MIC28510 75V/4A Hyper Speed Control Synchronous DC/DC Buck Regulator SuperSwitcher II General Description Features The Micrel MIC28510 is an adjustable–frequency, synchronous buck regulator featuring unique adaptive on– time control architecture. The MIC28510 operates over an input supply range of 4.5V to 75V and provides a regulated output of up to 4A of output current. The output voltage is adjustable down to 0.8V with a guaranteed accuracy of ±1%. Micrel’s Hyper Speed Control architecture allows for ultra– fast transient response while reducing the output capacitance and also makes (High VIN) / (Low VOUT) operation possible. This adaptive tON ripple control architecture combines the advantages of fixed–frequency operation and fast transient response in a single device. The MIC28510 offers a full suite of protection features to ensure protection of the IC during fault conditions. These include undervoltage lockout to ensure proper operation under power–sag conditions, internal soft–start to reduce inrush current, foldback current limit, “hiccup” mode shortcircuit protection, and thermal shutdown. All support documentation can be found on Micrel’s web site at: www.micrel.com. Hyper Speed Control architecture enables: High Delta V operation (VIN = 75V and VOUT = 0.8V) Small output capacitance 4.5V to 75V voltage input 4A output current capability, up to 95% efficiency Adjustable output voltage form 0.8V to 24V ±1% FB accuracy Any Capacitor stable: Zero-ESR to high–ESR output capacitors 100kHz to 500kHz switching frequency Internal compensation Foldback current–limit and “hiccup” mode short-circuit protection Thermal shutdown Supports safe startup into a pre–biased load –40C to +125C junction temperature range 28-pin 5mm 6mm MLF® package Applications Distributed power systems Communications/networking infrastructure Industrial power Solar energy ___________________________________________________________________________________________________________ Typical Application Efficiency (VIN = 48V) vs. Output Current 100 90 5.0V 3.3V 2.5V 1.8V 1.5V 1.2V 1.0V 0.8V EFFICIENCY (%) 80 70 60 50 40 fSW = 250kHz 30 20 10 0 1 2 3 4 5 6 OUTPUT CURRENT (A) Hyper Speed Control, SuperSwitcher II and Any Capacitor are trademarks of Micrel, Inc. MLF and MicroLeadFrame are registered trademarks of Amkor Technology, 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 2012 M9999-030912-A Micrel, Inc. MIC28510 Ordering Information Part Number Junction Temperature Range Package Lead Finish MIC28510YJL 40C to 125C 28-pin 5mm 6mm MLF® Pb-Free Pin Configuration 28-Pin 5mm 6mm MLF® (JL) Pin Description Pin Number Pin Name Pin Function 1, 3 NC No Connect. Power Ground. PGND is the ground path for the MIC28510 buck converter power stage. The PGND pin connects to the sources of low-side N-Channel internal MOSFETs, the negative terminals of input capacitors, and the negative terminals of output capacitors. The loop for the power ground should be as small as possible and separate from the signal ground (SGND) loop. 2, 5, 6, 7, 8, 21 PGND 4, 9, 10, 11, 12 SW 13, 14, 15, 16, 17, 18, 19 PVIN High-Side Internal N-Channel MOSFET Drain Connection (Input).The PVIN operating voltage range is from 4.5V to 75V. Input capacitors between the PVIN pins and the power ground (PGND) are required and keep the connection short. 20 BST Boost (Output). Bootstrapped voltage to the high-side N-channel internal MOSFET driver. A Schottky diode is connected between the VDD pin and the BST pin. A boost capacitor of 0.1μF is connected between the BST pin and the SW pin. CS Current Sense (Input). High current output driver return. The CS pin connects directly to the switch node. Due to the high-speed switching on this pin, the CS pin should be routed away from sensitive nodes. CS pin also senses the current by monitoring the voltage across the low-side internal MOSFET during OFF-time. 22 March 2012 Switch Node (Output). Internal connection for the high-side MOSFET source and low-side MOSFET drain. 2 M9999-030912-A Micrel, Inc. MIC28510 Pin Description (Continued) Pin Number Pin Name 23 FS Frequency Setting Pin. 24 EN Enable (Input). A logic level control of the output. The EN pin is CMOS-compatible. Logic high = enable, logic low = shutdown. In the off state, the VDD supply current of the device is reduced (typically 0.7mA). Do not pull the EN pin above the VDD supply. This pin has 100k pull-up resistor to VDD. 25 FB 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 adjust the desired output voltage. 26 SGND Signal Ground. SGND must be connected directly to the ground planes. Do not route the SGND pin to the PGND Pad on the top layer; see PCB layout guidelines for details. 