIN = 12V
2.5
0
0
0.5
1
1.5
2
3
0
5
10 15 20 25 30
INPUT VOLTAGE (V)
0
2
4
6
8
10 12 14 16 18 20
OUTPUT CURRENT (A)
INPUT VOLTAGE (V)
Minimum Duty Cycle
vs. Input Voltage
Reference Voltage
vs. Input Voltage
Quiescent Current
vs. Input Voltage
10.9
10.8
10.7
10.6
10.5
10.4
10.3
1.255
1.250
1.245
1.240
1.235
1.230
1.225
6.3
6.2
6.1
6
VIN = 12V
VOUT = 5V
FB = 1.3V
V
5.9
5.8
5.7
VIN = 12V
VOUT = VREF
VEN= 5V
IOUT = 500mA
0
5
10 15 20 25 30 35 40
INPUT VOLTAGE (V)
0
5
10 15 20 25 30 35 40
INPUT VOLTAGE (V)
0
5
10 15 20 25 30 35 40
INPUT VOLTAGE (V)
Shutdown Current
vs. Input Voltage
Saturation Voltage
vs. Input Voltage
Foldback Frequency
vs. Input Voltage
200
180
160
140
120
100
80
605
600
595
590
585
580
575
570
51.5
51
50.5
50
49.5
49
60
40
IOUT = 1A
VOUT = 5V
VFB = 0V
20
VEN = 0V
0
48.5
0
5
10 15 20 25 30 35 40
INPUT VOLTAGE (V)
0
5
10 15 20 25 30 35 40
INPUT VOLTAGE (V)
0
5
10 15 20 25 30 35 40
INPUT VOLTAGE (V)
July 2001
5
MIC4684
MIC4684
Micrel
Feedback Voltage
vs. Temperature
Shutdown Hysteresis vs.
Temperature
Load Regulation
1.210
6
5
5.020
5.018
5.016
5.014
5.012
5.010
5.008
5.006
5.004
5.002
5.000
VIN = 12V
1.209
1.208
1.207
1.206
1.205
1.204
ON
4
3
2
1.203 VIN = 12V
1
OFF
VOUT = VFB
IOUT = 100mA
1.202
1.201
1.200
0
-1
-50
0
50
100 150 200
0
0.2 0.4 0.6 0.8
1
1.2 1.4
TEMPERATURE (°C)
OUTPUT CURRENT (A)
TEMPERATURE (°C)
Enable Threshold
vs. Temperature
Line Regulation
5.08
5.07
5.06
5.05
5.04
5.03
5.02
5.01
5
1.2
1.18
1.16
1.14
1.12
1.1
Upper Threshold
Lower Threshold
1.08
1.06
1.04
1.02
1
VIN = 12V
VOUT = 5V
IOUT = 100mA
4.99
4.98
IOUT = 500mA
0
5
10 15 20 25 30 35 40
INPUT VOLTAGE (V)
TEMPERATURE (°C)
MIC4684
6
July 2001
MIC4684
Micrel
5V
SOA with Standard
Configuration
3.3V
SOA with Feed
OUT
OUT
Forward Diode
2.5
2
2.5
2
TA = 25°C
1.5
1
1.5
1
VOUT = 3.3V
TA = 60°C
TJ = 125°C
VOUT = 5V
TA = 60°C
TJ = 125°C
0.5
0.5
0
0
0
5
10
15
20
0
5
10 15 20 25 30 35
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
SOA Measured on the MIC4684 Evaluation Board.
SOA Measured on the MIC4684 Evaluation Board.
Note 1. With feed-forward diode implementation as seen in 5V to 3.3V
circuit on page 1.
2.5V
SOA with Feed
1.8V
SOA with Feed
OUT
OUT
Forward Diode
Forward Diode
2.5
2
2.5
2
1.5
1
1.5
1
VOUT = 1.8V
TA = 60°C
VOUT = 2.5V
TA = 60°C
0.5
0.5
TJ = 125°C
TJ = 125°C
0
0
0
5
10
15
20
0
5
10
15
20
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
SOA measured on the MIC4684 Evaluation Board.
