MIC4685 DATA SHEET (11/05/2015) DOWNLOAD

MIC4685
3A SPAK SuperSwitcher™
Buck Regulator
General Description
Features
The MIC4685 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 MIC4685 achieves 3A of continuous current in the
7-pin SPAK package.
The thermal performance of the SPAK allows it to replace
TO-220s and TO-263s (D2PAKs) in many applications.
The SPAK saves board space with a 36% smaller footprint
than TO-263.
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, only the ground plane of the PCB is
needed for a heat sink.
The MIC4685 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 MIC4685 is available in a 7-pin SPAK package with a
junction temperature range of –40°C to +125°C.
Data sheets and support documentation can be found on
Micrel’s web site at www.micrel.com.
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Low 2mm profile SPAK package
3A continuous output current
Wide 4V to 30V input voltage range (34V transient)
Fixed 200kHz PWM operation
Over 85% efficiency
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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Point-of-load power supplies
Simple high-efficiency step-down regulators
5V to 3.3V/2A conversion
12V to 5V/3.3V/2.5V/1.8V 3A conversion
Dual-output ±5V conversion
Base stations
LCD power supplies
Battery chargers
___________________________________________________________________________________________________________
Typical Application
V IN
8V to 30V
MIC4685_R
2
5
CIN
33µF
35V
IN
EN
BS
1
SW
6
FB
3
GND
4, Tab
CBS
0.33µF/50V
L1
39mH
D1
3A
40V
VOUT
1.8V/3A
R1
3.01k
R2
6.49k
COUT
330µF
6.3V
1.8V Output Converter
SuperSwitcher is a trademark of Micrel, Inc
Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
January 2010
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M9999-012610
Micrel, Inc.
MIC4685
Ordering Information
Part Number
Voltage
Junction
Temp. Range
Package
MIC4685WR
Adj.
–40° to +125°C
7-Pin SPAK
MIC4685WR EV
Adj.
Standard
RoHS Compliant*
MIC4685BR
Evaluation Board
* RoHS compliant with ‘high-melting solder’ exemption.
Pin Configuration
7
6
5
4
3
2
1
NC
SW
EN
GND
FB
IN
BS
7-Pin SPAK (R)
Pin Description
Pin Number
Pin Name
1
BS
Pin Function
Bootstrap Voltage Node (External Component): Connect to external boost
capacitor.
2
IN
Supply (Input): Unregulated +4V to 30V supply voltage (34V transient)
3
FB
Feedback (Input): Outback voltage feedback to regulator. Connect to 1.235V
tap of resistive divider.
4, Tab
GND
5
EN
Enable (Input): Logic high = enable; logic low = shutdown
6
SW
Switch (Output): Emitter of NPN output switch. Connect to external storage
inductor and Schottky diode.
7
NC
No Connect. Tie this pin-to-ground.
January 2010
Ground
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Detailed Pin Description
Switch (SW, Pin 6)
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
typically to a –0.5V.
Ground (GND, Pin 4, Tab)
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 it’s 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, it is necessary to place the input capacitor
ground lead as close as possible to the switching
regulator’s ground pin.
Input Voltage (VIN, Pin 2)
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.
January 2010
MIC4685
Bootstrap (BS, Pin 1)
The bootstrap pin, in conjunction with the external
bootstrap capacitor, provides a bias voltage higher than
the input voltage to the MIC4685’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 3)
The feedback pin is tied to the inverting side of an error
amplifier. The noninverting side is tied to a 1.235V
bandgap reference. An external resistor voltage divider is
required from the output-to-ground, with the center tied to
the feedback pin. See Tables 1 and 2 for recommended
resistor values.
Enable (EN, Pin 5)
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 logiclow shuts down the regulator and reduces the stand-by
quiescent input current to typically 150µA. The enable pin
has an up-per 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.
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MIC4685
Absolute Maximum Ratings(1)
Operating Ratings(2)
Supply Voltage (VIN) (1) .................................................+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
EDS Rating(3) .................................................................. 2kV
Supply Voltage (VIN) (4) ..................................... +4V to +30V
Junction Temperature (TJ) ........................ –40°C to +125°C
Package Thermal Resistance
SPAK-7 (θJA) ...................................................11.8°C/W
SPAK-7 (θJC).....................................................2.2°C/W
Electrical Characteristics
VIN = VEN = 12V; VOUT 5V; IOUT = 500mA; TA = 25°C, bold values indicate –40°C< TJ < +125°C, unless noted.
