MIC4685 [MICREL]
3A SPAK SuperSwitcher⑩ Buck Regulator; 3A SPAK SuperSwitcher ™降压稳压器
| 型号： | MIC4685 |
| 厂家： | 
MICREL SEMICONDUCTOR |
| 描述： | 3A SPAK SuperSwitcher⑩ Buck Regulator |
| 文件： | 总15页 (文件大小：155K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
MIC4685
3A SPAK SuperSwitcher™ Buck Regulator
Final
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.
TheMIC4685achieves3Aofcontinuouscurrentinthe7-lead
SPAK package.
• 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
The thermal performance of the SPAK allows it to replace
TO-220s and TO-263s (D PAKs) in many applications. The
SPAK saves board space with a 36% smaller footprint than
TO-263.
2
Highefficiencyismaintainedoverawideoutputcurrentrange
byutilizingaboostcapacitortoincreasethevoltageavailable
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.
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
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
beusedinapplicationswhereinputvoltagetransientsmaybe
present. Built-in safety features include over-current protec-
tion, frequency-foldback short-circuit protection, and thermal
shutdown.
• LCD power supplies
• Battery chargers
The MIC4685 is available in an 7-lead SPAK package with a
junction temperature range of –40°C to +125°C.
Ordering Information
Part Number
Voltage
Junction Temperature Range
Package
MIC4685BR
Adj
–40°C to +125°C
SPAK-07L
Typical Applications
DBS
3A, 20V
VIN
5V
±10%
CBS
0.33µF/50V
VIN
8V to 30V
MIC4685BR
MIC4685BR
CBS
2
1
6
3
2
5
1
6
3
0.33µF/50V
IN
BS
SW
FB
VOUT
3.3V/2A
IN
BS
SW
FB
VOUT
1.8V/3A
L1
L1
5
EN
EN
R1
39µH
R1
CIN
68µF
10V
39µH
CIN
33µF
35V
3.01k
330µF
6.3V
3.01k
COUT
330µF
6.3V
D1
GND
4, Tab
R2
D1
R2
6.49k
GND
4, Tab
3A
1.78k
3A
20V
40V
1.8V Output Converter
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
September 2002
1
MIC4685
MIC4685
Micrel
Pin Configuration
7
6
5
4
3
2
1
NC
SW
EN
GND
FB
IN
BS
SPAK-07L (R)
Pin Description
Pin Number
Pin Name
Pin Function
1
BS
Bootstrap Voltage Node (External Component): Connect to external boost
capacitor.
2
3
IN
Supply (Input): Unregulated +4V to 30V supply voltage (34V transient)
FB
Feedback (Input): Outback voltage feedback to regulator. Connect to 1.235V
tap of resistive divider.
4, Tab
GND
EN
Ground
5
6
Enable (Input): Logic high = enable; logic low = shutdown
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.
Bootstrap (BS, Pin 1)
Detailed Pin Description
Switch (SW, Pin 6)
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
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, Pin 4, Tab)
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
ground pin. To keep radiated EMI to a minimum it is neces-
sary to place the input capacitor ground lead as close as
possible to the switching regulator’s 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 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.
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
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 2)
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.
MIC4685
2
September 2002
MIC4685
Micrel
Absolute Maximum Ratings (Note 1)
Operating Ratings (Note 2)
Supply Voltage (V ), Note 1 ......................................+34V
Supply Voltage (V ) Note 4 ........................... +4V to +30V
IN
IN
Enable Voltage (V ) .................................... –0.3V to +V
Junction Temperature (T ) ....................... –40°C to +125°C
EN
IN
IN
J
Steady-State Output Switch Voltage (V ) ....... –1V to V
Package Thermal Resistance
SW
Feedback Voltage (V )..............................................+12V
θ
θ
, SPAK-7 Lead ............................................11.8°C/W
, SPAK-7 Lead ..............................................2.2°C/W
FB
JA
JC
Storage Temperature (T ) ....................... –65°C to +150°C
S
ESD Rating Note 3 ....................................................... 2kV
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, Note 4
1.186
1.173
1.235
1.284
1.297
V
V
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
70
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
3.5
2
6
A
150
200
µA
V
Enable Input Logic Level
regulator on
regulator off
0.8
50
V
Enable Pin Input Current
VEN = 0V (regulator off)
VEN = 12V (regulator on)
16
µA
mA
°C
–1
–0.83
160
Thermal Shutdown @ TJ
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. Human body model, 1.5kΩ in series with 100pF.