SOA measured on the MIC4684 Evaluation Board.
July 2001
7
MIC4684
MIC4684
Micrel
Functional Characteristics
Switching Frequency Foldback
Load Transient
VIN = 12V
VOUT = 5V
IOUT = 1.0A to 0.1A
Normal
5.1V
5V
Operation
200kHz
1A
0A
Short
Circuit
Operation
70kHz
TIME
TIME (100ms/div.)
Frequency Foldback
The MIC4684 folds the switching frequency back during a hard short
circuit condition to reduce the energy per cycle and protect the device.
MIC4684
8
July 2001
MIC4684
Micrel
Block Diagrams
VIN
IN
Bootstrap
Charger
Enable
Internal
Regulator
R1
R2
V
= V
+1
OUT
REF
V
OUT
R1= R2
−1
200kHz
Oscillator
Thermal
Shutdown
Current
Limit
V
REF
V
= 1.235V
REF
Com-
parator
VOUT
SW
FB
Driver
COUT
Reset
R1
R2
Error
Amp
1.235V
Bandgap
Reference
MIC4684
Adjustable Regulator
amplifier output voltage is compared to a 200kHz sawtooth
waveform to produce a voltage controlled variable duty cycle
output.
Functional Description
The MIC4684 is a variable duty cycle switch-mode regulator
with an internal power switch. Refer to the above block
diagram.
A higher feedback voltage increases the error amplifier
output voltage. A higher error amplifier voltage (comparator
inverting input) causes the comparator to detect only the
peaks of the sawtooth, reducing the duty cycle of the com-
parator output. A lower feedback voltage increases the duty
cycle. The MIC4684 uses a voltage-mode control architec-
ture.
Supply Voltage
The MIC4684 operates from a +4V to +30V (34V transient)
unregulated input. Highest efficiency operation is from a
supply voltage around +12V. See the efficiency curves on
page 5.
Enable/Shutdown
Output Switching
The enable (EN) input is TTL compatible. Tie the input high
if unused. A logic-high enables the regulator. A logic-low
shuts down the internal regulator which reduces the current
When the internal switch is ON, an increasing current flows
from the supply V through external storage inductor L1, to
IN,
output capacitor C
and the load. Energy is stored in the
OUT
to typically 150µA when V = 0V.
inductor as the current increases with time.
EN
Feedback
When the internal switch is turned OFF, the collapse of the
magnetic field in L1 forces current to flow through fast
Fixed-voltage versions of the regulator have an internal
resistive divider from the feedback (FB) pin. Connect FB
directly to the output voltage.
recovery diode D1, charging C
.
OUT
Output Capacitor
Adjustable versions require an external resistive voltage
dividerfromtheoutputvoltagetoground,centertappedtothe
FB pin. See Table 1 and Table 2 for recommended resistor
values.
External output capacitor C
reduces ripple.
provides stabilization and
OUT
Return Paths
During the ON portion of the cycle, the output capacitor and
load currents return to the supply ground. During the OFF
portion of the cycle, current is being supplied to the output
capacitor and load by storage inductor L1, which means that
D1 is part of the high-current return path.
Duty Cycle Control
A fixed-gain error amplifier compares the feedback signal
with a 1.235V bandgap voltage reference. The resulting error
July 2001
9
MIC4684
MIC4684
Micrel
Examining θ in more detail:
Applications Information
Adjustable Regulators
JA
θ
= (θ + θ
)
CA
JA
JC
where:
Adjustable regulators require a 1.23V feedback signal. Rec-
ommended voltage-divider resistor values for common out-
put voltages are included in Table 1.
