MIC28304 70V 3A Power Module Hyper Speed ControlTM Family General Description Micrel's MIC28304 is synchronous step-down regulator module, featuring a unique adaptive ON-time control architecture. The module incorporates a DC/DC controller, power MOSFETs, bootstrap diode, bootstrap capacitor and an inductor in a single package. The MIC28304 operates over an input supply range from 4.5V to 70V and can be used to supply up to 3A of output current. The output voltage is adjustable down to 0.8V with a guaranteed accuracy of 1%. The device operates with programmable switching frequency from 200kHz to 600kHz. (R) Micrel's HyperLight Load architecture provides the same high-efficiency and ultra-fast transient response as the Hyper Speed ControlTM architecture under the medium to heavy loads, but also maintains high efficiency under light load conditions by transitioning to variable frequency, discontinuous-mode operation. The MIC28304 offers a full suite of protection features. These include undervoltage lockout, internal soft-start, foldback current limit, "hiccup" mode short-circuit protection, and thermal shutdown. Datasheets and support documentation are available on Micrel's web site at: www.micrel.com. Hyper Speed ControlTM Features * Easy to use - Stable with low-ESR ceramic output capacitor - No compensation and no inductor to choose * 4.5V to 70V input voltage * Single-supply operation * Power Good (PG) output * Low radiated emission (EMI) per EN55022, Class B * Adjustable current limit * Adjustable output voltage from 0.9V to 24V (also limited by duty cycle) * 200kHz to 600kHz, programmable switching frequency * Supports safe start-up into a pre-biased output * -40C to +125C junction temperature range * Available in 64-pin, 12mm x 12mm x 3mm QFN package Applications * Distributed power systems * Industrial, medical, telecom, and automotive Typical Application Hyper Speed Control and Any Capacitor are trademarks of Micrel, Inc. HyperLight Load is a registered 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 March 25, 2014 Revision 1.1 Micrel, Inc. MIC28304 Ordering Information Switching Frequency Features Package Junction Temperature Range Lead Finish MIC28304-1YMP 200kHz to 600kHz HyperLight Load 64-pin 12mm x 12mm QFN -40C to +125C Pb-Free MIC28304-2YMP 200kHz to 600kHz Hyper Speed Control 64-pin 12mm x 12mm QFN -40C to +125C Pb-Free Part Number Pin Configuration 64-Pin 12mm x 12mm QFN (MP) (Top View) Pin Description Pin Number Pin Name 1, 2, 3, 54, 64 GND Analog Ground. Ground for internal controller and feedback resistor network. The analog ground return path should be separate from the power ground (PGND) return path. 4 ILIM Current Limit Setting. Connect a resistor from SW (pin #4) to ILIM to set the over-current threshold for the converter. 5, 60 VIN Supply Voltage for Controller. The VIN operating voltage range is from 4.5V to 70V. A 0.47F ceramic capacitor from VIN (pin # 60) to AGND is required for decoupling. The pin # 5 should be externally connected to either PVIN or pin # 60 on PCB. SW Switch Node and Current-Sense Input. High current output driver return. The SW pin connects directly to the switch node. Due to the high-speed switching on this pin, the SW pin should be routed away from sensitive nodes. The SW pin also senses the current by monitoring the voltage across the low-side MOSFET during OFF time. 6, 40 to 48, 51 March 25, 2014 Pin Function 2 Revision 1.1 Micrel, Inc. MIC28304 Pin Description (Continued) Pin Number Pin Name 7, 8 FREQ Switching Frequency Adjust Input. Leaving this pin open will set the switching frequency to 600kHz. Alternatively a resistor from this pin to ground can be used to lower the switching frequency. 9 to 13 PGND Power Ground. PGND is the return path for the buck converter power stage. The PGND pin connects to the sources of low-side N-Channel external MOSFET, the negative terminals of input capacitors, and the negative terminals of output capacitors. The return path for the power ground should be as small as possible and separate from the analog ground (GND) return path. 14 to 22 PVIN Power Input Voltage. Connection to the drain of the internal high-side power MOSFET. 23 to 38 VOUT Output Voltage. Connection with the internal inductor, the output capacitor should be connected from this pin to PGND as close to the module as possible. 39 NC 49, 50 ANODE 52, 53 BSTC Bootstrap Capacitor. Connection to the internal bootstrap capacitor. Leave floating, no connect. 55, 56 BSTR Bootstrap Resistor. Connection to the internal bootstrap resistor and high-side power MOSFET drive circuitry. Leave floating, no connect. 57 FB 58 PGOOD 59 EN 61, 62 PVDD 63 NC March 25, 2014 Pin Function No Connection. Leave it floating. Anode Bootstrap Diode Input. Anode connection of internal bootstrap diode, this pin should be connected to the PVDD pin. Feedback Input. Input to the transconductance amplifier of the control loop. The FB pin is regulated to 0.8V. A resistor divider connecting the feedback to the output is used to set the desired output voltage. Power Good Output. Open drain output, an external pull-up resistor to external power rails is required. Enable Input. A logic signal to enable or disable the buck converter operation. The EN pin is CMOS compatible. Logic high enables the device, logic low shutdowns the regulator. In the disable mode, the input supply current for the device is minimized to 4A typically. Do not pull EN to PVDD. Internal +5V Linear Regulator Output. PVDD is the internal supply bus for the device. In the applications with VIN < +5.5V, PVDD should be tied to VIN to by-pass the linear regulator. No Connection. Leave it floating. 3 Revision 1.1 Micrel, Inc. MIC28304 Absolute Maximum Ratings(1) Operating Ratings(2) PVIN, VIN to PGND ...................................... -0.3V to +76V PVDD, VANODE to PGND .................................. -0.3V to +6V VSW , VFREQ, VILIM, VEN........................ -0.3V to (PVIN +0.3V) VBSTC/BSTR to VSW ................................................ -0.3V to 6V VBSTC/BSTR to PGND .......................................... -0.3V to 82V VFB, VPG to PGND ......................... -0.3V to (PVDD + 0.3V) PGND to AGND............................................ -0.3V to +0.3V Junction Temperature .............................................. +150C Storage Temperature (TS) ......................... -65C to +150C Lead Temperature (soldering, 10s) ............................ 260C (3) ESD Rating ................................................. ESD Sensitive Supply Voltage (PVIN, VIN) .............................. 4.5V to 70V Enable Input (VEN) ................................................. 0V to VIN VSW , VFEQ, VILIM, VEN .............................................. 0V to VIN Power Good (VPGOOD)............................... ... 0V to PVDD Junction Temperature (TJ) ........................ -40C to +125C Junction Thermal Resistance 12mm x 12mm QFN-64 (JA) ............................ 20C/W 12mm x 12mm QFN-64 (JC)............................... 5C/W Electrical Characteristics(4) PVIN = VIN = 12V, VOUT = 5V, VBST - VSW = 5V; TA = 25C, unless noted. Bold values indicate -40C TJ +125C. Parameter Condition Min. Typ. Max. Units 70 V Power Supply Input 4.5 Input Voltage Range (PVIN, VIN) Controller Supply Current (5) Operating Current Shutdown Supply Current Current into Pin 60; VFB = 1.5V (MIC28304-1) 0.4 0.75 Current into Pin 60;VFB = 1.5V (MIC28304-2) 2.1 3 Current into Pin 60;VEN = 0V 0.1 10 IOUT = 0A (MIC28304-1) 0.7 IOUT = 0A (MIC28304-2) 27 PVIN = VIN = 12V, VEN = 0V 4 mA A mA A (5) PVDD Supply PVDD Output Voltage VIN = 7V to 70V, IPVDD = 10mA 4.8 5.2 5.4 V PVDD UVLO Threshold PVDD rising 3.8 4.2 4.7 V PVDD UVLO Hysteresis Load Regulation 400 mV IPVDD = 0 to 40mA 0.6 2 3.6 TJ = 25C (1.0%) 0.792 0.8 0.808 -40C TJ 125C (2%) 0.784 0.8 0.816 5 500 % (5) Reference Feedback Reference Voltage FB Bias Current VFB = 0.8V V nA Notes: 1. Exceeding the absolute maximum ratings may damage the device. 2. The device is not guaranteed to function outside its operating ratings. 3. Devices are ESD sensitive. Handling precautions are recommended. Human body model, 1.5k in series with 100pF. 4. Specification for packaged product only. 5. IC tested prior to assembly. March 25, 2014 4 Revision 1.1 Micrel, Inc. MIC28304 Electrical Characteristics(4) (Continued) PVIN = VIN = 12V, VOUT = 5V, VBST - VSW = 5V; TA = 25C, unless noted. Bold values indicate -40C TJ +125C. Parameter Condition Min. Typ. Max. Units Enable Control 1.8 EN Logic Level High V 0.6 EN Logic Level Low EN Hysteresis 200 EN Bias Current VEN = 12V V mV 5 20 600 750 A Oscillator 400 FREQ pin = open Switching Frequency RFREQ = 100k (FREQ pin-to-GND) Maximum Duty Cycle Minimum Duty Cycle VFB > 0.8V Minimum Off-Time Soft-Start kHz 300 140 85 % 0 % 200 260 ns (5) Soft-Start Time Short-Circuit Protection 5 ms (5) Current-Limit Threshold (VCL) VFB = 0.79V -30 -14 0 mV Short-Circuit Threshold VFB = 0V -23 -7 9 mV Current-Limit Source Current VFB = 0.79V 60 80 100 A Short-Circuit Source Current VFB = 0V 27 36 47 A 50 A 95 %VOUT Leakage SW, BSTR Leakage Current (5) Power Good 85 Power Good Threshold Voltage Sweep VFB from low-to-high 90 Power Good Hysteresis Sweep VFB from high-to-low 6 %VOUT Power Good Delay Time Sweep VFB from low-to-high 100 s Power Good Low Voltage VFB < 90% x VNOM, IPG = 1mA 70 TJ Rising 160 C 4 C 200 mV Thermal Protection Overtemperature Shutdown Overtemperature Shutdown Hysteresis March 25, 2014 5 Revision 1.1 Micrel, Inc. MIC28304 Electrical Characteristics(4) (Continued) PVIN = VIN = 12V, VOUT = 5V, VBST - VSW = 5V; TA = 25C, unless noted. Bold values indicate -40C TJ +125C. Parameter Condition Min. Typ. Max. Units Output Characteristic Output Voltage Ripple IOUT = 3A Line Regulation Load Regulation Output Voltage Deviation from Load Step March 25, 2014 16 mV PVIN = VIN = 7V to 70V, IOUT = 3A 0.36 % IOUT = 0A to 3A PVIN= VIN =12V (MIC28304-1) 0.75 IOUT = 0A to 3A PVIN= VIN =12V (MIC28304-2) 0.05 IOUT from 0A to 3A at 5A/s (MIC28304-1) 400 IOUT from 3A to 0A at 5A/s (MIC28304-1) 500 mV IOUT from 0A to 3A at 5A/s (MIC28304-2) 400 IOUT from 3A to 0A at 5A/s (MIC28304-2) 500 6 % Revision 1.1 Micrel, Inc. MIC28304 Typical Characteristics - 275kHz Switching Frequency Efficiency vs. Output Current (MIC28304-1) Efficiency vs. Output Current (MIC28304-2) 100 Thermal Derating 3 100 VOUT = 5V FSW = 275kHz Tj_MAX =125C 12VIN 12VIN 24VIN 95 24VIN 90 85 80 75 36VIN 48VIN 70 65 LOAD CURRENT (A) EFFICIENCY (%) EFFICIENCY (%) 90 80 70 36VIN 48VIN 60 50 MIC28304-2 2 VIN = 12V 1 VIN = 24V VIN = 48V 60 40 VOUT = 5V FSW = 275kHz 55 50 0 0.5 1 1.5 2 2.5 VOUT = 5V FSW = 275kHz 0 25 30 3 0 OUTPUT CURRENT (A) 0.5 1 1.5 2 2.5 3 OUTPUT CURRENT (A) 40 55 70 85 100 115 MAXIMUM AMBIENT TEMPERATURE (C) Table 1. Recommended Component Values for 275kHz Switching Frequency VOUT VIN R3 (Rinj) 5V 7V to 18V 16.5k 5V 18V to 70V 39.2k 3.3V 5V to 18V 16.5k 3.3V 18V to 70V 39.2k March 25, 2014 R19 R15 75k 3.57k 75k 3.57k 75k 3.57k 75k 3.57k R1 (Top Feedback Resistor) R11 (Bottom Feedback Resistor) C10 (Cinj) C12 (Cff) COUT 10k 1.9k 0.1F 2.2nF 2x47F/6.3V 10k 1.9k 0.1F 2.2nF 2x 47F/6.3V 10k 3.24k 0.1F 2.2nF 2x 47F/6.3V 10k 3.24k 0.1F 2.2nF 2x 47F/6.3V 7 Revision 1.1 Micrel, Inc. MIC28304 Typical Characteristics Output Regulation vs. Input Voltage (MIC28304-1) VIN Operating Supply Current vs. Input Voltage (MIC28304-1) 5.0% 1.60 1.20 0.80 0.40 0.00 0.817 VOUT = 5.0V IOUT = 0A to 3A FSW = 600kHz 4.0% FEEDBACK VOLTAGE (V) VOUT = 5V IOUT = 0A FSW = 600kHz TOTAL REGULATION (%) 3.0% 2.0% 1.0% 0.0% -1.0% 5 10 15 20 25 30 35 40 45 50 55 60 65 70 0.797 VOUT = 5.0V IOUT = 0A FSW = 600kHz 5 10 15 20 25 30 35 40 45 50 55 60 65 70 INPUT VOLTAGE (V) Feedback Voltage vs. Temperature (MIC28304-1) VIN Operating Supply Current vs. Temperature (MIC28304-1) 2.00 5.08 0.808 VIN = 12V VOUT = 5.0V IOUT = 0A FSW = 600kHz 5.04 5.02 5.00 4.98 4.96 VOUT = 5V IOUT = 0A FSW = 600kHz SUPPLY CURRENT (mA) 5.06 OUTPUT VOLTAGE (V) 0.802 INPUT VOLTAGE (V) Output Voltage vs. Input Voltage (MIC28304-1) 4.92 0.807 0.792 INPUT VOLTAGE (V) 4.94 0.812 7 12 17 22 27 32 37 42 47 52 57 62 67 1.60 FEEBACK VOLTAGE (V) SUPPLY CURRENT (mA) 2.00 Feedback Voltage vs. Input Voltage (MIC28304-1) 1.20 0.80 0.40 0.804 0.800 VIN= 12V VOUT = 5.0V IOUT = 0A FSW = 600kHz 0.796 4.90 0.00 5 10 15 20 25 30 35 40 45 50 55 60 65 70 0.792 -50 -25 INPUT VOLTAGE (V) 25 50 75 100 125 -50 -25 TEMPERATURE (C) 1.2% 0 25 50 75 100 125 TEMPERATURE (C) Line Regulation vs. Temperature (MIC28304-1) Load Regulation vs. Temperature (MIC28304-1) Line Regulation vs. Temperature (MIC28304-1) 0.8% 0.7% 1.0% 0.8% 0.6% 0.4% 0.2% 0.6% 0.5% 0.4% 0.3% 0.2% 0.1% 0.0% -0.1% -0.2% VIN = 7V to 70V VOUT = 5.0V IOUT = 0A FSW = 600kHz -0.3% -0.4% -0.5% 0.0% LINE REGULATION (%) VIN = 12V VOUT = 5.0V IOUT = 0A to 3A FSW = 600kHz LINE REGULATION (%) LOAD REGULATION (%) 0 -0.6% -50 -25 0 25 50 75 TEMPERATURE (C) March 25, 2014 100 125 -50 -25 0 25 50 75 TEMPERATURE (C) 8 100 125 0.8% 0.7% 0.6% 0.5% 0.4% 0.3% 0.2% 0.1% 0.0% -0.1% -0.2% -0.3% -0.4% -0.5% -0.6% VIN = 7V to 70V VOUT = 5.0V IOUT = 3A FSW = 600kHz -50 -25 0 25 50 75 100 125 TEMPERATURE (C) Revision 1.1 Micrel, Inc. MIC28304 Typical Characteristics (Continued) 0.800 0.796 1.0% 100 0.5% 90 -0.5% VIN = 12V to 75V VOUT = 5.0V FSW = 600kHz -1.0% -1.5% -2.0% 0.5 1.0 1.5 2.0 2.5 3.0 0.0 OUTPUT CURRENT (A) 90 1.0 1.5 2.0 2.5 40 Efficiency (VIN = 38V) vs. Output Current (MIC28304-1) 90 5.0V 3.3V 2.5V 1.8V 70 60 1.2V 50 0.8V 40 80 30 1 10 5.0V FSW = 600kHz CCM 0.1 1 100 80 30 10 0.01 0.1 OUTPUT CURRENT (A) EFFICIENCY (%) 50 20 FSW = 600kHz CCM 10 0.01 3.0 90 5.0V 3.3V 2.5V 1.8V 1.2V 0.8V EFFICIENCY (%) EFFICIENCY (%) 0.5 100 60 40 Efficiency (VIN = 24V) vs. Output Current (MIC28304-1) 100 70 50 OUTPUT CURRENT (A) Efficiency (VIN = 18V) vs. Output Current (MIC28304-1) 80 60 20 -3.0% 0.0 70 30 -2.5% 0.792 5.0V 3.3V 2.5V 1.8V 1.2V 0.8V 80 0.0% EFFICIENCY (%) 0.804 LINE REGULATION (%) FEEDBACK VOLTAGE (V) 0.808 VIN = 12V VOUT = 5.0V FSW = 600kHz Efficiency (VIN = 12V) vs. Output Current (MIC28304-1) Line Regulation vs. Output Current (MIC28304-1) Feedback Voltage vs. Output Current (MIC28304-1) 60 1.8V 50 1.2V 40 0.8V 30 FSW = 600kHz CCM 20 10 0.01 10 70 3.3V 2.5V OUTPUT CURRENT (A) 0.1 1 FSW = 600kHz CCM 20 10 0.01 10 OUTPUT CURRENT (A) Efficiency (VIN = 48V) vs. Output Current (MIC28304-1) 0.1 1 10 OUTPUT CURRENT (A) Efficiency (VIN = 70V) vs. Output Current (MIC28304-1) Efficiency vs. Output Current (MIC28304-1) 100 100 100 90 90 95 80 90 5.0V 70 3.3V 60 2.5V 1.8V 50 1.2V 40 0.8V 30 70 5.0V 60 3.3V 2.5V 1.8V 1.2V 50 40 0.8V 30 FSW = 600kHz CCM 20 10 0.01 0.1 1 OUTPUT CURRENT (A) March 25, 2014 10 24VIN 36VIN 48VIN 70VIN 85 80 75 70 65 VOUT = 12V FSW = 600kHz CCM R3 = 23.2k 60 FSW = 600kHz CCM 20 10 0.01 EFFICIENCY (%) 80 EFFICIENCY (%) EFFICIENCY (%) 18VIN 0.1 1 OUTPUT CURRENT (A) 9 55 10 50 0.01 0.1 1 10 OUTPUT CURRENT (A) Revision 1.1 Micrel, Inc. MIC28304 Typical Characteristics (Continued) VIN Operating Supply Current vs. Input Voltage (MIC28304-2) 0.812 30 20 10 VOUT = 5V IOUT = 0A FSW = 600kHz 0.808 0.804 0.800 0.796 0.8% 0.6% 0.4% 0.2% 0.0% -0.2% VOUT = 5.0V IOUT = 0A TO 3A FSW = 600kHz -0.4% -0.6% -0.8% 0 0.792 5 10 15 20 25 30 35 40 45 50 55 60 65 70 -1.0% 7 12 17 22 27 32 37 42 47 52 57 62 67 INPUT VOLTAGE (V) 7 12 17 22 27 32 37 42 47 52 57 62 67 INPUT VOLTAGE (V) INPUT VOLTAGE (V) Output Peak Current Limit vs. Input Voltage PVDD Voltage vs. Input Voltage VIN Shutdown Current vs. Input Voltage 50 10 10 8 8 40 35 30 25 20 15 10 4 IPVDD = 40mA VOUT = 5.0V FSW = 600kHz 2 VEN = 0V R16 = OPEN FSW = 600kHz 5 IPVDD = 10mA 6 0 CURRENT LIMIT (A) 45 VDD VOLTAGE (V) 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 12 17 22 27 32 37 42 47 52 57 62 67 7 VIN Shutdown Current vs. Temperature 1.50 10 RISING 550 500 ENABLE THRESHOLD (V) 750 600 1.20 0.90 FALLING 0.60 0.30 450 FSW = 600kHz 0.00 400 7 12 17 22 27 32 37 42 47 52 57 62 67 INPUT VOLTAGE (V) March 25, 2014 12 17 22 27 32 37 42 47 52 57 62 67 INPUT VOLTAGE (V) Enable Threshold vs. Input Voltage 800 650 VOUT = 5.0V FSW = 600kHz INPUT VOLTAGE (V) Switching Frequency vs. Input Voltage 700 4 0 7 INPUT VOLTAGE (V) VOUT = 5.0V IOUT = 2A 6 2 SHUTDOWN CURRENT (A) SHUTDOWN CURRENT (A) 1.0% VOUT = 5.0V IOUT = 0A FSW = 600kHz OUTPUT REGULATION (%) 40 FEEDBACK VOLTAGE (V) SUPPLY CURRENT (mA) 50 SWITCHING FREQUENCY (kHz) Output Regulation vs. Input Voltage (MIC28304-2) Feedback Voltage vs. Input Voltage (MIC28304-2) 9 8 7 6 5 4 3 VIN = 12V VEN = 0V IOUT = 0A FSW = 600kHz 2 1 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 INPUT VOLTAGE (V) 10 -50 -25 0 25 50 75 100 125 TEMPERATURE (C) Revision 1.1 Micrel, Inc. MIC28304 Typical Characteristics (Continued) 4.3 4.5 IPVDD = 40mA 4.0 3.5 3.0 2.5 2.0 1.5 VIN = 12V IOUT = 0A FSW = 600kHz 1.0 0.5 VDD THRESHOLD (V) 5.0 RISING 4.2 4.1 4.0 3.9 FALLING 3.8 3.7 3.6 3.4 0.0 3.3 -50 -25 0 25 50 75 100 125 -25 0 25 50 75 100 -50 -25 0 25 50 75 100 TEMPERATURE (C) TEMPERATURE (C) EN Bias Current vs. Temperature Enable Threshold vs. Temperature VIN Operating Supply Current vs. Temperature (MIC28304-2) ENABLE THRESHOLD (V) VIN = 12V VEN = 0V FSW = 600kHz 60 40 20 0 RISING 1.3 VIN = 12V VOUT = 5V FSW = 600kHz 36 1.2 1.1 1.0 FALLING 0.9 0.8 0.7 25 50 75 100 125 -25 0 25 50 75 100 125 0.804 0.800 VIN = 12V VOUT = 5.0V IOUT = 0A FSW = 600kHz March 25, 2014 -25 100 0 25 50 75 100 125 Line Regulation vs. Temperature (MIC28304-2) 1.00% VIN = 12V VOUT = 5.0V IOUT = 0A TO 3A FSW = 600kHz 0.3% 0.2% 0.1% 0.0% -0.1% VIN = 7V TO 70V VOUT = 5.0V IOUT = 0A FSW = 600kHz 0.50% 0.00% -0.50% -1.00% -0.3% TEMPERATURE (C) 8 -0.2% 0.792 75 VIN = 12V VOUT = 5.0V IOUT = 0A FSW = 600kHz 12 TEMPERATURE (C) LINE REGULATION (%) LOAD REGULATION (%) 0.808 50 16 -50 0.4% 25 20 Load Regulation vs. Temperature (MIC28304-2) 0.812 0 24 TEMPERATURE (C) Feedback Voltage vs. Temperature (MIC28304-2) -25 28 0 -50 TEMPERATURE (C) 0.796 32 4 0.5 0 125 40 1.4 0.6 FEEBACK VOLTAGE (V) VIN = 12V VOUT = 5.0V FSW = 600kHz TEMPERATURE (C) 80 -50 4 125 1.5 -25 6 0 -50 100 -50 8 2 VIN = 12V IOUT = 0A FSW = 600kHz 3.5 SUPPLY CURRENT (mA) PVDD VOLTAGE (V) 10 4.4 IPVDD = 10mA 5.5 CURRENT LIMIT (A) 6.0 EN BIAS CURRENT (A) Output Peak Current Limit vs. Temperature PVDD UVLO Threshold vs. Temperature PVDD Voltage vs. Temperature 125 -50 -25 0 25 50 75 TEMPERATURE (C) 11 100 125 -50 -25 0 25 50 75 100 125 TEMPERATURE (C) Revision 1.1 Micrel, Inc. MIC28304 Typical Characteristics (Continued) Switching Frequency vs. Temperature (MIC28304-2) Line Regulation vs. Temperature (MIC28304-2) 700 0.5% 0.0% VIN = 7V TO 70V VOUT = 5.0V IOUT = 3A FSW = 600kHz -0.5% -1.0% -50 -25 0 25 50 75 100 0.808 650 FEEDBACK VOLTAGE (V) SWITCHING FREQUENCY (kHz) 1.0% LINE REGULATION (%) Feedback Voltage vs. Output Current (MIC28304-2) 600 550 500 450 VIN = 12V VOUT = 5V IOUT = 0A 400 350 300 250 0.800 VIN = 12V VOUT = 5.0V FSW = 600kHz 0.796 200 150 100 125 0.804 0.792 -50 -25 TEMPERATURE (C) 0 25 50 75 100 0.0 125 0.4% 0.2% 0.2% 0.1% VIN = 12V to 70V VOUT = 5.0V FSW = 600kHz 80 2.5V 1.8V 70 1.2V 60 0.8V 50 1.0 1.5 2.0 2.5 3.0 0.5 1 1.5 2 2.5 3 3.5 0.8V 50 4 0 0.5 50 2 2.5 3 3.5 4 Efficiency (VIN = 48V) vs. Output Current (MIC28304-2) FSW = 600kHz 90 5.0V 80 EFFICIENCY (%) 0.8V 1.5 100 90 5.0V 3.3V 2.5V 1.8V 1.2V 1 OUTPUT CURRENT (A) 100 EFFICIENCY (%) EFFICIENCY (%) 1.2V 60 Efficiency (VIN = 38V) vs. Output Current (MIC28304-2) FSW = 600kHz 60 1.8V OUTPUT CURRENT (A) 100 70 2.5V 70 30 0 Efficiency (VIN = 24V) vs. Output Current (MIC28304-2) 80 3.3V 40 OUTPUT CURRENT (A) 90 5.0V 80 FSW = 600kHz 30 0.5 3.0 FSW = 600kHz 40 0.0% 0.0 2.5 90 3.3V EFFICIENCY (%) EFFICIENCY (%) LINE REGULATION (%) 90 0.3% 2.0 100 5.0V 0.3% 1.5 Efficiency (VIN = 18V) vs. Output Current (MIC28304-2) 100 0.4% 1.0 OUTPUT CURRENT (A) Efficiency (VIN =12V) vs. Output Current (MIC28304-2) Line Regulation vs. Output Current (MIC28304-2) 0.1% 0.5 TEMPERATURE (C) 3.3V 70 2.5V 1.8V 60 1.2V 0.8V 50 FSW = 600kHz 80 5.0V 70 3.3V 2.5V 60 1.8V 1.2V 50 0.8V 40 40 30 40 30 0 0.5 1 1.5 2 2.5 3 OUTPUT CURRENT (A) March 25, 2014 3.5 4 30 0 0.5 1 1.5 2 2.5 3 OUTPUT CURRENT (A) 12 3.5 4 0 0.5 1 1.5 2 2.5 3 3.5 4 OUTPUT CURRENT (A) Revision 1.1 Micrel, Inc. MIC28304 Typical Characteristics (Continued) Efficiency (VIN = 70V) vs. Output Current (MIC28304-2) 140 DIE TEMPERATURE (C) FSW = 600kHz 80 70 5.0V 3.3V 2.5V 1.8V 1.2V 0.8V 60 50 40 120 100 80 60 40 30 0.5 1 1.5 2 2.5 3 3.5 4 0.5 1.5 2.0 2.5 3.0 0.0 80 60 VIN = 70V VOUT = 5.0V FSW = 600kHz 20 VOUT = 5V IOUT = 2A 500 VIN =48V 400 300 200 100 1.0 1.5 2.0 2.5 3.0 100.00 1000.00 IC POWER DISSIPATION (W) VOUT = 5V, 3.3V, 2.5V, 1.8V, 1.2V, 0.8V 