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MIC4682
Micrel
MIC4682
Precision Current Limit SO-8 SuperSwitcherTM Buck Regulator
General Description
The MIC4682 is an easy-to-use step-down (buck) switchmode voltage regulator. It features a programmable current limit that allows 10% current limit accuracy over its full operating temperature range. The precision current limit makes the MIC4682 ideal for constant-voltage constantcurrent applications, such as simple battery chargers. The precision current limit also gives designers the ability to set the maximum output current below the saturation current rating of the inductor. This allows the use of the smallest possible inductors for a given application, saving valuable space and cost. The MIC4682 is a very robust device. Its 4V to 34V input voltage range allows the MIC4682 to safely be used in applications where voltage transients may be present. Additional protection features include cycle-by-cycle current limiting and over-temperature shutdown. The MIC4682 is available in a thermally optimized power SO-8 package that allows it to achieve 2A of continuous output current. The MIC4682 requires a minimum number of external components and can operate using a standard series of inductors. Compensation is provided internally for fast transient response and ease of use. The MIC4682 is available in the 8lead power SOP with a -40C to +125C junction temperature range.
Features
* Programmable output current limit * 10% accuracy over temperature * Wide 4V to 34V operating input voltage range * Fixed 200kHz PWM operation * Power SO-8 package allows 2A continuous output current * All surface mount solution * Internally compensated * Less than 1A typical shutdown-mode current * Thermal shutdown protection
Applications
* * * * * Battery chargers White LED drivers Constant voltage constant current step-down converters Simple step-down regulator with precise current limit USB power supplies
Typical Application
MIC4682
5
R1 3.01k R2 976
4
SHDN
3
FB GND
1
R3 ISET 10M R4 16.2k
D1 B240
C2 220F 10V
OUTPUT VOLTAGE (V)
+7.5V to +34V C1 10F 50V (x2)
IN
SW
8
L1 68H
5V/1A
6 5 4 3 2 1
MIC4682 Current Limit Characteristics
2, 6, 7
VIN = 12V 0 0 0.5 1 1.5 CURRENT LIMIT (A) 2
Constant Current/Constant Voltage Li Ion Battery Charger
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
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Ordering Information
Part Number MIC4682BM Voltage Adjustable Junction Temp. Range -40C to +125C Package 8-lead SOP
Pin Configuration
FB 1 GND 2 ISET 3 SHDN 4
8 SW 7 GND 6 GND 5 IN
Power SOP-8 (M)
Pin Description
Pin Number 1 2, 6, 7 3 4 5 8 Pin Name FB GND ISET SHDN IN SW Pin Function Feedback (Input): Output voltage sense node. Connect to 1.23V-tap of the output voltage-divider network. Ground (Return): Ground Current Limit Set (Input): Connect an external resistor to ground to set the current limit. Do not ground or float this pin. Shutdown (Input): Logic low (<0.8V) enables regulator. Logic high (>2V) shuts down regulator. Supply Voltage (Input): Unregulated +4V to +34V supply voltage. Switch (Output): Internal power emitter of NPN output switch.
