MICREL MIC4690_05

MIC4690
Micrel
MIC4690
500kHz 1A SuperSwitcher™ Buck Regulator
General Description
Features
The MIC4690 SuperSwitcher™ is an easy-to-use, 500kHz
step-down PWM voltage regulator. The MIC4690 achieves
over 1A of continuous output current over a wide input voltage
range in an 8-lead SO (small outline) package.
The high switching frequency of the MIC4690 allows the
smallest surface-mount inductors and capacitors to be used.
Internal compensation ensures fast transient response and a
minimum amount of external components.
The MIC4690 features a power SO-8 package with a special
lead frame that allows over 1A of continuous current. The
MIC4690, housed in an SO-8, can replace larger TO-220 and
TO-263 packages in many applications.
The MIC4690 allows for a high degree of safety. It has a wide
input voltage range of 4V to 34V, allowing for it to be used in
applications where input voltage transients may be present.
Built-in safety features include over-current protection, frequency foldback protection, and thermal shutdown.
The MIC4690 is available in an 8-lead SO package with a
junction temperature range of –40°C to +125°C.
•
•
•
•
•
•
•
•
•
•
SO-8 package with over 1A output current
Fixed 500kHz operation
Wide 4V to 34Vinput voltage range
Output voltage adjustable to 1.23V
All surface mount solution
Internally compensated with fast transient response
Up to 85% efficiency
Overcurrent protection
Frequency foldback short-circuit protection
Thermal shutdown
Applications
•
•
•
•
•
•
•
•
•
Simple 1A step-down (buck) regulator
Replacement of TO-220 and TO-263 designs
12V to 5V/3.3V/2.5V/1.8V/1.5V conversion
5V to 2.5V/1.8V/1.5V conversion
On-card switching regulators
Hard disk drives
Cable modems
Positive-to-negative converters
Simple battery chargers
Typical Application
MIC4690BM
Power
SOP-8
2.5V Adjustable Converter
!"#$!%
µ
&'
(
(
MIC4690BM
Power
SOP-8
)*
µ
µ
1.8V Adjustable 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
April 2005
1
MIC4690
MIC4690
Micrel
Ordering Information
Part Number
Standard
Lead-Free
Voltage
Temperature Range
Package
MIC4690BM
MIC4690YM
Adjustable
–40°C to +125°C
8-lead SOP
Pin Configuration
SHDN 1
8 GND
VIN 2
7 GND
SW 3
6 GND
FB 4
5 GND
SOP-8 (M)
Pin Description
Pin Number
Pin Name
1
SHDN
2
VIN
Supply Voltage (Input): Unregulated +4V to +30V continuous supply
voltage, with a maximum +34V transient voltage.
3
SW
Switch (Output): Emitter of NPN output switch. Connect to external storage
inductor and Schottky diode.
4
FB
Feedback (Input): Connect to output on fixed output voltage versions, or to
1.23V-tap of voltage-divider network for adjustable version.
5-8
GND
MIC4690
Pin Function
Shutdown (Input): Logic low enables regulator. Logic high (>1.5V) shuts
down regulator.
Ground
2
April 2005
MIC4690
Micrel
Absolute Maximum Ratings (Note 1)
Operating Ratings (Note 2)
Supply Voltage (VIN), Note 3 ...................................... +34V
Shutdown Voltage (VSHDN) ............................. –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 4
Supply Voltage (VIN) ....................................... +4V to +30V
Junction Temperature Range (TJ) ........... –40°C to +125°C
Package Thermal Resistance
(θJA), Note 5 ........................................................ 63°C/W
(θJC), ................................................................... 20°C/W
Electrical Characteristics
VIN = 12V, VOUT = 5V; ILOAD = 500mA; VSHDN = 0V, TJ = 25°C, unless otherwise noted. Bold values indicate –40°C ≤ TJ ≤ +125°C.