2.5 2 VOUT = 5V 1 VOUT = 0.8V OUTPUT CURRENT (A) 1 VOUT = 5V 0.5 0 1 3 2 3 IC Power Dissipation vs. Output Current (MIC28304-2) 9 VIN = 48V FSW = 600kHz 5 VOUT = 5V, 3.3V, 2.5V, 1.8V, 1.2V, 0.8V 4 3 VOUT = 5V 2 1 0 8 VIN = 70V FSW = 600kHz 7 VOUT = 5V, 3.3V, 2.5V, 1.8V, 1.2V, 0.8V 6 5 VOUT = 5V 4 3 2 VOUT = 0.8V 1 0 0 0 2 1.5 OUTPUT CURRENT (A) VOUT = 0.8V 1 VOUT = 5V, 3.3V, 2.5V, 1.8V, 1.2V, 0.8V 10000.00 6 0 VIN = 12V FSW = 600kHz IC Power Dissipation vs. Output Current (MIC28304-2) VIN = 24V FSW = 600kHz 3.0 2 R19 (k Ohm) 3.5 2.5 0 OUTPUT CURRENT (A) IC Power Dissipation vs. Output Current (MIC28304-2) 2.0 VOUT = 0.8V 0 10.00 0 1.5 2.5 VIN = 12V 600 100 1.0 IC Power Dissipation vs. Output Current (MIC28304-2) IC POWER DISSIPATION (W) 700 120 0.5 0.5 OUTPUT CURRENT (A) Switching Frequency SW FREQ (kHz) DIE TEMPERATURE (C) 1.0 800 0.0 VIN = 48V VOUT = 5.0V FSW = 600kHz 40 OUTPUT CURRENT (A) 140 40 60 0 0.0 Die Temperature* (VIN = 70V) vs. Output Current (MIC28304-2) 0.5 80 20 OUTPUT CURRENT (A) 1.5 100 0 0 3 120 20 IC POWER DISSIPATION (W) EFFICIENCY (%) 90 140 VIN = 12V VOUT = 5.0V FSW = 600kHz DIE TEMPERATURE (C) 100 IC POWER DISSIPATION (W) Die Temperature* (VIN = 48V) vs. Output Current (MIC28304-2) Die Temperature* (VIN = 12V) vs. Output Current (MIC28304-2) 1 2 OUTPUT CURRENT (A) 3 0 1 2 3 OUTPUT CURRENT (A) * Case Temperature: The temperature measurement was taken at the hottest point on the MIC28304 case mounted on a 5 square inch PCB (see Thermal Measurement section). Actual results will depend upon the size of the PCB, ambient temperature and proximity to other heat-emitting components. March 25, 2014 13 Revision 1.1 Micrel, Inc. MIC28304 Typical Characteristics (Continued) Thermal Derating Thermal Derating Thermal Derating 3 3 3 VIN = 12V VIN = 12V VIN = 18V 2 VIN = 48V VIN = 24V 1 VOUT = 5V FSW = 600kHz MIC28304-2 Tj_MAX = 125C LOAD CURRENT (A) LOAD CURRENT (A) LOAD CURRENT (A) VIN = 12V VIN = 18V 2 VIN = 48V VIN = 24V 1 VOUT = 3.3V FSW = 600kHz MIC28304-2 Tj_MAX = 125C 25 40 55 70 85 25 100 VIN =18V VIN = 48V MAXIMUM AMBIENT TEMPERATURE (C) 1 VOUT = 2.5V FSW = 600kHz MIC28304-2 Tj_MAX = 125C 40 55 70 85 25 100 Thermal Derating 40 70 85 100 Thermal Derating Thermal Derating 3 3 VIN = 12V VIN = 12V 55 MAXIMUM AMBIENT TEMPERATURE (C) MAXIMUM AMBIENT TEMPERATURE (C) 3 VIN = 24V 0 0 0 2 VIN = 12V VIN =18V VIN = 24V VIN = 48V 1 VOUT = 1.8V FSW = 600kHz MIC28304-2 Tj_MAX =125C 0 VIN =18V 2 VIN =18V VIN = 48V 1 VOUT = 1.2V FSW = 600kHz MIC28304-2 Tj_MAX =125C 0 40 55 70 85 100 25 MAXIMUM AMBIENT TEMPERATURE (C) Thermal Derating 3 VOUT = 12V FSW = 600kHz MIC28304-2 R3 = 23.2k Tj_MAX =125C IC POWER DISSIPATION (W) 18VIN VIN = 24V 48VIN VIN = 48V 0 25 40 55 70 85 MAXIMUM AMBIENT TEMPERATURE (C) March 25, 2014 55 70 85 100 2 VIN = 24V VIN = 48V 1 VOUT = 0.8V FSW = 600kHz MIC28304-2 Tj_MAX =125C 0 100 40 25 55 70 85 100 MAXIMUM AMBIENT TEMPERATURE (C) MAXIMUM AMBIENT TEMPERATURE (C) IC Power Dissipation vs. Output Current (MIC28304-2) Efficiency vs. Output Current (MIC28304-2) 9 2 1 40 100 VOUT = 12V R3 = 23.2k FSW = 600kHz 8 7 95 85 18VIN 24VIN 36VIN 80 48VIN 75 70VIN 90 70VIN 48VIN 36VIN 24VIN 18VIN 6 5 EFFICIENCY (%) 25 LOAD CURRENT (A) LOAD CURRENT (A) 2 LOAD CURRENT (A) LOAD CURRENT (A) VIN = 24V 4 3 70 60 1 55 0 VOUT = 12V FSW = 600kHz R3 = 23.2k 65 2 50 0 1 2 3 OUTPUT CURRENT (A) 14 4 0 0.6 1.2 1.8 2.4 3 3.6 OUTPUT CURRENT (A) Revision 1.1 Micrel, Inc. MIC28304 Functional Characteristics - 600kHz Switching Frequency March 25, 2014 15 Revision 1.1 Micrel, Inc. MIC28304 Functional Characteristics - 600kHz Switching Frequency (Continued) March 25, 2014 16 Revision 1.1 Micrel, Inc. MIC28304 Functional Characteristics - 600kHz Switching Frequency (Continued) March 25, 2014 17 Revision 1.1 Micrel, Inc. MIC28304 Functional Characteristics - 600kHz Switching Frequency (Continued) March 25, 2014 18 Revision 1.1 Micrel, Inc. MIC28304 Functional Characteristics - 600kHz Switching Frequency (Continued) March 25, 2014 19 Revision 1.1 Micrel, Inc. MIC28304 Functional Characteristics March 25, 2014 20 Revision 1.1 Micrel, Inc. MIC28304 Functional Diagram March 25, 2014 21 Revision 1.1 Micrel, Inc. MIC28304 Functional Description The maximum duty cycle is obtained from the 200ns tOFF(MIN): The MIC28304 is an adaptive on-time synchronous buck regulator module built for high-input voltage to low-output voltage conversion applications. The MIC28304 is designed to operate over a wide input voltage range, from 4.5V to 70V, and the output is adjustable with an external resistor divider. An adaptive on-time control scheme is employed to obtain a constant switching frequency and to simplify the control compensation. Hiccup mode over-current protection is implemented by sensing low-side MOSFET's RDS(ON). The device features internal soft-start, enable, UVLO, and thermal shutdown. The module has integrated switching FETs, inductor, bootstrap diode, resistor and capacitor. DMAX = VOUT VIN x fSW tS = 1/fSW . It is not recommended to use MIC28304 with an OFF-time close to tOFF(MIN) during steady-state operation. The adaptive ON-time control scheme results in a constant switching frequency in the MIC28304. The actual ON-time and resulting switching frequency will vary with the different rising and falling times of the external MOSFETs. Also, the minimum tON results in a lower switching frequency in high VIN to VOUT applications. During load transients, the switching frequency is changed due to the varying OFF-time. To illustrate the control loop operation, we will analyze both the steady-state and load transient scenarios. For easy analysis, the gain of the gm amplifier is assumed to be 1. With this assumption, the inverting input of the error comparator is the same as the feedback voltage. Eq. 1 Figure 1 shows the MIC28304 control loop timing during steady-state operation. During steady-state, the gm amplifier senses the feedback voltage ripple, which is proportional to the output voltage ripple plus injected voltage ripple, to trigger the ON-time period. The ON-time is predetermined by the tON estimator. The termination of the OFF-time is controlled by the feedback voltage. At the valley of the feedback voltage ripple, which occurs when VFB falls below VREF, the OFF period ends and the next ON-time period is triggered through the control logic circuitry. where VOUT is the output voltage, VIN is the power stage input voltage, and fSW is the switching frequency. At the end of the ON-time period, the internal high-side driver turns off the high-side MOSFET and the low-side driver turns on the low-side MOSFET. The OFF-time period length depends upon the feedback voltage in most cases. When the feedback voltage decreases and the output of the gm amplifier is below 0.8V, the ON-time period is triggered and the OFF-time period ends. If the OFF-time period determined by the feedback voltage is less