θ
θ
= junction-to-case thermal resistance
= case-to-ambient thermal resistance
JC
CA
For other voltages, the resistor values can be determined
using the following formulas:
θ
θ
is a relatively constant 25°C/W for a power SOP-8.
JC
is dependent on layout and is primarily governed by the
CA
connection of pins 2, 6, and 7 to the ground plane. The
purpose of the ground plane is to function as a heat sink.
R1
VOUT = VREF
+1
R2
θ
is ideally 75°C/W, but will vary depending on the size of
JA
the ground plane to which the power SOP-8 is attached.
VOUT
R1= R2
−1
Determining Ground-Plane Heat-Sink Area
VREF
Make sure that MIC4684 pins 2, 6, and 7 are connected to a
2
VREF = 1.235V
ground plane with a minimum area of 6cm . This ground
plane should be as close to the MIC4684 as possible. The
area may be distributed in any shape around the package or
on any pcb layer as long as there is good thermal contact to
pins2,6,and7.Thisgroundplaneareaismorethansufficient
for most designs.
Minimum Pulse Width
The minimum duty cycle of the MIC4684 is approximately
10%. See Minimum Duty Cycle Graph. If this input-to-output
voltage characteristic is exceeded, the MIC4684 will skip
cycles to maintain a regulated V
.
OUT
Max. V for a Given V
for
OUT
IN
Constant-Frequency Switching
40
SOP-8
35
30
25
20
15
10
5
θJA
ground plane
AMBIENTheat sink area
θJC
θCA
0
0
1
2
3
4
5
6
OUTPUT VOLTAGE (V)
printed circuit board
Figure 1. Minimum Pulse Width Characteristic
Thermal Considerations
Figure 2. Power SOP-8 Cross Section
When designing with the MIC4684, it is a good practice to
connect pins 2, 6, and 7 to the largest ground plane that is
practical for the specific design.
The MIC4684 SuperSwitcher™ features the power-SOP-8.
This package has a standard 8-lead small-outline package
profile, but with much higher power dissipation than a stan-
dard SOP-8. Micrel's MIC4684 SuperSwitcher™ family are
the first dc-to-dc converters to take full advantage of this
package.
Checking the Maximum Junction Temperature:
For this example, with an output power (P
) of 5W, (5V
OUT
output at 1A with V = 12V) and 60°C maximum ambient
IN
The reason that the power SOP-8 has higher power dissipa-
tion (lower thermal resistance) is that pins 2, 6, and 7 and the
die-attach paddle are a single piece of metal. The die is
attached to the paddle with thermally conductive adhesive.
This provides a low thermal resistance path from the junction
of the die to the ground pins. This design significantly im-
proves package power dissipation by allowing excellent heat
transfer through the ground leads to the printed circuit board.
temperature, what is the junction temperature?
Referring to the “Typical Characteristics: 5V Output Effi-
ciency” graph, read the efficiency (η) for 1A output current at
V
= 12V or perform you own measurement.
IN
η = 84%
The efficiency is used to determine how much of the output
power (P
) is dissipated in the regulator circuit (P ).
OUT
D
OnelimitationofthemaximumoutputcurrentonanyMIC4684
P
OUT
P =
−P
OUT
design is the junction-to-ambient thermal resistance (θ ) of
D
JA
η
the design (package and ground plane).
5W
PD =
− 5W
0.84
P = 0.95W
D
MIC4684
10
July 2001
MIC4684
Micrel
A worst-case rule of thumb is to assume that 80% of the total
This value is within the allowable maximum operating junc-
tion temperature of 125°C as listed in “Operating Ratings.”
Typical thermal shutdown is 160°C and is listed in Electrical
Characteristics. Also see SOA curves on pages 7 through 8.
output power dissipation is in the MIC4684 (P
is in the diode-inductor-capacitor circuit.
) and 20%
D(IC)
P
P
P
= 0.8 P
D
D(IC)
D(IC)
D(IC)
Layout Considerations
= 0.8 × 0.95W
Layout is very important when designing any switching regu-
lator. Rapidly changing currents through the printed circuit
board traces and stray inductance can generate voltage
transients which can cause problems.
