MICREL MIC4684

MIC4684
Micrel
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.
High efficiency is maintained over a wide output current range
by utilizing a boost capacitor to increase the voltage available
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.
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
be used in applications where input voltage transients may be
present. Built-in safety features include over-current protection, frequency-foldback short-circuit protection, and thermal
shutdown.
The MIC4684 is available in an 8-lead SO package with a
junction temperature range of –40°C to +125°C.
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•
•
•
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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
Applications
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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
Ordering Information
Part Number
Voltage
Junction Temperature Range
Package
MIC4684BM
Adj
–40°C to +125°C
SOP-8
Typical Application
3
8
MIC4684BM
VIN
BS
EN
CIN
33µF
35V
4
SW
1
FB
5
GND
CBS
0.33µF/50V
68µH
3A
40V
2, 6, 7
VOUT
2.5V/1.5A
R1
3.01k
R2
3.01k
Efficiency
vs. Output Current
330µF
6.3V
100
VOUT = 3.3V
80
EFFICIENCY (%)
VIN
6.5V to 25V
Adjustable Buck Converter
1A, 20V Feed forward diode
VIN
5V
±10%
3
8
CIN
68µF
10V
MIC4684BM
VIN
BS
EN
1
FB
5
2, 6, 7
CBS
0.33µF/50V
20
VOUT
3.3V/1.7A
47µH
VOUT = 1.8V
VOUT = 2.5V
40
0
4
SW
GND
60
0
VIN = 5.0V
0.5
1
1.5
OUTPUT CURRENT (A)
2
Efficiency vs. Output Current
220µF
10V
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
1
8
EN
GND
2
7
GND
VIN
3
6
GND
BS
4
5
FB
8-Pin SOP (M)
Pin Description
Pin Number
Pin Name
Pin Function
1
SW
2, 6, 7
GND
3
IN
Supply (Input): Unregulated +4V to 30V supply voltage (34V transient)
4
BS
Booststrap Voltage Node (External Component): Connect to external boost
capacitor.
5
FB
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.
8
EN
Enable (Input): Logic high = enable; logic low = shutdown
Switch (Output): Emitter of NPN output switch. Connect to external storage
inductor and Shottky diode.
Ground
Bootstrap (BS, pin 4)
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
of VIN where it is rectified and used to provide additional drive
to the main switch, in this case a NPN transistor.
This additional drive reduces the NPN’s saturation voltage
and increases efficiency, from a VSAT of 1.8V, and 75%
efficiency to a VSAT of 0.5V and 88% efficiency respectively.
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
down the regulator and reduces the stand-by quiescent 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.
Detailed Pin Description
Switch (SW, pin 1)
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
VSAT of the main NPN pass element. The emitter is also
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.
Ground (GND, pins 2,6,7)
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 resistance 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
grounds placed as close as possible to the switching regulator’s
ground pin. To keep radiated EMI to a minimum its necessary
to place the input capacitor ground lead as close as possible
to the switching regulators ground pin.
Input Voltage (VIN, pin 3)
The VIN pin is the collector of the main NPN pass element.
This pin is also connected to the internal regulator. The output
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 (VIN), Note 3 ...................................... +34V
Enable Voltage (VEN) .................................... –0.3V to +VIN
Steady-State Output Switch Voltage (VSW) ....... –1V to VIN
Feedback Voltage (VFB) .............................................. +12V
Storage Temperature (TS) ....................... –65°C to +150°C
ESD Rating .............................................................. Note 3
