MIC24046-H Pin-Programmable, 4.5V − 19V, 5A Step-Down Converter General Description Features Micrel’s MIC24046-H is a pin-programmable, highefficiency, wide-input range, 5A, synchronous step-down regulator. The MIC24046-H is perfectly suited for multiplevoltage rail application environments typically found in computing and telecommunication systems. It can be programmed by pin strapping various parameters, such as output voltage, switching frequency, and current-limit values. The pin-selectable switching frequency, valleycurrent-mode control technique, high-performance error amplifier, and external compensation allow for the best tradeoffs between high-efficiency and the smallest possible solution size. • • • • 2 The MIC24046-H is pin-out compatible with its I Cprogrammable counterparts from the same family. The MIC24046-H is available in a thermally-efficient, space-saving, 20-pin 3mm × 3mm QFN package with an operating junction temperature range of –40°C to +125°C. Datasheets and support documentation are available on Micrel’s website at: www.micrel.com. • • • • • • • 4.5V to 19V input voltage range 5A (maximum) output current High efficiency (>90%) Pin-selectable output voltages: − 0.7V, 0.8V, 0.9V, 1.0V, 1.2V, 1.5V, 1.8V, 2.5V, and 3.3V ±1% output voltage accuracy Supports safe start-up with pre-biased output Pin-selectable current limit and switching frequency Internal soft-start and thermal shutdown protection Hiccup-mode short-circuit protection Available in a 20-pin 3mm × 3mm QFN package –40°C to +125°C junction temperature range Applications • Servers, data storage, routers, and base stations • FPGAs, DSP, and low-voltage ASIC power Typical Application MIC24046-H 12VIN 5A DC-to-DC Converter Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com July 7, 2015 Revision 1.1. Micrel, Inc. MIC24046-H Ordering Information Part Number MIC24046-HYFL Junction Temperature Range Package Lead Finish –40°C to +125°C 20-Pin 3 mm × 3 mm QFN Pb-Free Pin Configuration 20-Pin 3mm × 3mm QFN (FL) (Top View) Pin Description Pin Number Pin Name Pin Function Input Voltage for the Buck Converter Power Stage: These pins are the drain terminal of the internal high-side N-channel MOSFET. A 10µF minimum ceramic capacitor should be connected from VIN to PGND as close as possible to the device. A combination of multiple ceramic capacitors of different sizes is recommended. 1−2 VIN 3 − 4, 13 PGND 5−6 LX 7 BST 8 IC 9 VOSET0 Three-state Pin (Low, High, and High-Z) for Output Voltage Programming: Together with VOSET1, VOSET0 defines nine logic values corresponding to nine output voltage selections. 10 VOSET1 Three-State Pin (Low, High, and High-Z) for Output Voltage Programming: Together with VOSET0, VOSET1 defines nine logic values corresponding to nine output voltage selections. July 7, 2015 Low-Side MOSFET Source Terminal and Low-Side Driver Return: Connect the ceramic input capacitors to PGND as close as possible to the device. Switch Node: Drain (low-side MOSFET) and source (high-side MOSFET) connection of the internal power N-channel FETs. The external inductor (switched side) and bootstrap capacitor (bottom terminal) must be connected to these pins. Bootstrap: Supply voltage for the driver of the high-side N-channel power MOSFET. Connect the bootstrap capacitor (top terminal) to this pin. Internally Connected for test mode purposes. Connect to AGND or leave floating in normal operation. 2 Revision 1.1 Micrel, Inc. MIC24046-H Pin Description (Continued) Pin Number Pin Name 11 ILIM 12 FREQ Three-State (Low, High, and High-Z) Switching Frequency Selection Pin. 14 AGND Analog Ground: Quiet ground for the analog circuitry of the internal regulator and return terminal for the external compensation network. 15 COMP Transconductance Error Amplifier Output: Connect a compensation network from this pin to AGND. 16 OUTSNS Output Sensing: Connect this pin directly to the buck converter output voltage. This pin is the top side terminal of the internal feedback divider. 17 EN/DLY Precision Enable/Turn-On Delay Input. The EN/DLY pin is first compared against a 507mV threshold to turn-on the on-board LDO regulator. The EN/DLY pin is then compared against a 1.21V (typical) threshold to initiate output power delivery. A 150mV typical hysteresis prevents chattering when power delivery is started. A 2µA (typical) current source pulls up the EN/DLY pin. Turn-on delay can be achieved by connecting a capacitor from EN/DLY to ground, while using an open-drain output to drive the EN/DLY pin. 18 VDDA Output of the internal linear regulator and internal supply for analog control. A 1µF minimum ceramic capacitor should be connected from this pin to AGND; 2.2µF nominal value recommended. 19 VDDP Internal Supply Rail for the MOSFET Drivers (fed by the VDDA pin): An internal resistor (10Ω) between pins VDDP and VDDA is provided in the regulator in order to implement an RC filter for switching noise suppression. A 1µF minimum ceramic capacitor should be connected from this pin to PGND; 2.2µF nominal value recommended. 