= 0.76W
Calculate the worst-case junction temperature:
T = P + (T – T ) + T
θ
J
D(IC) JC
C
A
A(max)
where:
T = MIC4684 junction temperature
To minimize stray inductance and ground loops, keep trace
lengths as short as possible. For example, keep D1 close to
pin 1 and pins 2, 6, and 7, keep L1 away from sensitive node
J
P
= MIC4684 power dissipation
D(IC)
FB, and keep C close to pin 3 and pins 2, 6, and 7. See
IN
θ
= junction-to-case thermal resistance.
JC
ApplicationsInformation:ThermalConsiderationsforground
plane layout.
The θ for the MIC4684’s power-SOP-8 is approximately
JC
Thefeedbackpinshouldbekeptasfarwayfromtheswitching
elements (usually L1 and D1) as possible.
25°C/W.
T = “pin” temperature measurement taken at the
C
A circuit with sample layouts are provided. See Figure 7.
Gerber files are available upon request.
entry point of pins 2, 6 or 7
T = ambient temperature
A
Feed Forward Diode
T
= maximum ambient operating temperature
A(max)
TheFFdiode(feedforward)providesanexternalbiassource
for the specific design.
directly to the main pass element, this reduces V
thus
SAT
Calculating the maximum junction temperature given a
maximum ambient temperature of 60°C:
allowing the MIC4684 to be used in very low head-room
applications I.E. 5V to 3.3V
IN
OUT.
T = 0.76 × 25°C/W + (41°C – 25°C) + 60°C
J
T = 95°C
J
VIN
+4V to +30V
MIC4684BM
(34V transient)
3
8
4
1
IN
EN
BS
L1
VOUT
R1
SW
CIN
68µH
COUT
5
FB
Power
SOP-8
GND
D1
2
6
7
R2
GND
Figure 5. Critical Traces for Layout
July 2001
11
MIC4684
MIC4684
Micrel
Recommended Components for a Given Output Voltage (Feed-Forward Configuration)
V
= 4V to 16V (in feed-forward configuration)
IN
VOUT IOUT
R1
R2
VIN
CIN
D1
D2
L1
COUT
5.0V 1.6A 3.01k 976kΩ
6.5V–16V 47µF, 20V
2A, 30V 1A, 20V
27µH
120µF, 6.3V
Vishay-Dale
Schottky Schottky Sumida
Vishay-Dale
595D476X0020D2T
SS23
MBRX120 CDH74-270MC
594D127X06R3C2T
3.3V 1.7A 3.01k 1.78k 4.85V–16V 47µF, 20V
2A, 30V 1A, 20V
27µH
220µF, 6.3V
Vishay-Dale
Schottky Schottky Sumida
Vishay-Dale
595D476X0020D2T
SS23
MBRX120 CDH74-270MC
594D227X06R3C2T
2.5V 1.8A 3.01k 2.94k
4.5V–16V 47µF, 20V
2A, 30V 1A, 20V
27µH
330µF, 6.3V
Vishay-Dale
Schottky Schottky Sumida
Vishay-Dale
595D476X0020D2T
SS23
MBRX120 CDH74-270MC
594D337X06R3D2T
1.8V
2A
3.01k 6.49k
4.2V–16V 47µF, 20V
2A, 30V 1A, 20V
27µH
330µF, 6.3V
Vishay-Dale
595D476X0020D2T
Schottky Schottky Sumida
SS23 MBRX120 CDH74-270MC
Vishay-Dale
594D337X06R3D2T
Note 1. This bill of materials assumes the use of feedforward schotty diode from V to the bootstrap pin.