Supply Voltage (VIN) Note 4 ........................... +4V to +30V
Ambient Temperature (TA) ......................... –40°C to +85°C
Junction Temperature (TJ) ....................... –40°C to +125°C
Package Thermal Resistance
θJA, Note 5 .......................................................... 75°C/W
θJC, Note 5 .......................................................... 25°C/W
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
Typ
Max
Units
Feedback Voltage
(±2%)
(±3%)
1.210
1.198
1.235
1.260
1.272
V
V
8V ≤ VIN ≤ 30V, 0.1A ≤ ILOAD ≤ 1A, VOUT = 5V
1.186
1.173
1.235
1.284
1.297
V
V
Feedback Bias Current
50
nA
%
Maximum Duty Cycle
VFB = 1.0V
94
Output Leakage Current
VIN = 30V, VEN = 0V, VSW = 0V
5
500
µA
VIN = 30V, VEN = 0V, VSW = –1V
1.4
20
mA
6
12
mA
Quiescent Current
VFB = 1.5V
Bootstrap Drive Current
VFB = 1.5V, VSW = 0V
250
380
mA
Bootstrap Voltage
IBS = 10mA, VFB = 1.5V, VSW = 0V
5.5
6.2
V
Frequency Fold Back
VFB = 0V
30
50
120
kHz
180
200
225
kHz
Oscillator Frequency
Saturation Voltage
IOUT = 1A
Short Circuit Current Limit
VFB = 0V, See Test Circuit
Shutdown Current
VEN = 0V
Enable Input Logic Level
regulator on
0.59
2.2
A
µA
150
2
V
regulator off
Enable Pin Input Current
V
VEN = 0V (regulator off)
16
VEN = 12V (regulator on)
–1
Thermal Shutdown @ TJ
0.8
V
50
µA
–0.83
mA
160
°C
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 VIN and VOUT. The headroom can be reduced by implementing a feed-forward diode a seen on the 5V
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
+12V
3
8
Device Under Test
1
VIN
SW
EN
BS
GND
SOP-8
68µH
4
I
FB
2,6,7
5
Current Limit Test Circuit
Shutdown Input Behavior
ON
OFF
GUARANTEED
OFF
0V
TYPICAL
OFF
0.8V
2V
1.25V
1.4V
GUARANTEED
ON
TYPICAL
ON
VIN(max)
Enable Hysteresis
MIC4684
4
July 2001
MIC4684
Micrel
Typical Characteristics
(TA = 25°C unless otherwise noted)
3.3VOUT Efficiency without
100
85
80
EFFICIECNY (%)
VIN = 12V
75
70
65
60
VIN = 24V
95
90 V = 8V
IN
85
80
75
70
VIN = 24V
55
VOUT = 5V
50
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6
OUTPUT CURRENT (A)
55
VOUT = 3.3V
50
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6
OUTPUT CURRENT (A)
Efficiency vs. Output Current
with Feed Forward Diode
Bootstrap Voltage
vs. Input Voltage
3.3VOUT
2.5VOUT
1.8VOUT
30
20
VIN = 12V
0.5
1
1.5
2
2.5
OUTPUT CURRENT (A)
10.6
10.5
10.4
5
10 15 20 25 30 35 40
INPUT VOLTAGE (V)
5
4
3
2
VIN = 12V
VFB = 1.5V
1
5
100
80
60
40
July 2001
VEN = 0V
5
10 15 20 25 30 35 40
INPUT VOLTAGE (V)
100
VIN = 12V
VFB = 1.5V
50
0
0 2 4 6 8 10 12 14 16 18 20
INPUT VOLTAGE (V)
30
Quiescent Current
vs. Input Voltage
6.2
1.245
1.240
1.235
VIN = 12V
VOUT = VREF
IOUT = 500mA
1.230
5
6.1
6
5.9
5.8
VEN= 5V
5.7
0
10 15 20 25 30 35 40
INPUT VOLTAGE (V)
Saturation Voltage
vs. Input Voltage
SATURATION VOLTAGE (mV)
140
120
10 15 20 25
INPUT VOLTAGE (V)
150
1.250
Shutdown Current
vs. Input Voltage
180
160
51.5
600
51
595
590
585
580
IOUT = 1A
VOUT = 5V
575
5
10 15 20 25 30 35 40
INPUT VOLTAGE (V)
5
5
10 15 20 25 30 35 40
INPUT VOLTAGE (V)
Foldback Frequency
vs. Input Voltage
605
570
0
2
200
6.3
200
= 5.0V
250
1.255
1.225
0
IN
300
Reference Voltage
vs. Input Voltage
REFERENCE VOLTAGE (V)
DUTY CYCLE (%)
VIN = 12V
10.8 VOUT = 5V
VFB = 1.3V
10.7
V
0.5
1
1.5
OUTPUT CURRENT (A)
350
0
0
3
10.9
20
0
0
55
50
0
VOUT = 1.8V
Bootstrap Drive Current
vs. Input Voltage
6
Minimum Duty Cycle
vs. Input Voltage
10.3
0
65
60
INPUT CURRENT (mA)
50
40
VOUT = 2.5V
75
70
BOOTSTRAP CURRENT (mA)
BOOTSTRAP VOLTAGE (V)
5VOUT
70
60
10
0
0
85
80
7
90
80
EFFICIENCY (%)
VIN = 12V
65
60
100
INPUT CURRENT (µA)
95
V
= 3.3V
90 OUT
FREQUENCY (kHz)
EFFICIECNY (%)
95
VIN = 8V
90
5VIN Efficiency with Feed
Forward Diode
100
Feed Forward Diode
EFFICIENCY (%)
5VOUT Efficiency without Feed
Forward Diode
100
50.5
50
49.5
49
48.5
0
VFB = 0V
5
10 15 20 25 30 35 40
INPUT VOLTAGE (V)
MIC4684
MIC4684
Micrel
Shutdown Hysteresis vs.