Note 4. 2.5V of headroom is required between V and V
. The headroom can be reduced by implementing a bootstrap diode as seen on the 5V to
OUT
IN
3.3V circuit on page 1.
September 2002
3
MIC4685
MIC4685
Micrel
Test Circuit
Device Under Test
68µH
+12V
2
5
6
1
VIN
SW
EN
BS
I
GND
4, Tab
FB
3
Current Limit Test Circuit
Shutdown Input Behavior
ON
OFF
GUARANTEED
OFF
GUARANTEED
ON
0.8V
1.25V
2V
TYPICAL
OFF
TYPICAL
ON
0V
1.4V
VIN(max)
Enable Hysteresis
MIC4685
4
September 2002
MIC4685
Micrel
Typical Characteristics
(T = 25°C unless otherwise noted)
A
Efficiency
vs. Output Current
100
Efficiency
Efficiency
vs. Output Current
vs. Output Current
100
90
80
70
60
50
40
30
20
10
0
100
90
80
70
60
50
40
30
20
10
0
VIN = 8V
VIN = 8V
VIN = 12V
VIN = 8V
90
80
VIN = 24V
VIN = 30V
70
60
50
40
30
20
10
0
VIN = 30V
VIN = 30V
VIN = 12V
VIN = 12V
Standard
Configuration
Standard
Configuration
OUT = 2.5V
Standard
Configuration
V
OUT = 3.3V
V
V
OUT = 5.0V
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
OUTPUT CURRENT (A)
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
OUTPUT CURRENT (A)
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
OUTPUT CURRENT (A)
Efficiency
Efficiency
Efficiency
vs. Output Current
vs. Output Current
vs. Output Current
90
80
70
60
50
40
30
20
10
0
100
100
90
80
70
60
50
40
30
20
10
0
VIN = 7.5V
VIN = 8V
VIN = 4.5V
90
80
70
60
50
40
30
20
10
0
VIN = 12V
VIN = 24V
VIN = 5V
VIN = 12V
VIN = 16V
VIN = 30V
VIN = 12V
VIN = 16V
Standard
Configuration
Bootstrap
Configuration
OUT = 5.0V
Bootstrap
Configuration
VOUT = 3.3V
V
OUT = 1.8V
V
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
OUTPUT CURRENT (A)
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
OUTPUT CURRENT (A)
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
OUTPUT CURRENT (A)
Efficiency
vs. Output Current
Efficiency
vs. Output Current
Quiescent Current
vs. Input Voltage
100
90
80
70
60
50
40
30
20
10
0
90
80
70
60
50
40
30
20
10
0
6.3
6.2
6.1
6
VIN = 5V
VIN = 5V
VIN = 12V
VIN = 12V
VIN = 16V
VIN = 16V
5.9
5.8
5.7
Bootstrap
Configuration
Bootstrap
Configuration
VOUT = 1.8V
VEN= 5V
VOUT = 2.5V
0
5
10 15 20 25 30 35 40
INPUT VOLTAGE (V)
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
OUTPUT CURRENT (A)
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
OUTPUT CURRENT (A)
Minimum Duty Cycle
vs. Input Voltage
Bootstrap Voltage
vs. Input Voltage
Bootstrap Drive Current
vs. Input Voltage
350
300
250
200
150
100
50
12
10
8
7
6
5
4
3
2
1
0
6
4
VIN = 12V
VIN = 12V
2
V
FB = 1.5V
VOUT = 1.8V
V
FB = 1.5V
0
0
0
5
10 15 20 25 30
INPUT VOLTAGE (V)
0
2
4
6
8
10 12 14 16 18 20
0
5
10 15 20 25 30
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
September 2002
5
MIC4685
MIC4685
Micrel
Feedback Voltage
vs. Input Voltage
Shutdown Current
vs. Input Voltage
Saturation Voltage
vs. Input Voltage
1.250
605
600
595
590
585
580
575
570
200
180
160
140
120
100
80
1.245
1.240
1.235
1.230
1.225
1.220
1.215
1.210
1.205
60
40
IOUT = 10mA
IOUT = 1A
VOUT = 5V
VOUT = 1.8V
20
VEN = 0V
0
0
5
10 15 20 25 30
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)
Feedback Voltage
vs. Temperature
Load Regulation
Shutdown Hysteresis vs.