Parameter
Condition
Min
Typ
Max
Units
(±2%)
(±3%)
1.210
1.198
1.235
1.260
1.272
V
V
8V ≤ VIN ≤ 30V, 0.1A ≤ ILOAD ≤ 1A, VOUT = 5V, Note 4
1.186
1.173
1.235
1.284
1.297
V
V
MIC4685 [Adjustable]
Feedback Voltage
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
Bootstrap Voltage
IBS = 10mA, VFB = 1.5V, VSW = 0V
5.5
6.2
Frequency Fold Back
VFB = 0V
30
70
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
V
0.59
3.5
150
V
6
A
200
µA
2
V
regulator off
Enable Pin Input Current
mA
VEN = 0V (regulator off)
16
VEN = 0V (regulator on)
–1
Thermal Shutdown @ TJ
0.8
V
50
µA
–0.83
mA
160
°C
Notes:
1. Exceeding the absolute maximum rating may damage the device.
2. The device is not guaranteed to function outside its operating rating.
3. Devices are ESD sensitive. Handling precautions recommended. Human body model, 1.5kΩ in series with 100pF.
4. 2.5V of headroom is required between VIN and VOUT. The headroom can be reduced by implementing a bootstrap diode as seen on the 5V to 3.3V
circuit on page 1.
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Micrel, Inc.
MIC4685
Test Circuit
+12V
2
5
Device Under Test
VIN
SW
EN
BS
68µH
6
1
I
FB
GND
4, Tab 3
Current Limit Test Circuit
Shutdown Input Behavior
ON
OFF
0.8V
0V
1.25V
2V
1.4V
VIN(max)
Enable Hysteresis
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MIC4685
Typical Characteristics
(TA = 25°C unless otherwise noted)
EFFICIENCY (%)
Efficiency
vs. Output Current
100
VIN = 8V
VIN = 12V
90
80
VIN = 30V
70
60
50
40
30
Standard
20
Configuration
10
VOUT = 5.0V
0
0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
OUTPUT CURRENT (A)
90
EFFICIENCY (%)
80
Efficiency
vs. Output Current
VIN = 8V
VIN = 24V
70
60
50
VIN = 30V
40
VIN = 12V
30
20
10
Standard
Configuration
VOUT = 1.8V
0
0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
OUTPUT CURRENT (A)
EFFICIENCY (%)
80
VIN = 5V
VIN = 12V
70
60
50
VIN = 16V
40
30
20
Bootstrap
Configuration
VOUT = 1.8V
10
0
0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
OUTPUT CURRENT (A)
January 2010
Quiescent Current
vs. Input Voltage
6.2
6.1
6
5.9
5.8
5.7
0
Bootstrap Drive Current
vs. Input Voltage
12
300
VEN= 5V
5 10 15 20 25 30 35 40
INPUT VOLTAGE (V)
Minimum Duty Cycle
vs. Input Voltage
10
DUTY CYCLE (%)
BOOTSTRAP CURRENT (mA)
350
6.3
INPUT CURRENT (mA)
90
Efficiency
vs. Output Current
250
200
150
100
VIN = 12V
VFB = 1.5V
50
0
0 2 4 6 8 10 12 14 16 18 20
INPUT VOLTAGE (V)
6
8
6
4
2
0
0
VOUT = 1.8V
5
10 15 20 25
INPUT VOLTAGE (V)
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Micrel, Inc.
FEEDBACK VOLTAGE (V)
1.250
Feedback Voltage
vs. Input Voltage
1.245
1.240
1.235
1.230
1.225
1.220
1.215
IOUT = 10mA
VOUT = 1.8V
1.210
1.205
0
1.258
FEEDBACK VOLTAGE (V)
MIC4685
5
10 15 20 25
INPUT VOLTAGE (V)
30
Feedback Voltage
vs. Temperature
1.248
1.238
1.228
1.218
1.208
IOUT = 10mA
VIN = 12V
VOUT = 1.8V
1.20
1.18
1.16
1.14
1.12
1.10
1.08
1.06
1.04
1.02
1.00
Enable Threshold
vs. Temperature
Upper Threshold
Lower Threshold
VIN = 12V
VOUT = 5V
IOUT = 100mA
-60
-40
-20
0
20
40
60
80
100
120
140
THRESHOLD TRIP POINTS
1.198
-40 -20 0 20 40 60 80 100120140
TEMPERATURE °C)
(
TEMPERATURE °C)
(
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MIC4685
Typical Safe Operating Area (SOA)
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
(SOA measured on the MIC4685 Evaluation Board*)
Typical 5V Output SOA
Standard Configuration
Typical 3.3V Output SOA
Typical 2.5V Output SOA
Typical 1.8V Output SOA
Standard Configuration
Typical 5.0V Output SOA
Typical 3.3V Output SOA
Typical 2.5V Output SOA
Typical 1.8V Output SOA
5.0
T = 25°C
4.5 A
TJ = 125°C
4.0
D = Max
3.5
3.0
2.5
2.0
TA = 60°C
1.5
TJ = 125°C
1.0
D = Max
0.5
0.0
0 5 10 15 20 25 30 35
INPUT VOLTAGE (V)
5.0
T = 25°C
4.5 A
TJ = 125°C
4.0
D = Max
3.5
3.0
2.5
2.0
1.5
TA = 60°C
1.0
TJ = 125°C
0.5
D = Max
0.0
0 5 10 15 20 25 30 35
INPUT VOLTAGE (V)
* IOUT <3A, D1: Diode Inc. B340 (3A/40V)
IOUT <3A, D1: SBM1040 (10A/40V)
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MIC4685
Functional Characteristics
Frequency Foldback
The MIC4685 folds the switching frequency back during
a hard short circuit condition to reduce the energy per
cycle and protect the device.