27 VDD VDD Bias (Input). Power to the internal reference and control sections of the MIC28510. The VDD operating voltage range is from 4.5V to 5.5V. A 2.2µF ceramic capacitor from the VDD pin to the PGND pin must be placed next to the IC. VDD must be powered up at the same time or after PVIN to make the soft-start function correctly. 28 PVDD March 2012 Pin Function Power Supply for Gate Driver of Bottom MOSFET. 3 M9999-030912-A Micrel, Inc. MIC28510 Absolute Maximum Ratings(1) Operating Ratings(3) PVIN to PGND................................................ 0.3V to +76V FS to PGND ....................................................0.3V to PVIN PVDD, VDD to PGND ......................................... 0.3V to +6V VSW, VCS to PGND .............................. 0.3V to (PVIN +0.3V) VBST to VSW ........................................................ 0.3V to 6V VBST to PGND .................................................. 0.3V to 82V VEN to PGND ...................................... 0.3V to (VDD + 0.3V) VFB to PGND....................................... 0.3V to (VDD + 0.3V) PGND to SGND ........................................... 0.3V to +0.3V Junction Temperature (TJ) ....................................... +150°C Storage Temperature (TS).........................65C to +150C Lead Temperature (soldering, 10s)............................ 260°C ESD Rating(2) ..............................................................1000V Supply Voltage (PVIN) ....................................... 4.5V to 75V Bias Voltage (PVDD, VDD).................................. 4.5V to 5.5V Enable Input (VEN) ................................................. 0V to VDD Junction Temperature (TJ) ........................ 40C to +125C Maximum Power Dissipation......................................Note 4 Package Thermal Resistance(4) 5mm x 6mm MLF® (JA) ....................................36C/W Electrical Characteristics(5) PVIN = VFS = 48V, VDD = 5V; VBST – VSW = 5V; TA = 25°C, unless noted. Bold values indicate 40°C ≤ TJ ≤ +125°C. Parameter Condition Min. Typ. Max. Units 4.5 75 V 2 75 V Power Supply Input Input Voltage Range ( PVIN) FS Voltage Range VDD Bias Voltage Operating Bias Voltage (VDD) Undervoltage Lockout Trip Level VDD Rising 4.5 5 5.5 V 3.2 3.85 4.45 V UVLO Hysteresis Quiescent Supply Current (IVDD) Shutdown Supply Current (IVDD) 380 VFB = 1.5V VDD = VBST = 5.5V, VIN = 48V SW = unconnected, VEN = 0V mV 1.4 3 mA 0.7 2 mA Reference Feedback Reference Voltage 0°C ≤ TJ ≤ 85°C (±1.0%) 0.792 0.8 0.808 40°C ≤ TJ ≤ 125°C (±1.5%) 0.788 0.8 0.812 V Load Regulation IOUT = 0A to 4A 0.04 % Line Regulation PVIN = 4.5 to 75V 0.1 % FB Bias Current VFB = 0.8V -0.5 EN Logic Level High 4.5V < VDD < 5.5V 1.2 EN Logic Level Low 4.5V < VDD < 5.5V EN Bias Current VEN = 0V 0.005 0.5 µA 0.4 V 100 µA Enable Control V 50 Notes: 1. Exceeding the absolute maximum rating may damage the device. 2. Devices are ESD sensitive. Handling precautions recommended. Human body model, 1.5kΩ in series with 100pF. 3. The device is not guaranteed to function outside operating range. 4. PD(MAX) = (TJ(MAX) – TA)/ JA, where JA depends upon the printed circuit layout. See “Applications Information.” 5. Specification for packaged product only. March 2012 4 M9999-030912-A Micrel, Inc. MIC28510 Electrical Characteristics(5) (Continued) PVIN = VFS = 48V, VDD = 5V; VBST – VSW = 5V; TA = 25°C, unless noted. Bold values indicate 40°C ≤ TJ ≤ +125°C. Parameter Condition Min. Typ. Max. Units VFS = PVIN 375 500 625 kHz Oscillator Switching Frequency Maximum Duty Cycle (6) Minimum Duty Cycle VFB = 0V, VFS=PVIN 80 % VFB > 0.8V 0 % 360 ns 6 ms Minimum Off-time Soft-Start Soft-Start time Short-Circuit Protection Current–Limit Threshold Short–Circuit Current VFB = 0.8V, TJ = 25°C 4.8 VFB = 0.8V, TJ = 125°C 4 VFB = 0V 2 7 10 10 4.3 5.7 A A Internal FETs Top–MOSFET RDS (ON) ISW = 1A 31 mΩ Bottom–MOSFET RDS (ON) ISW = 1A 31 mΩ SW Leakage Current PVIN = 36V, VSW = 36V, VEN = 0V, VBST = 41V 55 µA PVIN Leakage Current PVIN = 36V, VSW = 0V, VEN = 0V, VBST = 41V 55 µA Thermal Protection Over–Temperature Shutdown TJ Rising Over–Temperature Shutdown Hysteresis 160 °C 2 °C Note: 6. The maximum duty–cycle is limited by the fixed mandatory off-time (tOFF ) of typically 360ns. March 2012 5 M9999-030912-A Micrel, Inc. MIC28510 Typical Characteristics 400 SHUTDOWN CURRENT (uA) SUPPLY CURRENT (mA) 20 VOUT = 3.3V IOUT = 0A 16 VDD = 5V fSW = 250kHz 12 8 4 0 5 15 25 35 45 55 65 VIN Shutdown Current vs. Input Voltage 300 200 V DD = 5V V EN = 0V 100 0 75 VDD Operating Supply Current vs. Input Voltage 10 VDD SUPPLY CURRENT (mA) VIN Operating Supply Current vs. Input Voltage 8 6 VOUT = 3.3V VDD = 5V 4 fSW = 250kHz 2 0 5 15 25 35 45 55 65 75 5 15 25 35 45 55 65 75 INPUT VOLTAGE (V) INPUT VOLTAGE (V) Feedback Voltage vs. Input Voltage Total Regulation vs. Input Voltage Output Peak Current Limit vs. Input Voltage 1.0% TOTAL REGULATION (%) VOUT = 3.3V VDD = 5V 0.804 15 0.8% IOUT = 0A fSW = 250kHz 0.800 0.796 VOUT = 3.3V VOUT = 3.3V 0.6% VDD = 5V 0.4% IOUT = 0A to 4A CURRENT LIMIT (A) 0.808 FEEDBACK VOLTAGE (V) INPUT VOLTAGE (V) fSW = 250kHz 0.2% 0.0% -0.2% -0.4% -0.6% VDD = 5V 12 fSW = 250kHz 9 6 3 -0.8% 0.792 -1.0% 5 15 25 35 45 55 65 75 0 5 15 INPUT VOLTAGE (V) 35 45 55 65 5 75 VOUT = 3.3V VDD = 5V IOUT = 1A R18 =100k R19 =100k 10 8 VIN = 48V 6 VOUT = 3.3V VDD = 5V 4 IOUT = 0A fSW = 250kHz 2 0 100 5 15 25 35 45 55 65 75 45 55 65 75 1.0 SHUTDOWN CURRENT (mA) SUPPLY CURRENT (mA) 250 35 VDD Shutdown Current vs. Temperature 12 150 25 INPUT VOLTAGE (V) VDD Operating Supply Current vs. Temperature 300 200 15 INPUT VOLTAGE (V) Switching Frequency vs. Input Voltage SWITCHING FREQUENCY (kHz) 25 0.8 0.6 0.4 VIN = 48V 0.2 VEN = 0V IOUT = 0A VDD = 5V 0.0 -50 -25 0 25 50 75 TEMPERATURE (°C) 100 125 -50 -25 0 25 50 75 100 125 TEMPERATURE (°C) INPUT VOLTAGE (V) March 2012 6 M9999-030912-A Micrel, Inc. MIC28510 Typical Characteristics (Continued) 20 VIN = 48V IOUT = 0A 4.0 3.9 3.8 RISING 3.7 3.6 3.5 FALLING 3.4 400 VIN = 48V SUPPLY CURRENT (mA) 4.1 VIN Shutdown Current vs. Temperature SHUTDOWN CURRENT (uA) 4.2 VDD THRESHOLD (V) VIN Operating Supply Current vs. Temperature VDD UVLO Threshold vs. Temperature VOUT = 3.3V 16 VDD = 5V IOUT = 0A fSW = 250kHz 12 8 4 320 240 VIN = 48V VEN = 0V -25 0 25 50 75 100 125 0 0 -50 -25 TEMPERATURE (°C) 0 50 75 100 -50 125 0 V DD = 5V fSW = 250kHz 9 6 VOUT = 3.3V 0.804 50 75 100 125 100 125 0.4% VIN = 48V LOAD REGULATION (%) FEEBACK VOLTAGE (V) V OUT = 3.3V 25 Load Regulation vs. Temperature 0.808 V IN = 48V VDD = 5V IOUT = 0A 0.800 0.796 VIN = 48V 0.3% VOUT = 3.3V VDD = 5V 0.2% IOUT = 0A to 4A fSW = 250kHz 0.1% 0.0% -0.1% -0.2% 3 0.792 -50 0 -50 -25 0 25 50 75 100 -25 0 25 50 75 100 -0.3% 125 -50 Line Regulation vs. Temperature 0.4% IOUT = 0A 0.1% 0.0% -0.1% -0.2% 100 VIN = 48V 250 25°C 125°C 200 VIN = 48V VOUT = 3.3V 150 VDD = 5V R18 = 100k R19 =100k 100 -0.3% 0 25 50 75 TEMPERATURE (°C) March 2012 100 75 EN Bias Current vs. Temperature EN BIAS CURRENT (µA) SWITCHING FREQUENCY (kHz) V DD = 5V -25 50 Switching Frequency vs. Output Current -40°C V OUT = 3.3V -50 25 TEMPERATURE (°C) 300 0.2% 0 TEMPERATURE (°C) V IN = 5V to 75V 0.3% -25 125 TEMPERATURE (°C) LINE REGULATION (%) -25 TEMPERATURE (°C) Feedback Voltage vs. Temperature 15 CURRENT LIMIT (A) 25 TEMPERATURE (°C) Output Peak Current Limit vs. Temperature 12 IOUT = 0A 80 3.3 -50 VDD = 5V 160 125 VDD = 5V 80 VEN = 0V 60 40 20 0 0 1 2 3 OUTPUT CURRENT (A) 7 4 -50 -25 0 25 50 75 100 125 TEMPERATURE (°C) M9999-030912-A Micrel, Inc. MIC28510 Typical Characteristics (Continued) Enable Threshold vs. Temperature 100 EFFICIENCY (%) RISING 0.7 FALLING 0.6 85 80 75 65 VIN = 48V 60 VDD = 5V 55 0.5 -50 -25 0 25 50 75 100 48VIN 70 75VIN 0 1 100 0.2% 90 EFFICIENCY (%) LINE REGULATION (%) 0.804 fSW = 250kHz 0.800 0.796 2 3 0.792 4 0 1 0.1% VIN = 5V to 75V VOUT = 3.3V VDD = 5V 2 3 4 OUTPUT CURRENT (A) Efficiency (VIN = 5V) vs. Output Current 0.3% Efficiency (VIN = 48V) vs. Output Current 100 90 3.3V 2.5V 1.8V 1.5V 1.2V 1.0V 0.9V 0.8V 80 70 fsw = 250kHz 60 5.0V 3.3V 2.5V 1.8V 1.5V 1.2V 1.0V 0.9V 0.8V 80 50 fSW = 250kHz -0.2% VOUT = 3.3V VDD = 5V OUTPUT CURRENT (A) Line Regulation vs. Output Current -0.1% VIN = 48V fSW = 250kHz 50 125 TEMPERATURE (°C) 0.0% VOUT = 3.3V VDD = 5V EFFICIENCY (%) ENABLE THRESHOLD (V) 6VIN 90 0.9 0.808 4.5VIN 95 FEEDBACK VOLTAGE (V) 1.0 0.8 Feedback Voltage vs. Output Current Efficiency vs. Output Current 70 60 50 40 fSW = 250kHz 30 40 20 -0.3% 30 1 2 3 4 0 OUTPUT CURRENT (A) EFFICIENCY (%) DIE TEMPERATURE (°C) 90 5.0V 3.3V 2.5V 1.8V 1.5V 1.2V 1.0V 0.9V 60 50 40 30 0.8V fSW = 250kHz 3 4 5 3 4 OUTPUT CURRENT (A) March 2012 2 3 5 6 4 5 6 Die Temperature* (VIN = 48V) vs. Output Current 60 40 VIN = 5.0V VOUT = 3.3V 20 VDD = 5V 60 40 ` V IN = 48V V OUT = 3.3V 20 V DD = 5V fSW = 250kHz 10 2 1 OUTPUT CURRENT (A) fSW = 250kHz 0 1 0 80 20 0 10 6 Die Temperature* (VIN = 5.0V) vs. Output Current 80 100 70 2 OUTPUT CURRENT (A) Efficiency (VIN = 75V) vs. Output Current 80 1 DIE TEMPERATURE (°C) 0 0 0 1 2 3 OUTPUT CURRENT (A) 8 4 0 1 2 3 4 OUTPUT CURRENT (A) M9999-030912-A Micrel, Inc. MIC28510 Typical Characteristics (Continued) Efficiency (VIN =12V) vs. Output Current Die Temperature* (VIN = 75V) vs. Output Current 100 100 5.0V 3.3V 2.5V 1.8V 1.2V 0.8V 90 EFFICIENCY (%) 80 60 40 V IN = 75V 80 70 60 50 fSW = 250kHz V OUT = 3.3V 20 V DD = 5V 5.0V 3.3V 2.5V 1.8V 1.2V 0.8V 90 EFFICIENCY (%) 100 DIE TEMPERATURE (°C) Efficiency (VIN = 18V) vs. Output Current 40 80 70 60 50 fSW = 250kHz 40 fSW = 250kHz 30 0 0 1 2 3 0 4 1 2 3 4 5 30 6 0 1 OUTPUT CURRENT (A) 2 3 4 5 6 OUTPUT CURRENT (A) OUTPUT CURRENT (A) 100 4 4 VOUT = 5V 5.0V 3.3V 2.5V 1.8V 1.2V 0.8V 80 70 60 50 V OUT = 0.8V LOAD CURRENT (A) LOAD CURRENT (A) 90 EFFICIENCY (%) Thermal Derating Thermal Derating Efficiency (VIN = 24V) vs. Output Current VIN = 