MIC4685 Micrel Semiconductor, MIC4685 Datasheet

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MIC4685

Manufacturer Part Number
MIC4685
Description
Manufacturer
Micrel Semiconductor
Datasheet
General Description
The MIC4685 is a high-efficiency 200kHz stepdown (buck)
switching regulator. Power conversion efficiency of above
85% is easily obtainable for a wide variety of applications.
The MIC4685 achieves 3A of continuous current in the
7-pin SPAK package.
The thermal performance of the SPAK allows it to replace
TO-220s and TO-263s (D
The SPAK saves board space with a 36% smaller footprint
than TO-263.
High-efficiency is maintained over a wide output current
range by utilizing a boost capacitor to increase the voltage
available to saturate the internal power switch. As a result
of this high-efficiency, only the ground plane of the PCB is
needed for a heat sink.
The MIC4685 allows for a high degree of safety. It has a
wide input voltage range of 4V to 30V (34V transient),
allowing it to be used in applications where input voltage
transients may be present. Built-in safety features include
over-current protection, frequency-foldback short-circuit
protection, and thermal shutdown.
The MIC4685 is available in a 7-pin SPAK package with a
junction temperature range of –40°C to +125°C.
Data sheets and support documentation can be found on
Micrel’s web site at www.micrel.com.
___________________________________________________________________________________________________________
Typical Application
SuperSwitcher is a trademark of Micrel, Inc
March 2007
8V to 30V
Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (
V
IN
33µF
35V
C
IN
2
5
IN
EN
MIC4685_R
1.8V Output Converter
GND
4, Tab
SW
BS
FB
2
PAKs) in many applications.
1
6
3
C
0.33µF/50V
BS
D1
3A
40V
39mH
L1
3.01k
6.49k
R1
R2
1.8V/3A
C
330µF
6.3V
V
OUT
OUT
1
Features
• Low 2mm profile SPAK package
• 3A continuous output current
• Wide 4V to 30V input voltage range (34V transient)
• Fixed 200kHz PWM operation
• Over 85% efficiency
• Output voltage adjustable to 1.235V
• All surface mount solution
• Internally compensated with fast transient response
• Over-current protection
• Frequency foldback short-circuit protection
• Thermal shutdown
Applications
• Point-of-load power supplies
• Simple high-efficiency step-down regulators
• 5V to 3.3V/2A conversion
• 12V to 5V/3.3V/2.5V/1.8V 3A conversion
• Dual-output ±5V conversion
• Base stations
• LCD power supplies
• Battery chargers
408
) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
±10%
V
5V
IN
68µF
10V
C
IN
3A SPAK SuperSwitcher™
2
5
IN
EN
MIC4685_R
Buck Regulator
3A, 20V
GND
D
5V to 3.3V Converter
MIC4685
BS
4, Tab
SW
BS
FB
1
6
3
D1
3A
20V
C
0.33µF/50V
BS
39µH
L1
3.01k
1.78k
R1
R2
M9999-031407
3.3V/2A
330µF
6.3V
V
OUT

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MIC4685 Summary of contents

Page 1

... As a result of this high-efficiency, only the ground plane of the PCB is needed for a heat sink. The MIC4685 allows for a high degree of safety. It has a wide input voltage range 30V (34V transient), allowing used in applications where input voltage transients may be present ...

Page 2

... Micrel, Inc. Ordering Information Part Number Standard RoHS Compliant* MIC4685BR MIC4685WR MIC4685WR EV * RoHS compliant with ‘high-melting solder’ exemption. Pin Configuration Pin Description Pin Number Pin Name Tab GND March 2007 Junction Voltage Temp. Range Adj. – ...

Page 3

... Bootstrap (BS, Pin 1) The bootstrap pin, in conjunction with the external bootstrap capacitor, provides a bias voltage higher than the input voltage to the MIC4685’s main NPN pass element. The bootstrap capacitor sees the dv/dt of the switching action at the SW pin voltage. The bootstrap capacitor then couples the AC voltage back to the BS pin, plus the dc offset of V used to provide additional drive to the main switch ...

Page 4

... EDS Rating .................................................................. 2kV Electrical Characteristics 12V 500mA OUT OUT Parameter Condition MIC4685 [Adjustable] Feedback Voltage (±2%) (±3%) 8V ≤ V Feedback Bias Current Maximum Duty Cycle V FB Output Leakage Current Quiescent Current V FB ...