IN
Table 1. Recommended Components for Common Ouput Voltages
(V = 4V to 16V)
IN
D2
MBRX120
1A/20V
J1
VIN
J2
VOUT
2A
L1
47µH
U1 MIC4684BM
4V to +16V
3
8
1
VIN
SW
C6
0.33µF
50V
4
5
C2
0.1µF
50V
BS
FB
C3*
R1
optional
C1
15µF
35V
J3
GND
3.01k
ON
EN
C4
330 F
6.3V
C5
OFF
D1
R2
6.49k
R3
2.94k
R4
1.78k
R5
0.1µF
GND
2, 6, 7
B340A
or
976Ω
50V
SOP-8
1
2
3
5
SS34
JP1a
1.8V
JP1b
2.5V
JP1c7
JP1d
5.0V
3.3V
J4
GND
8
4
6
* C3 can be used to provide additional stability
and improved transient response.
Note: optimized for 5VOUT
Figure 6. 4V - 16V Input Evaluation Board Schematic Diagram
MIC4684
12
July 2001
MIC4684
Micrel
Printed Circuit Board
Evaluation Board Optimized for Low Input Voltage by using Feed-Forward Diode Configuration (V = 4V to 16V)
IN
Figure 7a. Bottom Side Copper
Figure 7b. Top Side Copper
Figure 7c. Bottom Side Silk Screen
Figure 7d. Top Side Silk Screen
Abbreviated Bill of Material (Critical Components)
Reference
C1
Part Number
Manufacturer
Vishay Sprague1
Vitramon
Description
Qty
1
594D156X0035D2T
VJ0805Y104KXAAB
GRM426X7R334K50
Optional
15µF 35V
C2, C5
C6
0.1µF 50V
2
Murata
0.33µF, 50V ceramic capacitor
1800pF, 50V ceramic
330µF, 6.3V, tantalum
Schottky 3A, 40V
C3
(1)
1
C4
594D337X06R3D2T
B340A
Vishay Sprague2
Diode Inc3
D1
1
D2
MBRX120
Micro Com. Components5
Sumida4
Schottky 1A, 20V
1
L1
CDRH104R-470MC
MIC4684BM
47µH, 2.1A ISAT
1
U1
Micrel Semiconductor6
1A 200kHz power-SO-8 buck regulator
1
1
2
3
4
5
6
Vishay Dale, Inc., tel: 1 402-644-4218, http://www.vishay.com
Vishay Sprague, Inc., tel: 1 207-490-7256, http://www.vishay.com
Diodes Inc, tel: (805) 446-4800, http://www.diodes.com
Sumida, tel: (408) 982-9960, http://www.sumida.com
Micro Commercial Components, tel: (800) 346-3371
Micrel, tel: (408) 944-0800, http://www.micrel.com
July 2001
13
MIC4684
MIC4684
Micrel
Recommended Components for a Given Output Voltage (Standard Configuration)
V
= 4V to 30V
IN
VOUT IOUT
R1
R2
VIN
CIN
D1
L1
COUT
5.0V
3.3V
2.5V
1.8V
1.7A 3.01k 976kΩ
8V–30V
33µF, 35V
Vishay-Dale
595D336X0035R2T
3A, 40V
Schotty
SS34
68µH
Sumida
CDRH104R-680MC
120µF, 6.3V
Vishay-Dale
594D127X06R3C2T
1.5A 3.01k
1.5A 3.01k
1.5A 3.01k
1.78k
2.94k
6.49k
7V–28V
6.5V–23V
6V–17V
33µF, 35V
Vishay-Dale
595D336X0035R2T
3A, 40V
Schotty
SS34
68µH
Sumida
CDRH104R-680MC
220µF, 6.3V
Vishay-Dale
594D227X06R3C2T
33µF, 35V
Vishay-Dale
595D336X0035R2T
3A, 40V
Schotty
SS334
68µH
Sumida
CDRH104R-680MC
330µF, 6.3V
Vishay-Dale
594D337X06R3D2T
47µF, 25V
Vishay-Dale
595D476X0025D2T
3A, 40V
Schotty
SS334
68µH
Sumida
CDRH104R-680MC
330µF, 6.3V
Vishay-Dale
594D337X06R3D2T
Table 2. Recommended Components for Common Ouput Voltages
(V = 4V to 30V)
IN
J1
VIN
L1
J2
VOUT
2A
4V to +30V
(34V transient)
U1 MIC4684BM
47µH
3
8
1
VIN
SW
C6
0.33µF
50V
4
5
C2
0.1µF
50V
BS
FB
C3*
R1
optional
C1
15µF
35V
J3
GND
3.01k
ON
EN
C4
330 F
6.3V
C5
0.1µF
50V
OFF
D1
R2
6.49k
R3
2.94k
R4
1.78k
R5
GND
2, 6, 7
B340A
or
976Ω
SOP-8
1
2
3
5
SS34
JP1a
1.8V
JP1b
2.5V
JP1c7
JP1d
5.0V
3.3V
J4
GND
8
4
6
* C3 can be used to provide additional stability
and improved transient response.
