MIC45208-1/-2 26V 10A DC-to-DC Power Module General Description Features Micrel’s MIC45208 is a synchronous step-down regulator module, featuring a unique adaptive ON-time control architecture. The module incorporates a DC-to-DC controller, power MOSFETs, bootstrap diode, bootstrap capacitor, and an inductor in a single package; simplifying the design and layout process for the end user. • • • • • • • This highly-integrated solution expedites system design and improves product time-to-market. The internal MOSFETs and inductor are optimized to achieve high efficiency at a low output voltage. The fully-optimized design can deliver up to 10A current under a wide input voltage range of 4.5V to 26V, without requiring additional cooling. ® The MIC45208-1 uses Micrel’s HyperLight Load (HLL) while the MIC45208-2 uses Micrel’s Hyper Speed Control™ (HSC) architecture, which enables ultra-fast load transient response, allowing for a reduction of output capacitance. The MIC45208 offers 1% output accuracy that can be adjusted from 0.8V to 5.5V with two external resistors. Additional features include thermal shutdown protection, input undervoltage lockout, adjustable current limit, and short circuit protection. The MIC45208 allows for safe start-up into a pre-biased output. Datasheet and other support documentation can be found on Micrel’s web site at: www.micrel.com. • • • • • • • • No compensation required Up to 10A output current >93% peak efficiency Output voltage: 0.8V to 5.5V with ±1% accuracy Adjustable switching frequency from 200kHz to 600kHz Enable input and open-drain power good (PG) output Hyper Speed Control (MIC45208-2) architecture enables fast transient response HyperLight Load (MIC45208-1) improves light load efficiency Supports safe startup into pre-biased output CISPR22, Class B compliant –40°C to +125°C junction temperature range Thermal-shutdown protection Short-circuit protection with hiccup mode Adjustable current limit Available in 52-pin 10mm × 10mm × 4mm QFN package Applications • • • • High power density point-of-load conversion Servers, routers, networking, and base stations FPGAs, DSP, and low-voltage ASIC power supplies Industrial and medical equipment Typical Application Efficiency (VIN = 12V) vs. Output Current (MIC45208-1) 100 5.0VOUT 3.3VOUT 90 2.5VOUT 1.8VOUT 1.5VOUT 1.2VOUT 1.0VOUT EFFICIENCY (%) 80 70 60 0.8VOUT 50 40 30 20 fSW = 600kHz 10 0 2 4 6 8 10 12 14 OUTPUT CURRENT (A) Hyper Speed Control is a trademark 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 February 6, 2015 Revision 2.0 Micrel, Inc. MIC45208 Ordering Information Features Junction Temperature Range MIC45208-1YMP 200kHz to 600kHz Hyper Light Load –40°C to +125°C 52-pin 10mm × 10mm × 4mm QFN Pb-Free MIC45208-2YMP 200kHz to 600kHz Hyper Speed Control –40°C to +125°C 52-pin 10mm × 10mm × 4mm QFN Pb-Free Part Number Switching Frequency Package (1) Lead Finish Note: 1. QFN is a lead-free package. Lead-free lead finish is matte tin. Pin Configuration 52-Pin 10mm × 10mm QFN (MP) (Top View) February 6, 2015 2 Revision 2.0 Micrel, Inc. MIC45208 Pin Description MIC45208 Pin Number Pin Name 1, 2 5VDD Internal +5V Linear Regulator Output. Powered by VIN, 5VDD is the internal supply bus for the device. In the applications with VIN<+5.5V, 5VDD should be tied to VIN to bypass the linear regulator. 3, 4 PVDD PVDD: Supply input for the internal low-side power MOSFET driver. 