Temperature
1.258
1.248
1.238
1.228
1.218
1.208
1.198
6
5
1.809
1.808
1.807
1.806
1.805
1.804
1.803
1.802
ON
4
3
2
IOUT = 10mA
1
OFF
V
V
IN = 12V
OUT = 1.8V
0
VOUT = 13V
0.5
OUTPUT CURRENT (A)
-1
-40 -20
0
20 40 60 80 100120140
-50
0
50
100 150 200
0
1
1.5
2
2.5
3
3.5
TEMPERATURE (°C)
TEMPERATURE (°C)
Line Regulation
Enable Threshold
vs. Temperature
1.83
1.82
1.81
1.80
1.79
1.78
1.77
1.76
1.20
1.18
1.16
1.14
1.12
1.10
1.08
1.06
1.04
1.02
1.00
Upper Threshold
Lower Threshold
VIN = 12V
V
OUT = 5V
IOUT = 0.100A
I
OUT = 100mA
0
5
10 15 20 25 30 35
OUTPUT CURRENT (A)
TEMPERATURE (°C)
MIC4685
6
September 2002
MIC4685
Micrel
Typical Safe Operating Area (SOA)
(SOA measured on the MIC4685 Evaluation Board*)
5V Output SOA
Standard Configuration
3.3V Output SOA
Standard Configuration
2.5V Output SOA
Standard Configuration
5.0
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
TA = 25°C
4.5
TA = 25°C
TA = 25°C
TJ = 125°C
TJ = 125°C
TJ = 125°C
4.0
D = Max
D = Max
D = Max
3.5
3.0
2.5
2.0
TA = 60°C
TJ = 125°C
1.5
TA = 60°C
J = 125°C
D = Max
TA = 60°C
J = 125°C
D = Max
1.0
T
T
D = Max
0.5
0.0
0
5
10 15 20 25 30 35
INPUT VOLTAGE (V)
0
5
10 15 20 25 30 35
INPUT VOLTAGE (V)
0
5
10 15 20 25 30 35
INPUT VOLTAGE (V)
5.0V Output SOA
Bootstrap Configuration
1.8V Output SOA
Standard Configuration
3.3V Output SOA
Bootstrap Configuration
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
TA = 25°C
TA = 25°C
TA = 25°C
TJ = 125°C
D = Max
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
TJ = 125°C
TJ = 125°C
D = Max
D = Max
TA = 60°C
TJ = 125°C
D = Max
TA = 60°C
J = 125°C
D = Max
TA = 60°C
J = 125°C
D = Max
T
T
6
8
10 12 14 16 18
INPUT VOLTAGE (V)
0
5
10 15 20 25 30 35
INPUT VOLTAGE (V)
3
5
7
9
11 13 15 17
INPUT VOLTAGE (V)
2.5V Output SOA
Bootstrap Configuration
1.8V Output SOA
Bootstrap Configuration
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
TA = 25°C
TA = 25°C
TJ = 125°C
TJ = 125°C
D = Max
D = Max
TA = 60°C
J = 125°C
D = Max
TA = 60°C
J = 125°C
D = Max
T
T
3
5
7
9
11 13 15 17
3
5
7
9
11 13 15 17
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
* I
I
< 3A, D1: Diode Inc. B340 (3A/40V)
> 3A, D1: SBM1040 (10A/40V)
OUT
OUT
September 2002
7
MIC4685
MIC4685
Micrel
Functional Characteristics
Load Transient
Switching Frequency Foldback
VIN = 12V
VOUT = 5V
IOUT = 1.0A to 0.1A
Normal
Operation
5.1V
5V
200kHz
1A
0A
Short
Circuit
Operation
Typical
70kHz
TIME (25µs/div.)