Parameter
Condition
Min
Typ
Max
Units
Feedback Voltage
(±1%)
(±2%)
1.217
1.205
1.230
1.243
1.255
V
V
8V ≤ VIN ≤ 30V, 0.1A ≤ ILOAD ≤ 1A, VOUT = 5V
1.193
1.180
1.230
1.267
1.280
V
V
90
93
Maximum Duty Cycle
VFB = 1.0V
Quiescent Current
VFB = 1.5V
7
12
mA
Standby Quiescent Current
VSHDN = 5V (regulator off)
30
100
µA
VSHDN = 12V (regulator off)
1.5
VFB = 0V
220
300
KHz
500
550
kHz
Frequency Foldback
Oscillator Frequency
450
%
µA
Saturation Voltage
IOUT = 1A
1.2
Output Leakage Current
VIN = 30V, VSHDN = 5V, VSW = 0V
50
500
µA
VIN = 30V, VSHDN = 5V, VSW = –1V
4
20
mA
1.3
2.5
3.0
A
2
1.5
Short Circuit Current Limit
VFB = 0V, VOUT = 0V, See Test Circuit
Shutdown Pin Input Logic Level
regulator off
regulator on
Shutdown Pin Input Current
V
V
1.25
0.8
V
VSHDN = 5V (regulator off)
–10
–0.7
10
µA
VSHDN = 0V (regulator on)
–10
–1.5
10
µA
Thermal Shutdown @ TJ
160
°C
Note 1.
Exceeding the absolute maximum rating may damage the device.
Note 2.
With input voltages above the operating rating, the device may be damaged if a short-circuit is applied to the output. The device will otherwise
not be damaged up to its absolute maximum voltage rating.
Note 3.
Absolute maximum rating is intended for voltage transients only, prolonged dc operation is not recommended.
Note 4.
Devices are ESD sensitive. Handling precautions recommended.
Note 5.
Measured on 1" square of 1 oz. copper FR4 printed circuit board connected to the device ground leads.
April 2005
3
MIC4690
MIC4690
Micrel
Test Circuit
+12V
2
1
Device Under Test
3
VIN
SW
SHDN
18µH
4
FB
I
GND
SOP-8
5–8
Current Limit Test Circuit
Shutdown Input Behavior
OFF
ON
GUARANTEED
ON
0V
TYPICAL
ON
0.8V
1.25V
2V
1.5V
GUARANTEED
OFF
TYPICAL
OFF
VIN(max)
Shutdown Hysteresis
MIC4690
4
April 2005
MIC4690
Micrel
Typical Characteristics
Quiescent Current
vs. Temperature
8.6
1.241
1.239
1.237
1.235
1.233
1.231
VIN = 12V
1.229
VOUT = 5V
1.227
IOUT = 100mA
1.225
1.223
-40 -20 0 20 40 60 80 100120140
TEMPERTURE (°C)
8.5 VIN = 12.0V
8.4 VOUT = 5.0V
8.3 IOUT = 0
8.2
8.1
8
7.9
7.8
7.7
7.6
-40 -20 0 20 40 60 80 100120140
TEMPERATURE (°C)
80
Efficiency
vs. Input Voltage
50
40
30
20 VOUT = 5V
= 1A
I
10 OUT
5
250
400
300
VIN = 12V
VOUT = 5V
IOUT = 100mA
0
-50
10 15 20 25 30 35 40
INPUT VOLTAGE (V)
0
50
100
Temperature (°C)
150
100
5.005
OUTPUT VOLTAGE (V)
5.010
0
-50
150
0.2 0.4 0.6 0.8 1 1.2 1.4
OUTPUT CURRENT (A)
0
50
100
Temperature (°C)
150
Shutdown Current
vs. Temperature
3.5
5.04
5.02
5.00
VIN = 12V
VOUT = 5V
IOUT = 500mA
4.98
4.96
0
VIN = 12V
VOUT = 5V
IOUT = 100mA
50
5.06
5.015
0.2 0.4 0.6 0.8 1 1.2 1.4
OUTPUT CURRENT (A)
200
Line Regulation
5.025
5.000
0
EFFICIENCY (%)
500
200
VIN = 12.0V
VOUT = 5.0V
Frequency Foldback
vs. Temperature
300
Load Regulation
5.020
72
600
100
VIN = 12V
VOUT = 5V
74
68
0
5
10 15 20 25 30 35 40
INPUT VOLTAGE (V)
SHUTDOWN CURRENT (µA)
0
0
76
70
FREQUENCY (kHz)
FREQUENCY (kHz)
EFFICIENCY (%)
70
60
78
Frequency vs.