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Absolute Maximum Ratings (Note 1)
Supply Voltage (VIN), Note 3 ........................................ 38V Shutdown Voltage (VSHDN) .......................... -0.3V to +38V Steady-State Output Switch Voltage (VSW) .................. -1V Feedback Voltage (VFB) ................................................ 12V Current Limit Set Voltage (VISET) ..................... 1.23V to 7V Ambient Storage Temperature (TS) ......... -65C to +150C ESD Rating, Note 5 ...................................................... 2kV
Operating Ratings (Note 2)
Supply Voltage (VIN) Note 4 and 7 ..................... 4V to 34V Junction Temperature Range (TJ) ........... -40C to +125C Package Thermal Impedance JA SOP-8, Note 6 .............................................. 63C/W JC SOP-8, Note 6 .............................................. 20C/W
Electrical Characteristics
VIN = 12V; IOUT=500mA; RISET = 16.2k (1A current limit); TJ = 25C, bold values indicate -40C TJ +125C; unless otherwise noted. Symbol VIN IIN IIN VFB Parameter Supply Voltage Range Quiescent Current Standby Quiescent Current Condition Note 4 VFB = 1.5V VSHDN = 5V (Regulator off) VSHDN = VIN Feedback Voltage (1%) (2%) 8V VIN 34V, 0.1A ILOAD 0.8A ILIM fSW DMAX VSW ISW VSHDN ISHDN TJ Current Limit Accuracy, Note 7 Oscillator Frequency Maximum Duty Cycle Switch Saturation Voltage Switch Leakage Current VFB = 1.0V IOUT = 1A VIN = 34V, VSHDN = 5V, VSW = 0V VIN = 34V, VSHDN = 5V, VSW = -1V Shutdown Input Logic Level Regulator Off Regulator On Shutdown Input Current VSHDN = 5V (Regulator Off) VSHDN = 0V (Regulator On) Thermal Shutdown -10 -10 2 See Test Circuit, VOUT = 3.6V 1.217 1.205 1.193 1.180 0.90 180 93 Min 4 7 35 1 1.230 1.230 1 200 95 1.4 2 2 1.4 1.25 -0.5 -1.5 160 0.8 1 1 1.8 100 10 1.243 1.255 1.267 1.280 1.10 220 Typ Max 34 12 100 Units V mA A A V V V V A kHz % V A mA V V A A C
Note 1. Exceeding the absolute maximum rating may damage the device. Note 2. This device is not guaranteed to operate beyond its specified operating rating. Note 3. Absolute maximum rating is intended for voltage transients only; prolonged DC operation is not recommended. Note 4. VIN(MIN) = VOUT + 2.5V or 4V whichever is greater. Note 5. Devices are ESD sensitive. Handling precautions recommended. Human body model, 1.5k in series with 100pF. Note 6. Measured on 1.5" square of 1oz. copper FR4 printed circuit board connected to the device ground leads. Note 7. Short circuit protection is guaranteed to VIN = 30V max.
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Test Circuit
OUTPUT VOLTAGE (V)
VIN C1 (x2) 10F 50V R3 10M
MIC4682
5
IN
SW
8
L1 68H R1 3.01k R2 976
VOUT C2 220F 10V
5.0
4
SHDN ISET
3
FB GND
1
D1 B240A
3.6 10% 0 0.90 OUTPUT CURRENT (A) 1.10
2, 6, 7
RISET
Current Limit Test Circuit
Constant-Current Constant-Voltage Accuracy
Shutdown Input Behavior
OFF ON
GUARANTEED ON TYPICAL ON
0.8V 1.25V 1.4V
2V
GUARANTEED OFF TYPICAL OFF
0V
VIN(max)
Shutdown Hysteresis
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Typical Characteristics