5, 6, 7 PGND Power Ground. PGND is the return path for the step-down power module power stage. The PGND pin connects to the sources of internal low-side power MOSFET, the negative terminals of input capacitors, and the negative terminals of output capacitors. 9 − 11 31 − 35 SW 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. 12 − 19 PVIN Power Input Voltage: Connection to the drain of the internal high side power MOSFET. Connect an input capacitor from PVIN to PGND. 20 − 29 VOUT Power Output Voltage: Connected to the internal inductor, the output capacitor should be connected from this pin to PGND as close to the module as possible. 37, 38 RIA Ripple Injection Pin A. Leave floating, no connection. 39 RIB Ripple Injection Pin B. Connect this pin to FB. 40, 41 ANODE 42, 43, 44 BST Connection to the internal bootstrap circuitry and high-side power MOSFET drive circuitry. Leave floating, no connection. 45, 52 GND Analog Ground. Connect bottom feedback resistor to GND. GND and PGND should be connected together at a low impedance point. 46 FB Feedback: Input to the transconductance amplifier of the control loop. The FB pin is referenced to 0.8V. A resistor divider connecting the feedback to the output is used to set the desired output voltage. Connect the bottom resistor from FB to GND. 47 PG Power Good: Open Drain Output. If used, connect to an external pull-up resistor of at least 10kohm between PG and the external bias voltage. 48 EN Enable: A logic signal to enable or disable the step-down regulator module operation. The EN pin is TTL/CMOS compatible. Logic high = enable, logic low = disable or shutdown. Do not leave floating 49 VIN Internal 5V Linear Regulator Input. A 1μF ceramic capacitor from VIN to GND is required for decoupling. 50 FREQ 51 ILIM 8, 12, 20, 30, 36 KEEPOUT Depopulated pin positions − PVIN ePAD PVIN Exposed Pad. Internally connected to PVIN pins. Please see PCB Layout Recommendations section. − VOUT ePAD VOUT Exposed Pad. Internally connected to VOUT pins. Please see PCB Layout Recommendations section. February 6, 2015 Pin Function Anode Bootstrap Diode: Anode connection of internal bootstrap diode, this pin should be connected to the PVDD pin. Switching Frequency Adjust: Use a resistor divider from VIN to GND to program the switching frequency. Connecting FREQ to VIN sets frequency = 600kHz. Current Limit: Connect a resistor between ILIM and SW to program the current limit. 3 Revision 2.0 Micrel, Inc. MIC45208 Absolute Maximum Ratings(2) Operating Ratings(3) VPVIN, VVIN to PGND ....................................... −0.3V to +30V VPVDD, V5VDD, VANODE to PGND......................... −0.3V to +6V VSW , VFREQ, VILIM, VEN to PGND ............ −0.3V to (VIN +0.3V) VBST to VSW ........................................................ −0.3V to 6V VBST to PGND .................................................. −0.3V to 36V VPG to PGND .................................. −0.3V to (5VDD + 0.3V) VFB, VRIB to PGND .......................... −0.3V to (5VDD + 0.3V) PGND to GND .............................................. −0.3V to +0.3V Junction Temperature .............................................. +150°C Storage Temperature (TS) ......................... −65°C to +150°C Lead Temperature (soldering, 10s) ............................ 260°C ESD Rating…………………………………….ESD Sensitive Supply Voltage (VPVIN, VVIN) .............................. 