MIC4685
3A SPAK SuperSwitcher™
Buck Regulator
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 1 M9999-012610
General Description
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.
Features
• 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
• 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
BSIN 1
6
3
4, Tab
2
5SW
FB
EN
GND
MIC4685_R CBS
0.33µF/50V
CIN
33µF
35V
COUT
330µF
6.3V
D1
3A
40V
R1
3.01k
R2
6.49k
L1
39mH
VIN
8V to 30V VOUT
1.8V/3A
1.8V Output Converter
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January 2010 2 M9999-012610
Ordering Information
Part Number
Standard RoHS Compliant*
Voltage Junction
Temp. Range Package
MIC4685BR MIC4685WR Adj. –40° to +125°C 7-Pin SPAK
MIC4685WR EV Adj. Evaluation Board
* RoHS compliant with ‘high-melting solder’ exemption.
Pin Configur ation
7NC
6SW
5EN
4GN
D
3FB
2IN
1BS
7-Pin SPAK (R)
Pin Description
Pin Number Pin Name Pin Function
1 BS
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 Ground
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.
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January 2010 3 M9999-012610
Detailed Pin Descr iption
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.
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 logic-
low 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.
Micrel, Inc. MIC4685
January 2010 4 M9999-012610
Absolute Maximum Ratings(1)
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
Operating Ratings(2)
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
MIC4685 [Adjustable]
(±2%)
(±3%)
1.210
1.198
1.235 1.260
1.272
V
V
Feedback Voltage
8V ≤ VIN ≤ 30V, 0.1A ≤ ILOAD ≤ 1A, VOUT = 5V, Note 4 1.186
1.173
1.235 1.284
1.297
V
V
Feedback Bias Current 50 nA
Maximum Duty Cycle VFB = 1.0V 94 %
VIN = 30V, VEN = 0V, VSW = 0V 5 500 µA Output Leakage Current
VIN = 30V, VEN = 0V, VSW = 1V 1.4 20 mA
Quiescent Current VFB = 1.5V 6 12 mA
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 70 120 kHz
Oscillator Frequency 180 200 225 kHz
Saturation Voltage IOUT = 1A 0.59 V
Short Circuit Current Limit VFB = 0V, See Test Circuit 3.5 6 A
Shutdown Current VEN = 0V 150 200 µA
Enable Input Logic Level regulator on 2 V
regulator off 0.8 V
Enable Pin Input Current VEN = 0V (regulator off) 16 50 µA
V
EN = 0V (regulator on) –1 –0.83 mA
Thermal Shutdown @ TJ 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.
Micrel, Inc. MIC4685
January 2010 5 M9999-012610
Test Circuit
SW
68µH
I
VIN
BS
FB
EN
Device Unde
r
Test
+12V
3
GND
4, Tab
1
62
5
Current Limit Test Circuit
Shutdown Input Behavior
ON
OFF
0.8V
1.25V0V 1.4V VIN(max)
2V
Enable Hysteresis
Micrel, Inc. MIC4685
January 2010 6 M9999-012610
Typical Characteristics
(TA = 25°C unless otherwise noted)
0
50
100
150
200
250
300
350
0 2 4 6 8 101214161820
)Am(TNERRUCPARTSTOOB
INPUT VOLTAGE (V)
Bootstrap Drive Current
vs. Input Vo ltag e
VIN = 12V
VFB = 1.5V
0
10
20
30
40
50
60
70
80
90
100
0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
)%(YCNEICIFFE
OUTPUT CURRENT (A)
Efficienc
y
vs. Output Current
Standard
Configuration
VOUT = 5.0V
VIN = 8V VIN = 12V
VIN = 30V
0
10
20
30
40
50
60
70
80
90
0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
)%(YCNEICIFFE
OUTPUT CURRENT (A)
Efficiency
vs. Output Current
Standard
Configuration
VOUT = 1.8V
VIN = 8V
VIN = 12V
VIN = 24V
VIN = 30V
0
10
20
30
40
50
60
70
80
90
0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
)%(YCNEICIFFE
