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MIC4690
Micrel
MIC4690
500kHz 1A SuperSwitcherTM Buck Regulator Final Information
General Description
The MIC4690 SuperSwitcherTM 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 -40C to +125C.
Features
* * * * * * * * * * * * * * * * * * * 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 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
Applications
Typical Application
5V
SHUTDOWN ENABLE 2 1
C1 22F 10V
VIN
MIC4690BM
Power SOP-8
SW
3 4
L1 10H D1 2A 20V
2.5V/1A R1 3.01k R2 2.94k C2 100F 4V
SHDN FB GND
58
2.5V Adjustable Converter
4V to 30V (34V Transient) C1 22F 10V SHUTDOWN
ENABLE
2 1
VIN
MIC4690BM
Power SOP-8
SW
3 4
L1 18H D1 2A 20V
1.8V/1A R1 3.01k R2 6.49k C2 220F 4V
SHDN FB GND
58
1.8V Adjustable Converter
SuperSwitcher is a trademark of Micrel, Inc. Micrel, Inc. * 1849 Fortune Drive * San Jose, CA 95131 * USA * tel + 1 (408) 944-0800 * fax + 1 (408) 944-0970 * http://www.micrel.com
June 2001
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MIC4690
MIC4690
Micrel
Ordering Information
Part Number MIC4690BM Voltage Adjustable Junction Temp. Range -40C to +125C Package 8-lead SOP
Pin Configuration
SHDN 1 VIN 2 SW 3 FB 4 8 GND 7 GND 6 GND 5 GND
SOP-8 (M)
Pin Description
Pin Number 1 2 3 4 5-8 Pin Name SHDN VIN SW FB GND Pin Function Shutdown (Input): Logic low enables regulator. Logic high (>1.5V) shuts down regulator. Supply Voltage (Input): Unregulated +4V to +30V continuous supply voltage, with a maximum +34V transient voltage. Switch (Output): Emitter of NPN output switch. Connect to external storage inductor and Schottky diode. Feedback (Input): Connect to output on fixed output voltage versions, or to 1.23V-tap of voltage-divider network for adjustable version. Ground
MIC4690
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MIC4690
Micrel
Absolute Maximum Ratings (Note 1)
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) ....................... -65C to +150C ESD Rating .............................................................. Note 4
Operating Ratings (Note 2)
Supply Voltage (VIN) ....................................... +4V to +30V Junction Temperature Range (TJ) ........... -40C to +125C Package Thermal Resistance (JA), Note 5 ........................................................ 63C/W (JC), ................................................................... 20C/W
Electrical Characteristics
VIN = 12V, VOUT = 5V; ILOAD = 500mA; VSHDN = 0V, TJ = 25C, unless otherwise noted. Bold values indicate -40C TJ +125C. Parameter Feedback Voltage Condition (1%) (2%) 8V VIN 30V, 0.1A ILOAD 1A, VOUT = 5V Maximum Duty Cycle Quiescent Current Standby Quiescent Current VFB = 1.0V VFB = 1.5V VSHDN = 5V (regulator off) VSHDN = 12V (regulator off) Frequency Foldback Oscillator Frequency Saturation Voltage Output Leakage Current IOUT = 1A VIN = 30V, VSHDN = 5V, VSW = 0V VIN = 30V, VSHDN = 5V, VSW = -1V Short Circuit Current Limit Shutdown Pin Input Logic Level VFB = 0V, VOUT = 0V, See Test Circuit regulator off regulator on Shutdown Pin Input Current VSHDN = 5V (regulator off) VSHDN = 0V (regulator on) Thermal Shutdown @ TJ
Note 1. Note 2. Note 3. Note 4. Note 5. Exceeding the absolute maximum rating may damage the device. 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. Absolute maximum rating is intended for voltage transients only, prolonged dc operation is not recommended. Devices are ESD sensitive. Handling precautions recommended. Measured on 1" square of 1 oz. copper FR4 printed circuit board connected to the device ground leads.