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MIC4685
Functional Diagram
V IN
IN
Bootstrap
Charger
Enable
Internal
Regulator
200kHz
Oscillator
⎛ R1 ⎞
VOUT = VREF ⎜
+ 1⎟
⎝ R2 ⎠
⎛V
⎞
R1 = R2 ⎜ OUT –1⎟
⎝ VREF
⎠
Current
Limit
Thermal
Shutdown
VREF = 1.235V
Comparator
VOUT
SW
Driver
COUT
Reset
R1
FB
Error
Amp
1.235V
Bandgap
Reference
R2
MIC4685
Figure 1. Adjustable Regulator
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 MIC4685 uses a voltagemode control architecture.
Functional Description
The MIC4685 is a variable duty cycle switch-mode
regulator with an internal power switch. Refer to the
above block diagram.
Supply Voltage
The MIC4685 operates from a +4V to +30V (34V
transient) unregulated input. Highest efficiency operation
is from a supply voltage around +12V. See the efficiency
curves in the “Typical Characteristics” section on page 5.
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.
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
In the adjustable version, an external resistive voltage
divider is required from the output voltage to ground,
center tapped to the FB pin. See Table 1 and Table 2 for
recommended resistor values.
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.
Duty Cycle Control
A fixed-gain error amplifier compares the feedback
signal with a 1.235V bandgap voltage reference. The
resulting error amplifier output voltage is compared to a
200kHz sawtooth waveform to produce a voltage
controlled variable duty cycle output.
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MIC4685
The efficiency is used to determine how much of the
output power (POUT) is dissipated in the regulator circuit
(PD).
Application Information
Adjustable Regulators
Adjustable regulators require a 1.235V feedback signal.
Recommended voltage-divider resistor values for
common output voltages are detailed in Table 1.
For other voltages, the resistor values can be
determined using the following formulas:
⎛ R1 ⎞
VOUT = VREF ⎜
+ 1⎟
⎝ R2
⎠
POUT
− POUT
η
PD =
7.5W
− 7. 5 W
0.84
PD = 1.43W
A worst-case rule of thumb is to assume that 80% of the
total output power dissipation is in the MIC4685 (PD(IC))
and 20% is in the diode-inductor-capacitor circuit.
PD(IC) = 0.8 PD
PD(IC) = 0.8 × 1.43W
PD(IC) = 1.14W
Calculate the worst-case junction temperature:
TJ = PD(IC) θJC + (TC – TA) + TA(max)
where:
TJ = MIC4685 junction temperature
PD(IC) = MIC4685 power dissipation
θJC = junction-to-case thermal resistance.
The θJC for the MIC4685’s 7-pin SPAK is approximately
2.2°C/W.
TC = “pin” temperature measurement taken at
the Tab.
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 = 1.14 × 2.2°C + (46°C – 25°C) + 60°C
TJ = 83.5°C
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 refer to the
“Typical Safe Operating Area (SOA)” graphs in this
document.
⎛V
⎞
R1 = R2⎜⎜ OUT − 1⎟⎟
⎝ VREF
⎠
VREF = 1.235V
Thermal Considerations
The MIC4685 is capable of high current due to the
thermally optimized SPAK package.
One limitation of the maximum output current on any
MIC4685 design is the junction-to-ambient thermal
resistance (θJA) of the design (package and ground
plane).
Examining θJA in more detail:
θJA = (θJC + θCA)
where:
θJC = junction-to-case thermal resistance
θCA = case-to-ambient thermal resistance
θJC is a relatively constant 2.2°C/W for a 7-pin SPAK.