OUTPUT CURRENT (A)
Efficiency
vs. Output Current
Bootstrap
Configuration
VOUT = 1.8V
VIN = 5V VIN = 12V
VIN = 16V
0
2
4
6
8
10
12
0 5 10 15 20 25 30
)%(ELCYCYTUD
INPUT VOLTAGE (V)
Minimum Duty Cycle
vs. Input Vo ltag e
VOUT = 1.8V
5.7
5.8
5.9
6
6.1
6.2
6.3
0 5 10 15 20 25 30 35 40
)Am(TNERRUCTUPNI
INPUT VOLTAGE (V)
Quiescent Cur r ent
vs. Input Vo ltag e
VEN= 5V
Micrel, Inc. MIC4685
January 2010 7 M9999-012610
1.00
1.02
1.04
1.06
1.08
1.10
1.12
1.14
1.16
1.18
1.20
06-
04-
02-
0
02
04
06
08
001
021
041
STNIOPPIRTDLOHSERHT
TEMPERATURE (°C)
Enable Threshold
vs. Temperatu re
Upper Threshold
Lower Threshold
VIN = 12V
VOUT = 5V
IOUT = 100mA
1.198
1.208
1.218
1.228
1.238
1.248
1.258
-40 -20 0 20 40 60 80 100120140
)V(EGATLOVKCABDEEF
TEMPERATURE (°C)
Feedback Voltage
vs. Temperatu re
IOUT = 10mA
VIN = 12V
VOUT = 1.8V
1.205
1.210
1.215
1.220
1.225
1.230
1.235
1.240
1.245
1.250
0 5 10 15 20 25 30
)V(EGATLOVKCABDEEF
INPUT VOLTAGE (V)
Feedback Voltage
vs. Input Vo ltag e
IOUT = 10mA
VOUT = 1.8V
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January 2010 8 M9999-012610
Typical Safe Oper ating Area (SOA)
(SOA measured on the MIC4685 Evaluation Board*)
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
0 5 10 15 20 25 30 35
)A(TNERRUCTUPTUO
INPUT VOLTAGE (V)
Typical 5V Outp ut SO
A
Standard Configuration
TA = 25°C
TJ = 125°C
D = Max
TA = 60°C
TJ = 125°C
D = Max
Typical 3.3V Outp ut SO
A
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
0 5 10 15 20 25 30 35
)A(TNERRUCTUPTUO
INPUT VOLTAGE (V)
Typical 1.8V Output SOA
Standard Configuration
TA = 60°C
TJ = 125°C
D = Max
TA = 25°C
TJ = 125°C
D = Max
Typical 2.5V Ou tput SO
A
Typical 5.0V Outp ut SOA Typical 3.3V Ou tput SOA
Typical 2.5V Output SOA Typ ical 1.8V Out put SOA
* IOUT <3A, D1: Diode Inc. B340 (3A/40V)
I
OUT <3A, D1: SBM1040 (10A/40V)
Micrel, Inc. MIC4685
January 2010 9 M9999-012610
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.
Micrel, Inc. MIC4685
January 2010 10 M9999-012610
Functional Diagram
SW
FB
R1
R2
COUT
VIN
IN
VOUT
MIC4685
Internal
Regulator
Bootstrap
Charger
Enable
200kHz
Oscillator
Thermal
Shutdown
Reset
Current
Limit
Com-
parator
Error
Amp
Driver
1.235V
Bandgap
Reference
VV
R1
R2 1
R1 R2 V
V–1
V 1.235V
OUT REF
OUT
REF
REF
=+
⎛
⎝
⎜⎞
⎠
⎟
=⎛
⎝
⎜
⎞
⎠
⎟
=
Figure 1. Adjustable Regulator
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.
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.
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.
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 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.
Micrel, Inc. MIC4685
January 2010 11 M9999-012610
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:
⎟
⎠
⎞
⎜
⎝
⎛+= 1
R2
R1
VV REFOUT
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛−= 1
V
V
R2R1
REF
OUT
V
REF = 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%
The efficiency is used to determine how much of the
output power (POUT) is dissipated in the regulator circuit
(PD).
OUT
OUT
DP
η
P
P−=
W5.7
0.84
7.5W
PD−=
P
D = 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.
P
D(IC) = 0.8 PD
P
D(IC) = 0.8 × 1.43W
P
D(IC) = 1.14W
Calculate the worst-case junction temperature:
T
J = PD(IC) θJC + (TC – TA) + TA(max)
where:
T
J = MIC4685 junction temperature
P
D(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.
T
A = ambient temperature
TA(max) = maximum ambient operating temp-
erature for the specific design.