20 VINLDO Input of the Internal Linear Regulator: This pin is typically connected to the input voltage of the buck converter stage (VIN). If VINLDO and VIN are connected to different voltage rails, individually bypass VINLDO to ground with a 100nF ceramic capacitor. PGND_EP PGND VIN_EP VIN VIN Exposed Pad: Electrically connected to VIN pins. If an input power distribution plane is available, connect with thermal vias to that plane to improve heat-sinking. Follow recommendations as illustrated in the PCB Layout Recommendations section LX_EP LX LX Exposed Pad: Electrically connected to LX pins. Follow recommendations as illustrated in the PCB Layout Recommendations section July 7, 2015 Pin Function Three-State (Low, High, and High-Z) Current-Limit Selection Pin. PGND Exposed Pad: Electrically connected to PGND pins. Connect with thermal vias to the ground plane to ensure adequate heat-sinking. Follow recommendations as illustrated in the PCB Layout Recommendations section 3 Revision 1.1 Micrel, Inc. MIC24046-H Absolute Maximum Ratings(1) Operating Ratings(2) VVIN, VVINLDO to AGND ................................... −0.3V to +20V VVDDP, VVDDA to AGND ..................................... −0.3V to +6V VVINLDO to VVDDA ............................................. −0.3V to +20V VVDDP to VVDDA............................................... −0.3V to +0.3V VVOSETx, VFREQ, VILIM, to AGND .........................−0.3V to +6V VBST to VLX ....................................................... −0.3V to +6V VBST to AGND ................................................ −0.3V to +26V VEN/DLY to AGND ........................ −0.3V to VVDDA + 0.3V, +6V VCOMP, VOUTSNS to AGND ........... −0.3V to VVDDA + 0.3V, +6V AGND to PGND............................................ −0.3V to +0.3V Junction Temperature .............................................. +150°C Storage Temperature (TS) ......................... −65°C to +150°C Lead Temperature (soldering, 10s) ............................ 260°C (4) ESD Rating HBM ......................................................................... 2kV MM ......................................................................... 150V Supply Voltage (VVIN, VVINLDO) ........................... 4.5V to 19V Externally Applied Analog and Drivers Supply Voltage (VVINLDO = VVDDA = VVDDP) .................................. 4.5V to 5.5V Enable Voltage (VEN/DLY) .................................... 0V to VVDDA Output Current ................................................................. 5A Junction Temperature (TJ) ........................ −40°C to +125°C Junction to Ambient Thermal Resistance (3) 20-pin 3mm x 3mm QFN (θJA) ........................ 29°C/W Electrical Characteristics(5) VVIN = VVINLDO = 12V; CVDDA= 2.2µF, CVDDP = 2.2µF, TA = 25°C, unless otherwise noted. Bold values indicate −40°C ≤ TJ ≤ +125°C. Symbol Parameter Test Conditions Min. Typ. Max. Units 19 V VIN Supply 4.5 VIN Input Range IVINQ Disable Current EN/DLY = 0V IVINOp Operating Current EN/DLY > 1.28V, OUTSNS = 1.15 × VOUT(NOM), no switching, TA = TJ = 25°C TA = TJ = 25°C 35 −40°C ≤ TJ ≤ +125°C 42 56 µA 5.6 7 mA 5.4 V VDDA 5V Supply VDDA Operating Voltage EN/DLY > 0.58V, I(VDDA) = 0mA to 10mA 4.8 5.1 Dropout Operation VINLDO = 4.5V, EN/DLY > 0.58V, I(VDDA) = 10mA 3.6 3.75 V VDDA Undervoltage Lockout UVLO_R VDDA UVLO Rising VVDDA Rising, EN/DLY > 1.28V 3.1 3.5 3.9 V UVLO_F VDDA UVLO Falling VVDDA Falling, EN/DLY > 1.28V 2.87 3.2 3.45 V UVLO_H VDDA UVLO Hysteresis 300 mV Notes: 1. Exceeding the absolute maximum ratings may damage the device. 2. The device is not guaranteed to function outside operating range. 3. θJA is measured on the MIC24046-H evaluation board. 4. Devices are ESD sensitive. Handling precautions recommended. Human body model, 1.5kΩ in series with 100pF. 5. Specification for packaged product only. July 7, 2015 4 Revision 1.1 Micrel, Inc. MIC24046-H Electrical Characteristics(5) (Continued) VVIN = VVINLDO = 12V; CVDDA= 2.2µF, CVDDP = 2.2µF, TA = 25°C, unless otherwise noted. Bold values indicate −40°C ≤ TJ ≤ +125°C. Symbol Parameter Test Conditions Min. Typ. Max. Units 507 580 mV EN/DLY Control EN_LDO_R LDO Enable Threshold Turns On VDDA LDO EN_LDO_F LDO Disable Threshold Turns Off VDDA LDO 460 EN_LDO_H LDO Threshold Hysteresis 1.14 491 mV 16 EN_R EN/DLY Rising Threshold Initiates power-stage operation EN_F EN/DLY Falling Threshold Stops power-stage operation EN_H EN/DLY Hysteresis EN_I EN/DLY Pull-Up Current TA = TJ = 25°C 1.21 mV 1.28 V 1.06 V 150 mV 1 2 3 µA Switching Frequency fSZ Programmable Frequency (High Z) FREQ = High Z (open) 360 400 440 kHz fS0 Programmable Frequency 0 FREQ = Low (GND) 500 565 630 kHz fS1 Programmable Frequency 1 FREQ = High (VDDA) 700 790 880 kHz Overcurrent Protection ILIM_HS0 HS Current Limit 0 ILIM = Low (GND) 6.0 7.1 8.1 A ILIM_HS1 HS Current Limit 1 ILIM = High (VDDA) 8.1 9.3 10.3 A ILIM_HSZ HS Current Limit High Z ILIM = High Z (open) 9.3 10.5 11.9 A LEB Top FET Current-Limit Leading Edge-Blanking Time ILIM_LS0 LS Current Limit 0 ILIM = Low (GND) 3.0 4.6 6.3 A ILIM_LS1 LS Current Limit 1 ILIM = High (VDDA) 4.0 6.2 7.9 A ILIM_LSZ LS Current Limit Hi Z ILIM = High Z (Open) 5.0 6.8 8.6 A INHICC_DE OC Events Count for Hiccup Number of subsequent cycles in current limit before entering hiccup overload protection. 15 tHICC_WAIT Hiccup Wait Time Duration of the High-Z state on LX before new soft-start. 