4.5V to 26V Output Current ............................................................... 10A Enable Input (VEN) .................................................. 0V to VIN Power Good (VPG) ............................................. 0V to 5VDD Junction Temperature (TJ) ........................ −40°C to +125°C (4) Junction Thermal Resistance 10mm × 10mm × 4mm QFN-52 (θJA) ............ 16.6°C/W 10mm × 10mm × 4mm QFN-52 (θJC) ................. 4°C/W Electrical Characteristics(5) VPIN = VIN = VEN = 12V, VOUT = 3.3V, VBST − VSW = 5V, TJ = +25ºC. Bold values indicate −40ºC < TJ < +125ºC, unless otherwise noted. Parameter Condition Min. Typ. Max. Units 26 V 0.75 mA 3 mA Power Supply Input 4.5 Input Voltage Range (VPVIN, VIN) Quiescent Supply Current (MIC45208-1) VFB = 1.5V Quiescent Supply Current (MIC45208-2) VFB = 1.5V Operating Current VPVIN = VIN = 12V, VOUT = 1.8V, IOUT = 0A, fSW = 600kHz Shutdown Supply Current 2.1 MIC45208-1 0.4 MIC45208-2 43 mA SW = Unconnected, VEN = 0V 4 10 µA 5VDD Output 5VDD Output Voltage VIN = 7V to 26V, I5VDD = 10mA 4.8 5.1 5.4 V 5VDD UVLO Threshold V5VDD Rising 3.8 4.2 4.6 V 5VDD UVLO Hysteresis V5VDD Falling LDO Load Regulation I5VDD = 0 to 40mA 400 mV 0.6 2 3.6 TJ = 25°C 0.792 0.8 0.808 −40°C ≤ TJ ≤ 125°C 0.784 0.8 0.816 5 500 % Reference Feedback Reference Voltage FB Bias Current VFB = 0.8V V nA Enable Control 1.8 EN Logic Level High V 0.6 EN Logic Level Low EN Hysteresis EN Bias Current 200 VEN = 12V 5 V mV 10 µA Notes: 2. Exceeding the absolute maximum ratings may damage the device. 3. The device is not guaranteed to function outside operating range. 4. θJA and θJC were measured using the MIC45208 evaluation board. 5. Specification for packaged product only. February 6, 2015 4 Revision 2.0 Micrel, Inc. MIC45208 Electrical Characteristics(5) (Continued) VPIN = VIN = VEN = 12V, VOUT = 3.3V, VBST − VSW = 5V, TJ = +25ºC. Bold values indicate −40ºC < TJ < +125ºC, unless otherwise noted. Parameter Condition Min. Typ. Max. VFREQ = VIN, IOUT = 2A 400 600 750 Units Oscillator Switching Frequency VFREQ = 50%VIN, IOUT = 2A 350 Maximum Duty Cycle Minimum Duty Cycle VFB = 1V Minimum Off-Time 140 kHz 85 % 0 % 200 260 ns Soft-Start Soft-Start Time 3 ms Short-Circuit Protection Current-Limit Threshold VFB = 0.79V −30 −14 0 mV Short-Circuit Threshold VFB = 0V −23 −7 9 mV Current-Limit Source Current VFB = 0.79V 50 70 90 µA Short-Circuit Source Current VFB = 0V 25 35 45 µA SW, BST Leakage Current 10 µA FREQ Leakage Current 10 µA 95 %VOUT Leakage Power Good (PG) 85 PG Threshold Voltage Sweep VFB from Low-to-High 90 PG Hysteresis Sweep VFB from High-to-Low 6 %VOUT PG Delay Time Sweep VFB from Low-to-High 100 µs PG Low Voltage VFB < 90% × VNOM, IPG = 1mA 70 TJ Rising 160 °C 15 °C 200 mV Thermal Protection Overtemperature Shutdown Overtemperature Shutdown Hysteresis February 6, 2015 5 Revision 2.0 Micrel, Inc. MIC45208 Typical Characteristics 100 480 360 VIN = 12V VOUT = 1.8V IOUT = 0A 240 120 80 60 40 20 0 0 -50 -25 0 25 50 75 100 -25 25 0 50 75 100 10 4.5 8.8 13.1 17.4 21.7 INPUT VOLTAGE (V) VDD Supply Voltage vs. Temperature Enable Threshold vs. Temperature EN Bias Current vs. Temperature 4 2 1.6 RISING 1.2 FALLING 0.8 VIN = 12V VOUT = 1.8V 0.4 0.0 0 25 50 75 100 -25 Feedback Voltage vs. Temperature 1.0 2.0 OUTPUT VOLTAGE (V) 2.1 0.9 0.8 VIN = 12V VOUT = 1.8V IOUT = 0A 0.6 0 25 50 0.5 75 100 125 75 TEMPERATURE (°C) February 6, 2015 -50 -25 100 125 0 25 50 75 100 125 TEMPERATURE (°C) Switching