TIME
Frequency Foldback
The MIC4685 folds the switching frequency back during a
hardshortcircuitconditiontoreducetheenergypercycleand
protect the device.
MIC4685
8
September 2002
MIC4685
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
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 com-
parator output. A lower feedback voltage increases the duty
cycle. The MIC4685 uses a voltage-mode control architec-
ture.
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 V through external storage inductor L1, to
IN,
Enable/Shutdown
output capacitor C
and the load. Energy is stored in the
OUT
inductor as the current increases with time.
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 turned OFF, the collapse of the
magnetic field in L1 forces current to flow through fast
to typically 150µA when V = 0V.
recovery diode D1, charging C
.
EN
OUT
Feedback
Output Capacitor
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.
External output capacitor C
reduces ripple.
provides stabilization and
OUT
Return Paths
Duty Cycle Control
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.
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.
September 2002
9
MIC4685
MIC4685
Micrel
The efficiency is used to determine how much of the output
Applications Information
Adjustable Regulators
power (P
) is dissipated in the regulator circuit (P ).
OUT
D
P
Adjustable regulators require a 1.235V feedback signal.
Recommended voltage-divider resistor values for common
output voltages are included in Table 1.
OUT
P =
−P
OUT
D
η
7.5W
0.84
PD =
− 7.5W
For other voltages, the resistor values can be determined
using the following formulas:
P = 1.43W
D
A worst-case rule of thumb is to assume that 80% of the total
R1
VOUT = VREF
+1
output power dissipation is in the MIC4685 (P
is in the diode-inductor-capacitor circuit.
) and 20%
R2
D(IC)
VOUT
P
P
P
= 0.8 P
D
D(IC)
D(IC)
D(IC)
R1= R2
−1
VREF
= 0.8 × 1.43W
= 1.14W
VREF = 1.235V
Calculate the worst-case junction temperature:
T = P + (T – T ) + T
Thermal Considerations
θ
J
D(IC) JC
C
A
A(max)
The MIC4685 is capable of high current due to the thermally
optimized SPAK package.
where:
T = MIC4685 junction temperature
J
OnelimitationofthemaximumoutputcurrentonanyMIC4685
P
= MIC4685 power dissipation
D(IC)
design is the junction-to-ambient thermal resistance (θ ) of
JA
θ
= junction-to-case thermal resistance.
JC
the design (package and ground plane).
Examining θ in more detail:
JA
The θ for the MIC4685’s 7-lead SPAK is approximately
2.2°C/W.
JC
θ
= (θ + θ
)
CA
JA
JC
where:
T = “pin” temperature measurement taken at the
C
θ
θ
= junction-to-case thermal resistance
= case-to-ambient thermal resistance
Tab.
JC
CA
T = ambient temperature
A
θ
θ
is a relatively constant 2.2°C/W for a 7-lead SPAK.
T
= maximum ambient operating temperature
JC
A(max)
for the specific design.
is dependent on layout and is primarily governed by the
CA
connection of pins 4, and Tab to the ground plane. The
purpose of the ground plane is to function as a heat sink.
Calculating the maximum junction temperature given a
maximum ambient temperature of 60°C:
Checking the Maximum Junction Temperature:
T = 1.14 × 2.2°C + (46°C – 25°C) + 60°C
J
For this example, with an output power (P
) of 7.5W, (5V
T = 83.5°C
OUT
J
output at 1.5A with V = 12V) and 60°C maximum ambient
IN
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. Alsosee TypicalSafeOperatingArea(SOA)
graphs on page 7.
temperature, what is the junction temperature?