TA = 25C unless otherwise noted.
Efficiency vs. Output Current Efficiency vs. Output Current
Efficiency vs. Output Current
90 80
EFFICIENCY (%)
80 70
EFFICIENCY (%)
80 70 EFFICIENCY (%)
70 60 50 40 30 20 10 0 0
VIN = 7.5V VIN = 12V VIN = 24V VIN = 30V
60 50 40 30 20 10 0 0
VIN = 5.8V VIN = 12V VIN = 24V VIN = 30V
60 50 40 30 20 10
VIN = 6V VIN = 12V VIN = 30V VIN = 5V
VOUT = 5V 0.4 0.8 1.2 1.6 OUTPUT CURRENT (A)
VOUT = 3.3V 0.4 0.8 1.2 1.6 OUTPUT CURRENT (A) 2
VOUT = 2.5V 0.4 0.8 1.2 1.6 OUTPUT CURRENT (A) 2
0 0
6
Output Voltage vs. Current Limit
OUTPUT VOLTAGE (V)
TA = 25C
6 5 4
Output Voltage vs. Current Limit
OUTPUT VOLTAGE (V)
6 5 4
Output Voltage vs. Current Limit
OUTPUT VOLTAGE (V)
5 4 TA = -40C
TA = 60C
VIN = 12V 3R = 16.2k ISET Load = 2 Continuous L = 68H R3 = 10M 1 0 0.4 0.8 1.2 1.6 CURRENT LIMIT (A)
2
TA = -40C VIN = 24V 3R ISET = 16.2k Load = TA = 25C 2 Continuous TA = 60C L = 68H R3 = 10M 1 0 0.4 0.8 1.2 1.6 2 CURRENT LIMIT (A)
VIN = 30V TA = -40C 3R = 16.2k ISET Load = TA = 25C 2 Continuous TA = 60C L = 68H R3 = 10M 1 0 0.4 0.8 1.2 1.6 2 CURRENT LIMIT (A)
2
CURRENT LIMIT (A)
Current Limit vs. RISET at T = -40C J
CURRENT LIMIT (A)
2 1.8 1.6 1.4 1.2 1 0.8 0.6
Current Limit vs. RISET at T = 25C J
VIN = 4V VIN = 5V VIN = 12V VIN = 24V VIN = 30V VIN = 34V
2
Current Limit vs. RISET at T = 85C J
VIN = 4V VIN = 5V VIN = 12V VIN = 24V VIN = 30V VIN = 34V
CURRENT LIMIT (A)
SHORT CIRCUIT CURRENT LIMIT (A)
1.8 1.6 1.4 1.2 1 0.8 0.6
VIN = 4V VIN = 5V VIN = 12V VIN = 24V VIN = 30V VIN = 34V
1.8 1.6 1.4 1.2 1 0.8
0.4 L = 68H R3 = 10M 0.2 V OUT = 1.0V (Pulsed Load) 0 10 15 20 25 30 35 40 45 50 RISET (k)
0.4 L = 68H R3 = 10M 0.2 V = 1.0V (Pulsed Load) OUT 0 10 15 20 25 30 35 40 45 50 RISET (k)
0.6 0.4 L = 68H R3 = 10M 0.2 V OUT = 1.0V (Pulsed Load) 0 10 15 20 25 30 35 40 45 50 RISET (k)
SHORT CIRCUIT CURRENT LIMIT (A)
2 CURRENT LIMIT (A) 1.8 1.6 1.4 1.2 1 0.8 0.6
Current Limit vs. RISET at TJ = 125C
VIN = 4V VIN = 5V VIN = 12V VIN = 24V VIN = 30V VIN = 34V
Short Circuit Current Limit vs. Input Voltage at T = -40C
2 R =10k 1.8 ISET RISET=15.8k 1.6 1.4 R ISET=20k 1.2 RISET=25k 1 0.8 0.6 0.4 0.2 RISET=30k RISET=40k RISET=50k J
Short Circuit Current Limit vs. Input Voltage at T = 25C
2 1.8 RISET=10k 1.6 1.4 RISET=15.8k 1.2 1 0.8 0.6 0.4 0.2 0 4 8 J
0.4 L = 68H R3 = 10M 0.2 V = 1.0V (Pulsed Load) OUT 0 10 15 20 25 30 35 40 45 50 RISET (k)
0 4 7 10 13 16 19 22 25 28 31 34 INPUT VOLTAGE (V)
L = 68H R3 = 10M VOUT~0V (Pulsed Load)
L = 68H R3 = 10M VOUT~0V (Pulsed Load) 12 16 20 24 28 INPUT VOLTAGE (V) 32
RISET=20k RISET=25k RISET=30k RISET=40k RISET=50k
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SHORT CIRCUIT CURRENT LIMIT (A)
2
SHORT CIRCUIT CURRENT LIMIT (A)
Short Circuit Current Limit vs. Input Voltage at TJ = 85C
2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2
Short Circuit Current Limit vs. Input Voltage at TJ = 125C
RISET=10k 15.8k RISET=20k RISET=25k RISET=30k RISET=40k RISET=50k INPUT CURRENT (mA)
12 10 8 6 4 2 0 0 5
Quiescent Current vs. Input Voltage
1.8 RISET=10k 1.6 1.4 RISET=15.8k 1.2 1 0.8 0.6 0.4 0.2 0 4 8 RISET=20k RISET=25k RISET=30k RISET=40k RISET=50k