Frequency vs. Temperature 1.9 1.8 1.7 VIN = 12V VOUT= 1.8V IOUT = 0A 800 700 600 500 VIN = 12V VOUT = 1.8V IOUT = 2A 400 300 1.5 50 2 900 1.6 25 4 Output Voltage vs. Temperature 1.1 0 6 TEMPERATURE (°C) TEMPERATURE (°C) 0.7 VIN = 12V VOUT = 1.8V IOUT = 0A 8 0 -50 125 SWITCHING FREQUENCY (kHz) 0 26 10 EN BIAS CURRENT (µA) ENABLE THRESHOLD (V) 6 -25 20 TEMPERATURE (°C) VIN = 12V VOUT = 1.8V IOUT = 0A -50 30 TEMPERATURE (°C) 8 -25 40 125 2.0 -50 VEN = 0V R10 = OPEN 0 -50 125 10 VDD SUPPLY VOLTAGE (V) 50 VOUT = 1.8V IOUT = 0A fSW = 600kHz SHUTDOWN CURRENT (µA) SUPPLY CURRENT (mA) SUPPLY CURRENT (µA) 600 FEEBACK VOLTAGE (V) VIN Shutdown Current vs. Input Voltage VIN Operating Supply Current vs. Temperature (MIC45208-2) VIN Operating Supply Current vs. Temperature (MIC45208-1) -50 -25 0 25 50 75 TEMPERATURE (°C) 6 100 125 -50 -25 0 25 50 75 100 125 TEMPERATURE (°C) Revision 2.0 Micrel, Inc. MIC45208 Typical Characteristics (Continued) Efficiency (VIN = 5V) vs. Output Current (MIC45208-1) Output Peak Current Limit vs. Temperature 100 5.0VOUT 3.3VOUT 16 80 14 12 10 8 6 VIN =12V VOUT = 1.8V fSW = 600kHz RLIM = 1.07kΩ 4 90 2.5VOUT 1.8VOUT 1.5VOUT 1.2VOUT 1.0VOUT 70 60 0.8VOUT 50 40 30 -25 0 25 50 75 100 fSW = 600kHz 2 4 6 8 10 12 14 0 2 4 6 8 10 12 14 OUTPUT CURRENT (A) OUTPUT CURRENT (A) Efficiency (VIN = 24V) vs. Output Current (MIC45208-1) Efficiency (VIN = 5V) vs. Output Current (MIC45208-2) Efficiency (VIN = 12V) vs. Output Current (MIC45208-2) 100 0.8VOUT 2.5VOUT 1.8VOUT 1.5VOUT 1.2VOUT 1.0VOUT 0.8VOUT 80 40 30 70 60 50 40 EFFICIENCY (%) 50 70 90 EFFICIENCY (%) 60 2.5VOUT 1.8VOUT 1.5VOUT 1.2VOUT 1.0VOUT 80 100 3.3VOUT 5.0VOUT 3.3VOUT 90 30 fSW = 600kHz 4 6 8 10 12 14 0 2 4 6 8 10 12 60 50 40 14 fSW = 600kHz/200kHz 0 1.95 80 2.5VOUT 1.90 VOUT(V) 10 12 14 2.0 1.80 1.75 1.65 1.60 fSW = 600kHz 8 2.1 1.70 30 6 VOUT = 1.8V 1.85 40 4 Line Regulation OUTPUT VOLTAGE (V) 5.0VOUT 3.3VOUT 1.8VOUT 1.5VOUT 1.2VOUT 1.0VOUT 0.8VOUT 2 OUTPUT CURRENT (A) 2.00 90 20 1.8VOUT 1.5VOUT 1.2VOUT 1.0VOUT 0.8VOUT 70 Load Regulation vs. Input Voltage 100 50 2.5VOUT OUTPUT CURRENT (A) Efficiency (VIN = 24V) vs. Output Current (MIC45208-2) 60 80 10 OUTPUT CURRENT (A) 70 5.0VOUT 3.3VOUT 20 10 2 90 30 20 fSW = 600kHz 10 0 40 TEMPERATURE (°C) 100 20 0.8VOUT 50 10 0 125 60 20 10 -50 70 30 fSW = 600kHz 20 0 2.5VOUT 1.8VOUT 1.5VOUT 1.2VOUT 1.0VOUT 80 EFFICIENCY (%) 90 2 EFFICIENCY (%) 100 3.3VOUT 18 EFFICIENCY (%) CURRENT LIMIT (A) 20 EFFICIENCY (%) Efficiency (VIN = 12V) vs. Output Current (MIC45208-1) VOUT = 1.8V IOUT = 10A 1.9 1.8 1.7 1.6 1.55 10 0 2 4 6 8 10 OUTPUT CURRENT (A) February 6, 2015 12 14 1.50 0.00 1.5 2.00 4.00 6.00 8.00 10.00 OUTPUT CURRENT (A) 7 12.00 4.5 8.8 13.1 17.4 21.7 26.0 INPUT VOLTAGE (V) Revision 2.0 Micrel, Inc. MIC45208 Typical Characteristics (Continued) IC Power Dissipation (VIN = 5V) vs. Output Current 3.5 8 5 3 2.5 2 0.8VOUT VIN = 5V fSW = 600kHz 1.5 1 0.5 0 3.3VOUT 4 2.5VOUT 3.5 1.8VOUT 3 1.5VOUT 1.2VOUT 2.5 1.0VOUT 2 0.8VOUT 1.5 1 0.5 2 4 6 8 10 OUTPUT CURRENT (A) February 6, 2015 12 14 7 3.3VOUT 2.5VOUT 6 1.8VOUT 1.5VOUT 5 1.2VOUT 4 1.0VOUT 3 0.8VOUT 2 1 0 0 0 5.0VOUT VIN = 24V fSW = 600kHz 5.0VOUT VIN = 12V fSW = 600kHz 4.5 IC POWER DISSIPATION (W) 2.5VOUT 1.8VOUT 1.5VOUT 1.2VOUT 1.0VOUT 3.3VOUT IC POWER DISSIPATION (W) IC POWER DISSIPATION (W) IC Power Dissipation (VIN = 24V) vs. Output Current IC Power Dissipation (VIN = 12V) vs. Output Current 0 2 4 6 8 10 OUTPUT