Referring to the “Typical Characteristics: 5V Output Effi-
ciency” graph, read the efficiency (η) for 1.5A output current
at V = 12V or perform you own measurement.
IN
η = 84%
MIC4685
10
September 2002
MIC4685
Micrel
Layout Considerations
Bootstrap Diode
Thebootstrapdiodeprovidesanexternalbiassourcedirectly
tothemainpasselement, thisreducesV thusallowingthe
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.
SAT
MIC4685 to be used in very low head-room applications i.e.
5V to3.3V withhighefficiencies.Bootstrapdiodenotfor
IN
OUT
use if V exceeds 16V, V . See Figure 3.
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
IN
IN
FB, and keep C close to pin 2 and pin 4, and Tab. See
IN
ApplicationsInformation:ThermalConsiderationsforground
plane layout.
Thefeedbackpinshouldbekeptasfarwayfromtheswitching
elements (usually L1 and D1) as possible.
A circuit with sample layouts are provided. See Figure 7.
Gerber files are available upon request.
VIN
+4V to +30V
MIC4685BR
(34V transient)
2
5
1
6
IN
EN
BS
L1
39µH
VOUT
R1
SW
CIN
COUT
3
FB
7-lead
SPAK
GND
4, Tab
D1
R2
GND
Figure 2. Critical Traces for Layout
September 2002
11
MIC4685
MIC4685
Micrel
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
3.3V 2.2A 3.01k 1.78k
2.5V 2.0A 3.01k 2.94k
1.8V 2.0A 3.01k 6.49k
7.5V–16V 47µF, 20V
3A, 30V 1A, 20V
39µH
330µF, 6.3V
Vishay-Dale
Vishay-Dale
595D476X0020D2T
Schottky Schottky Sumida
B330A
MBRX120 CDRH127R-390MC 594D337X06R3D2T
6.0V–16V 47µF, 20V
3A, 30V 1A, 20V
Schottky Schottky Sumida
B330A
39µH
330µF, 6.3V
Vishay-Dale
Vishay-Dale
595D476X0020D2T
MBRX120 CDRH127R-390MC 594D337X06R3D2T
5.0V–16V 47µF, 20V
3A, 30V 1A, 20V
Schottky Schottky Sumida
B330A
39µH
330µF, 6.3V
Vishay-Dale
Vishay-Dale
595D476X0020D2T
MBRX120 CDRH127R-390MC 594D337X06R3D2T
5.0V–16V 47µF, 20V
3A, 30V 1A, 20V
Schottky Schottky Sumida
B330A
39µH
330µF, 6.3V
Vishay-Dale
Vishay-Dale
595D476X0020D2T
MBRX120 CDRH127R-390MC 594D337X06R3D2T
*
Maximum output current at minimum input voltage. See SOA curves for maximum output current vs. input voltage.
Table 1. Recommended Components for Common Ouput Voltages
D2
MBRX120
1A/20V
JP3
L1
39µH
J1
J2
U1 MIC4685BR
VIN
VOUT
2
5
6
IN
SW
C3
0.33µF
50V
1
3
C2
0.1µF
50V
BS
FB
C4*
optional
R1
R2
C1
ON
47µF
20V
J3
GND
EN
C5
330µF
6.3V
C7
0.1µF
50V
OFF
D1
GND
4, Tab
B330A
or
SS33
J4
GND
* C4 can be used to provide additional stability
and improved transient response.