Min 1.217 1.205 1.193 1.180 90
Typ 1.230 1.230 93 7 30 1.5 220
Max 1.243 1.255 1.267 1.280
Units V V V V %
12 100
mA A A
VFB = 0V 450
300 550
KHz kHz V A mA A V
500 1.2 50 4
500 20 3.0
1.3 2
2.5 1.5 1.25
0.8 10 10
V A A C
-10 -10
-0.7 -1.5 160
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MIC4690
MIC4690
Micrel
Test Circuit
+12V
2
Device Under Test VIN SW 3
4
18H
1
SHDN GND
SOP-8 5-8
FB
I
Current Limit Test Circuit
Shutdown Input Behavior
OFF ON
GUARANTEED ON TYPICAL ON
0.8V 1.25V 1.5V
2V
GUARANTEED OFF TYPICAL OFF
0V
VIN(max)
Shutdown Hysteresis
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Typical Characteristics
Reference Voltage vs. Temperature
1.243 1.241 1.239 VOLTAGE (V) 1.237 1.235 1.233 1.231 1.229 1.227 VIN = 12V VOUT = 5V IOUT = 100mA
CURRENT (mA)
Quiescent Current vs. Temperature
8.6 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 78
EFFICIENCY (%)
Efficiency vs. Output Current
76 74 72 70 68 0 VIN = 12.0V VOUT = 5.0V 0.2 0.4 0.6 0.8 1 1.2 1.4 OUTPUT CURRENT (A)
1.225 1.223 -40 -20 0 20 40 60 80 100120140 TEMPERTURE (C)
Efficiency vs. Input Voltage
80 70 EFFICIENCY (%) 60 50 40 30 20 VOUT = 5V = 1A I 10 OUT 0 0 5 10 15 20 25 30 35 40 INPUT VOLTAGE (V)
FREQUENCY (kHz)
Frequency vs. Temperature
600 500
FREQUENCY (kHz) 300 250 200 150 100 50
Frequency Foldback vs. Temperature
400 300 200 100 0 -50 VIN = 12V VOUT = 5V IOUT = 100mA 0 50 100 Temperature (C) 150
VIN = 12V VOUT = 5V IOUT = 100mA 0 50 100 Temperature (C) 150
0 -50
Load Regulation
5.025 5.06 OUTPUT VOLTAGE (V) VIN = 12V VOUT = 5V
Line Regulation
3.5
Shutdown Current vs. Temperature
SHUTDOWN CURRENT (A)
3.0 2.5 2.0 1.5 1.0 0.5 0 -40 -20 0 20 40 60 80 100120140 TEMPERATURE (C) VSHDN = V = 12V IN VOUT = 5V
OUTPUT VOLTAGE (V)
5.020 5.015 5.010 5.005 5.000 0
5.04 5.02 5.00 4.98 4.96 0 VIN = 12V VOUT = 5V IOUT = 500mA 5 10 15 20 25 30 35 40 INPUT VOLTAGE (V)
0.2 0.4 0.6 0.8 1 1.2 1.4 OUTPUT CURRENT (A)
Shutdown Hysteresis vs. Temperature
SHUTDOWN PIN VOLTAGE (V)
1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 0 -40
OFF ON
VIN = 12.0V VOUT = 5.0V IOUT = 100mA 0 40 80 120 160 TEMPERATURE (C)
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MIC4690
MIC4690
Micrel
Functional Characteristics
Load Transient
VSW (NORMAL) 12V IN, 5V/1A OUT
Switching Frequency Foldback
1.5A
IOUT (1A/div)
Normal Operation
0A 100mV
500kHz
VOUT (100mV/div)
VSW (SHORTED) 12V IN, 0V OUT
Short Circuit Operation
VIN = 12V VOUT = 5V
TIME (100s/div)
190kHz
TIME
CONTINUOUS OUTPUT CURRENT (A)
SOA for MIC4690*
1.4 1.2 1.0 0.8 0.6 0.4 0.2 0 0 5 VOUT = 5V TA = 50C TJ = 125C 10 15 20 25 30 INPUT VOLTAGE (V) 35 TA = 25C
MIC4690BM IN SW
3
1N4148 SHDN GND
5678
82
D1
FB 2.2nF
Snubber Circuit
MIC4690
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MIC4690
Micrel
Block Diagrams
VIN IN SHDN Internal Regulator R1 VOUT = VREF + 1 R2 Current Limit V R1 = R2 OUT - 1 VREF VREF = 1.23V Comparator SW Driver Reset R1 FB Error Amp MIC4690 [adj.] 1.23V Bandgap Reference R2 COUT
500kHz Oscillator