CURRENT (A) 8 12 14 0 2 4 6 8 10 12 14 OUTPUT CURRENT (A) Revision 2.0 Micrel, Inc. MIC45208 Functional Characteristics February 6, 2015 9 Revision 2.0 Micrel, Inc. MIC45208 Functional Characteristics (Continued) February 6, 2015 10 Revision 2.0 Micrel, Inc. MIC45208 Functional Characteristics (Continued) February 6, 2015 11 Revision 2.0 Micrel, Inc. MIC45208 Functional Diagram February 6, 2015 12 Revision 2.0 Micrel, Inc. MIC45208 Functional Description 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 falls 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 MIC45208 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. The MIC45208 is an adaptive on-time synchronous buck regulator module built for high-input voltage to low-output voltage conversion applications. The MIC45208 is designed to operate over a wide input voltage range, from 4.5V to 26V, and the output is adjustable with an external resistor divider. An adaptive on-time control scheme is employed to obtain a constant switching frequency in steady state 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, capacitor, and controller. The maximum duty cycle is obtained from the 200ns tOFF(MIN): Theory of Operation As shown in Figure 1, in association with Equation 1, the output voltage is sensed by the MIC45208 feedback pin FB via the voltage divider RFB1 and RFB2, 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 falls 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 Estimator” circuitry: DMAX = t S − t OFF(MIN) tS = 1− 200ns tS Eq. 2 Where: tS = 1/fSW . It is not recommended to use MIC45208 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 MIC45208 during steady state operation. 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. Figure 2 shows the MIC45208 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. Figure 1. Output Voltage Sense via FB Pin t ON(ESTIMATED) = VOUT VIN × fSW Eq. 1 where VOUT is the output voltage, VIN is the power stage input voltage, and fSW is the switching frequency. February 6, 2015 13 Revision 2.0 Micrel, Inc. MIC45208 Unlike true current-mode control, the MIC45208 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 MIC45208 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 the Application Information section for more details about the ripple injection technique. Figure 2. MIC45208 Control Loop Timing Figure 3 shows the operation of the MIC45208 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. Note that the instantaneous switching frequency during load transient remains bounded and cannot increase arbitrarily. The minimum is limited by tON + tOFF(MIN) .Since the variation in VOUT is relatively limited during load transient, tON stays virtually close to its steady-state value. Discontinuous Mode (MIC45208-1 only) In continuous mode, the inductor current is always greater than zero; however, at light loads, the MIC452081 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 4. During this period, the efficiency is optimized by shutting down all the non-essential circuits and minimizing the supply current as the switching frequency is reduced. The MIC45208-1 wakes up and turns on the high-side MOSFET when the feedback voltage VFB drops below 0.8V. The MIC45208-1 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 MIC45208-1 automatically powers down most of the IC circuitry and goes into a low-power mode. Once the MIC45208-1 