Temperature
80
OUTPUT VOLTAGE (V)
Efficiency vs.
Output Current
1.243
CURRENT (mA)
VOLTAGE (V)
Reference Voltage
vs. Temperature
3.0
VSHDN = V = 12V
IN
V
= 5V
OUT
2.5
2.0
1.5
1.0
0.5
0
-40 -20 0 20 40 60 80 100120140
TEMPERATURE (°C)
SHUTDOWN PIN VOLTAGE (V)
Shutdown Hysteresis
vs. Temperature
April 2005
1.6
OFF
1.4
ON
1.2
1
0.8
0.6
VIN = 12.0V
VOUT = 5.0V
IOUT = 100mA
0.4
0.2
0
-40
0
40
80 120 160
TEMPERATURE (°C)
5
MIC4690
MIC4690
Micrel
Functional Characteristics
Switching Frequency Foldback
VSW (NORMAL)
12V IN, 5V/1A OUT
Load Transient
IOUT
(1A/div)
1.5A
0A
500kHz
VSW (SHORTED)
12V IN, 0V OUT
VOUT
(100mV/div)
100mV
Normal
Operation
VIN = 12V
VOUT = 5V
Short
Circuit
Operation
190kHz
TIME
CONTINUOUS OUTPUT CURRENT (A)
TIME (100µs/div)
SOA for MIC4690*
1.4
1.2
TA = 25°C
1.0
0.8
0.6
0.4
VOUT = 5V
TA = 50°C
TJ = 125°C
0.2
0
0
5
10 15 20 25 30
INPUT VOLTAGE (V)
MIC4690BM
IN
SW
3
1N4148 82‰
SHDN
35
D1
FB
2.2nF
GND
5 6 7 8
Snubber Circuit
MIC4690
6
April 2005
MIC4690
Micrel
Block Diagrams
VIN
IN
SHDN
Internal
Regulator
500kHz
Oscillator
Thermal
Shutdown
⎛ R1 ⎞
VOUT = VREF ⎜
+ 1⎟
⎝ R2 ⎠
⎛V
⎞
R1 = R2 ⎜ OUT − 1⎟
⎝ VREF
⎠
Current
Limit
VREF = 1.23V
Comparator
VOUT
SW
Driver
COUT
Reset
R1
FB
Error
Amp
1.23V
Bandgap
Reference
R2
MIC4690 [adj.]
Adjustable Regulator
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 MIC4690 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 MIC4690 is a variable duty cycle switch-mode regulator
with an internal power switch. Refer to the block diagrams.
Supply Voltage
The MIC4690 operates from a +4V to +30V (transients to
34V) unregulated input. Highest efficiency operation is from
a supply voltage around +12V. See the efficiency curve on
page 5.
Enable/Shutdown
The shutdown (SHDN) input is TTL compatible. A logic-low
enables the regulator. A logic-high shuts down the internal
regulator which reduces the current to typically 1.5µA when
VSHDN = VIN = 12V and 30µA when VSHDN = 5V. See
“Shutdown Input Behavior: Shutdown Hysteresis.”
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 Figure 1b for recommended resistor values.