Temperature
Load Regulation
5.020
1.209
1.208
5
5.018
5.016
1.207
1.206
1.205
1.204
3
2
1
MIC4684
5.006
5.004
5.002
5.000
0
0.2 0.4 0.6 0.8 1 1.2 1.4
OUTPUT CURRENT (A)
1.02
1
VIN = 12V
VOUT = 5V
IOUT = 100mA
140
10 15 20 25 30 35 40
INPUT VOLTAGE (V)
1.06
1.04
20
40
5
5.010
5.008
Lower Threshold
1.1
1.08
-20
0
IOUT = 500mA
1.14
1.12
-60
-40
4.99
4.98
0
200
5.014
5.012
Upper Threshold
100
120
1.18
1.16
60
80
1.2
5.07
5.06
THRESHOLD TRIP POINTS
OUTPUT VOLTAGE (V)
5.08
5.01
5
0
50
100 150
TEMPERATURE (°C)
VIN = 12V
Enable Threshold
vs. Temperature
Line Regulation
5.03
5.02
OFF
0
TEMPERATURE (°C)
5.05
5.04
ON
4
-1
-50
120
140
80
100
40
60
-60
-40
1.200
20
1.203 VIN = 12V
1.202 VOUT = VFB
1.201 IOUT = 100mA
OUTPUT VOLTAGE (V)
6
OUTPUT VOLTAGE (V)
1.210
-20
0
FEEDBACK VOLTAGE (V)
Feedback Voltage
vs. Temperature
TEMPERATURE (°C)
6
July 2001
Micrel
5VOUT SOA with Standard
Configuration
3.3V
OUT
2.5
2.5
TA = 25°C
2
OUTPUT CURRENT (A)
CONTINUOUS OUTPUT CURRENT (A)
MIC4684
1.5
1
VOUT = 5V
TA = 60°C
TJ = 125°C
0.5
0
0
5
10 15 20 25 30
INPUT VOLTAGE (V)
SOA Measured on the MIC4684 Evaluation Board.
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
1.5
1
VOUT = 2.5V
TA = 60°C
TJ = 125°C
VOUT = 3.3V
TA = 60°C
TJ = 125°C
5
10
15
INPUT VOLTAGE (V)
20
2
1.5
1
0.5
0
0
20
SOA measured on the MIC4684 Evaluation Board.
July 2001
0.5
1.8VOUT SOA with Feed
Forward Diode
2.5
2
5
10
15
INPUT VOLTAGE (V)
1
With feed-forward diode implementation as seen in 5V to 3.3V
circuit on page 1.
2.5VOUT SOA with Feed
Forward Diode
2.5
0
0
1.5
SOA Measured on the MIC4684 Evaluation Board.
Note 1.
0.5
Forward Diode
2
0
0
35
SOA with Feed
VOUT = 1.8V
TA = 60°C
TJ = 125°C
5
10
15
INPUT VOLTAGE (V)
20
SOA measured on the MIC4684 Evaluation Board.
7
MIC4684
MIC4684
Micrel
Functional Characteristics
Load Transient
VOUT
(100mV/div.)
Normal
Operation
200kHz
VIN = 12V
VOUT = 5V
IOUT = 1.0A to 0.1A
Short
Circuit
Operation
5.1V
5V
1A
IOUT
(500mA/div.)
VSW (SHORTED)
12V IN, 0V OUT
VSW (NORMAL)
12V IN, 5V/1A OUT
Switching Frequency Foldback
0A
70kHz
TIME (100ms/div.)
TIME
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
200kHz
Oscillator
Thermal
Shutdown
 R1 
VOUT = VREF 
+ 1
 R2 
V

R1 = R2  OUT − 1
 VREF

Current
Limit
VREF = 1.235V
Comparator
VOUT
SW
Driver
COUT
Reset
R1
FB
Error
Amp
1.235V
Bandgap
Reference
R2
MIC4684
Adjustable Regulator
amplifier output voltage is compared to a 200kHz sawtooth
waveform to produce a voltage controlled variable duty cycle
output.