θCA is dependent upon layout and is primarily governed
by the connection of pins 4, and Tab to the ground
plane. The purpose of the ground plane is to function as
a heat sink.
Checking the Maximum Junction Temperature:
For this example, with an output power (POUT) of 7.5W,
(5V output at 1.5A 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 1.5A output
current at VIN = 12V or perform you own measurement.
η = 84%
January 2010
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Micrel, Inc.
MIC4685
V IN
+4V to +30V
(34V transient)
CIN
7-pin
SPAK
Bootstrap Diode
The bootstrap diode provides an external bias source
directly to the main pass element, this reduces VSAT thus
allowing the MIC4685 to be used in very low head-room
applications i.e., 5VIN to 3.3VOUT with high efficiencies.
Bootstrap diode not for use if VIN exceeds 16V, VIN. See
Figure 2.
MIC4685_R
2 IN
BS 1
5
6
EN
SW
COUT
FB 3
GND
4,Tab
4, Tab
VOUT
L1
39µH
D1
R1
R2
Load
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 6 and pin 4, and Tab, keep L1 away from
sensitive node FB, and keep CIN close to pin 2 and pin 4,
and Tab. 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 6.
Gerber files are available upon request.
GND
Figure 2. Critical Traces for Layout
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MIC4685
Recommended Components for a Given Output Voltage (Bootstrap Configuration)
VOUT
IOUT*
R1
R2
VIN
C1
D1
D2
L1
C4
5.0V
2.1A
3.01k
976Ω
7.5V – 16V
47µF, 20V
Vishay-Dale
595D476X0020D2T
3A, 30V
Schottky
+ Vishay
B330A
1A, 20V
Schottky
B120-E3
39µH
Sumida
CDRH127R-390MC
330µF, 6.3V
Vishay-Dale
594D337X06R3D2T
3.3V
2.2A
3.01k
1.78k
6.0V – 16V
47µF, 20V
Vishay-Dale
595D476X0020D2T
3A, 30V
Schottky
B330A
1A, 20V
Schottky
B120-E3
39µH
Sumida
CDRH127R-390MC
330µF, 6.3V
Vishay-Dale
594D337X06R3D2T
2.5V
2.0A
3.01k
2.94k
5.0V – 16V
47µF, 20V
Vishay-Dale
595D476X0020D2T
3A, 30V
Schottky
B330A
1A, 20V
Schottky
B120-E3
39µH
Sumida
CDRH127R-390MC
330µF, 6.3V
Vishay-Dale
594D337X06R3D2T
1.8V
2.0A
3.01k
6.49k
5.0V – 16V
47µF, 20V
Vishay-Dale
595D476X0020D2T
3A, 30V
Schottky
+ Vishay
B330A
1A, 20V
Schottky
B120-E3
39µH
Sumida
CDRH127R-390MC
330µF, 6.3V
Vishay-Dale
594D337X06R3D2T
*
Maximum output current at minimum input voltage. See SOA curves for maximum output current vs. Input voltage.
Table 1. Recommended Components for Common Output Voltages
JP3
J1
VIN
C1
47µF
20V
J3
GND
D2
MBRX120
1A/20V
U1 MIC4685_R
2 IN
SW 6
ON
OFF
C2
0.1µF
50V
BS 1
5 EN
L1
39µH
C3
0.33µF
50V
J2
VOUT
R1
FB 3
GND
4, Tab
D1
B330A
or
SS33
R2
C4*
optional
C5
330µF
6.3V
C7
0.1µF
50V
J4
GND
* C4 can be used to provide additional stability
and improved transient response.
Note: optimized for 5VOUT
Figure 3. Schematic Diagram
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MIC4685
Recommended Components for a Given Output Voltage (Standard Configuration)
VOUT
IOUT*
R1
R2
VIN
C1
D1
L1
C5
5.0V
2.0A
3.01k
976Ω
8V – 30V
33µF, 35V
Vishay-Dale
595D336X0035R2T
3A, 40V
Schottky
B340A-E3
39µH
Sumida
CDRH127-390MC
330µF, 6.3V
Vishay-Dale
594D337X06R3D2T
3.3V
2.4A
3.01k
1.78k
8V – 26V
33µF, 35V
Vishay-Dale
595D336X0035R2T
3A, 40V
Schottky
B340A-E3
39µH
Sumida
CDRH127-390MC
330µF, 6.3V
Vishay-Dale
594D337X06R3D2T
2.5V
2.35A
3.01k
2.94k
7V – 23V
33µF, 35V
Vishay-Dale
595D336X0035R2T
3A, 40V
Schottky
B340A-E3
39µH
Sumida
CDRH127-390MC
330µF, 6.3V
Vishay-Dale
594D337X06R3D2T
1.8V
2.0A
3.01k
6.49k
6V – 16V
33µF, 35V
Vishay-Dale
595D336X0035R2T
3A, 40V
Schottky
+ Vishay
B340A-E3
39µH
Sumida
CDRH127-390MC
330µF, 6.3V
Vishay-Dale
594D337X06R3D2T
*
Maximum output current at minimum input voltage. See SOA curves for maximum output current vs. Input voltage.