than the minimum OFF-time tOFF(MIN), which is about 200ns, the MIC28304 control logic will apply the tOFF(MIN) instead. tOFF(MIN) is required to maintain enough energy in the boost capacitor (CBST) to drive the high-side MOSFET. March 25, 2014 Eq. 2 Where: Theory of Operation Per the Functional Diagram of the MIC28304 module, the output voltage is sensed by the MIC28304 feedback pin FB via the voltage divider R1 and R11, and compared to a 0.8V reference voltage VREF at the error comparator through a low-gain transconductance (gm) amplifier. If the feedback voltage decreases and the amplifier output is below 0.8V, then the error comparator will trigger the control logic and generate an ON-time period. The ONtime period length is predetermined by the "Fixed tON Estimator" circuitry: t ON(ESTIMATED) = t S - t OFF(MIN) 200ns = 1- tS tS 22 Revision 1.1 Micrel, Inc. MIC28304 Unlike true current-mode control, the MIC28304 uses the output voltage ripple to trigger an ON-time period. The output voltage ripple is proportional to the inductor current ripple if the ESR of the output capacitor is large enough. In order to meet the stability requirements, the MIC28304 feedback voltage ripple should be in phase with the inductor current ripple and are large enough to be sensed by the gm amplifier and the error comparator. The recommended feedback voltage ripple is 20mV~100mV over full input voltage range. If a low ESR output capacitor is selected, then the feedback voltage ripple may be too small to be sensed by the gm amplifier and the error comparator. Also, the output voltage ripple and the feedback voltage ripple are not necessarily in phase with the inductor current ripple if the ESR of the output capacitor is very low. In these cases, ripple injection is required to ensure proper operation. Please refer to "Ripple Injection" subsection in Application Information for more details about the ripple injection technique. Figure 1. MIC28304 Control Loop Timing Figure 2 shows the operation of the MIC28304 during a load transient. The output voltage drops due to the sudden load increase, which causes the VFB to be less than VREF. This will cause the error comparator to trigger an ON-time period. At the end of the ON-time period, a minimum OFF-time tOFF(MIN) is generated to charge the bootstrap capacitor (CBST) since the feedback voltage is still below VREF. Then, the next ON-time period is triggered due to the low feedback voltage. Therefore, the switching frequency changes during the load transient, but returns to the nominal fixed frequency once the output has stabilized at the new load current level. With the varying duty cycle and switching frequency, the output recovery time is fast and the output voltage deviation is small. Discontinuous Mode (MIC28304-1 only) In continuous mode, the inductor current is always greater than zero; however, at light loads, the MIC283041 is able to force the inductor current to operate in discontinuous mode. Discontinuous mode is where the inductor current falls to zero, as indicated by trace (IL) shown in Figure 3. During this period, the efficiency is optimized by shutting down all the non-essential circuits and minimizing the supply current. The MIC28304-1 wakes up and turns on the high-side MOSFET when the feedback voltage VFB drops below 0.8V. The MIC28304-1 has a zero crossing comparator (ZC) that monitors the inductor current by sensing the voltage drop across the low-side MOSFET during its ON-time. If the VFB > 0.8V and the inductor current goes slightly negative, then the MIC28304-1 automatically powers down most of the IC circuitry and goes into a low-power mode. Once the MIC28304-1 goes into discontinuous mode, both DL and DH are low, which turns off the high-side and low-side MOSFETs. The load current is supplied by the output capacitors and VOUT drops. If the drop of VOUT causes VFB to go below VREF, then all the circuits will wake up into normal continuous mode. First, the bias currents of most circuits reduced during the discontinuous mode are restored, and then a tON pulse is triggered before the drivers are turned on to avoid any possible glitches. Finally, the high-side driver is turned on. Figure 3 shows the control loop timing in discontinuous mode. Figure 2. MIC28304 Load Transient Response March 25, 2014 23 Revision 1.1 Micrel, Inc. MIC28304 Figure 4. MIC28304 Current-Limiting Circuit In each switching cycle of the MIC28304, the inductor current is sensed by monitoring the low-side MOSFET in the OFF period. The sensed voltage V(ILIM) is compared with the power ground (PGND) after a blanking time of 150ns. In this way the drop voltage over the resistor R15 (VCL) is compared with the drop over the bottom FET generating the short current limit. The small capacitor (C6) connected from ILIM pin to PGND filters the switching node ringing during the off-time allowing a better short limit measurement. The time constant created by R15 and C6 should be much less than the minimum off time. Figure 3. MIC28302-1 Control Loop Timing (Discontinuous Mode) During discontinuous mode, the bias current of most circuits is substantially reduced. As a result, the total power supply current during discontinuous mode is only about 400A, allowing the MIC28304-1 to achieve high efficiency in light load applications. Soft-Start Soft-start reduces the input power supply surge current at startup by controlling the output voltage rise time. The input surge appears while the output capacitor is charged up. A slower output rise time will draw a lower input surge current. The VCL drop allows programming of short limit through the value of the resistor (R15), If the absolute value of the voltage drop on the bottom FET is greater than VCL. In that case the V(ILIM) is lower than PGND and a short circuit event is triggered. A hiccup cycle to treat the short event is generated. The hiccup sequence including the soft start reduces the stress on the switching FETs and protects the load and supply for severe short conditions. The MIC28304 implements an internal digital soft-start by making the 0.8V reference voltage VREF ramp from 0 to 100% in about 5ms with 9.7mV steps. Therefore, the output voltage is controlled to increase slowly by a staircase VFB ramp. Once the soft-start cycle ends, the related circuitry is disabled to reduce current consumption. PVDD must be powered up at the same time or after VIN to make the soft-start function correctly. Current Limit The MIC28304 uses the RDS(ON) of the low side MOSEFET and external resistor connected from ILIM pin to SW node to decide the current limit. March 25, 2014 24 Revision 1.1 Micrel, Inc. MIC28304 The short-circuit current limit can be programmed by using Equation 3. R15 = The MOSFET RDS(ON) varies 30% to 40% with temperature; therefore, it is recommended to add a 50% margin to ICLIM in Equation 3 to avoid false current