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 4 shows the control loop timing in discontinuous mode. Figure 3. MIC45208 Load Transient Response February 6, 2015 14 Revision 2.0 Micrel, Inc. MIC45208 Figure 5. MIC45208 Current-Limiting Circuit In each switching cycle of the MIC45208, the inductor current is sensed by monitoring the low-side MOSFET in the OFF period. The sensed voltage VILIM 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 (C15) 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 4. MIC45208-1 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 350µA, allowing the MIC45208-1 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. 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 becomes greater than VCL, and the VILIM falls below PGND, an over-current is triggered causing the IC to enter hiccup mode. 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 MIC45208 implements an internal digital soft-start by making the 0.8V reference voltage VREF ramp from 0 to 100% in about 4ms 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. The short-circuit current limit can be programmed by using Equation 3. Current Limit The MIC45208 uses the RDS(ON) of the low-side MOSFET and external resistor connected from ILIM pin to SW node to set the current limit. R15 = (ICLIM − DIL (PP) × 0.5) × R DS(ON) + VCL ICL Eq. 3 Where: ICLIM = Desired current limit RDS(ON) = On-resistance of low-side power MOSFET, 6mΩ typically. VCL = Current-limit threshold (typical absolute value is 14mV per the Electrical Characteristics table). ICL = Current-limit source current (typical value is 70µA, per the Electrical Characteristics table). February 6, 2015 15 Revision 2.0 Micrel, Inc. MIC45208 ΔIL(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 × (VIN(max) − VOUT ) VIN(max) × fsw × L Eq. 4 The MIC45208 has a 0.8µH inductor integrated into the module. In case of a 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 finish the soft-start successfully. 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. With R15 = 1.24kΩ and C15=10pF, the typical output current limit is 16A. February 6, 2015 16 Revision 2.0 Micrel, Inc. MIC45208 Application Information Setting the Switching Frequency The MIC45208 switching frequency can be adjusted by changing the value of resistors R1 and R2. The switching frequency also depends upon VIN, VOUT and load conditions as MIC45208 uses and adaptive ONtime architecture as explained in Theory of Operation. At lower switching frequencies, the IRMS current will increase due to higher ripple current. Designs need to take this into account when calculating for safe operating area. 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, OS-CON and POSCAP. The output capacitor’s ESR is usually the main cause of the output ripple. The MIC45208 requires ripple injection and the output capacitor ESR affects the control loop from a stability point of view. Figure 6. Switching Frequency Adjustment The maximum value of ESR is calculated as in Equation 6: Equation 5 gives the estimated switching frequency: fSW = fO × R2 R1 + R 2 ESR COUT ≤ Eq. 5 ΔVOUT(PP) Eq. 6 ΔIL(PP) Where: Where: fO = 600kHz (typical per Electrical Characteristics table) ΔVOUT(PP) = Peak-to-peak output voltage ripple R1= 100kΩ is recommended. ΔIL(PP) = Peak-to-peak inductor current ripple R2 needs to be selected in order to set the required switching frequency. Switching Frequency 800 SW FREQ (kHz) 