L = 68H R3 = 10M VOUT~0V (Pulsed Load) 12 16 20 24 28 INPUT VOLTAGE (V) 32
0 4
L = 68H R3 = 10M VOUT~0V (Pulsed Load) 8 12 16 20 24 28 INPUT VOLTAGE (V) 32
VFB = 1.5V VEN = 0V 10 15 20 25 30 35 40 INPUT VOLTAGE (V)
12 INPUT CURRENT (mA) 10 8 6 4 2
Quiescent Current vs. Temperature
VIN = 24V SHUTDOWN CURRENT (A)
140 120 100 80 60
Shutdown Current vs. Input Voltage
SHUTDOWN CURRENT (A)
2.5 2 1.5 1 0.5
Shutdown Current vs. Temperature
VIN = 12V
VIN = 12V
VFB = 1.5V VEN = 0V
40 V = 1.5V FB 20 VEN = VIN 0 0 5 10 15 20 25 30 35 40 INPUT VOLTAGE (V)
VFB = 1.5V VEN = VIN
0 -40 -20 0 20 40 60 80 100120 TEMPERATURE (C)
0 -40 -20 0 20 40 60 80 100120 TEMPERATURE (C)
1.255
Feedback Voltage vs. Input Voltage & Temperature
125C FREQUENCY (kHz)
250 245 240 235 230 225 220 215
Frequency vs. Temperature
SATURATION VOLTAGE (V)
2 1.8 1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 0 0
Saturation Voltage vs. Input Voltage
FEEDBACK VOLTAGE (V)
1.25 1.245
VIN = 24V
25C 1.24 1.235 1.23 1.225 1.22 0 5 VOUT = 5V IOUT = 100mA 10 15 20 25 30 35 40 INPUT VOLTAGE (V) -40C
VIN = 12V
210 -40 -20 0 20 40 60 80 100 120 TEMPERATURE (C)
VFB = 0V
VOUT = 5V IOUT = 100mA 5 10 15 20 25 30 35 40 INPUT VOLTAGE (V)
5.02
OUTPUT VOLTAGE (V)
Line Regulation
OUTPUT VOLTAGE (V)
5.016 5.014 5.012 5.01 5.008 5.006 5.004
Load Regulation
REFERENCE VOLTAGE (V)
1.2 1.0 0.8 0.6 0.4 0.2 0.0
Thermal Shutdown Hysteresis
Upper Threshold Lower Threshold
5.01 5 4.99 4.98 4.97 4.96 4.95 0 5 IOUT = 1A 10 15 20 25 30 35 40 INPUT VOLTAGE (V)
5.002 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 OUTPUT CURRENT (A)
0 20 40
60 80
100 120
140 160
TJ (C)
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180 200
-0.2
MIC4682
Micrel
Typical Safe Operating Area (SOA)(Note 1)
2 1.8
5V Output SOA
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
2 1.8 1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 0 0 5
3.3V Output SOA
TA = 25C
1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 0 0 5
TA = 25C
TA = 60C VOUT = 5V TJ = 125C D = Max = 2A Peak I
LIMIT
TA = 60C VOUT = 3.3V TJ = 125C D = Max = 2A Peak I
LIMIT
10 15 20 25 30 35 40 INPUT VOLTAGE (V)
10 15 20 25 30 35 40 INPUT VOLTAGE (V)
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
2 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0 0
2.5V Output SOA
TA = 25C
2 1.8 1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 0 0 5
1.8V Output SOA
TA = 25C
TA = 60C VOUT = 2.5V TJ = 125C D = Max Peak ILIMIT= 2A 5 10 15 20 25 30 35 40 INPUT VOLTAGE (V)
TA = 60C VOUT = 1.8V TJ = 125C D = Max Peak ILIMIT= 2A 10 15 20 25 30 35 40 INPUT VOLTAGE (V)
Note 1. SOA measured on the MIC4682 evaluation board.
Functional Characteristics
Load Transient
VOUT (200mV/div)
VIN = 12V VOUT = 5V
IOUT (2A/div)
2A 0A
TIME (20s/div)
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Typical Bode Plots
The following bode plots show that the MIC4682 is stable using a 68H inductor (L) and a 220F output capacitor (COUT). To assure stability, it is a good practice to maintain a phase margin of greater than 35C.