Table 2. Recommended Components for Common Output Voltages
JP3
J1
VIN
(34V transient)
C1
33µF
35V
J3
GND
D2***
B340
U1 MIC4685_R
2 IN
ON
OFF
C2
0.1µF
50V
SW 6
BS
5
EN
FB
1
J2
VOUT
2A
L1
39µH
C3
0.33µF
50V
R1
3.01k
3
GND
4, Tab
D1
B340A
1
2
R2
6.49k
3
JP1a
1.8V
4
C4*
optional
R3
2.94k
5
JP1b
2.5V
6
R4
1.78k
7
JP1c
3.3V
8
R5
976W
JP1d
5.0V
C5
330µF
6.3V
C6**
C7
0.1µF
50V
J4
GND
* C4 can be used to provide additional stability
and improved transient response.
Note: optimized for 5VOUT
** C6 Optional
*** D2 is not used for standard configuration and JP3 is open.
Figure 4. Evaluation Board Schematic Diagram
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MIC4685
Printed Circuit Board
Figure 5a. Top Layer
Figure 5b. Bottom Layer
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MIC4685
Abbreviated Bill of Materials (Critical Components)
Item
C1
C2, C7
C3
Part Number
594D336X0035R2T
Manufacturer
(1)
Vishay Sprague
33µF 35V
1
2
VJ0805Y104KXAAB
Vitramon
0.1µF 50V
Murata(5)
0.33µF, 50V ceramic capacitor
VJ1206Y334KXAAT
Vishay(1)
0.33µF, 50V ceramic capacitor
1800pF, 50V ceramic
1
Vishay Sprague(1)
330µF, 6.3V, tantalum
1
Optional
C5
594D337X06R3D2T
B340A
Diode Inc
B340LA-EA
D1
SSA34A
B120-EA
D2
(2)
Schottky 3A 40V
1
(1)
Schottky 3A 40V
1
(1)
Vishay
Schottky 3A 40V
1
Vishay(1)
Schottky 3A 40V
1
(1)
Schottky 3A 40V
1
Vishay
B340A
R1
Qty.
GRM426X7R334K50
C4*
L1
Description
Vishay
B340A
Diode Inc
(2)
Schottky 3A 40V
MBRX120
Micro Commercial Component(4)
Schottky 1A 20V
CDRH127-390MC
Sumida(3)
CRCW08053011FKEY3
1
39µH
1
(1)
3K01, 1%, 1/10W, 805
1
(1)
Vishay
R2
CRCW08056491FKEY3
Vishay
6K49, 1%, 1/10W, 805
1
R3
CRCW08052941FKEY3
Vishay(1)
2K94, 1%, 1/10W, 805
1
CRCW08051781FKEY3
(1)
1K78, 1%, 1/10W, 805
1
R4
R5
CRCW08051781FKEY3
U1
MIC4685BR/WR
Vishay
(1)
Vishay
Micrel, Inc.(6)
976Ω, 1%, 1/10W, 805
1
3A 200kHz SPAK Buck Regulator
1
Notes:
1. Vishay Sprague, Inc.: www.vishay.com
2. Diodes Inc.: www.diodes.com
3. Sumida: www.sumida.com
4. Micro Commercial Component: www.mccsemi.com
5. Murata: www.murata.com
6. Micrel, Inc.: www.website.com
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MIC4685
Package Information
7-SPAK (R)
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
The information furnished by Micrel in this data sheet is believed to be accurate and reliable. However, no responsibility is assumed by Micrel for its
use. Micrel reserves the right to change circuitry and specifications at any time without notification to the customer.
Micrel Products are not designed or authorized for use as components in life support appliances, devices or systems where malfunction of a product
can reasonably be expected to result in personal injury. Life support devices or systems are devices or systems that (a) are intended for surgical implant
into the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significant injury to the user. A
Purchaser’s use or sale of Micrel Products for use in life support appliances, devices or systems is a Purchaser’s own risk and Purchaser agrees to fully
indemnify Micrel for any damages resulting from such use or sale.
© 2004 Micrel, Incorporated.
January 2010
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