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 comparator output. A lower feedback voltage increases the duty
cycle. The MIC4684 uses a voltage-mode control architecture.
Output Switching
When the internal switch is ON, an increasing current flows
from the supply VIN, through external storage inductor L1, to
output capacitor COUT and the load. Energy is stored in the
inductor as the current increases with time.
When the internal switch is turned OFF, the collapse of the
magnetic field in L1 forces current to flow through fast
recovery diode D1, charging COUT.
Output Capacitor
External output capacitor COUT provides stabilization and
reduces ripple.
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.
Functional Description
The MIC4684 is a variable duty cycle switch-mode regulator
with an internal power switch. Refer to the above block
diagram.
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
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
to typically 150µA when VEN = 0V.
Feedback
Fixed-voltage versions of the regulator have an internal
resistive divider from the feedback (FB) pin. Connect FB
directly to the output voltage.
Adjustable versions require an external resistive voltage
divider from the output voltage to ground, center tapped to the
FB pin. See Table 1 and Table 2 for recommended resistor
values.
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 θJA in more detail:
Applications Information
θJA = (θJC + θCA)
where:
θJC = junction-to-case thermal resistance
θCA = case-to-ambient thermal resistance
θJC is a relatively constant 25°C/W for a power SOP-8.
θCA is dependent on layout and is primarily governed by the
connection of pins 2, 6, and 7 to the ground plane. The
purpose of the ground plane is to function as a heat sink.
θJA is ideally 75°C/W, but will vary depending on the size of
the ground plane to which the power SOP-8 is attached.
Determining Ground-Plane Heat-Sink Area
Make sure that MIC4684 pins 2, 6, and 7 are connected to a
ground plane with a minimum area of 6cm2. 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
pins 2, 6, and 7. This ground plane area is more than sufficient
for most designs.
Adjustable Regulators
Adjustable regulators require a 1.23V feedback signal. Recommended voltage-divider resistor values for common output voltages are included in Table 1.
For other voltages, the resistor values can be determined
using the following formulas:
 R1 
VOUT = VREF 
+ 1
 R2 
V

R1 = R2  OUT − 1
 VREF

VREF = 1.235V
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 VOUT.
Max. VIN for a Given VOUT for
Constant-Frequency Switching
MAX. INPUT VOLTAGE (V)
40
SOP-8
35
30
25
20
15
θJA
10
θJC
5
0
0
1
2
3
4
5
OUTPUT VOLTAGE (V)
θCA
AM
6
Figure 1. Minimum Pulse Width Characteristic
BIE
ground plane
heat sink area
NT
printed circuit board
Figure 2. Power SOP-8 Cross Section
Thermal Considerations
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 standard SOP-8. Micrel's MIC4684 SuperSwitcher™ family are
the first dc-to-dc converters to take full advantage of this
package.
The reason that the power SOP-8 has higher power dissipation (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 improves package power dissipation by allowing excellent heat
transfer through the ground leads to the printed circuit board.
One limitation of the maximum output current on any MIC4684
design is the junction-to-ambient thermal resistance (θJA) of
the design (package and ground plane).
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.
Checking the Maximum Junction Temperature:
For this example, with an output power (POUT) of 5W, (5V
output at 1A with VIN = 12V) and 60°C maximum ambient
temperature, what is the junction temperature?
Referring to the “Typical Characteristics: 5V Output Efficiency” graph, read the efficiency (η) for 1A output current at
VIN = 12V or perform you own measurement.
η = 84%
The efficiency is used to determine how much of the output
power (POUT) is dissipated in the regulator circuit (PD).
PD =
POUT
η
− POUT
5W
− 5W
0.84
PD = 0.95W
PD =
MIC4684
10
July 2001
MIC4684
Micrel
A worst-case rule of thumb is to assume that 80% of the total
output power dissipation is in the MIC4684 (PD(IC)) and 20%
is in the diode-inductor-capacitor circuit.
PD(IC) = 0.8 PD
PD(IC) = 0.8 × 0.95W
PD(IC) = 0.76W
Calculate the worst-case junction temperature:
TJ = PD(IC) θJC + (TC – TA) + TA(max)
where:
TJ = MIC4684 junction temperature
PD(IC) = MIC4684 power dissipation
θJC = junction-to-case thermal resistance.
This value is within the allowable maximum operating junction 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.