3x Soft-Start Time 108 ns Clock Cycles Power Switches RBOTTOM Bottom FET ON resistance VVIN = VVINLDO = VVDDP = VVDDA = 5V, VBST-VLX = 5V, TA = TJ = 25°C 16 21 mΩ RTOP Top FET ON resistance VVIN = VVINLDO = VVDDP = VVDDA = 5V, VBST-VLX = 5V, TA = TJ = 25°C 38 50 mΩ Minimum LX ON Time TA = TJ = 25°C 26 TOFF(MIN) Minimum LX OFF time VVIN = VVINLDO = VVDDA = 5V, VOUTSNS = 3V, FREQ = Open (400kHz setting), VVOSET0 = VVOSET1 = 0V (3.3V setting),TA = TJ = 25°C DMIN Minimum Duty Cycle VOUTSNS >1.1 × VOUT(NOM) Pulse-Width Modulation (PWM) TON(MIN) July 7, 2015 5 90 135 0 ns 190 ns % Revision 1.1 Micrel, Inc. MIC24046-H Electrical Characteristics(5) (Continued) VVIN = VVINLDO = 12V; CVDDA= 2.2µF, CVDDP = 2.2µF, TA = 25°C, unless otherwise noted. Bold values indicate −40°C ≤ TJ ≤ +125°C. Symbol Parameter Test Conditions Min. Typ. Max. Units Gm Error Amplifier GmEA Error-Amplifier Transconductance AEA Error-Amplifier DC Gain ISR_SNK Error-Amplifier Source/Sink Current COMP_H COMP Output Swing High 2.4 V COMP_L COMP Output Swing Low 0.8 V GmPS COMP-to-Inductor Current Transconductance 12.5 A/V 1.5 mmho 50000 V/V −400 VOUT = 1.2V, IOUT = 4A +400 µA Output Voltage DC Accuracy OutErr12 Output Voltage Accuracy for Ranges 1 and 2 OutErr3 Output Voltage Accuracy for Range 3 4.75V ≤ VIN ≤ 19V, VOUT = 0.7V to 1.8V TA = TJ = −40°C to 125°C, IOUT = 0A 4.75V ≤ VIN ≤ 19V, VOUT = 2.49V to 3.3V −1 1 % −1.5 1.5 % TA = TJ = −40°C to 125°C, IOUT = 0A LoadReg Load Regulation IOUT = 0A to 5A 0.25 % LineReg Line Regulation 6V< VIN < 19V, IOUT = 2A 0.1 % VOUT = 0.7V, 0.8V, 0.9V, 1.0V, 1.2V 0.45 V/ms Internal Soft-Start SS_SR Reference Soft-Start Slew Rate Thermal Shutdown TSHDN Thermal Shutdown 160 °C TSHDN_HYST Thermal-Shutdown Hysteresis 25 °C 82.3 % Efficiency η July 7, 2015 Efficiency VIN = 12V, VOUT = 0.9V, IOUT = 2A fS = fSZ = 400kHz, L = 1.2µH, TA = 25°C 6 Revision 1.1 Micrel, Inc. MIC24046-H Typical Characteristics Output Voltage vs. Output Current Efficiency vs. Output Current 100 VOUT = 2.49V OUTPUT VOLTAGE (V) 80 VOUT = 1.2V VOUT = 1.0V VOUT = 1.5V VOUT = 0.9V VOUT = 0.8V 60 50 VIN = 12V VOUT = 0.7V 1.215 0.91 1.21 0.905 0.9 0.895 VIN = 12V VOUT = 0.9V 0.89 40 1 2 3 4 5 0 OUTPUT CURRENT (A) Output Voltage vs. Output Current 1.195 1 2 3 4 2.505 VIN = 12V VOUT = 1.5V 1.805 1.8 1.795 VIN = 12V VOUT = 1.8V 1.79 1.485 1 2 3 4 5 OUTPUT CURRENT (A) 5 2.5 2.495 2.49 VIN = 12V VOUT = 2.49V 2.485 1.785 0 4 Output Voltage vs. Output Current 1.81 1.49 3 Output Voltage vs. Output Current 1.51 1.495 2 OUTPUT CURRENT (A) 2.51 1.5 1 OUTPUT CURRENT (A) 1.815 1.505 VIN = 12V VOUT = 1.2V 0 5 1.515 OUTPUT VOLTAGE (V) OUTPUT VOLTAGE (V) 1.2 1.185 0.885 0 1.205 1.19 OUTPUT VOLTAGE (V) EFFICIENCY (%) 90 70 0.915 VOUT = 1.8V OUTPUT VOLTAGE (V) VOUT = 3.3V Output Voltage vs. Output Current 2.48 0 1 2 3 OUTPUT CURRENT (A) 4 5 0 1 2 3 4 5 OUTPUT CURRENT (A) Output Voltage vs. Output Current 3.33 OUTPUT VOLTAGE (V) 3.32 3.31 3.3 3.29 VIN = 12V VOUT = 3.3V 3.28 3.27 0 1 2 3 4 5 OUTPUT CURRENT (A) July 7, 2015 7 Revision 1.1 Micrel, Inc. MIC24046-H Functional Diagram July 7, 2015 8 Revision 1.1 Micrel, Inc. MIC24046-H Functional Description The MIC24046-H is a pin-programmable, 5A valley current-mode controlled regulator, with an input voltage range from 4.5V to 19V. Internal LDO, Supply Rails (VIN, VINLDO, VDDA, VDDP) VIN represents the power train input. These pins are the drain connection of the internal high-side MOSFET and should be bypassed to GND with a X5R or X7R 10µF (minimum) ceramic capacitor, placed as close as possible to the IC. A combination of ceramic capacitors of different sizes is recommended. The MIC24046-H requires a minimal amount of external components. Only inductor, supply decoupling capacitors and compensation network are external. The flexibility in designing the external compensation allows the user to optimize the design across the entire input voltage and selectable output voltages range. An internal LDO (input = VINLDO) provides a clean supply (5.1V typ.) for the analog circuits at pin VDDA. The internal LDO is typically powered from the same power rail fed at VIN; however VINLDO can also be higher or lower than VIN and can be connected to any other voltage within its recommended limits. VINLDO and VDDA should be locally bypassed (see Pin Description). A small series resistor (typically 2Ω-10Ω) can be used in combination with the VINLDO bypass capacitor to implement a RC filter for suppression of large highfrequency switching noise. Theory of Operation Valley current-mode control is a fixed-frequency, leadingedge-modulated PWM current mode control. As opposed to peak-current-mode, in valley current mode the clock marks the turn-off of the high-side switch, and the turn on of the low-side switch. After this instant, in the MIC24046H the low-side switch current level is compared against the reference current signal from the error amplifier. As soon as the falling low-side switch current signal drops below the current reference signal, the high side switch is turned on. As a result, the inductor valley current is regulated to a level dictated by the output of the error amplifier. The internal LDO is enabled when the voltage at the EN/DLY pin exceeds about 0.51V and regulation takes place as soon as enough voltage has established between the VINLDO and VDDA pins. If an external 5V±10% is available it is possible to bypass the internal LDO by connecting VINLDO, VDDA and VDDP together at the external 5V rail, thus improving