limiting due to increased MOSFET junction temperature rise. Table 2 shows typical output current limit value for a given R15 with C6 = 10pF. (ICLIM - DIL (PP) x 0.5) x R DS(ON) + VCL ICL Table 2. Typical Output Current-Limit Value Eq. 3 Where: R15 Typical Output Current Limit 1.81k 3A 2.7k 6.3A ICLIM = Desired current limit RDS(ON) = On-resistance of low-side power MOSFET, 57m typically VCL = Current-limit threshold (typical absolute value is (4) 14mV per the Electrical Characteristics ) ICL = Current-limit source current (typical value is 80A, per the Electrical Characteristics table). IL(PP) = Inductor current peak-to-peak, since the inductor is integrated use Equation 4 to calculate the inductor ripple current. The peak-to-peak inductor current ripple is: IL(PP) = VOUT x (VIN(max) - VOUT ) VIN(max) x fsw x L Eq. 4 The MIC28304 has 4.7H inductor integrated into the module. The typical value of RWINDING(DCR) of this particular inductor is in the range of 45m. In case of hard short, the short limit is folded down to allow an indefinite hard short on the output without any destructive effect. It is mandatory to make sure that the inductor current used to charge the output capacitance during soft start is under the folded short limit; otherwise the supply will go in hiccup mode and may not be finishing the soft start successfully. March 25, 2014 25 Revision 1.1 Micrel, Inc. MIC28304 Application Information Simplified Input Transient Circuitry The 76V absolute maximum rating of MIC28304 allows simplifying the transient voltage suppressor on the input supply side which is very common in industrial applications. The input supply voltage VIN Figure 5 may be operating at 12V input rail most of the time, but can encounter noise spike of 60V for a short duration. By using MIC28304, which has 76V absolute maximum voltage rating, the input transient suppressor is not needed. Which saves on component count, form factor, and ultimately the system becomes less expensive. Equation 5 gives the estimated switching frequency: fS _ ADJ = fO x R19 R19 + 100k Eq. 5 Where: fO = Switching frequency when R19 is open For more precise setting, it is recommended to use Figure 7: Switching Frequency 800 700 VOUT = 5V IOUT = 2A VIN = 12V 600 SW FREQ (kHz) Figure 5. Simplified Input Transient Circuitry Setting the Switching Frequency The MIC28304 switching frequency can be adjusted by changing the value of resistor R19. The top resistor of 100k is internal to module and is connected between VIN and FREQ pin, so the value of R19 sets the switching frequency. The switching frequency also depends upon VIN, VOUT and load conditions. 500 VIN =48V 400 300 200 100 0 10.00 100.00 1000.00 10000.00 R19 (k Ohm) Figure 7. Switching Frequency vs. R19 Output Capacitor Selection The type of the output capacitor is usually determined by the application and its equivalent series resistance (ESR). Voltage and RMS current capability are two other important factors for selecting the output capacitor. Recommended capacitor types are MLCC, tantalum, lowESR aluminum electrolytic, OS-CON and POSCAP. The output capacitor's ESR is usually the main cause of the output ripple. The MIC28304 requires ripple injection and the output capacitor ESR effects the control loop from a stability point of view. Figure 6. Switching Frequency Adjustment March 25, 2014 26 Revision 1.1 Micrel, Inc. MIC28304 The maximum value of ESR is calculated as in Equation 6: ESR COUT The output capacitor RMS current is calculated in Equation 8: VOUT(pp) IL(PP) ICOUT (RMS) = Eq. 6 Where: IL(PP) 12 Eq. 8 The power dissipated in the output capacitor is: VOUT(pp) = Peak-to-peak output voltage ripple IL(PP) = Peak-to-peak inductor current ripple 2 PDISS(COUT ) = ICOUT (RMS) x ESR COUT Input Capacitor Selection The input capacitor for the power stage input PVIN should be selected for ripple current rating and voltage rating. Tantalum input capacitors may fail when subjected to high inrush currents, caused by turning the input supply on. A tantalum input capacitor's voltage rating should be at least two times the maximum input voltage to maximize reliability. Aluminum electrolytic, OS-CON, and multilayer polymer film capacitors can handle the higher inrush currents without voltage de-rating. The input voltage ripple will primarily depend on the input capacitor's ESR. The peak input current is equal to the peak inductor current, so: The total output ripple is a combination of the ESR and output capacitance. The total ripple is calculated in Equation 7: 2 IL(PP) + IL(PP) x ESR C VOUT(pp) = OUT C OUT x f SW x 8 ( Eq. 9 )2 Eq. 7 Where: D = Duty cycle VIN = IL(pk) x ESRCIN COUT = Output capacitance value Eq. 10 fsw = Switching frequency The input capacitor must be rated for the input current ripple. The RMS value of input capacitor current is determined at the maximum output current. Assuming the peak-to-peak inductor current ripple is low: As described in the "Theory of Operation" subsection in Functional Description, the MIC28304 requires at least 20mV peak-to-peak ripple at the FB pin to make the gm amplifier and the error comparator behave properly. Also, the output voltage ripple should be in phase with the inductor current. Therefore, the output voltage ripple caused by the output capacitors value should be much smaller than the ripple caused by the output capacitor ESR. If low-ESR capacitors, such as ceramic capacitors, are selected as the output capacitors, a ripple injection method should be applied to provide enough feedback voltage ripple. Please refer to the "Ripple Injection" subsection for more details. ICIN(RMS) IOUT(max) x D x (1 - D) The power dissipated in the input capacitor is: 2 PDISS(CIN) = ICIN(RMS) x ESRCIN The voltage rating of the capacitor should be twice the output voltage for a tantalum and 20% greater for aluminum electrolytic or OS-CON. March 25, 2014 Eq.11 Eq. 12 The general rule is to pick the capacitor with a ripple current rating equal to or greater than the calculated worst (VIN_MAX) case RMS capacitor current. Its voltage rating should be 20% to 50% higher than the maximum input voltage. Typically the input ripple (dV) needs to be kept down to less than 10% of input voltage. The ESR also increases the input ripple. 