Thermal Shutdown
VOUT
Adjustable Regulator
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 1.5A when VSHDN = VIN = 12V and 30A 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
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. 7 MIC4690
June 2001
MIC4690
Micrel
MIC4690BM VIN SW
Applications Information
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:
+6.8V to +30V C1 22F 35V SHUTDOWN
ENABLE 2 3
L1 18H D1 2A 40V
5.0V/1A R1 3.01k R2 1.27k
1
SHDN GND
58
FB
4
SOP-8
Power
C2 220F 10V
R1 VOUT = VREF + 1 R2 V R1 = R2 OUT - 1 VREF VREF = 1.23V
Figure 1a. Adjustable Regulator Circuit
Bill of Material Matrix
VOUT 5.0V R1(1) 3.01k R2(1) 976 VIN 6.8V-30V CIN 22F, 35V Vishay-Dale 595D226X0035D2T Micro Commercial 47F, 20V Vishay-Dale 595D476X0020C2T Micro Commercial 47F, 20V Vishay-Dale 595D476X0020C2T Micro Commercial D1 2A, 40V Schotty SS24 2A, 20V Schotty SS22 2A, 20V Schotty SS22 2A, 20V Schotty SS22 2A, 20V Schotty SS22 L1 18H Sumida CDRH6D38-180ML 18H Sumida CDRH6D38-180ML 15H Sumida CDRH6D38-150ML 10H Sumida CDRH6D38-100ML 10H Sumida CDRH6D38-100ML COUT 220F, 10V Vishay-Dale 594D227X0010D2T 100F, 6.3V Vishay-Dale 595D107X06R3C2T 120F, 4.0V Vishay-Dale 595D127X0004C2T 120F, 4.0V Vishay-Dale 595D127X0004C2T 120F, 4.0V Vishay-Dale 595D127X0004C2T IOUT see SOA
5.0V
3.01k
976
6.8V-14V
1.0A
3.3V
3.01k
1.78k
4.9V-14V
1.0A
2.5V
3.01k
2.94k
4.25V-14V 47F, 20V Vishay-Dale 595D476X0020C2T Micro Commercial 4.0V-14V 47F, 20V Vishay-Dale 595D476X0020C2T Micro Commercial
1.0A
1.8V
3.01k
6.49k
1.0A
Note 1.
All resistors 1%
Figure 1b. Recommended Components for Common Ouput Voltages
MIC4690
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June 2001
MIC4690
Thermal Considerations The MIC4690 SuperSwitcherTM 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 SuperSwitcherTM 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 (JA) of the design (package and ground plane). Examining JA in more detail: JA = (JC + CA) where: JC = junction-to-case thermal resistance CA = case-to-ambient thermal resistance JC is a relatively constant 20C/W for a power SOP-8. CA 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. JA is ideally 63C/W, but will vary depending on the size of the ground plane to which the power SOP-8 is attached.
Determining Ground-Plane Heat-Sink Area
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.
Checking the Maximum Junction Temperature:
For this example, with an output power (POUT) of 5W, (5V output at 1A maximum with VIN = 12V) and 50C maximum ambient temperature, what is the maximum junction temperature? Referring to the "Typical Characteristics: 5V Output Efficiency" graph, read the efficiency () for 1A output current at VIN = 12V or perform you own measurement. = 75% The efficiency is used to determine how much of the output power (POUT) is dissipated in the regulator circuit (PD). PD = PD = POUT - POUT
There are two methods of determining the minimum ground plane area required by the MIC4690.