No-Load Stability Phase Margin = 98
Full-Load Stability Phase Margin = 56
VIN = 7.5V VOUT = 5V IOUT = 0A TA = 25C
VIN = 7.5V VOUT = 5V IOUT = 1A TA = 25C
No-Load Stability Phase Margin = 109
Full-Load Stability Phase Margin = 50
VIN = 12V VOUT = 5V IOUT = 0A TA = 25C
VIN = 12V VOUT = 5V IOUT = 1A TA = 25C
No-Load Stability Phase Margin = 122
Full-Load Stability Phase Margin = 45
VIN = 34V VOUT = 5V IOUT = 0A TA = 25C
VIN = 34V VOUT = 5V IOUT = 1A TA = 25C
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Block Diagram
VIN IN SHDN ISET 200kHz Oscillator Internal Regulator
R1 VOUT = VFB + 1 R2 VFB = 1.23V
Thermal Shutdown
Current Limit
V R1 = R2 OUT - 1 VFB R2 = R1 VOUT - 1 V FB
VOUT COUT R1 FB
Comparator SW Driver Reset 2A Switch
Error Amp MIC4682
1.23V Bandgap Reference GND
R2
Figure 1. MIC4682 Block Diagram
Functional Description
The MIC4862 is a constant frequency, voltage mode-switching regulator. Referring to the block diagram, regulation is achieved when the feedback voltage is equal to the band gap reference. The FB pin senses the output voltage and feeds into the input of the Error Amp. The output of the Error Amp produces a positive voltage to compare with the 200kHz sawtooth waveform. These two signals are fed into the comparator to generate the Pulse Width Modulation (PWM) signal to turn on and off the internal switch. The duty cycle is defined as the time the switch turns on divided by the period of the saw-tooth oscillator. Initially, when power is applied to the IN pin, the duty cycle is high because the feedback is close to ground. As the output and feedback voltage start to rise, the duty cycle decreases. During the on time, current flows through the switch and into the inductor until it reaches the peak current limit or the maximum duty cycle which turns the switch off. The external resistor at the ISET pin sets the peak current limit. The maximum duty cycle is controlled by the Reset circuitry. At this time, energy is stored in the inductor. The current charges the output capacitor and supplies to the load. The Schottky diode is reversed bias. When the internal switch is off, the stored energy in the inductor starts to collapse. The voltage across the inductor reverses polarity and the inductor current starts to decrease. The Schottky diode clamps the switch voltage from going too negative and provides the path for the inductor current. During the off time, the inductor and the output capacitor provide current to the load. An internal regulator provides power to the control circuitry and the thermal protection circuitry turns off the internal switch when the junction temperature exceeds about 160C.
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Inductor and Output Capacitor A 68H inductor and a 220F tantalum output capacitor are chosen because of their stability over the input voltage range with maximum output current listed in the SOA typical tables. The Sumida CDRH127-680 and Vishay Sprague 593D106X9050D2T are recommended. See "Bode Plots" for additional information. With the same conditions, a lower value inductor and a higher output capacitor can be used. The disadvantages for this combination are that the output ripple voltage will be higher and the output capacitor's package size will be bigger. For example, a 47H inductor and 330F output capacitor are good combination. Another option is to use a higher value inductor and a lower output capacitor. The advantages of this combination are that the switch peak current and the output ripple voltage will be lower. The disadvantage is that the inductor's package size will be bigger. Applications that have lower output current requirement can use lower inductor value and output capacitor. See "Typical Application Circuits" for an example. A 0.1F ceramic capacitor is recommended in parallel with the tantalum output capacitor to reduce the high frequency ripple. Current Limit Set Resistor An external resistor connects between the ISET pin and ground to control the current limit of the MIC4682 ranging from 400mA to 2A. For resistor value selections, see the "Typical Characteristics: Current Limit vs. RISET." In addition to the RISET, a resistor, ranging from 10M to 15M, between the ISET and IN pin is recommended for current limit accuracy over the input voltage range. When the MIC4682 is in current limit, the regulator is in current mode. If the duty cycle is equal or greater than 50%, the regulator is in the sub-harmonic region. This lowers the average current limit. The below simplified equation determines at which input and output voltage the MIC4682 exhibits this condition.