27 Revision 1.1 Micrel, Inc. MIC28304 Ripple Injection The VFB ripple required for proper operation of the MIC28304 gM amplifier and error comparator is 20mV to 100mV. However, the output voltage ripple is generally designed as 1% to 2% of the output voltage. For a low output voltage, such as a 1V, the output voltage ripple is only 10mV to 20mV, and the feedback voltage ripple is less than 20mV. If the feedback voltage ripple is so small that the gM amplifier and error comparator cannot sense it, then the MIC28304 will lose control and the output voltage is not regulated. In order to have some amount of VFB ripple, a ripple injection method is applied for low output voltage ripple applications. The table 2 summarizes the ripple injection component values for ceramic output capacitor. Equation 13 should be used to calculate the input capacitor. Also it is recommended to keep some margin on the calculated value: CIN IOUT(max) x (1 - D) FSW x dV Eq. 13 Where: dV = The input ripple and FSW is the switching frequency Output Voltage Setting Components The MIC28304 requires two resistors to set the output voltage as shown in Figure 8: The applications are divided into three situations according to the amount of the feedback voltage ripple: 1. Enough ripple at the feedback voltage due to the large ESR of the output capacitors (Figure 9): Figure 8. Voltage-Divider Configuration Figure 9. Enough Ripple at FB The output voltage is determined by Equation 14: VOUT R1 = VFB x 1 + 11 R As shown in Figure 10, the converter is stable without any ripple injection. Eq. 14 Where: VFB = 0.8V A typical value of R1 used on the standard evaluation board is 10k. If R1 is too large, it may allow noise to be introduced into the voltage feedback loop. If R1 is too small in value, it will decrease the efficiency of the power supply, especially at light loads. Once R1 is selected, R11 can be calculated using Equation 15: R11 = VFB x R1 VOUT - VFB March 25, 2014 Figure 10. Inadequate Ripple at FB Eq. 15 28 Revision 1.1 Micrel, Inc. MIC28304 VIN = Power stage input voltage The feedback voltage ripple is: D = Duty cycle VFB(PP) = R11 x ESR COUT x I L(PP) R1 + R11 fSW = Switching frequency Eq. 16 = (R1//R11//Rinj) x Cff Where: In Equations 18 and 19, it is assumed that the time constant associated with Cff must be much greater than the switching period: IL(PP) = The peak-to-peak value of the inductor current ripple 2. Inadequate ripple at the feedback voltage due to the small ESR of the output capacitors, such is the case with ceramic output capacitor. 1 T = << 1 fSW x The output voltage ripple is fed into the FB pin through a feed-forward capacitor Cff in this situation, as shown in Figure 11. The typical Cff value is between 1nF and 100nF. Eq. 20 If the voltage divider resistors R1 and R11 are in the k range, then a Cff of 1nF to 100nF can easily satisfy the large time constant requirements. Also, a 100nF injection capacitor Cinj is used in order to be considered as short for a wide range of the frequencies. The process of sizing the ripple injection resistor and capacitors is: Step 1. Select Cff to feed all output ripples into the feedback pin and make sure the large time constant assumption is satisfied. Typical choice of Cff is 1nF to 100nF if R1 and R11 are in k range. Step 2. Select Rinj according to the expected feedback voltage ripple using Equation 22: Figure 11. Invisible Ripple at FB With the feed-forward capacitor, the feedback voltage ripple is very close to the output voltage ripple: VFB(PP) ESR x IL(PP) K div = VFB(pp) VIN x fSW x D x (1 - D) Eq. 21 Eq. 17 Then the value of Rinj is obtained as: 3. Virtually no ripple at the FB pin voltage due to the very-low ESR of the output capacitors. R inj = (R1//R11) x ( In this situation, the output voltage ripple is less than 20mV. Therefore, additional ripple is injected into the FB pin from the switching node SW via a resistor Rinj and a capacitor Cinj, as shown in Figure 11. The injected ripple is: VFB(pp) = VIN x K div x D x (1 - D) x K div = R1//R11 R inj + R1//R11 Eq. 22 Step 3. Select Cinj as 100nF, which could be considered as short for a wide range of the frequencies. Table 3 summarizes the typical value of components for particular input and output voltage, and 600kHz switching frequency design, for details refer to the Bill of Materials section. 1 fSW x 1 - 1) K div Eq. 18 Eq. 19 Where: March 25, 2014 29 Revision 1.1 Micrel, Inc. MIC28304 Table 3. Recommended Component Values for 600kHz Switching Frequency VOUT VIN R3 (Rinj) R1 (Top Feedback Resistor) R11 (Bottom Feedback Resistor) 0.9V 5V to 70V 16.5k 10k 80.6k 1.2V 5V to 70V 16.5k 10k 20k 1.8V 5V to 70V 16.5k 10k 8.06k 2.5V 5V to 70V 16.5k 10k 4.75k 3.3V 5V to 70V 16.5k 10k 3.24k 5V 7V to 70V 16.5k 10k 1.9k 12V 18V to 70V 23.2k 10k 715 Thermal Measurements and Safe Operating Area Measuring the IC's case temperature is recommended to ensure it is within its operating limits. Although this might seem like a very elementary task, it is easy to get erroneous results. The most common mistake is to use the standard thermal couple that comes with a thermal meter. This thermal couple wire gauge is large, typically 22 gauge, and behaves like a heatsink, resulting in a lower case measurement. DNP DNP DNP DNP DNP DNP DNP C10 (Cinj) C12 (Cff) COUT 0.1F 2.2nF 47F/6.3V or 2 x 22F 0.1F 2.2nF 47F/6.3V or 2 x 22F 0.1F 2.2nF 47F/6.3V or 2 x 22F 0.1F 2.2nF 47F/6.3V or 2 x 22F 0.1F 2.2nF 47F/6.3V or 2 x 22F 0.1F 2.2nF 47F/6.3V or 2 x 22F 0.1F 2.2nF 47F/16V or 2 x 22F However, an IR thermometer from Optris has a 1mm spot size, which makes it a good choice for measuring the hottest point on the case. An optional stand makes it easy to hold the beam on the IC for long periods of time. The safe operating area (SOA) of the MIC28304 is shown in the Typical Characteristics - 275kHz Switching Frequency section. These thermal measurements were taken on MIC28304 evaluation board. Since the MIC28304 is an entire system comprised of switching regulator controller, MOSFETs and inductor, the part needs to be considered as a system. The SOA curves will give guidance to reasonable use of the MIC28304. Two methods of temperature measurement are using a smaller thermal couple wire or an infrared thermometer. If a thermal couple wire is used, it must be constructed of 36-gauge wire or higher (smaller wire size) to minimize the wire heat-sinking effect. In addition, the thermal couple tip must be covered in either thermal grease or thermal glue to make sure that the thermal couple junction is making good contact with the case of the IC. Omega brand thermal couple (5SC-TT-K-36-36) is adequate for most applications. Emission Characteristics of MIC28304 The MIC28304 integrates switching components in a single package, so the MIC28304 has reduced emission compared to standard buck regulator with external MOSFETS and inductors. The radiated EMI scans for MIC28304 are shown in the Typical Characteristics section. The limit on the graph is per EN55022 Class B standard. Wherever possible, an infrared thermometer is recommended. The measurement spot size of most infrared thermometers is too large for an accurate reading on a small form factor ICs. March 25, 2014 R19 30 Revision 1.1 Micrel, Inc. MIC28304 PCB Layout Guidelines Warning: To minimize EMI and output noise, follow these layout recommendations. Input Capacitor * Place the input capacitors on the same side of the board and as close to the IC as possible. * Place several vias to the ground plane