Duty Cycle Control
A fixed-gain error amplifier compares the feedback signal
with a 1.23V bandgap voltage reference. The resulting error
amplifier output voltage is compared to a 500kHz sawtooth
April 2005
7
MIC4690
MIC4690
Micrel
Applications Information
µ
Adjustable Regulators
Adjustable regulators require a 1.23V feedback signal. Recommended voltage-divider resistor values for common output voltages are included in Figure 1b.
For other voltages, the resistor values can be determined
using the following formulas:
!!
Power
MIC4690BM
#$
"
µ
µ
Figure 1a. Adjustable Regulator Circuit
⎛ R1 ⎞
VOUT = VREF ⎜
+ 1⎟
⎝ R2 ⎠
⎛V
⎞
R1 = R2 ⎜ OUT − 1⎟
⎝ VREF
⎠
VREF = 1.23V
Bill of Material Matrix
VOUT
R1(1)
R2(1)
VIN
CIN
D1
L1
COUT
IOUT
5.0V
3.01k
976Ω
6.8V-30V
22µF, 35V
Vishay-Dale
595D226X0035D2T
Micro Commercial
2A, 40V
Schotty
SS24
18µH
Sumida
CDRH6D38-180ML
220µF, 10V
Vishay-Dale
594D227X0010D2T
see SOA
5.0V
3.01k
976Ω
6.8V-14V
47µF, 20V
Vishay-Dale
595D476X0020C2T
Micro Commercial
2A, 20V
Schotty
SS22
18µH
Sumida
CDRH6D38-180ML
100µF, 6.3V
Vishay-Dale
595D107X06R3C2T
1.0A
3.3V
3.01k
1.78k
4.9V-14V
47µF, 20V
Vishay-Dale
595D476X0020C2T
Micro Commercial
2A, 20V
Schotty
SS22
15µH
Sumida
CDRH6D38-150ML
120µF, 4.0V
Vishay-Dale
595D127X0004C2T
1.0A
2.5V
3.01k
2.94k
4.25V-14V 47µF, 20V
Vishay-Dale
595D476X0020C2T
Micro Commercial
2A, 20V
Schotty
SS22
10µH
Sumida
CDRH6D38-100ML
120µF, 4.0V
Vishay-Dale
595D127X0004C2T
1.0A
1.8V
3.01k
6.49k
4.0V-14V
2A, 20V
Schotty
SS22
10µH
Sumida
CDRH6D38-100ML
120µF, 4.0V
Vishay-Dale
595D127X0004C2T
1.0A
Note 1.
47µF, 20V
Vishay-Dale
595D476X0020C2T
Micro Commercial
All resistors 1%
Figure 1b. Recommended Components for Common Ouput Voltages
MIC4690
8
April 2005
MIC4690
Micrel
When designing with the MIC4690, it is a good practice to
connect pins 5 through 8 to the largest ground plane that is
practical for the specific design.
Thermal Considerations
The MIC4690 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 MIC4690 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 5 through 8 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 MIC4690
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 20°C/W for a power SOP-8.
θCA is dependent on layout and is primarily governed by the
connection of pins 5 though 8 to the ground plane. The
purpose of the ground plane is to function as a heat sink.
θJA is ideally 63°C/W, but will vary depending on the size of
the ground plane to which the power SOP-8 is attached.
Checking the Maximum Junction Temperature:
For this example, with an output power (POUT) of 5W, (5V
output at 1A maximum with VIN = 12V) and 50°C maximum
ambient temperature, what is the maximum 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 = 75%
The efficiency is used to determine how much of the output
power (POUT) is dissipated in the regulator circuit (PD).
PD =
Quick Method
Make sure that MIC4690 pins 5 though 8 are connected to a
ground plane with a minimum area of 6cm2. This ground
plane should be as close to the MIC4690 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 5 though 8. This ground plane area is more than
sufficient for most designs.