48V 3 fSW = 250kHz L = 10µH Tj_MAX =125°C VOUT = 3.3V 2 VOUT =2.5V 1 3 V OUT = 1.2V 2 VIN = 48V fSW = 250kHz L = 10µH Tj_MAX =125°C 1 fSW = 250kHz 40 0 0 30 25 0 1 2 3 4 5 6 40 55 70 85 25 100 MAXIMUM AMBIENT TEMPERATURE (°C) OUTPUT CURRENT (A) Thermal Derating 40 70 85 100 Thermal Derating Thermal Derating 4 55 MAXIMUM AMBIENT TEMPERATURE (°C) 4 4 VOUT =3.3V 2 V OUT = 5V V IN = 12V fSW = 250kHz L = 10µH Tj_MAX = 125°C 1 VOUT = 2.5V 3 LOAD CURRENT (A) 3 LOAD CURRENT (A) LOAD CURRENT (A) V OUT = 2.5V VOUT =3.3V 2 VOUT = 5V VIN = 18V 1 fSW = 250kHz L = 10µH Tj_MAX = 125°C VOUT = 2.5V 25 40 55 70 85 MAXIMUM AMBIENT TEMPERATURE (°C) March 2012 100 3 2 V OUT = 5V V IN = 24V fSW = 250kHz L = 10µH Tj_MAX =125°C 1 0 0 0 V OUT =3.3V 25 40 55 70 85 MAXIMUM AMBIENT TEMPERATURE (°C) 9 100 25 40 55 70 85 100 MAXIMUM AMBIENT TEMPERATURE (°C) M9999-030912-A Micrel, Inc. MIC28510 Typical Characteristics (Continued) Thermal Derating Thermal Derating VOUT = 1.8V 2 VOUT = 0.8V V IN = 12V fSW = 250kHz L = 10µH Tj_MAX = 125°C 1 LOAD CURRENT (A) V OUT = 1.2V 3 LOAD CURRENT (A) LOAD CURRENT (A) Thermal Derating 4 4 4 VOUT =1.8V 3 VOUT = 1.2V 2 V IN = 18V 1 fSW = 250kHz L = 10µH Tj_MAX = 125°C VOUT = 0.8V 25 40 55 70 85 100 25 40 55 70 85 MAXIMUM AMBIENT TEMPERATURE (°C) MAXIMUM AMBIENT TEMPERATURE (°C) VOUT = 1.8V 2 VOUT = 1.2V V IN = 24V 1 fSW = 250kHz L = 10µH Tj_MAX = 125°C V OUT = 0.8V 0 0 0 3 100 25 40 55 70 85 100 MAXIMUM AMBIENT TEMPERATURE (°C) Thermal Derating LOAD CURRENT (A) 4 3 24VIN 2 48VIN VOUT = 12V 1 fSW = 250kHz L = 27µH Tj_MAX = 125°C 0 25 40 55 70 85 100 MAXIMUM AMBIENT TEMPERATURE (°C) Die Temperature*: The temperature measurement was taken at the hottest point on the MIC28510 case mounted on a five–square inch, four–layer, 0.62”, FR–4 PCB with 2 oz. finish copper weight–pre–layer (see Thermal Measurement section). Actual results will depend upon the size of the PCB, ambient temperature and proximity to other heat–emitting components. March 2012 10 M9999-030912-A Micrel, Inc. MIC28510 Functional Characteristics March 2012 11 M9999-030912-A Micrel, Inc. MIC28510 Functional Characteristics (Continued) March 2012 12 M9999-030912-A Micrel, Inc. MIC28510 Functional Characteristics (Continued) March 2012 13 M9999-030912-A Micrel, Inc. MIC28510 Functional Diagram Figure 1. MIC28510 Block Diagram March 2012 14 M9999-030912-A Micrel, Inc. MIC28510 The maximum duty cycle is obtained from the 360ns tOFF(MIN): Functional Description The MIC28510 is an adaptive ON-time synchronous step-down DC/DC regulator. It is designed to operate over a wide input voltage range from, 4.5V to 75V, and provides a regulated output voltage at up to 4A of output current. A digitally-modified adaptive ON-time control scheme is employed in order to obtain a constantswitching frequency and to simplify the control compensation. Over current protection is implemented without the use of an external sense resistor. The device includes an internal soft-start function which reduces the power supply input surge current at start-up by controlling the output voltage rise time. D MAX VOUT VIN fSW 360ns tS Eq. 2 Eq. 1 where VOUT is the output voltage and 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 360ns, then the MIC28510 control logic will apply the tOFF(MIN) instead. The minimum tOFF(MIN) period is required to maintain enough energy in the boost capacitor (CBST) to drive the high–side MOSFET. March 2012 tS 1 where tS = 1/fSW. It is not recommended to use MIC28510 with a OFF-time close to tOFF(MIN) during steady-state operation. The actual ON–time and resulting switching frequency will vary with the part–to–part variation in the rise and fall times of the internal MOSFETs, the output load current, and variations in the VDD voltage. Also, the minimum tON results in a lower switching frequency in high VIN to VOUT applications, such as 75V to 1.0V. Figure 2 shows the MIC28510 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 and the inductor current 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. Theory of Operation Figure 1 illustrates the block diagram for the control loop of the MIC28510. The output voltage is sensed by the MIC28510 feedback pin FB via the voltage divider R1 and R2, 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 output of the gm amplifier is below 0.8V, then the error comparator will trigger the control logic and generate an ON–time period. The ON–time period length is predetermined by the “FIXED tON ESTIMATION” circuitry: t ON(estimated) t S t OFF(MIN) Figure 2. MIC28510 Control Loop Timing 15 M9999-030912-A Micrel, Inc. MIC28510 Figure 3 shows the operation of the MIC28510 during 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 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 in MIC28510 converter. Soft–Start Soft–start reduces the power supply input 