overall efficiency. An internal undervoltage lock-out circuit (UVLO) monitors the level of VDDA. As shown in the “Compensation Design” sub-section within the Application Information section, the feedback loop includes an internal programmable reference (REFDAC) and output voltage sensing attenuator (R2/R1), removing the need for external feedback components and improving regulation accuracy. Output voltage feedback is achieved by connecting OUTSNS directly to the output. The high-performance transconductance error amplifier drives an external compensation network at the COMP pin. The voltage at COMP represents the reference current signal. The latter is fed to the valley current mode modulator, which also adds slope compensation to guarantee current-loop stability. Valley current-mode control requires slope compensation at duty cycles less than 50% for current-loop stability. The slope compensation circuit is internal, and it is automatically adapted in amplitude depending upon the frequency, output voltage range, and voltage differential (VVIN − VOUTSNS). Internal low-RDS(ON) power MOSFETs, the associated adaptive gate driver and internal bootstrap diode complete the power train. VDDP is the power supply rail for the gate drivers and bootstrap circuit. This pin is subject to high-current spike with high-frequency content. To prevent these from polluting the analog VDDA supply, a separate capacitor is needed for VDDP pin bypassing. An internal 10Ω resistor is provided between VDDA and VDDP allowing a switching noise attenuation RC filter with the minimum amount of external components to be implemented. It is possible − although typically not necessary − to lower the RC time constant by connecting an external resistor between VDDA and VDDP. Enable/Delay (EN/DLY) EN/DLY is a dual-threshold pin that turns the internal LDO ON/OFF and starts/stops the power delivery to the output. This is shown in Figure 1: Overcurrent protection and thermal shutdown protect the MIC24046-H from faults or abnormal operating conditions. July 7, 2015 9 Revision 1.1 Micrel, Inc. MIC24046-H Switching Frequency (FREQ) The MIC24046-H features three different selectable switching frequencies: 400kHz, 565kHz, and 790kHz. Pre-Biased Output Start-Up The MIC24046-H is designed to achieve safe start-up into a pre-biased output without discharging the output capacitors. Thermal Shutdown The MIC24046-H has thermal-shutdown protection that prevents operation at excessive temperature. The thermal-shutdown threshold is typically set at 160°C with a hysteresis of 25°C. Overcurrent Protection (ILIM) and Hiccup Mode Short-Circuit Protection The MIC24046-H features instantaneous cycle-by-cycle current limit with current sensing both on the low-side and high-side switches, and hiccup mode for prolonged overloads or short-circuit conditions. Figure 1. EN/DLY Pin Functionality The threshold for power delivery (EN_R) is a precise 1.21V ±70mV. A 150mV typical hysteresis prevents chattering due to switching noise and/or slow edges. A 2µA typical pull-up current with ±1µA accuracy permits the implementation of a start-up delay by means of an external capacitor. In this case, it is necessary to use an open-drain driver to disable the MIC24046-H while maintaining the start-up delay function. Low-side cycle-by-cycle protection detects the current level of the inductor current during the low-side MOSFET ON time. The high-side MOSFET turn-on is inhibited as long as the low-side MOSFET current limit is above the current-limit threshold level. The inductor current will continue decaying until the current falls below the threshold, then the high-side MOSFET will be enabled again according to the duty cycle requirement from the PWM modulator. The mechanism is illustrated in Figure 2. Inductor (LX) and Bootstrap (BST) The external inductor is connected to LX. The high-side MOSFET driver circuit is powered between BST and LX by means of an external capacitor (typically 100nF) that is replenished from rail VDDP during the low-side MOSFET ON-time. The bootstrap diode is internal. Output Sensing (OUTSNS) and Compensation (COMP) OUTSNS should be connected exactly to the desired point-of-load regulation avoiding parasitic resistive drops. The impedance seen into OUTSNS is high (tens of kΩ), therefore its loading effect is typically negligible. OUTSNS is also used by the slope compensation generator. COMP is the connection for the external compensation network. COMP is driven by the output of the transconductance error amplifier. Care must be taken to return the compensation network ground directly to AGND. Figure 2. Low-Side Cycle-by-Cycle Current-Limit Action Soft-Start The MIC24046-H internal reference is ramped up at a 0.45V/ms rate. Note that this is the internal reference soft-start slew rate and that the actual slew rate seen at the output should take into account the internal divider attenuation as detailed in the Application Information section. July 7, 2015 10 Revision 1.1 Micrel, Inc. MIC24046-H The low-side current limit is programmable at three different levels (3A, 4A, and 5A loads), in order to fit different application requirements. Note that since the low-side current limit acts on the valley current, the DC output current level IOUT at which the low-side cycle-bycycle current limit