Layout Considerations
Layout is very important when designing any switching regulator. Rapidly changing currents through the printed circuit
board traces and stray inductance can generate voltage
transients which can cause problems.
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
FB, and keep CIN close to pin 3 and pins 2, 6, and 7. See
Applications Information: Thermal Considerations for ground
plane layout.
The feedback pin should be kept as far way from the switching
elements (usually L1 and D1) as possible.
A circuit with sample layouts are provided. See Figure 7.
Gerber files are available upon request.
Feed Forward Diode
The FF diode (feed forward) provides an external bias source
directly to the main pass element, this reduces VSAT thus
allowing the MIC4684 to be used in very low head-room
applications I.E. 5VIN to 3.3VOUT.
The θJC for the MIC4684’s power-SOP-8 is approximately
25°C/W.
TC = “pin” temperature measurement taken at the
entry point of pins 2, 6 or 7
TA = ambient temperature
TA(max) = maximum ambient operating temperature
for the specific design.
Calculating the maximum junction temperature given a
maximum ambient temperature of 60°C:
TJ = 0.76 × 25°C/W + (41°C – 25°C) + 60°C
TJ = 95°C
MIC4684BM
3
8
CIN
Power
SOP-8
IN
EN
BS
SW
4
FB
5
6
VOUT
68µH
GND
2
L1
1
COUT
D1
7
R1
R2
Load
VIN
+4V to +30V
(34V transient)
GND
Figure 5. Critical Traces for Layout
July 2001
11
MIC4684
MIC4684
Micrel
Recommended Components for a Given Output Voltage (Feed-Forward Configuration)
VIN = 4V to 16V (in feed-forward configuration)
VOUT
IOUT
5.0V
1.6A
3.01k 976kΩ
6.5V–16V
3.3V
1.7A
3.01k
2.5V
1.8A
1.8V
2A
Note 1.
R1
R2
VIN
CIN
D1
D2
L1
COUT
47µF, 20V
Vishay-Dale
595D476X0020D2T
2A, 30V 1A, 20V
27µH
Schottky Schottky Sumida
SS23
MBRX120 CDH74-270MC
120µF, 6.3V
Vishay-Dale
594D127X06R3C2T
1.78k
4.85V–16V 47µF, 20V
Vishay-Dale
595D476X0020D2T
2A, 30V 1A, 20V
27µH
Schottky Schottky Sumida
SS23
MBRX120 CDH74-270MC
220µF, 6.3V
Vishay-Dale
594D227X06R3C2T
3.01k
2.94k
4.5V–16V
47µF, 20V
Vishay-Dale
595D476X0020D2T
2A, 30V 1A, 20V
27µH
Schottky Schottky Sumida
SS23
MBRX120 CDH74-270MC
330µF, 6.3V
Vishay-Dale
594D337X06R3D2T
3.01k
6.49k
4.2V–16V
47µF, 20V
Vishay-Dale
595D476X0020D2T
2A, 30V 1A, 20V
27µH
Schottky Schottky Sumida
SS23
MBRX120 CDH74-270MC
330µF, 6.3V
Vishay-Dale
594D337X06R3D2T
This bill of materials assumes the use of feedforward schotty diode from VIN to the bootstrap pin.