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 MIC28510 implements an internal digital soft–start by making the 0.8V reference voltage VREF ramp from 0 to 100% in approximately 6ms with 9.7mV steps. Therefore, the output voltage is controlled to increase slowly with a stair–case VFB ramp. Once the soft–start cycle ends, the related circuitry is disabled to reduce current consumption. VDD must be powered up at the same time or after VIN to allow the soft–start function correctly. Current Limit The MIC28510 uses the RDS(ON) of the internal low–side power MOSFET to sense over–current conditions. This method will avoid adding cost, use of additional board space and power losses taken by a discrete current sense resistor. In each switching cycle of the MIC28510 converter, the inductor current is sensed by monitoring the low–side MOSFET in the OFF period. If the peak inductor current is greater than 7A, then the MIC28510 turns off the high–side MOSFET and a soft–start sequence is triggered. This mode of operation is called “hiccup mode” and its purpose is to protect the downstream load in case of a hard short. The current–limit threshold has a foldback characteristic related to the feedback voltage, as shown in Figure 4. Figure 3. MIC28510 Load Transient Response Unlike true current–mode control, the MIC28510 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 MIC28510 feedback voltage ripple should be in phase with the inductor current ripple and large enough to be sensed by the gm amplifier and the error comparator. The recommended feedback voltage ripple is 20mV~100mV. 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 of this datatsheet for more details regarding the ripple injection technique. March 2012 Current-Limit Threshold vs. Feedback Voltage CURRENT LIMIT THRESHOLD (A) 12 VIN = 48V 10 8 6 4 2 0 0.0 0.2 0.4 0.6 0.8 1.0 FEEDBACK VOLTAGE (V) Figure 4. MIC28510 Current–Limit Foldback Characteristic 16 M9999-030912-A Micrel, Inc. MIC28510 Internal MOSFET Gate Drive Figure 1 (the block diagram) shows a bootstrap circuit, consisting of D1 (a Schottky diode is recommended) and a capacitor connected from the SW pin to the BST pin (CBST). This circuit supplies energy to the high–side drive circuit. Capacitor CBST is charged, while the low–side MOSFET is on, and the voltage on the SW pin is approximately 0V. When the high–side MOSFET driver is turned on, energy from CBST is used to turn the MOSFET on. As the high–side MOSFET turns on, the voltage on the SW pin increases to approximately VIN. Diode D1 is reverse biased and CBST floats high while continuing to keep the high–side MOSFET on. The bias current of the high–side driver is less than 10mA so a 0.1μF to 1μF is sufficient to hold the gate voltage with minimal droop for the power stroke (high–side switching) cycle, i.e. ΔBST = 10mA x 4μs/0.1μF = 400mV. When the low–side MOSFET is turned back on, CBST is recharged through D1. A small resistor in series with CBST, can be used to slow down the turn–on time of the high–side N–channel MOSFET. The drive voltage is derived from the PVDD supply voltage. The nominal low–side gate drive voltage is PVDD and the nominal high–side gate drive voltage is approximately PVDD – VDIODE, where VDIODE is the voltage drop across D1. An approximate 30ns delay between the high–side and low–side driver transitions is used to prevent current from simultaneously flowing unimpeded through both MOSFETs. March 2012 17 M9999-030912-A Micrel, Inc. MIC28510 Application Information Inductor Selection Values for inductance, peak, and RMS currents are required to select the output inductor. The input and output voltages and the inductance value determine the peak–to–peak inductor ripple current. Generally, higher inductance values are used with higher input voltages. Larger peak–to–peak ripple currents will increase the power dissipation in the inductor and MOSFETs. Larger output ripple currents will also require more output capacitance to smooth out the larger ripple current. Smaller peak–to–peak ripple currents require a larger inductance value and therefore a larger and more expensive inductor. A good compromise between size, loss and cost is to set the inductor ripple current to be equal to 20% of the maximum output current. The inductance value is calculated by Equation 4: Setting the Switching Frequency The MIC28510 is an adjustable–frequency, synchronous buck regulator featuring a unique digitally-modified, adaptive on–time control architecture. The switching frequency can be adjusted between 100kHz and 500kHz by changing the resistor divider network consisting of R18 and R19. L The following formula gives the estimated switching frequency: fSW _ ADJ VIN(max) fsw 20% IOUT(max) Eq. 4 where: fSW = Switching frequency 20% = Ratio of AC ripple current to DC output current VIN(MAX) = Maximum