is engaged is higher than the current limit value by an amount equal to ΔILPP/2, where ΔILPP is the peak-to-peak inductor ripple current. The high-side current limit is approximately 1.4 − 1.5 times bigger than the low-side current limit (typical values). The high-side cycle-by-cycle current limit immediately truncates the high-side ON time without waiting for the OFF clocking event. A leading-edge-blanking (LEB) timer (108ns, typical) is provided on the high-side cycle-by-cycle current limit to mask switching noise and to prevent false triggering of the protection. Before the LEB timer has expired, highside cycle-by-cycle current limit action cannot take place. Hiccup mode protection reduces power dissipation in permanent short circuit conditions. On each clock cycle at which a low-side cycle-by-cycle current limit event is detected, a 4-bits up/down counter is incremented. On each clock cycle without a concurrent low-side current limit event, the counter is decremented or left at zero (counter cannot wrap-around below 0000 and above 1111). Note that high-side current limit events do not increment the counter, only low-side current limit event detections do. If the counter reaches 1111 (15 events), then the highand low-side MOSFETs are tri-stated and power delivery to the output is inhibited for the duration of 3x the softstart time. This digital integration mechanism provides immunity to momentary overloading of the output. After the wait time, the MIC24046-H retries entering operation and initiates a new soft-start sequence. The flowchart of Figure 3 illustrates the hiccup mode short-circuit protection logic flow. Note that hiccup mode short-circuit protection is active at all times, including the soft-start ramp. July 7, 2015 11 Revision 1.1 Micrel, Inc. MIC24046-H Figure 3. Hiccup Mode Short-Circuit Protection Logic July 7, 2015 12 Revision 1.1 Micrel, Inc. MIC24046-H Application Information The programmed VIN UVLO threshold VIN_RISE is given by: Programming Start-Up Delay and External UVLO The EN/DLY pin allows programming of an external startup delay. In this case, the driver for the EN/DLY pin should be an open-drain/open-collector type as shown in Figure 4: R2 VIN _ RISE = EN _ R × 1 + − EN _ I × R2 R1 Eq. 2 where: EN_R = 1.21V EN_I = 2µA R1 and R2 = External resistors. To desensitize the VIN UVLO threshold against variations of the pull-up current EN_I, it is recommended to run the R1 − R2 voltage divider at a significantly higher current level than the EN_I current. The corresponding VIN UVLO hysteresis VIN_HYS is calculated as follows: Figure 4. Programmable Start-Up Delay Function The start-up delay is the delay time from the OFF falling edge to the assertion of the enable power delivery signal and can be calculated as shown in Equation 1: t SU _ DLY = EN _ R × CDLY EN _ I R2 VIN _ HYS = 150mV ⋅ 1 + R1 Eq. 3 Similar calculations also apply to the internal LDO activation threshold. Eq. 1 Setting the Switching Frequency The MIC24046-H switching frequency can programmed using FREQ as shown in Table 1: where: EN_R = 1.21V be Table 1. Switching Frequency Settings EN_I = 2µA FREQ CDLY = Delay programming external capacitor The EN/DLY pin can also be used to program an UVLO threshold for power delivery by means of an external resistor divider, as described in the following Figure 5. Frequency Hi-Z (open) 400 kHz 0 (GND) 565 kHz 1 (VDDA) 790 kHz Figure 5. Programmable External UVLO Function July 7, 2015 13 Revision 1.1 Micrel, Inc. MIC24046-H Setting the Output Voltage The MIC24046-H output voltage can be programmed by means of VOSET0, VOSET1 as shown in Table 2. Ensure the maximum operating junction temperature is not exceeded in high output power applications. Inductor Selection When selecting an inductor, it is important to consider the following factors: Table 2. Output Voltage Settings VOSET1 VOSET0 Output Voltage 0 (GND) 0 (GND) 3.3V 0 (GND) 1 (VDDA) 2.5V (2.49V) 1 (VDDA) 0 (GND) 1.8V 1 (VDDA) 1 (VDDA) 1.5V 0 (GND) Hi-Z (Open) 1.2V Hi-Z (Open) 0 (GND) 1.0V 1 (VDDA) Hi-Z (Open) 0.9V Hi-Z (Open) 1 (VDDA) 0.8V Hi-Z (Open) Hi-Z (Open) 0.7V • • • • • Inductance Rated current value Size requirements DC resistance (DCR) Core losses The inductance value is critical to the operation of MIC24046-H. Since the MIC24046-H is a valley currentmode regulator, it needs slope compensation for stable current loop operation at duty cycles below 50%. Slope compensation is internally added according to the frequency and output voltage selection, assuming a minimum inductance value for the given operating condition. According to this assumption, the minimum inductor values recommended for stable current loop operation are listed in Table 4. Note that the minimum suggested inductance values should be met when taking into account inductor tolerance and its change with bias level. To achieve accurate output voltage regulation, the OUTSNS pin (internal feedback divider top terminal) shall be Kelvin-connected as close as possible to the point-ofregulation top terminal. Also, since both the internal reference and the internal feedback divider bottom terminal are referred to AGND, it is important to minimize voltage drops between the AGND and the point-ofregulation return terminal. Table 4. Recommended Inductance Values at VIN = 12V Setting the Current