MIC4684 Micrel, Inc. MIC4684 2A High-Efficiency SuperSwitcher Buck Regulator General Description Features The MIC4684 is a high-efficiency 200kHz stepdown (buck) SO-8 package with 2A continuous output current switching regulator. Power conversion efficiency of above Over 85% efficiency 85% is easily obtainable for a wide variety of applications. Fixed 200kHz PWM operation The MIC4684 achieves 2A of continuous current in an 8-lead Wide 4V to 30V input voltage range SO (small outline) package at 60C ambient temperature. Output voltage adjustable to 1.235V All surface mount solution High efficiency is maintained over a wide output current range Internally compensated with fast transient response by utilizing a boost capacitor to increase the voltage available Over-current protection to saturate the internal power switch. As a result of this high Frequency foldback short-circuit protection efficiency, no external heat sink is required. The MIC4684, Thermal shutdown housed in an SO-8, can replace larger TO-220 and TO-263 packages in many applications. Applications The MIC4684 allows for a high degree of safety. It has a wide Simple high-efficiency step-down regulator input voltage range of 4V to 30V (34V transient), allowing 5V to 3.3V/1.7A converter (60C ambient) it to be used in applications where input voltage transients 12V to 1.8V/2A converter (60C ambient) may be present. Built-in safety features include over-current On-card switching regulator protection, frequency-foldback short-circuit protection, and Dual-output 5V converter thermal shutdown. Battery charger The MIC4684 is available in an 8-lead SO package with a junction temperature range of 40C to +125C. Ordering Information Part Number Voltage Junction Temp. Range Package Standard Pb-Free MIC4684BM MIC4684YM Adj -40C to +125C SOP-8 Typical Application V Efficiency IN MIC4684BM C BS 6.5V to 25V vs. Output Current 3 4 0.33F/50V VIN BS V 100 OUT V = 3.3V 2.5V/1.5A OUT 8 1 EN SW 68H R1 80 C IN 5 3.01k 330F FB 33F 6.3V R2 35V GND 60 V = 1.8V 3A OUT 3.01k V = 2.5V 2, 6, 7 OUT 40V 40 Adjustable Buck Converter 20 V = 5.0V IN 0 0 0.5 1 1.5 2 OUTPUT CURRENT (A) Efficiency vs. Output Current 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 Micrel, Inc. MIC4684 Pin Configuration SW 1 8 EN GND 2 7 GND VIN 3 6 GND BS 4 5 FB 8-Pin SOP (M) Pin Description Pin Number Pin Name Pin Function 1 SW Switch (Output): Emitter of NPN output switch. Connect to external storage inductor and Shottky diode. 2, 6, 7 GND Ground 3 IN Supply (Input): Unregulated +4V to 30V supply voltage (34V transient) 4 BS Booststrap Voltage Node (External Component): Connect to external boost capacitor. 5 FB Feedback (Input): Outback voltage feedback to regulator. Connect to output of supply for fixed versions. Connect to 1.23V tap of resistive divider for adjustable versions. 8 EN Enable (Input): Logic high = enable logic low = shutdown Bootstrap (BS, pin 4) Detailed Pin Description The bootstrap pin in conjunction with the external bootstrap Switch (SW, pin 1) capacitor provides a bias voltage higher than the input volt- The switch pin is tied to the emitter of the main internal NPN age to the MIC4684s main NPN pass element. The bootstrap transistor. This pin is biased up to the input voltage minus the capacitor sees the dv/dt of the switching action at the SW V of the main NPN pass element. The emitter is also driven SAT pin as an AC voltage. The bootstrap capacitor then couples negative when the output inductors magnetic field collapses the AC voltage back to the BS pin plus the dc offset of V IN at turn-off. During the OFF time the SW pin is clamped by where it is rectified and used to provide additional drive to the output schottky diode to a 0.5V typically. the main switch, in this case a NPN transistor. Ground (GND, pins 2,6,7) This additional drive reduces the NPNs saturation voltage and There are two main areas of concern when it comes to the increases efficiency, from a V of 1.8V, and 75% efficiency SAT ground pin, EMI and ground current. In a buck regulator to a V of 0.5V and 88% efficiency respectively. SAT or any other non-isolated switching regulator the output Feedback (FB, pin 5) capacitor(s) and diode(s) ground is referenced back to the The feedback pin is tied to the inverting side of a GM error switching regulators or controllers ground pin. Any resistance amplifier. The noninverting side is tied to a 1.235V bandgap between these reference points causes an offset voltage/IR reference. Fixed voltage versions have an internal voltage drop proportional to load current and poor load regulation. divider from the feedback pin. Adjustable versions require an This is why its important to keep the output grounds placed external resistor voltage divider from the output to ground, as close as possible to the switching regulators ground pin. with the center tied to the feedback pin. To keep radiated EMI to a minimum its necessary to place the input capacitor ground lead as close as possible to the Enable (EN, pin 8) switching regulators ground pin. The enable (EN) input is used to turn on the regulator and is Input Voltage (V , pin 3) TTL compatible. Note: connect the enable pin to the input if IN unused. A logic-high enables the regulator. A logic-low shuts The V pin is the collector of the main NPN pass element. IN down the regulator and reduces the stand-by quiescent This pin is also connected to the internal regulator. The output input current to typically 150A. The enable pin has an up- diode or clamping diode should have its cathode as close as per threshold of 2.0V minimum and lower threshold of 0.8V possible to this point to avoid voltage spikes adding to the maximum. The hysterisis provided by the upper and lower voltage across the collector. thresholds acts as an UVLO and prevents unwanted turn on of the regulator due to noise. January 2010 2 M9999-012610