power stage input voltage Figure 5. Switching Frequency Adjustment R19 fO R18 R19 VOUT (VIN(max) VOUT ) The peak–to–peak inductor current ripple is: Eq. 3 IL(pp) where fO = switching frequency when R18 is 100k and R19 being open, fO is typically 450kHz. For more precise setting, it is recommended to use the graph illustrated in Figure 6: VOUT (VIN(max) VOUT ) VIN(max) fsw L Eq. 5 The peak inductor current is equal to the average output current plus one half of the peak–to–peak inductor current ripple. IL(pk) =IOUT(max) + 0.5 ΔIL(pp) Eq. 6 The RMS inductor current is used to calculate the I2R losses in the inductor: 2 IL(RMS) IOUT(max) ΔIL(PP) 12 2 Eq. 7 Figure 6. Switching Frequency vs. R19 March 2012 18 M9999-030912-A Micrel, Inc. MIC28510 The maximum value of ESR is calculated: Maximizing efficiency requires the proper selection of core material while minimizing the winding resistance. The high frequency operation of the MIC28510 requires the use of ferrite materials for all but the most cost sensitive applications. Lower cost iron powder cores may be used but the increase in core loss will reduce the efficiency of the power supply. This is especially noticeable at low output power. The winding resistance decreases efficiency at the higher output current levels. The winding resistance must be minimized although this usually comes at the expense of a larger inductor. The power dissipated in the inductor is equal to the sum of the core and copper losses. At higher output loads, the core losses are usually insignificant and can be ignored. At lower output currents, the core losses can be a significant contributor. Core loss information is usually available from the magnetics vendor. Copper loss in the inductor is calculated by Equation 8: PINDUCTOR(Cu) = IL(RMS)2 × RWINDING ESR COUT ΔVOUT(pp) Eq. 10 ΔIL(PP) where: ΔVOUT(pp) = peak–to–peak output voltage ripple ΔIL(PP) = peak–to–peak inductor current ripple The total output ripple is a combination of the ESR and output capacitance. The total ripple is calculated in Equation 10: 2 ΔVOUT(pp) ΔIL(PP) ΔIL(PP) ESR C OUT C f 8 OUT SW 2 Eq. 11 Eq. 8 where: COUT = Output capacitance value fSW = Switching frequency The resistance of the copper wire, RWINDING, increases with the temperature. The value of the winding resistance used should be at the operating temperature: PWINDING(Ht) = RWINDING(20°C) × (1 + 0.0042 × (TH – T20°C)) Eq. 9 As described in the “Theory of Operation” subsection in Functional Description, the MIC28510 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 the enough feedback voltage ripple. Please refer to the “Ripple Injection” subsection for more details. The voltage rating of the capacitor should be 20% greater for aluminum electrolytic or OS–CON. The output capacitor RMS current is calculated in Equation 12: where: TH = Temperature of wire under full load T20°C = Ambient temperature RWINDING(20°C) = Room temperature winding resistance (usually specified by the manufacturer) Output Capacitor Selection The type of the output capacitor is usually determined by its equivalent series resistance (ESR). Voltage and RMS current capability are two other important factors for selecting the output capacitor. Recommended capacitor types are ceramic, low–ESR aluminum electrolytic, OS– CON and POSCAP. The output capacitor’s ESR is usually the main cause of the output ripple. The output capacitor ESR also affects the control loop from a stability point of view. ICOUT (RMS) ΔIL(PP) Eq. 12 12 The power dissipated in the output capacitor is: 2 PDISS(COUT ) ICOUT (RMS) ESR COUT March 2012 19 Eq. 13 M9999-030912-A Micrel, Inc. MIC28510 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. As shown in Figure 7a, the converter is stable without any ripple injection. The feedback voltage ripple is: Input Capacitor Selection The input capacitor for the power stage input VIN 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: ΔVIN = IL(pk) × CESR ΔVFB(pp) Eq. 14 Eq. 15 ΔVFB(pp) ESR ΔIL (pp) The power dissipated in the input capacitor is: PDISS(CIN) = ICIN(RMS)2 × CESR Eq. 17 where ΔIL(pp) is 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. The output voltage ripple is fed into the FB pin through a feedforward capacitor CFF in this situation, as shown in Figure 7b. The typical CFF value is between 1nF and 22nF. With the feedforward capacitor, the feedback voltage ripple is very close to the output voltage ripple: 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: ICIN(RMS) IOUT(MAX ) D (1 D) R2 ESR COUT ΔIL (pp) R1 R2 Eq. 18 3) Virtually no ripple at the FB pin voltage due to the very low ESR of the output capacitors. Eq. 16 Ripple Injection The VFB ripple required for proper operation of the MIC28510 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 can’t sense it, then the MIC28510 