Applications Information
Output Voltage The output voltage of the MIC4682 is determined by using the following formulas: R1 VOUT = VFB + 1 R2
R2= R1 VOUT V -1 FB
VFB = 1.23V
For most applications, a 3.01k resistor is recommended for R1 and R2 can be calculated. Input Capacitor Low ESR (Equivalent Series Resistance) capacitor should be used for the input capacitor of the MIC4862 to minimize the input ripple voltage. Selection of the capacitor value will depend on the input voltage range, inductor value, and the load. Two Vishay Sprague 593D106X9050D2T(10F/50V), tantalum capacitors are good values to use for the conditions listed in the SOA typical tables. A 0.1F ceramic capacitor is recommended in parallel with the tantalum capacitors to filter the high frequency ripple. The ceramic capacitor should be placed close to the IN pin of the MIC4682 for optimum result. For applications that are cost sensitive, electrolytic capacitors can be used but the input ripple voltage will be higher. Diode A Schottky diode is recommended for the output diode. Most of the application circuits on this data sheet specify the Diode Inc. B340A or Micro Commercial SS34A surface mount Schottky diode. Both diodes have forward current of 3A and low forward voltage drop. These diodes are chosen to operate at wide input voltage range and at maximum output current. For lower output current and lower input voltage applications, a smaller Schottky diode such as B240A or equivalence can be used.
(VOUT + 1.4) > 50%
VIN
Do not short or float the ISET pin. Shorting the ISET pin will set a peak current limit greater than 2.1A. Floating the ISET pin will exhibit unstable conditions. To disable the current limit circuitry, the voltage at the ISET pin has to be between 2V and 7V.
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Micrel pins 2, 6 and 7. This ground plane area is more than sufficient
for most designs.
Minimum Copper/Maximum Current Method
Thermal Considerations
The MIC4682 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 MIC4682 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 2, 6, 7 and the dieattach 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 MIC4682 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 2, 6 and 7 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
Using Figure 3, for a given input voltage range, determine the minimum ground-plane heat-sink area required for the application's maximum continuous output current. Figure 3 assumes a constant die temperature of 75C above ambient.
CONTINUOUS OUTPUT CURRENT (A)
1.5 8V 1.0
12V
24V VIN = 30V
0.5
TA = 50C 0 0 5 10 15 20 25 AREA (cm2)
Figure 3. Output Current vs. Ground Plane Area When designing with the MIC4682, it is a good practice to connect pins 2, 6 and 7 to the largest ground plane that is practical for the specific design.
Checking the Maximum Junction Temperature
There are two methods of determining the minimum ground plane area required by the MIC4682.
Quick Method
For this example, with an output power (POUT) of 5W, (5V output at 1A maximum with VIN = 12V) and 65C maximum ambient temperature, what is the maximum junction temperature? Referring to the "Typical Characteristics: Efficiency vs. Output Current" graph, read the efficiency () for 1A output current at VIN = 12V or perform you own measurement. = 81% The efficiency is used to determine how much of the output power (POUT) is dissipated in the regulator circuit (PD). PD = PD = POUT - POUT
Make sure that MIC4682 pins 2, 6 and 7 are connected to a ground plane with a minimum area of 6cm2. This ground plane should be as close to the MIC4682 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
SOP-8
JA JC CA
AM BIE
5W - 5W 0.81 PD = 1.17W A worst-case rule of thumb is to assume that 80% of the total output power dissipation is in the MIC4682 (PD(IC)) and 20% is in the diode-inductor-capacitor circuit. PD(IC) = 0.8 PD PD(IC) = 0.8 x 1.17W PD(IC) = 0.936W Calculate the worst-case junction temperature: TJ = PD(IC) JC + (TC - TA) + TA(max) where: TJ = MIC4682 junction temperature PD(IC) = MIC4682 power dissipation JC = junction-to-case thermal resistance. The JC for the MIC4682's power-SOP-8 is approximately 20C/W. 11
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ground plane heat sink area
NT
printed circuit board
Figure 2. Power SOP-8 Cross Section October 2003
MIC4682
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 65C: TJ = 0.936 x 20C/W + (45C - 25C) + 65C TJ = 103.7C 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."
Micrel
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, indicated by the heavy lines in Figure 4, as short as possible. For example, D1 should be close to pin 7 and pin 8. CIN should be close to pin 5 and pin 6. 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 Figures 5a though 5e. Gerber files are available upon request.