Page 5

... Micrel, Inc. Test Circuit +12V Shutdown Input Behavior March 2007 Device Under Test 2 6 VIN GND FB 4, Tab 3 Current Limit Test Circuit OFF 0.8V 0V 1.25V 1.4V Enable Hysteresis 5 68µ IN(max) MIC4685 M9999-031407 ...

Page 6

... Bootstrap Drive Current vs. Input Voltage 350 300 250 200 150 100 V = 12V 1. INPUT VOLTAGE (V) 6 MIC4685 Quiescent Current vs. Input Voltage 6.3 6.2 6.1 6 5 INPUT VOLTAGE (V) Minimum Duty Cycle vs. Input Voltage 12 ...

Page 7

... INPUT VOLTAGE (V) Feedback Voltage vs. Temperature 1.258 1.248 1.238 1.228 1.218 I = 10mA OUT V = 12V 1.208 1.8V OUT 1.198 -40 - 100120140 TEMPERATURE ( °C) March 2007 Enable Threshold vs. Temperature 1.20 1.18 Upper Threshold 1.16 1.14 1.12 Lower Threshold 1.10 1.08 1. 12V IN 1. OUT 1. 100mA OUT 1.00 TEMPERATURE ( °C) 7 MIC4685 M9999-031407 ...

Page 8

... Micrel, Inc. Typical Safe Operating Area (SOA) (SOA measured on the MIC4685 Evaluation Board*) 5V Output SOA Standard Configuration 5 25° 125° Max 3.5 3.0 2.5 2 60°C 1 125°C 1 Max 0.5 0 INPUT VOLTAGE (V) 1.8V Output SOA Standard Configuration 5 ...

Page 9

... Micrel, Inc. Functional Characteristics Frequency Foldback The MIC4685 folds the switching frequency back during a hard short circuit condition to reduce the energy per cycle and protect the device. March 2007 9 MIC4685 M9999-031407 ...

Page 10

... A lower feedback voltage increases the duty cycle. The MIC4685 uses a voltage- mode control architecture. Output Switching When the internal switch is ON, an increasing current fl ...

Page 11

... V ⎝ ⎠ REF V = 1.235V REF Thermal Considerations The MIC4685 is capable of high current due to the thermally optimized SPAK package. One limitation of the maximum output current on any MIC4685 design is the junction-to-ambient thermal resistance (θ the design (package and ground JA plane). Examining θ ...

Page 12

... March 2007 Bootstrap Diode The bootstrap diode provides an external bias source directly to the main pass element, this reduces V allowing the MIC4685 to be used in very low head-room applications i.e., 5V Bootstrap diode not for use if V Figure 2. close to pin 2 and pin 4, V ...

Page 13

... Vishay-Dale Schottky 595D476X0020D2T B330A 47µF, 20V 3A, 30V Vishay-Dale Schottky 595D476X0020D2T B330A 47µF, 20V 3A, 30V Vishay-Dale Schottky 595D476X0020D2T + Vishay B330A D2 MBRX120 1A/20V JP3 L1 U1 MIC4685_R 39µ 0.33µ 50V 0.1µF 50V GND B330A 4, Tab or SS33 OUT Figure 3 ...

Page 14

... Vishay-Dale Schottky 595D336X0035R2T B340A-E3 33µF, 35V 3A, 40V Vishay-Dale Schottky 595D336X0035R2T B340A-E3 33µF, 35V 3A, 40V Vishay-Dale Schottky 595D336X0035R2T + Vishay B340A-E3 D2*** B340 JP3 L1 U1 MIC4685_R 39µ 0.33µ 50V GND B340A 4, Tab 1 2 Figure 4. Evaluation Board Schematic Diagram ...

Page 15

... Micrel, Inc. Printed Circuit Board March 2007 Figure 5a. Top Layer Figure 5b. Bottom Layer 15 MIC4685 M9999-031407 ...

Page 16

... Schottky 3A 40V Schottky 3A 40V Schottky 3A 40V Schottky 3A 40V Schottky 3A 40V Schottky 1A 20V 39µH 3K01, 1%, 1/10W, 805 6K49, 1%, 1/10W, 805 2K94, 1%, 1/10W, 805 1K78, 1%, 1/10W, 805 976Ω, 1%, 1/10W, 805 3A 200kHz SPAK Buck Regulator M9999-031407 MIC4685 Qty ...

Page 17

... Purchaser’s use or sale of Micrel Products for use in life support appliances, devices or systems is a Purchaser’s own risk and Purchaser agrees to fully March 2007 7-SPAK (R) indemnify Micrel for any damages resulting from such use or sale. © 2004 Micrel, Incorporated. 17 MIC4685 M9999-031407 ...

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