Calculating the maximum junction temperature given a
maximum ambient temperature of 60°C:
T
J = 1.14 × 2.2°C + (46°C – 25°C) + 60°C
T
J = 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.
Micrel, Inc. MIC4685
January 2010 12 M9999-012610
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.
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.
Load
BS L1
39µH
IN
FB
GND
COUT R1
R2
D1
VOUT
MIC4685_R
GND
CIN
VIN
+4V to +30V
(34V transient)
7-pin
SPAK 4,Tab
3
12
SWEN 65
4, Tab
Figure 2. Critical Traces for Layout
Micrel, Inc. MIC4685
January 2010 13 M9999-012610
Recommended Components for a Given Output Voltage (Bootstrap Configuration)
VOUT I
OUT* 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
SW
L1
39µH
IN
FB
GND
EN
D1
B330A
or
SS33
J2
VOUT
J4
GND
U1 MIC4685_R
C2
0.1µF
50V
C1
47µF
20V
J1
VIN
D2
MBRX120
1A/20V
J3
GND
JP3
4, Tab
3
BS 1
62
5
ON
OFF C5
330µF
6.3V
C4*
optional
C7
0.1µF
50V
C3
0.33µF
50V R1
R2
* C4 can be used to provide additional stability
and improved transient response.
Note: optimized for 5VOUT
Figure 3. Schematic Diagram
Micrel, Inc. MIC4685
January 2010 14 M9999-012610
Recommended Components for a Given Output Voltage (Standard Configuration)
VOUT I
OUT* 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
SW
L1
39µH
IN
FB
GND
EN
D1
B340A
J2
VOUT
2A
J4
GND
U1 MIC4685_R
C2
0.1µF
50V
C1
33µF
35V
J1
VIN
(34V transient)
J3
GND
3
BS 1
62
5
ON
OFF C5
330µF
6.3V
C4*
optional
C7
0.1µF
50V
C3
0.33µF
50V R1
3.01k
R2
6.49k
JP1a
1.8V
R3
2.94k
R4
1.78k
R5
976W
C6**
JP1b
2.5V
JP1c
3.3V
JP1d
5.0V
1
2
3
4
5
6
7
8
* 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.
D2***
B340
JP3
4, Tab
Figure 4. Evaluation Board Schematic Diagram
Micrel, Inc. MIC4685
January 2010 15 M9999-012610
Printed Circuit Board
Figure 5a. Top Layer
Figure 5b. Bottom Layer
Micrel, Inc. MIC4685
January 2010 16 M9999-012610
Abbreviated Bill of Materi als (Critical Components)
Item Part Number Manufacturer Description Qty.
C1 594D336X0035R2T Vishay Sprague(1) 33µF 35V 1
C2, C7 VJ0805Y104KXAAB Vitramon 0.1µF 50V 2
GRM426X7R334K50 Murata(5) 0.33µF, 50V ceramic capacitor
C3 VJ1206Y334KXAAT Vishay(1) 0.33µF, 50V ceramic capacitor
C4* Optional 1800pF, 50V ceramic 1
C5 594D337X06R3D2T Vishay Sprague(1) 330µF, 6.3V, tantalum 1
B340A Diode Inc(2) Schottky 3A 40V 1
B340LA-EA Vishay(1) Schottky 3A 40V 1
SSA34A Vishay(1) Schottky 3A 40V 1
D1
B340A Vishay(1) Schottky 3A 40V 1
B120-EA Vishay(1) Schottky 3A 40V 1
B340A Diode Inc(2) Schottky 3A 40V
D2
MBRX120 Micro Commercial Component(4) Schottky 1A 20V 1
L1 CDRH127-390MC Sumida(3) 39µH 1
R1 CRCW08053011FKEY3 Vishay(1) 3K01, 1%, 1/10W, 805 1
R2 CRCW08056491FKEY3 Vishay(1) 6K49, 1%, 1/10W, 805 1
R3 CRCW08052941FKEY3 Vishay(1) 2K94, 1%, 1/10W, 805 1
R4 CRCW08051781FKEY3 Vishay(1) 1K78, 1%, 1/10W, 805 1
R5 CRCW08051781FKEY3 Vishay(1) 976Ω, 1%, 1/10W, 805 1
U1 MIC4685BR/WR Micrel, Inc.(6) 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
Micrel, Inc. MIC4685
January 2010 17 M9999-012610
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.
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