Note: optimized for 5VOUT
Figure 3. Schematic Diagram
MIC4685
12
September 2002
MIC4685
Micrel
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
3A, 40V
39µH
330µF, 6.3V
Vishay-Dale
Schottky Sumida
Vishay-Dale
595D336X0035R2T
B340A
CDRH127-390MC
594D337X06R3D2T
3.3V
2.4A 3.01k
1.78k
2.94k
6.49k
8V–26V
7V–23V
6V–16V
33µF, 35V
Vishay-Dale
595D336X0035R2T
3A, 40V
Schottky Sumida
B340A
39µH
330µF, 6.3V
Vishay-Dale
594D337X06R3D2T
CDRH127-390MC
2.5V 2.35A 3.01k
33µF, 35V
Vishay-Dale
595D336X0035R2T
3A, 40V
Schottky Sumida
B340A
39µH
330µF, 6.3V
Vishay-Dale
594D337X06R3D2T
CDRH127-390MC
1.8V
2.0A 3.01k
47µF, 25V
3A, 40V
39µH
330µF, 6.3V
Vishay-Dale
595D476X0025D2T
Schottky Sumida
B340A CDRH127-390MC
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 Ouput Voltages
D2***
B340
JP3
J1
VIN
J2
VOUT
2A
L1
39µH
U1 MIC4685BR
(34V transient)
2
5
6
IN
SW
C3
0.33µF
50V
1
3
C2
0.1µF
50V
BS
FB
C4*
R1
optional
C1
33µF
35V
J3
GND
3.01k
ON
EN
C5
C7
OFF
D1
B340A
R2
6.49k
R3
2.94k
R4
1.78k
R5
330µF
C6**
0.1µF
GND
976Ω
6.3V
50V
4, Tab
1
2
3
5
JP1a
1.8V
JP1b
2.5V
JP1c7 JP1d
3.3V 5.0V
J4
GND
8
4
6
*
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
September 2002
13
MIC4685
MIC4685
Micrel
Printed Circuit Board
Figure 5b. Bottom Silk Screen
Figure 5a. Top Silk Screen
Figure 5d. Bottom Side Copper
Figure 5c. Top Side Copper
Abbreviated Bill of Material (Critical Components)
Reference
C1
Part Number
Manufacturer
Vishay Sprague1
Vitramon
Description
Qty
1
594D336X0035R2T
VJ0805Y104KXAAB
GRM426X7R334K50
Optional
33µF 35V
C2, C7
C3
0.1µF 50V
2
Murata
0.33µF, 50V ceramic capacitor
1800pF, 50V ceramic
330µF, 6.3V, tantalum
Schottky 3A 40V
Schottky 3A 40V
C4*
(1)
1
C5
594D337X06R3D2T
B340A
Vishay Sprague1
Diode Inc2
D1
1
D2
B340A
MBRX120
Diode Inc2
1
Micro Commercial Component5 Schottky 1A 22V
L1
CDRH127-390MC
Sumida3
39µH
1
1
U1
MIC4685BR
Micrel Semiconductor4
3A 200kHz SPAK buck regulator
1
2
3
4
5
Vishay Sprague, Inc., tel: 207-490-7256, http://www.vishay.com
Diodes Inc, tel: 805-446-4800, http://www.diodes.com
Sumida, tel: 510-668-0660, http://www.sumida.com
Micrel, tel: 408-944-0800, httzp://www.micrel.com
Micro Commercial Component, tel: 818-701-4933, http://www.mccsemi.com
MIC4685
14
September 2002
MIC4685
Micrel
Package Information
DIMENSIONS:
INCH (MM)
0.375 (9.52)
0.365 (9.27)
0.360 (9.14)
0.350 (8.89)
0.080 (2.03)
0.070 (1.78)
0.050 (1.27)
0.256 BSC
(6.50 BSC)
0.030 (0.76)
0.010 BSC
(0.25 BSC)
0.316 BSC
(8.03 BSC)
0.045 (1.14)
0.035 (0.89)
0.320 (8.13)
0.310 (7.87)
0.420 (10.67)
0.410 (10.41)
0.031 (0.79)
0.025 (0.63)
0.050 BSC
(1.27 BSC)
0.005 (0.13)
0.001 (0.03)
0.031 (0.89)
0.041 (1.14)
0.010 BSC
(0.25 BSC)
6¡
0¡
SCALE 20:1
SPAK-07L (R)
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.
© 2002 Micrel Incorporated
September 2002
15
MIC4685
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