Limit The MIC24046-H valley-mode current limit on the lowside MOSFET can be programmed by means of ILIM as shown in Table 3. VOUT SELECTION 0.7V, 0.8V, 0.9V, 1.0V, 1.2V Table 3. Current-Limit Setting FREQUENCY MINIMUM INDUCTANCE 400kHz 0.97 565kHz 0.68 790kHz 0.49 400kHz 1.51 565kHz 1.06 Low-Side Valley Current Limit (Typical Value) Rated Output Current 0 (GND) 4.6 A 3A 790kHz 0.76 1 (VDDA) 6.2 A 4A 400kHz 2.42 Hi-Z (Open) 6.8 A 5A 565kHz 1.70 790kHz 1.21 ILIM 1.5V, 1.8V 2.49V, 3.3V Note that the programmed current-limit values act as pulse-by-pulse current-limit thresholds on the valley inductor current. If the inductor current has not decayed below the threshold at the time the PWM requires a new ON time, the high-side MOSFET turn-on is either delayed until the valley current recovers below the threshold or skipped. Each time the high-side MOSFET turn-on is skipped, a 4-bit up-down counter is incremented. When the counter reaches the configuration 1111, a hiccup sequence is invoked in order to reduce power dissipation under prolonged short-circuit conditions. Slope compensation is also internally adapted to input voltage, however higher inductance values than those listed in Table 4 may be required to maintain current loop stability, especially at the lower end of the input voltage range (4.5V to 8V). The highest current-limit setting (6.8A) is intended to comfortably accommodate a 5A application. July 7, 2015 14 Revision 1.1 Micrel, Inc. MIC24046-H From the switching frequency, input voltage, output voltage setting, and load current the peak-to-peak inductor current ripple and the peak inductor current can be calculated as: Inductor current ratings are generally given in two methods: permissible DC current, and saturation current. Permissible DC current can be rated for a 20°C to 40°C temperature rise. Saturation current can be rated for a 10% to 30% loss in inductance. Make sure that the nominal current of the application is well within the permissible DC current ratings of the inductor, also depending on the allowed temperature rise. Note that the inductor permissible DC current rating typically does not include inductor core losses. These are a very important contribution to the total inductor core loss and temperature increase in high-frequency DC-to-DC converters, since core losses increase rapidly with the excitation frequency. 1 − VO /VIN ∆IL_PP = VO fS × L IL, PEAK = IO + When saturation current is specified, make sure that there is enough design margins, so that the peak current does not cause the inductor to enter deep saturation. ∆IL_PP Eq. 6 2 The capacitive ripple ΔVR, C and the ESR ripple ΔVR, are given by: Also pay attention to the inductor saturation characteristic in current limit. The inductor should not heavily saturate even in current limit operation, otherwise the current might instantaneously run away and reach potentially destructive levels. Typically, ferrite-core inductors exhibit an abrupt saturation characteristic, while powdered-iron or composite inductors have a soft-saturation characteristic. Peak current can be calculated as illustrated in Equation 4: ∆VR, C = ∆IL_PP ∆VR, ESR = ESR × ∆IL_PP output As shown in Equation 4, the peak inductor current is inversely proportional to the switching frequency and the inductance. The lower the switching frequency or inductance, the higher the peak current. As input voltage increases, the peak current also increases. ripple is then size Eq. 9 Choose the output capacitor value and ESR such that ΔVR is within specifications. Capacitor tolerance should be considered for worst case calculations. In case of ceramic output capacitors, also take into account the decrease of effective capacitance versus applied DC bias. and The worst-case load transient for output capacitor calculation is an instantaneous 100% to 0% load release when the inductor current is at its peak value. In this case, all the energy stored in the inductor is absorbed by the output capacitor while the converter stops switching and keeps the low-side FET ON. • Steady-state ripple • Maximum voltage deviation during load transient For steady-state ripple calculation, the ESR and the capacitive ripple both contribute to the total ripple amplitude. July 7, 2015 Eq. 8 Eq. 4 ∆VR ≅ ∆VR, C + ∆VR, ESR Output Capacitor Selection Two main requirements determine the characteristics of the output capacitor CO: ESR Eq. 7 8 × fs × C O The total peak-to-peak conservatively estimated as: 1 − VO /VIN IL, PEAK = IO + VO 2 × f × L Eq. 5 15 Revision 1.1 Micrel, Inc. MIC24046-H The peak output voltage overshoot ΔVOUT happens when the inductor current has decayed to zero, and can be calculated as in Equation 10: ΔVO = VO2 + L 2 I − VO C O L, PEAK For ideal input filtering (assuming a DC input current feeding the filtered buck power stage), and by neglecting the capacitor ESR contribution to the input ripple (typically possible for ceramic input capacitors), the minimum capacitance value CIN(MIN) needed for a given input peak-to-peak ripple voltage ΔVr, IN can be estimated as shown in Equation 12: Eq. 10 CIN(MIN) = The minimum output capacitance value CO(MIN) needed to limit the output overshoot below ΔVOUT is: C O(MIN) = IO × D × (1 − D) DVr,IN × fS Eq. 12 where: 2 L × IL, PEAK Eq. 11 (ΔVO + VO )2 − VO2 D is the duty