Note: optimized for 5VOUT
Figure 6a. 4V - 30V Input Evaluation Board Schematic Diagram
MIC4684
14
July 2001
MIC4684
Micrel
Printed Circuit Board
General Purpose Evaluation Board (V = 4V to 30V)
IN
Figure 7a. Bottom Side Copper
Figure 7b. Top Side Copper
Figure 7c. Bottom Side Silk Screen
Figure 7d. Top Side Silk Screen
Abbreviated Bill of Material (Critical Components)
Reference
C1
Part Number
Manufacturer
Vishay Sprague1
Vitramon
Description
Qty
1
594D156X0035D2T
VJ0805Y104KXAAB
GRM426X7R334K50
Optional
15µF 35V
C2, C5
C6
0.1µF 50V
2
Murata
0.33µF, 50V ceramic capacitor
1800pF, 50V ceramic
330µF, 6.3V, tantalum
Schottky 3A 40V
C3
(1)
1
C4
594D337X06R3D2T
B340A
Vishay Sprague2
Diode Inc3
D1
1
L1
CDRH104R-470MC
MIC4684BM
Sumida4
47µH, 2.1A ISAT
1
U1
Micrel Semiconductor5
1A 200kHz power-SO-8 buck regulator
1
1
2
3
4
5
Vishay Dale, Inc., tel: 1 402-644-4218, http://www.vishay.com
Vishay Sprague, Inc., tel: 1 207-490-7256, http://www.vishay.com
Diodes Inc, tel: (805) 446-4800, http://www.diodes.com
Sumida, tel: (408) 982-9960, http://www.sumida.com
Micrel, tel: (408) 944-0800, http://www.micrel.com
July 2001
15
MIC4684
MIC4684
Micrel
Package Information
0.026 (0.65)
MAX)
PIN 1
0.157 (3.99)
0.150 (3.81)
DIMENSIONS:
INCHES (MM)
0.020 (0.51)
0.013 (0.33)
0.050 (1.27)
TYP
45°
0.0098 (0.249)
0.0040 (0.102)
0.010 (0.25)
0.007 (0.18)
0°–8°
0.197 (5.0)
0.189 (4.8)
0.050 (1.27)
0.016 (0.40)
SEATING
PLANE
0.064 (1.63)
0.045 (1.14)
0.244 (6.20)
0.228 (5.79)
8-Lead SOP (M)
MICREL INC. 1849 FORTUNE DRIVE SAN JOSE, CA 95131 USA
TEL + 1 (408) 944-0800 FAX + 1 (408) 944-0970 WEB http://www.micrel.com
This information is believed to be accurate and reliable, however no responsibility is assumed by Micrel for its use nor for any infringement of patents or
other rights of third parties resulting from its use. No license is granted by implication or otherwise under any patent or patent right of Micrel Inc.
© 2001 Micrel Incorporated
MIC4684
16
July 2001
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