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. Figure 7a. Enough Ripple at FB Figure 7b. Inadequate Ripple at FB March 2012 20 M9999-030912-A Micrel, Inc. MIC28510 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 22nF if R1 and R2 are in kΩ range. Step 2. Select RINJ according to the expected feedback voltage ripple using Equation 22: K DIV Figure 7c. Invisible Ripple at FB 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 7c. The injected ripple is: ΔVFB(PP) VIN K DIV D (1- D) K DIV R1//R2 R INJ R1//R2 1 f SW τ ΔVFB(PP) VIN f SW τ D (1 D) Eq. 22 Then the value of Rinj is obtained as: R INJ (R1//R2) ( 1 K DIV 1) Eq. 23 Step 3. Select CINJ as 100nF, which could be considered as short for a wide range of the frequencies. Setting Output Voltage The MIC28510 requires two resistors to set the output voltage as shown in Figure 8. Eq. 19 Eq. 20 where: VIN = Power stage input voltage D = Duty cycle fSW = Switching frequency τ = (R1//R2//RINJ) × CFF In Equations 19 and 20, it is assumed that the time constant associated with CFF must be much greater than the switching period: Figure 8. Voltage–Divider Configuration 1 fSW T 1 Eq. 21 If the voltage divider resistors R1 and R2 are in the kΩ range, a CFF of 1nF to 22nF 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. March 2012 21 M9999-030912-A Micrel, Inc. MIC28510 The output voltage is determined by Equation 24: R1 VO VFB 1 R2 Eq. 24 where, VFB = 0.8V. A typical value of R1 can be between 3kΩ and 10kΩ. If R1 is too large, it may allow noise to be introduced into the voltage feedback loop. If R1 is too small, it will decrease the efficiency of the power supply, especially at light loads. Once R1 is selected, R2 can be calculated using: R2 VFB R1 VOUT VFB VIN (V) L COUT R3 (RINJ) C3 (CINJ) 0.8V to 3.3V 5V to 75V 10H 100F 16.5k 0.1F 5V 5.88V to 75V 10H 100F 10k 0.1F 12V 15V to 75V 27H 2x47F 45.3k 0.1F 24V 30V to 75V 47H 10F+220F 133k 0.1F Table 1. Recommended Component values Eq. 25 ` The inverting input voltage VINJ is clamped to 1.2V. As the injected ripple increases, the swing of VINJ will be clamped. The clamped VINJ reduces the line regulation because it is reflected back as a DC error on the FB terminal. The Figure 9 shows the typical input output relationship. The typical operating point should fall under the nongrey part of the graph shown in Figure 9. This should be used in conjunction with the recommended component values indicated in Table 1 and Bill of Matrials Table. Thermal Measurements 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. 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. 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. 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. Figure 9. Output Voltage vs Input Voltage March 2012 VOUT (V) 22 M9999-030912-A Micrel, Inc. MIC28510 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. Inductor PCB Layout Guidelines Warning!!! To minimize EMI and output noise, follow these layout recommendations. 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. Thickness of the copper planes is also important in terms of dissipating heat. The 2 oz copper thickness is adequate from thermal point of view and also thick copper plain helps in terms of noise immunity. Keep in mind thinner planes can be easily penetrated by noise The following guidelines should be followed to insure proper operation of the MIC28510 converter. IC The 2.2µF ceramic capacitor, which is connected to the VDD pin, must be located right at the IC. The VDD pin is very noise sensitive and placement of the capacitor is very critical. Use wide traces to connect to the VDD and PGND pins. The signal ground pin (SGND) must be connected directly to the ground planes. The SGND and PGND connection should be done at a single point near the IC. Do not route the SGND pin to the PGND Pad 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. Signal and power grounds should be kept separate and connected at only one location. Place the input capacitor next to the power pins. Place the input capacitors on the same side of the board and as close to the IC as possible. Keep both the PVIN pin and PGND connections short. 