VIN +4V to +34V CIN
5
MIC4682BM IN SW
8
L1 68H COUT
VOUT R1
Load
4
SHDN GND ISET
267 3
FB
1
Power SOP-8
D1
R2
GND
Figure 4. Critical Traces for Layout
L1 68H
J1 VIN 4V to 34V C1 10F 50V J2 GND C2 10F 50V C3 0.1F 50V
OFF ON
U1 MIC4682BM
5 1
IN
SW
8 1
1
2
JP1 1-2=OFF JP1 2-3-ON
2 4
D1 B340A
J3 VOUT C4 Option C5 220F 10V R4 2.94k R3 1.78k
6
SHDN ISET GND
2
GND FB GND
6
7 2 1
JP1
3
R9 10M R8 option R7 16.2k JP3b 1.0A
6
R1 3.01k
C6 Option
3
C7 0.1F 50V
R6 25k JP3a 0.6A
R5 6.49k
2
R2 976
8
2
JP3c 2.0A
4
JP2a 1.8V
4
JP2b 2.5V
JP2c 3.3V
JP2d 5.0V J4 GND
1
3
5
1
3
5
7
Figure 5a. Evaluation Board Schematic Diagram
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M0334-102203
MIC4682
Layout Example
Micrel
Figure 5b. Top Silkscreen
Figure 5d. Bottom Silkscreen
Figure 5c. Top Layer
Figure 5e. Bottom Layer
Abbreviated Bill of Materials (Critical Components)
Reference C1, C2 C3, C7 C5 D1 L1 U1 Part Number 593D106X005D2T VJ0805Y104KXAMT 593D227X0010D2T B340A CDRH127-680MC MIC4682BM Manufacturer Vishay Sprague1 Vishay Vishay Vitramon2 Sprague1 Inc3 Description 10F/50V 0.1F/50V 220F/10V Schottky 3A/40V 68H, 2.1A ISAT Precision Circuit Limit Buck Regulator Qty 2 2 1 1 1 1
Diodes,
Sumida4 Micrel Semiconductor5
Note 1. Vishay Sprague, Inc., www.vishay.com Note 2. Vishay Vitramon, Inc., www.vishay.com Note 3. Diodes, Inc., www.diodes.com Note 4. Sumida, www.sumida.com Note 5. Micrel Semiconductor, www.micrel.com
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MIC4682
Micrel
Typical Application Circuits
MIC4682 VIN 11V to 24V C1 10F/25V Taiyo Yuden TMK432BJ106MM R1 10M R2 28k
5
IN ISET SHDN
4
SW FB GND
2,6,7
8
L1 47H Sumida CDRH6D28-470NC R3 3.01k R4 976
MIC79050
2
IN
BAT FB
3
VOUT 4.2V 0.75% C3 4.7F/20V AVX TPSA475M020R1800
3
1
C2 EN 100F GND 10V(x2) 5-8 AVX TPSC107M010R0200
1
4
GND D1 1A/40V MBRX140 Micro Commercial Components
GND
4.5 OUTPUT VOLTAGE (V)
MIC4682 Current Limit Characteristics
4
3.5
3 VIN = 12V 2.5 0 250 500 750 1000 OUTPUT CURRENT (mA)
5 4.5
VOLTAGE (V)
Typical Charging Characteristics
Constant Current Constant Voltage
0.6 0.5 0.4 0.3 0.2 0.1
CURRENT (A)
4 3.5 3 2.5 2 1.5 1 0.5 0 0
VIN = 12V Batt = 1.25Ah Cutoff Voltage = 3.0V
1
2
3 4 5 TIME (hrs)
6
7
0
Figure 6. Low-Cost Li Ion Battery Charger with 0.75% Precision Output Voltage
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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-Pin SOP (M)
MICREL, INC. 1849 FORTUNE DRIVE
TEL
SAN JOSE, CA 95131
WEB
USA
+ 1 (408) 944-0800
FAX
+ 1 (408) 944-0970
http://www.micrel.com
The information furnished by Micrel in this datasheet 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. (c) 2003 Micrel, Incorporated.
October 2003
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M0334-102203

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