MIC4685-5.0BR TR

MIC4685 3A SPAK SuperSwitcher™ Buck Regulator 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. 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 (D2PAKs) in many applications. 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. • • • • • • • • • • • 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 ___________________________________________________________________________________________________________ Typical Application V IN 8V to 30V MIC4685_R 2 5 CIN 33µF 35V IN EN BS 1 SW 6 FB 3 GND 4, Tab CBS 0.33µF/50V L1 39mH D1 3A 40V VOUT 1.8V/3A R1 3.01k R2 6.49k COUT 330µF 6.3V 1.8V Output 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 January 2010 1 M9999-012610 Micrel, Inc. MIC4685 Ordering Information Part Number Voltage Junction Temp. Range Package MIC4685WR Adj. –40° to +125°C 7-Pin SPAK MIC4685WR EV Adj. Standard RoHS Compliant* MIC4685BR Evaluation Board * RoHS compliant with ‘high-melting solder’ exemption. Pin Configuration 7 6 5 4 3 2 1 NC SW EN GND FB IN BS 7-Pin SPAK (R) Pin Description Pin Number Pin Name 1 BS Pin Function Bootstrap Voltage Node (External Component): Connect to external boost capacitor. 2 IN Supply (Input): Unregulated +4V to 30V supply voltage (34V transient) 3 FB Feedback (Input): Outback voltage feedback to regulator. Connect to 1.235V tap of resistive divider. 4, Tab GND 5 EN Enable (Input): Logic high = enable; logic low = shutdown 6 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. January 2010 Ground 2 M9999-012610 Micrel, Inc. Detailed Pin Description Switch (SW, Pin 6) 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 VSAT, of the main NPN pass element. The emitter is also 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 typically to a –0.5V. Ground (GND, Pin 4, Tab) 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 resistance between these reference points causes an offset voltage/IR drop proportional to load current and poor load regulation. This is why it’s important to keep the output grounds placed as close as possible to the switching regulator’s ground pin. To keep radiated EMI to a minimum, it is necessary to place the input capacitor ground lead as close as possible to the switching regulator’s ground pin. Input Voltage (VIN, Pin 2) The VIN pin is the collector of the main NPN pass element. This pin is also connected to the internal regulator. The output 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. January 2010 MIC4685 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 as an AC voltage. The bootstrap capacitor then couples the AC voltage back to the BS pin, plus the dc offset of VIN where it is rectified and used to provide additional drive to the main switch; in this case, a NPN transistor. This additional drive reduces the NPN’s saturation voltage and increases efficiency, from a VSAT of 1.8V, and 75% efficiency to a VSAT of 0.5V and 88% efficiency respectively. 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. See Tables 1 and 2 for recommended resistor values. 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 logiclow shuts down the regulator and reduces the stand-by quiescent input current to typically 150µA. The enable pin has an up-per 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. 3 M9999-012610 Micrel, Inc. MIC4685 Absolute Maximum Ratings(1) Operating Ratings(2) Supply Voltage (VIN) (1) .................................................+34V Enable Voltage (VEN)......................................... –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 EDS Rating(3) .................................................................. 2kV Supply Voltage (VIN) (4) ..................................... +4V to +30V Junction Temperature (TJ) ........................ –40°C to +125°C Package Thermal Resistance SPAK-7 (θJA) ...................................................11.8°C/W SPAK-7 (θJC).....................................................2.2°C/W Electrical Characteristics VIN = VEN = 12V; VOUT 5V; IOUT = 500mA; TA = 25°C, bold values indicate –40°C< TJ < +125°C, unless noted. Parameter Condition Min Typ Max Units (±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 MIC4685 [Adjustable] Feedback Voltage Feedback Bias Current 50 nA % Maximum Duty Cycle VFB = 1.0V 94 Output Leakage Current VIN = 30V, VEN = 0V, VSW = 0V 5 500 µA VIN = 30V, VEN = 0V, VSW = 1V 1.4 20 mA 6 12 mA Quiescent Current VFB = 1.5V Bootstrap Drive Current VFB = 1.5V, VSW = 0V 250 380 Bootstrap Voltage IBS = 10mA, VFB = 1.5V, VSW = 0V 5.5 6.2 Frequency Fold Back VFB = 0V 30 70 120 kHz 180 200 225 kHz Oscillator Frequency Saturation Voltage IOUT = 1A Short Circuit Current Limit VFB = 0V, See Test Circuit Shutdown Current VEN = 0V Enable Input Logic Level regulator on V 0.59 3.5 150 V 6 A 200 µA 2 V regulator off Enable Pin Input Current mA VEN = 0V (regulator off) 16 VEN = 0V (regulator on) –1 Thermal Shutdown @ TJ 0.8 V 50 µA –0.83 mA 160 °C Notes: 1. Exceeding the absolute maximum rating may damage the device. 2. The device is not guaranteed to function outside its operating rating. 3. Devices are ESD sensitive. Handling precautions recommended. Human body model, 1.5kΩ in series with 100pF. 4. 2.5V of headroom is required between VIN and VOUT. The headroom can be reduced by implementing a bootstrap diode as seen on the 5V to 3.3V circuit on page 1. January 2010 4 M9999-012610 Micrel, Inc. MIC4685 Test Circuit +12V 2 5 Device Under Test VIN SW EN BS 68µH 6 1 I FB GND 4, Tab 3 Current Limit Test Circuit Shutdown Input Behavior ON OFF 0.8V 0V 1.25V 2V 1.4V VIN(max) Enable Hysteresis January 2010 5 M9999-012610 Micrel, Inc. MIC4685 Typical Characteristics (TA = 25°C unless otherwise noted) EFFICIENCY (%) Efficiency vs. Output Current 100 VIN = 8V VIN = 12V 90 80 VIN = 30V 70 60 50 40 30 Standard 20 Configuration 10 VOUT = 5.0V 0 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 OUTPUT CURRENT (A) 90 EFFICIENCY (%) 80 Efficiency vs. Output Current VIN = 8V VIN = 24V 70 60 50 VIN = 30V 40 VIN = 12V 30 20 10 Standard Configuration VOUT = 1.8V 0 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 OUTPUT CURRENT (A) EFFICIENCY (%) 80 VIN = 5V VIN = 12V 70 60 50 VIN = 16V 40 30 20 Bootstrap Configuration VOUT = 1.8V 10 0 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 OUTPUT CURRENT (A) January 2010 Quiescent Current vs. Input Voltage 6.2 6.1 6 5.9 5.8 5.7 0 Bootstrap Drive Current vs. Input Voltage 12 300 VEN= 5V 5 10 15 20 25 30 35 40 INPUT VOLTAGE (V) Minimum Duty Cycle vs. Input Voltage 10 DUTY CYCLE (%) BOOTSTRAP CURRENT (mA) 350 6.3 INPUT CURRENT (mA) 90 Efficiency vs. Output Current 250 200 150 100 VIN = 12V VFB = 1.5V 50 0 0 2 4 6 8 10 12 14 16 18 20 INPUT VOLTAGE (V) 6 8 6 4 2 0 0 VOUT = 1.8V 5 10 15 20 25 INPUT VOLTAGE (V) 30 M9999-012610 Micrel, Inc. FEEDBACK VOLTAGE (V) 1.250 Feedback Voltage vs. Input Voltage 1.245 1.240 1.235 1.230 1.225 1.220 1.215 IOUT = 10mA VOUT = 1.8V 1.210 1.205 0 1.258 FEEDBACK VOLTAGE (V) MIC4685 5 10 15 20 25 INPUT VOLTAGE (V) 30 Feedback Voltage vs. Temperature 1.248 1.238 1.228 1.218 1.208 IOUT = 10mA VIN = 12V VOUT = 1.8V 1.20 1.18 1.16 1.14 1.12 1.10 1.08 1.06 1.04 1.02 1.00 Enable Threshold vs. Temperature Upper Threshold Lower Threshold VIN = 12V VOUT = 5V IOUT = 100mA -60 -40 -20 0 20 40 60 80 100 120 140 THRESHOLD TRIP POINTS 1.198 -40 -20 0 20 40 60 80 100120140 TEMPERATURE °C) ( TEMPERATURE °C) ( January 2010 7 M9999-012610 Micrel, Inc. MIC4685 Typical Safe Operating Area (SOA) OUTPUT CURRENT (A) OUTPUT CURRENT (A) (SOA measured on the MIC4685 Evaluation Board*) Typical 5V Output SOA Standard Configuration Typical 3.3V Output SOA Typical 2.5V Output SOA Typical 1.8V Output SOA Standard Configuration Typical 5.0V Output SOA Typical 3.3V Output SOA Typical 2.5V Output SOA Typical 1.8V Output SOA 5.0 T = 25°C 4.5 A TJ = 125°C 4.0 D = Max 3.5 3.0 2.5 2.0 TA = 60°C 1.5 TJ = 125°C 1.0 D = Max 0.5 0.0 0 5 10 15 20 25 30 35 INPUT VOLTAGE (V) 5.0 T = 25°C 4.5 A TJ = 125°C 4.0 D = Max 3.5 3.0 2.5 2.0 1.5 TA = 60°C 1.0 TJ = 125°C 0.5 D = Max 0.0 0 5 10 15 20 25 30 35 INPUT VOLTAGE (V) * IOUT