cycle at the given operating point. The RMS current IIN,RMS of the input capacitor is estimated as in Equation 13: The latter turns out to be the most stringent requirement on capacitor value in most applications. Low equivalent series resistance (ESR) ceramic output capacitors with X5R or X7R temperature characteristics are recommended. IIN, RMS = IO × D × (1 - D) Eq. 13 For low output voltage applications with demanding load transient requirements, it is often more convenient to use a combination of polarized and ceramic output capacitors for smallest solution size. Note that for a given output current IO, the worst case values are obtained at D = 0.5. Input Capacitor Selection Two main requirements determine characteristics of the input capacitor: Compensation Design As a simple first-order approximation, the valley-currentmode-controlled buck power stage can be modeled as a voltage-controlled current-source feeding the output capacitor and load. The inductor current state-variable is removed and the power-stage transfer function from COMP to the inductor current is modeled as a transconductance (GmPS). The simplified model of the control loop is shown in Figure 6. The power-stage transconductance GmPS shows some dependence on current levels and it is also somewhat affected by process variations, therefore some design margin is recommended against the typical value GmPS = 12.5 A/V (see Electrical Characteristics). the size Multiple input capacitors can be used to reduce input ripple amplitude and/or individual capacitor RMS current. and • Steady-state ripple • RMS current The buck converter input current is a pulse train with very fast rising and falling times so low-ESR ceramic capacitors are recommended for input filtering, because of their good high-frequency characteristics. July 7, 2015 16 Revision 1.1 Micrel, Inc. MIC24046-H The MIC24046-H uses a transconductance (GmEA = 1.5mA/V) error amplifier. Frequency compensation is implemented with a Type-II network (RC1, CC1, and CC2) connected from COMP to AGND. The compensator transfer function consists of an integrator for zero DC (voltage regulation error), of one zero to boost the phase margin of the overall loop gain around the crossover frequency and one additional pole that can be used to cancel the output capacitor ESR zero, or to further attenuate switching frequency ripple. In both cases, the additional pole makes the regulation loop less susceptible to switching frequency noise. The additional pole is created by capacitor CC2. The compensator transfer function HC(S) (from OUTSNS to COMP) is as Equation 17: Figure 6. Simplified Small-Signal Model of the Voltage Regulation Loop This simplified approach disregards all issues related to the inner current loop, like its stability and bandwidth. This approximation is good enough for most operating scenarios, where the voltage-loop bandwidth is not pushed to aggressively high frequencies. HC(S) = − × Based on the model shown in Figure 6, the control-tooutput transfer function is: s 1 + VO(S) π × f Z 2 = GmPS × R L × GCO(S) = VC(S) s 1 + 2π × fP 1 R1 × GmEA × S × (C C1 + C C2 ) R1 + R 2 (1 + S × R C1 × C C1 ) C × C C2 1 + S × R C1 × C1 C C1 + C C2 Eq. 17 The overall voltage loop gain TV(S) is the product of the control-to-output and of the compensator transfer functions: Eq. 14 TV (S) = GCO(S) × HC(S) Eq. 18 where: The value of the attenuation ratio R1/(R1 + R2) depends on the output voltage selection, and can be retrieved as illustrated in Table 5: fZ and fP = The frequencies associated with the output capacitor ESR zero and with the load pole, respectively: Table 5. Internal Feedback Divider Attenuation Values fZ = 1 2π × C O × ESR 1 fP = 2π × C O × (ESR + R L ) July 7, 2015 R1/(R1 + R2) A (A = 1 + R2/R1) 0.7V − 1.2V 1 1 1.5V − 1.8V 0.5 2 0.333 3 VO Range Eq. 15 2.5V(2.49V) − 3.3V Eq. 16 17 Revision 1.1 Micrel, Inc. MIC24046-H The procedure for compensation design follows these steps: CC2 is intended to place the compensator pole at the frequency of the output capacitor ESR zero, and/or to achieve additional switching ripple/noise attenuation. 1. Set the TV(S) loop gain crossover frequency fXO in the range fS/20 to fS/10. Lower values of fXO permit a more predictable and robust phase margin. Higher values of fXO would involve additional considerations about the current loop bandwidth in order to achieve a robust phase margin, therefore a more conservative approach is highly recommended: fS 20 f XO ≈ If the output capacitor is a polarized one, its ESR zero will typically occur at low enough frequencies to cause the loop gain to flatten out and not roll-off at a -20 dB/decade slope around or just after the crossover frequency fXO. This is undesirable, because of scarce compensation design robustness, and because of switching noise susceptibility. The compensator pole is then used to cancel the output capacitor ESR zero and to achieve a well-behaved roll-off of the loop gain above the crossover frequency. Eq. 19 If the output capacitors are only ceramic ones, their ESR zeroes frequencies could be very high (in many cases even above the switching frequency itself). Loop gain rolloff at −20dB/decade well beyond the crossover frequency is ensured, but even in this case, it is good practice to still make use of the compensator pole