close to the input capacitor ground terminal. * Use either X7R or X5R dielectric input capacitors. Do not use Y5V or Z5U type capacitors. * Do not replace the ceramic input capacitor with any other type of capacitor. Any type of capacitor can be placed in parallel with the input capacitor. * If a Tantalum input capacitor is placed in parallel with the input capacitor, it must be recommended for switching regulator applications and the operating voltage must be derated by 50%. * In "Hot-Plug" applications, a Tantalum or Electrolytic bypass capacitor must be used to limit the over-voltage spike seen on the input supply with power is suddenly applied. PCB layout is critical to achieve reliable, stable and efficient performance. A ground plane is required to control EMI and minimize the inductance in power, signal and return paths. The following figures optimized from small form factor point of view shows top and bottom layer of a four layer PCB. It is recommended to use mid layer 1 as a continuous ground plane. RC Snubber * Place the RC snubber on the same side of the board and as close to the SW pin as possible. SW Node * Do not route any digital lines underneath or close to the SW node. * Keep the switch node (SW) away from the feedback (FB) pin. Figure 12. Top And Bottom Layer of a Four-Layer Board Output Capacitor The following guidelines should be followed to insure proper operation of the MIC28304 converter: * Use a wide trace to connect the output capacitor ground terminal to the input capacitor ground terminal. * Phase margin will change as the output capacitor value and ESR changes. Contact the factory if the output capacitor is different from what is shown in the BOM. * The feedback trace should be separate from the power trace and connected as close as possible to the output capacitor. Sensing a long high-current load trace can degrade the DC load regulation. IC * The analog ground pin (GND) must be connected directly to the ground planes. Do not route the GND pin to the PGND pin on the top layer. * Place the IC close to the point of load (POL). * Use fat traces to route the input and output power lines. * Analog and power grounds should be kept separate and connected at only one location. March 25, 2014 31 Revision 1.1 Micrel, Inc. MIC28304 Evaluation Board Schematics Figure 13. Schematic of MIC28304 Evaluation Board (J1, J8, J10, J11, J12, J13, R14, R20, and R21 are for Testing Purposes) March 25, 2014 32 Revision 1.1 Micrel, Inc. MIC28304 Evaluation Board Schematics (Continued) Figure 14. Schematic of MIC28304 Evaluation Board (Optimized for Smallest Footprint) March 25, 2014 33 Revision 1.1 Micrel, Inc. MIC28304 Bill of Materials Item C1 C2, C3 C6 Part Number EEU-FC2A101 C9 C10, C17 Murata C3225X7R2A225K TDK Murata C1608X5R0J105K TDK 08051C474KAT2A GRM188R72A104KA35D AVX Murata 2.2F/100V Ceramic Capacitor, X7R, Size 1210 2 10pF, 100V, 0603, NPO 1 1F/6.3V Ceramic Capacitor, X7R, Size 0603 1 0.47F/100V Ceramic Capacitor, X7R, Size 0805 1 2 0.1F/100V, X7S, 0603 Murata C1608X7R2A102K TDK 1nF/100V Ceramic Capacitor, X7R, Size 0603 1 2.2nF/100V Ceramic Capacitor, X7R, Size 0603 1 47F/6.3V Ceramic Capacitor, X5R, Size 1210 1 0.1F/6.3V Ceramic Capacitor, X7R, Size 0603 1 Murata 06031C222KAT2A AVX C1608X7R2A222K TDK 12106D476MAT2A 1 0.1F/100V Ceramic Capacitor, X7R, Size 0603 TDK AVX GRM188R71H104KA93D C16 Murata 06031C102KAT2A GRM31CR60J476ME19K 100F Aluminum Capacitor, 100V Murata AVX GRM188R72A222KA01D C14 AVX 06036C105KAT2A GRM21BR72A474KA73 Qty. (9) GCM1885C2A100JA16D GRM188R72A102KA01D C12 (8) AVX 06031A100JAT2A (6) (7) 12101C225KAT2A C1608X7S2A104K C11 Panasonic GRM32ER72A225K GRM188R70J105KA01D C8 Manufacturer Description Murata AVX Murata 06035C104KAT2A AVX C1608X7R1H104K TDK C4, C5, C7, C13, C15 DNP Notes: 6. Panasonic: www.panasonic.com. 7. Murata: www.murata.com. 8. TDK: www.tdk.com. 9. AVX: www.avx.com. March 25, 2014 34 Revision 1.1 Micrel, Inc. MIC28304 Bill of Materials (Continued) Item Part Number R1 CRCW060310K0FKEA R2 CRCW08051R21FKEA R3 Manufacturer Vishay Dale (10) Description Qty. 10k Resistor, Size 0603, 1% 1 Vishay Dale 1.21 Resistor, Size 0805, 5% 1 CRCW06031652F Vishay Dale 16.5k Resistor, Size 0603, 1% 1 R10 CRCW06033K24FKEA Vishay Dale 3.24k Resistor, Size 0603, 1% 1 R11 CRCW06031K91FKEA Vishay Dale 1.91k Resistor, Size 0603, 1% 1 R12 CRCW0603715R0FKEA Vishay Dale 715 Resistor, Size 0603, 1% R14, R20 CRCW06030000FKEA Vishay Dale 0 Resistor, Size 0603, 5% 2 R15 CRCW04022K70JNED Vishay Dale 2.7k Resistor, Size 0603, 1% 1 R16 CRCW0603100KFKEAHP Vishay Dale 100k Resistor, Size 0603, 1% 1 R18 CRCW060349K9FKEA Vishay Dale 49.9k Resistor, Size 0603, 1% 1 R21 CRCW060349R9FKEA Vishay Dale 49.9 Resistor, Size 0603, 1% 1 R23 CRCW06031R21FKEA Vishay Dale 1.21 Resistor, Size 0603, 1% 1 R4, R19 All reference designators ending with "A" U1 DNP DNP Open MIC28304-1YMP MIC28304-2YMP (11) Micrel, Inc. 70V, 3A Power Module - Hyper Speed Control Family 1 Notes: 10. Vishay: www.vishay.com. 11. Micrel, Inc.: www.micrel.com. March 25, 2014 35 Revision 1.1 Micrel, Inc. MIC28304 PCB Layout Recommendations Evaluation Board Top Layer Evaluation Board Mid-Layer 1 (Ground Plane) March 25, 2014 36 Revision 1.1 Micrel, Inc. MIC28304 PCB Layout Recommendations (Continued) Evaluation Board Mid-Layer 2 Evaluation Board Bottom Layer March 25, 2014 37 Revision 1.1 Micrel, Inc. MIC28304 Package Information(12) 64-Pin 12mm x 12mm QFN (MP) Note: 12. Package information is correct as of the publication date. For updates and most current information, go to www.micrel.com. March 25, 2014 38 Revision 1.1 Micrel, Inc. MIC28304 Recommended Land Pattern MICREL, INC. 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA TEL +1 (408) 944-0800 FAX +1 (408) 474-1000 WEB http://www.micrel.com Micrel makes no representations or warranties with respect to the accuracy or completeness of the information furnished in this data sheet. This information is not intended as a warranty and Micrel does not assume responsibility for its use. Micrel reserves the right to change circuitry, specifications and descriptions at any time without notice. No license, whether express, implied, arising by estoppel or otherwise, to any intellectual property rights is granted by this document. Except as provided in Micrel's terms and conditions of sale for such products, Micrel assumes no liability whatsoever, and Micrel disclaims any express or implied warranty relating to the sale and/or use of Micrel products including liability or warranties relating to fitness for a particular purpose, merchantability, or infringement of any patent, copyright or other intellectual property right. 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 a Purchaser's own risk and Purchaser agrees to fully indemnify Micrel for any damages resulting from such use or sale. (c) 2014 Micrel, Incorporated. March 25, 2014 39 Revision 1.1