Table 1. Recommended Components for Common Ouput Voltages
(VIN = 4V to 16V)
D2
MBRX120
1A/20V
J1
VIN
4V to +16V
C1
15µF
35V
J3
GND
3
ON
C2
0.1µF
50V
8
VIN
EN
SW
1
BS
4
FB
5
OFF
GND
SOP-8
2, 6, 7
J2
VOUT
2A
L1
47µH
U1 MIC4684BM
C6
0.33µF
50V
D1
B340A
or
SS34
R1
3.01k
R2
6.49k
1
2
3
JP1a
1.8V
4
C3*
optional
R3
2.94k
5
JP1b
2.5V
6
R4
1.78k
7
JP1c
3.3V
R5
976Ω
JP1d
5.0V
8
C4
330 F
6.3V
C5
0.1µF
50V
J4
GND
* 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 (VIN = 4V to 16V)
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
Part Number
Manufacturer
C1
594D156X0035D2T
Vishay
C2, C5
VJ0805Y104KXAAB
C6
GRM426X7R334K50
C3
Optional
C4
594D337X06R3D2T
Description
Sprague1
Qty
15µF 35V
1
Vitramon
0.1µF 50V
2
Murata
0.33µF, 50V ceramic capacitor
Vishay
Sprague2
Inc3
1800pF, 50V ceramic
(1)
330µF, 6.3V, tantalum
1
Schottky 3A, 40V
1
D1
B340A
Diode
D2
MBRX120
Micro Com. Components5
Schottky 1A, 20V
1
L1
CDRH104R-470MC
Sumida4
47µH, 2.1A ISAT
1
U1
MIC4684BM
Micrel Semiconductor6
1A 200kHz power-SO-8 buck regulator
1
1
Vishay Dale, Inc., tel: 1 402-644-4218, http://www.vishay.com
2
Vishay Sprague, Inc., tel: 1 207-490-7256, http://www.vishay.com
3
Diodes Inc, tel: (805) 446-4800, http://www.diodes.com
4
Sumida, tel: (408) 982-9960, http://www.sumida.com
5
Micro Commercial Components, tel: (800) 346-3371
6
Micrel, tel: (408) 944-0800, http://www.micrel.com
July 2001
13
MIC4684
MIC4684
Micrel
Recommended Components for a Given Output Voltage (Standard Configuration)
VIN = 4V to 30V
VOUT
IOUT
R1
R2
VIN
CIN
D1
L1
COUT
5.0V
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
3.3V
1.5A
3.01k
1.78k
7V–28V
33µF, 35V
Vishay-Dale
595D336X0035R2T
3A, 40V
Schotty
SS34
68µH
Sumida
CDRH104R-680MC
220µF, 6.3V
Vishay-Dale
594D227X06R3C2T
2.5V
1.5A
3.01k
2.94k
6.5V–23V
33µF, 35V
Vishay-Dale
595D336X0035R2T
3A, 40V
Schotty
SS334
68µH
Sumida
CDRH104R-680MC
330µF, 6.3V
Vishay-Dale
594D337X06R3D2T
1.8V
1.5A
3.01k
6.49k
6V–17V
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
(VIN = 4V to 30V)
J1
VIN
4V to +30V
(34V transient)
C1
15µF
35V
J3
GND
L1
3
ON
C2
0.1µF
50V
8
U1 MIC4684BM
VIN
SW
EN
4
FB
5
GND
SOP-8
1
BS
OFF
2, 6, 7
J2
VOUT
2A
47µH
C6
0.33µF
50V
D1
B340A
or
SS34
R1
3.01k
R2
6.49k
1
2
3
JP1a
1.8V
4
C3*
optional
R3
2.94k
5
JP1b
2.5V
6
R4
1.78k
7
JP1c
3.3V
R5
976Ω
JP1d
5.0V
8
C4
330 F
6.3V
C5
0.1µF
50V
J4
GND
* 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 (VIN = 4V to 30V)
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
Part Number
Manufacturer
Description
C1
594D156X0035D2T
Vishay Sprague1
15µF 35V
1
C2, C5
VJ0805Y104KXAAB
Vitramon
0.1µF 50V
2
C6
GRM426X7R334K50
Murata
0.33µF, 50V ceramic capacitor
C3
Optional
C4
D1
L1
U1
594D337X06R3D2T
Vishay
Sprague2
Inc3
B340A
Diode
CDRH104R-470MC
Sumida4
MIC4684BM
Micrel
Semiconductor5
1
Vishay Dale, Inc., tel: 1 402-644-4218, http://www.vishay.com
2
Vishay Sprague, Inc., tel: 1 207-490-7256, http://www.vishay.com
3
Diodes Inc, tel: (805) 446-4800, http://www.diodes.com
4
Sumida, tel: (408) 982-9960, http://www.sumida.com
5
Micrel, tel: (408) 944-0800, http://www.micrel.com
July 2001
15
Qty
1800pF, 50V ceramic
(1)
330µF, 6.3V, tantalum
1
Schottky 3A 40V
1
47µH, 2.1A ISAT
1
1A 200kHz power-SO-8 buck regulator
1
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
0.064 (1.63)
0.045 (1.14)
45°
0.0098 (0.249)
0.0040 (0.102)
0.197 (5.0)
0.189 (4.8)
0°–8°
SEATING
PLANE
0.010 (0.25)
0.007 (0.18)
0.050 (1.27)
0.016 (0.40)
0.244 (6.20)
0.228 (5.79)
8-Lead SOP (M)
MICREL INC. 1849 FORTUNE DRIVE SAN JOSE, CA 95131
TEL
+ 1 (408) 944-0800
FAX
+ 1 (408) 944-0970
WEB
USA
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