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%. March 2012 Keep the inductor connection to the switch node (SW) short. Do not route any digital lines underneath or close to the inductor. Keep the switch node (SW) away from the feedback (FB) pin. The CS pin should be connected directly to the SW pin to accurate sense the voltage across the low– side MOSFET. To minimize noise, place a ground plane underneath the inductor. The inductor can be placed on the opposite side of the PCB with respect to the IC. It does not matter whether the IC or inductor is on the top or bottom as long as there is enough air flow to keep the power components within their temperature limits. The input and output capacitors must be placed on the same side of the board as the IC. Output Capacitor 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. RC Snubber Input Capacitor 23 Place the RC snubber on either side of the board and as close to the SW pin as possible. M9999-030912-A Micrel, Inc. MIC28510 Evaluation Board Schematic Figure 10. Schematic of MIC28510 Evaluation Board (J9, J10, J11, R13, R15 are for testing purposes) March 2012 24 M9999-030912-A Micrel, Inc. MIC28510 Bill of Materials Item C1 C2, C3 C13 C6 Part Number EEU–FC2A101B GRM32ER72A225KA35L C3225X7R2A225KT5 GRM32ER60J107ME20L C8, C9 GRM188R72A104KA35D D1 D2 L1 Q1 R1 R2, R16 R3 R4 R5 R6 March 2012 Murata(2) TDK Murata(2) 0805ZC225MAT2A AVX(4) GRM21BR71A225KA01L Murata(2) TDK 06031C102KAT2A (4) C2012X7R1A105K 1 2.2µF Ceramic Capacitor, X7R, Size 1210, 100V 2 100µF Ceramic Capacitor, X5R, Size 1210, 6.3V 1 0.1µF Ceramic Capacitor, X7R, Size 0603, 50V 1 0.1µF Ceramic Capacitor, X7R, Size 0603, 100V 1 2.2µF Ceramic Capacitor, X7R, Size 0805, 10V 2 1nF Ceramic Capacitor, X7R, Size 0603, 100V 1 4.7nF Ceramic Capacitor, X7R, Size 0603, 50V 1 1µF Ceramic Capacitor, X7R, Size 0805, 10V 1 Small Signal Schottky Diode 1 Murata(2) TDK(3) GRM21BR71A105KA01L 100µF Aluminum Capacitor, SMD, 100V (3) C1608X7R2A102K C1608X7R2A472K Qty. (3) TDK(3) 06035C472KAT2A C4, C5, C7, C14, C15 Murata(2) C1608X7S2A104K GRM188R71H472KA01D C16 TDK(3) AVX(4) GRM188R72A102KA01D C12 Murata 06035C104KAT2A GRM188R71H104KA93D Description (1) (2) AVX(4) C2012X7R1A225K C11 Panasonic 12106D107MAT2A C1608X7R1H104K C10 Manufacturer AVX (2) Murata (3) TDK (4) AVX Murata(2) TDK(3) Open BAT46W–TP MCC(5) BAT46W–7–F Diodes Inc.(6) MMXZ5232B–TP CMDZ5L6 DR125–100–R FCX493 CRCW06034R75FKEA CRCW08051R21FKEA CRCW060316K5FKEA CRCW060310K0FKEA CRCW060380K6FKEA CRCW060340K2FKEA MCC(5) 5.6V Zener Diode (7) Central Semi Cooper Bussmann(8) 10µH Inductor, 5.35A RMS, 7A Saturation Current (6) Diodes Inc/ZETEX 1 1 100V NPN Transistor 1 (9) 4.75Ω Resistor, Size 0603, 1% 1 (9) 1.21Ω Resistor, Size 0805, 1% 2 (9) 16.5kΩ Resistor, Size 0603, 1% 1 (9) 10kΩ Resistor, Size 0603, 1% 1 (9) 80.6kΩ Resistor, Size 0603, 1% 1 (9) 40.2kΩ Resistor, Size 0603, 1% 1 Vishay Dale Vishay Dale Vishay Dale Vishay Dale Vishay Dale Vishay Dale 25 M9999-030912-A Micrel, Inc. MIC28510 Bill of Materials (Continued) Item R7 Part Number CRCW060320K0FKEA Manufacturer Description Qty. (9) 20kΩ Resistor, Size 0603, 1% 1 (9) Vishay Dale R8 CRCW060311K5FKEA Vishay Dale 11.5kΩ Resistor, Size 0603, 1% 1 R9 CRCW06038K06FKEA Vishay Dale(9) 8.06kΩ Resistor, Size 0603, 1% 1 CRCW06034K75FKEA (9) 4.75kΩ Resistor, Size 0603, 1% 1 (9) 3.24kΩ Resistor, Size 0603, 1% 1 (9) 1.91kΩ Resistor, Size 0603, 1% 1 (9) 0Ω Resistor, Size 0603 1 (9) 10kΩ Resistor, Size 0805, 1% 1 (9) 49.9Ω Resistor, Size 0603, 1% 1 (9) 715Ω Resistor, Size 0603, 1% (9) 100kΩ Resistor, Size 0603, 1% 2 (9) 1 R10 R11 R12 R13 R14 R15 CRCW06033K24FKEA CRCW06031K91FKEA CRCW06030000Z0EAHP CRCW080510K0JNEA CRCW060349R9FKEA R17 (OPEN) CRCW0603715RFKEA R18, R19 R20 CRCW0603100KFKEAHP CRCW06032R00FKEA Vishay Dale Vishay Dale Vishay Dale Vishay Dale Vishay Dale Vishay Dale Vishay Dale Vishay Dale Vishay Dale 2Ω Resistor, Size 0603, 1% R21 (OPEN) CRCW0603348RFKEA Vishay Dale(9) 348Ω Resistor, Size 0603, 1% U1 Micrel. Inc.(10) 75V/4A Synchronous Buck DC/DC Regulator MIC28510YJL 1 Notes: 1. Panasonic: www.panasonic.com. 2. Murata: www.murata.com. 3. TDK: www.tdk.com. 4. AVX: www.avx.com. 5. MCC: www.mccsemi.com. 6. Diodes Inc.: www.diodes.com. 7. Central Semi: www.centralsemi.com. 8. Cooper: www.cooperbussman.com. 9. Vishay Dale : www.vishay.com. 10. Micrel, Inc.: www.micrel.com. March 2012 26 M9999-030912-A Micrel, Inc. MIC28510 PCB Layout Recommendations Figure 11. MIC28510 Evaluation Board Top Layer Figure 12. MIC28510 Evaluation Board Mid–Layer 1 (Ground Plane) March 2012 27 M9999-030912-A Micrel, Inc. MIC28510 PCB Layout Recommendations (Continued) Figure 13. MIC28510 Evaluation Board Mid–Layer 2 Figure 14. MIC28510 Evaluation Board Bottom Layer March 2012 28 M9999-030912-A Micrel, Inc. MIC28510 Recommended Land Pattern Red circle indicates Thermal Via. Size and must be connected to GND plane for maximum thermal performance. Green rectangle (with shaded area) indicates Solder Stencil Opening on exposed pad area. Blue and Magenta colored pads indicate different potential. DO NOT connect to GND plane. Thermal Via Via Size/Pitch Solder Stencil Opening/Pitch X 0.300 0.35mm/0.80mm 1.551.20mm/1.75mm Blue Circle/Black Pad X 0.300 0.35mm/0.80mm 0.801.11mm/1.31mm Magenta Circle/Black Pad X 0.300 0.35mm/0.80mm 0.501.11mm/1.31mm Red Circle/Black Pad March 2012 29 M9999-030912-A Micrel, Inc. MIC28510 Package Information 28–Pin 5mm 6mm MLF® (JL) 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. © 2011 Micrel, Incorporated. March 2012 30 M9999-030912-A