to further attenuate switching noise, while conserving phase margin at the crossover frequency. For example, setting the compensator pole at 5 fXO, will limit its associated phase loss at the crossover frequency to about 11°. Placement at even higher frequencies N × fXO (N > 5) will reduce phase loss even further, at the expense of less noise/ripple attenuation at the switching frequency. Some attenuation of the switching frequency noise/ripple is achieved as long as N × fXO < fS. 2. Select RC1 to achieve the target crossover frequency fXO of the overall voltage loop. This typically happens where the power stage transfer function GCO(S) is rolling off at -20dB/dec. The compensator transfer function HC(S) is in the so-called mid-band gain region where CC1 can be considered a DC-blocking short circuit while CC2 can still be considered as an open circuit, as illustrated in Equation 20: R1 + R2 2π × C O × f XO R C1 = ⋅ R1 GmEA ⋅ GmPS Eq. 20 For polarized output capacitor, compensator pole placement at the ESR zero frequency is achieved shown in Equation 23: 3. Select capacitor CC1 to place the compensator zero at the load pole. The load pole moves around with load variations, so to calculate the load pole use as a load resistance RL the value determined by the nominal output current IO of the application, as shown in Equation 21 and Equation 22: RL = VO IO C C1 = C O × (ESR + R L ) R C1 C C2 = Eq. 23 Eq. 21 For ceramic output capacitor, compensator pole placement at N × fXO (N ≥ 5, N × fXO < fS) is achieved as detailed in Equation 24: Eq. 22 C C2 = 4. Select capacitor CC2 to place the compensator pole at the frequency of the output capacitor ESR zero, or at ≥ 5 fXO, whichever is lower. July 7, 2015 1 R C1 1 − C O × ESR C C1 18 1 2π × R C1 × N × f XO − 1 C C1 Eq. 24 Revision 1.1 Micrel, Inc. MIC24046-H Output Voltage Soft-Start Rate The MIC24046-H features internal analog soft-start, such that the output voltage can be smoothly increased to the target regulation voltage. The soft-start rate given in the Electrical Characteristics is referred to the error amplifier reference, and therefore the effective soft-start rate value seen at the output of the module has to be scaled according to the internal feedback divider attenuation values listed in Table 5. To calculate the effective output voltage soft-start slew rate SS_SROUT based on the particular output voltage setting and the reference softstart slew rate SS_SR, use the following formula: SS _ SR OUT = A ⋅ SS _ SR Eq. 24 Where: The value of A (amplification, A =1 + R2/R1 ) is given in the right column of Table 5. July 7, 2015 19 Revision 1.1 Micrel, Inc. MIC24046-H Typical Application Schematic Bill of Materials Item Part Number C1 GRM31CR61E226ME15 C2, C7 GRM155R71E104KE14 C3, C4 Manufacturer Description Qty. X5R, 22µF 25V 20%, Size 1206 Capacitor 1 Murata X7R, 100nF 25V 10%, Size 0402 Capacitor 2 GRM31CR60J107ME39 Murata X5R, 100uF 6.3V 20%, Size 1206 Capacitor C5, C6 GRM155R61C225KE11 Murata X5R, 2.2µF 16V 10%, Size 0402 Capacitor 2 C8 GRM1555C1H470JA01 Murata C0G, 47pF 50V 5%, Size 0402 Capacitor 1 C9 GRM155R71E103KA01 Murata X7R, 10nF 25V 10%, Size 0402 Capacitor 1 R1 RC0402-2551F Chip, 2.55kΩ 1%, Size 0402 Resistor 1 SMT, 1.5µH, ISAT = 7.1A IRMS = 5.2A Inductor 1 Pin-Programmable, 4.5V − 19V, 5A Step-Down Converter 1 L1 U1 XAL4020-152ME MIC24046-HYFL Murata (6) ANY Coilcraft (7) (8) Micrel, Inc. Notes: 6. Murata: www.murata.com. 7. Coilcraft: www.coilcraft.com. 8. Micrel, Inc.: www.micrel.com. July 7, 2015 20 Revision 1.1 Micrel, Inc. MIC24046-H PCB Layout Recommendations Top Layer Layer 1 July 7, 2015 21 Revision 1.1 Micrel, Inc. MIC24046-H PCB Layout Recommendations (Continued) Layer 2 Bottom Layer July 7, 2015 22 Revision 1.1 Micrel, Inc. MIC24046-H Package Information and Recommended Landing Pattern(9) 20-Pin 3mm × 3mm QFN (FL) Note: 9. Package information is correct as of the publication date. For updates and most current information, go to www.micrel.com. July 7, 2015 23 Revision 1.1 Micrel, Inc. MIC24046-H 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, Inc. is a leading global manufacturer of IC solutions for the worldwide high performance linear and power, LAN, and timing & communications markets. The Company’s products include advanced mixed-signal, analog & power semiconductors; high-performance communication, clock management, MEMs-based clock oscillators & crystal-less clock generators, Ethernet switches, and physical layer transceiver ICs. Company customers include leading manufacturers of enterprise, consumer, industrial, mobile, telecommunications, automotive, and computer products. Corporation headquarters and state-of-the-art wafer fabrication facilities are located in San Jose, CA, with regional sales and support offices and advanced technology design centers situated throughout the Americas, Europe, and Asia. Additionally, the Company maintains an extensive network of distributors and reps worldwide. Micrel makes no representations or warranties with respect to the accuracy or completeness of the information furnished in this datasheet. 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. 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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. © 2015 Micrel, Incorporated. July 7, 2015 24 Revision 1.1