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
JA JC CA
AM BIE
ground plane heat sink area
NT
printed circuit board
Figure 2. Power SOP-8 Cross Section June 2001 9
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 x 1.67W PD(IC) = 1.336W Calculate the worst-case junction temperature: TJ = PD(IC) JC + (TC - TA) + TA(max) where: TJ = MIC4690 junction temperature PD(IC) = MIC4690 power dissipation JC = junction-to-case thermal resistance. The JC for the MIC4690's power-SOP-8 is approximately 20C/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 50C: TJ = 1.336W x 20C/W + (63C - 25C) + 50C TJ = 114.72C This value is within the allowable maximum operating junction temperature of 125C as listed in "Operating Ratings." Typical thermal shutdown is 160C 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.
MIC4690
MIC4690
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.
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.
+4V to +30V (34V transients)
2
VIN
MIC4690BM
VIN SW
3
L1
VOUT
CIN
COUT
1
R1
Power SOP-8
GND
5 6 7 8
D1
R2
GND
Figure 5. Critical Traces for Layout
J1 4V to +30V (34V transients) C2 C1 22F 35V J3 GND
SOP-8 2
VIN
Load
SHDN
FB
4
U1 IN
MIC4690BM
SW
3
J2 L1 18H R1 3.01k D1 2A 40V R6 optional
1
VOUT 1A
0.1F
OFF ON
C3* 1800pF / 50V optional C4 C5 0.1F 50V R3 2.94k JP2b 2.5V
4 6 5 3
50V JP1
1
SHDN GND
58
FB
4
R2 6.49k JP2a 1.8V
R4 1.78k JP2c 3.3V
8 7
R5 9761/2 JP2d 5.0V
220F 10V
J4 GND
* C3 can be used to provide additional stability and improved transient response.
2
Figure 6a. Evaluation Board Schematic Diagram
MIC4690
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MIC4690
Printed Circuit Board Layouts
Micrel
Figure 6b. Top-Side Silk Screen Figure 6d. Bottom-Side Silk Screen
Figure 6c. Top-Side Copper
Figure 6e. Bottom-Side Copper
Abbreviated Bill of Material (Critical Components)
Reference C1 Part Number 595D2260035D2T ECE-A1HFS470 TPSD226M035R0300 VJ0805Y104KXAMB 594D227X0010D2T SS24 B240A CDRH6D38-180MC MIC4690BM Manufacturer Vishay Panasonic AVX2 Sprague1 Description 22F, 35V 47F, 50V, 8mm X 11.5mm 22F, 35V 0.1F 50V 220F, 10V Corp3 Schottky 2A, 40A 18H, 1.5A ISAT 1A 200kHz power-SO-8 buck regulator Qty 1
C2, C6 C4 D1 L1 U1
1 2
Vishay Vitramon2 Vishay Sprague1
2 1 1 1 1
Micro Commercial Diode Inc Sumida4 Micrel
Semiconductor5
Vishay Dale, Inc., tel: 1 877-847-4291, http://www.vishay.com Diodes Inc, tel: (805) 446-4800, http://www.diodes.com Commercial Corp., tel: (800) 346-3371 Sumida, tel: (408) 982-9960, http://www.sumida.com Micrel, tel: (408) 944-0800, http://www.micrel.com
3 Micro 4 5
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MIC4690
MIC4690
Micrel
Package Information
0.026 (0.65) MAX)
PIN 1
0.157 (3.99) 0.150 (3.81)
DIMENSIONS: INCHES (MM)
0.050 (1.27) TYP
0.020 (0.51) 0.013 (0.33) 0.0098 (0.249) 0.0040 (0.102) 0-8 SEATING PLANE 45 0.010 (0.25) 0.007 (0.18)
0.064 (1.63) 0.045 (1.14)
0.197 (5.0) 0.189 (4.8)
0.050 (1.27) 0.016 (0.40) 0.244 (6.20) 0.228 (5.79)
8-Lead SOP (M)
MICREL INC. 1849 FORTUNE DRIVE SAN JOSE, CA 95131
TEL
USA
+ 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. (c) 2001 Micrel Incorporated
MIC4690
12
June 2001

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