SOP-8
θJA
ground plane
heat sink area
AM
BIE
NT
printed circuit board
Figure 2. Power SOP-8 Cross Section
April 2005
− POUT
5W
− 5W
0.75
PD = 1.67W
A worst-case rule of thumb is to assume that 80% of the total
output power dissipation is in the MIC4690 (PD(IC)) and 20%
is in the diode-inductor-capacitor circuit.
PD(IC) = 0.8 PD
PD(IC) = 0.8 × 1.67W
PD(IC) = 1.336W
Calculate the worst-case junction temperature:
TJ = PD(IC) θJC + (TC – TA) + TA(max)
where:
TJ = MIC4690 junction temperature
PD(IC) = MIC4690 power dissipation
θJC = junction-to-case thermal resistance.
The θJC for the MIC4690’s power-SOP-8 is approximately
20°C/W.
TC = “pin” temperature measurement taken at the
entry point of pins 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 50°C:
TJ = 1.336W × 20°C/W + (63°C – 25°C) + 50°C
TJ = 114.72°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.”
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.
There are two methods of determining the minimum ground
plane area required by the MIC4690.
θCA
η
PD =
Determining Ground-Plane Heat-Sink Area
θJC
POUT
9
MIC4690
MIC4690
Micrel
!
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 Figures 6a
though 6e. Gerber files are available upon request.
MIC4690BM
Power
SOP-8
To minimize stray inductance and ground loops, keep trace
lengths, indicated by the heavy lines in Figure 5, as short as
possible. For example, keep D1 close to pin 3 and pins 5
through 8, keep L1 away from sensitive node FB, and keep
CIN close to pin 2 and pins 5 though 8. See “Applications
Information: Thermal Considerations” for ground plane layout.
" # $ %
Figure 5. Critical Traces for Layout
!"# !$
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MIC4690BM
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µ
,
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( 3 2# 6!#4 )7"4# 44"" + !2"+"8
4 "9)7#4 !"# #!) !#
( ) * )" +
,
,
,
,
./- /- 0- /0.1
0
% %2 %3 %4
.
µ
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Figure 6a. Evaluation Board Schematic Diagram
MIC4690
10
April 2005
MIC4690
Micrel
Printed Circuit Board Layouts
Figure 6b. Top-Side Silk Screen
Figure 6d. Bottom-Side Silk Screen
Figure 6e. Bottom-Side Copper
Figure 6c. Top-Side Copper
Abbreviated Bill of Material (Critical Components)
Reference
Part Number
Manufacturer
Description
Sprague1
Qty
C1
595D2260035D2T
ECE-A1HFS470
TPSD226M035R0300
Vishay
Panasonic
AVX2
22µF, 35V
47µF, 50V, 8mm X 11.5mm
22µF, 35V
1
C2, C6
VJ0805Y104KXAMB
Vishay Vitramon2
0.1µF 50V
2
220µF, 10V
1
Schottky 2A, 40A
1
18µH, 1.5A ISAT
1
1A 200kHz power-SO-8 buck regulator
1
C4
594D227X0010D2T
Vishay
Sprague1
D1
SS24
B240A
Micro Commercial
Diode Inc
L1
CDRH6D38-180MC
Sumida4
U1
MIC4690BM
Micrel
1
Vishay Dale, Inc., tel: 1 877-847-4291, http://www.vishay.com
2
Diodes Inc, tel: (805) 446-4800, http://www.diodes.com
3 Micro
Corp3
Semiconductor5
Commercial Corp., tel: (800) 346-3371
4
Sumida, tel: (408) 982-9960, http://www.sumida.com
5
Micrel, tel: (408) 944-0800, http://www.micrel.com
April 2005
11
MIC4690
MIC4690
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. 2180 FORTUNE DRIVE SAN JOSE, CA 95131
TEL
+ 1 (408) 944-0800
FAX
+ 1 (408) 474-1000
WEB
USA
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 at Purchaser’s own risk and Purchaser agrees to fully indemnify
Micrel for any damages resulting from such use or sale.
© 2005 Micrel, Incorporated.
MIC4690
12
April 2005