700 VOUT = 5V VIN = 12V 600 500 400 300 200 R1 = 100kΩ 100 0 10.00 100.00 1000.00 10000.00 R2 (kΩ) Figure 7. Switching Frequency vs. R2 February 6, 2015 17 Revision 2.0 Micrel, Inc. MIC45208 Input Capacitor Selection The input capacitor for the power stage input PVIN should be selected for ripple current rating and voltage 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 ΔIL(PP) 2 + ΔIL(PP) × ESR C ΔVOUT(PP) = OUT C × f × 8 OUT SW ( ) ΔVIN = IL(pk) × ESRCIN Eq. 7 Eq. 10 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: Where: D = Duty cycle COUT = Output capacitance value fsw = Switching frequency ICIN(RMS) ≈ IOUT(max) × D × (1 − D) As described in the “Theory of Operation” subsection in the Functional Description, the MIC45208 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 “Ripple Injection” subsection in the Application Information section for more details. The power dissipated in the input capacitor is: 2 PDISS(CIN) = ICIN(RMS) × ESRCIN Equation 13 should be used to calculate the input capacitor. Also it is recommended to keep some margin on the calculated value: CIN ≈ ΔIL(PP) 12 Eq. 12 The general rule is to pick the capacitor with a ripple current rating equal to or greater than the calculated worst case RMS capacitor current. The output capacitor RMS current is calculated in Equation 8: ICOUT (RMS) = Eq.11 Eq. 8 IOUT(MAX) × (1 − D) fSW × dV Eq. 13 Where: dV = The input ripple The power dissipated in the output capacitor is: fSW = Switching frequency 2 PDISS(COUT ) = ICOUT (RMS) × ESR COUT February 6, 2015 Eq. 9 18 Revision 2.0 Micrel, Inc. MIC45208 Output Voltage Setting Components The MIC45208 requires two resistors to set the output voltage as shown in Figure 8: Table 1. VOUT Programming Resistor Look-Up Table The output voltage is determined by Equation 14: Eq. 14 OPEN 0.8V 40.2kΩ 1.0V 20kΩ 1.2V 11.5kΩ 1.5V 8.06kΩ 1.8V 4.75kΩ 2.5V 3.24kΩ 3.3V 1.91kΩ 5.0V The applications are divided into two 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: Where: VFB = 0.8V As shown in Figure 9, the converter is stable without any ripple injection. A typical value of RFB1 used on the standard evaluation board is 10kΩ. If R1 is too large, it may allow noise to be introduced into the voltage feedback loop. If RFB1 is too small in value, it will decrease the efficiency of the power supply, especially at light loads. Once RFB1 is selected, RFB2 can be calculated using Equation 15: R FB2 = VOUT Ripple Injection The VFB ripple required for proper operation of the MIC45208 gM amplifier and error comparator is 20mV to 100mV. However, the output voltage ripple is generally too small to provide enough ripple amplitude at the FB pin and this issue is more visible in lower output voltage applications. If the feedback voltage ripple is so small that the gM amplifier and error comparator cannot sense it, then the MIC45208 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 8. Voltage-Divider Configuration R VOUT = VFB × 1 + FB1 R FB2 RFB2 VFB × R FB1 VOUT − VFB Eq. 15 For fixed RFB1 = 10kΩ, output voltage can be selected by RFB2. Table 1 provides RFB2 values for some common output voltages. February 6, 2015 Figure 9. Enough Ripple at FB from ESR 19 Revision 2.0 Micrel, Inc. MIC45208 The feedback voltage ripple is: ΔVFB(PP) = The injected ripple is: R FB2 × ESR C OUT × ΔIL(PP) R FB1 + R FB2 ΔVFB(PP) = VIN × K div × D × (1 - D) × Eq. 16 1 fSW × τ Eq.17 Where: K div = ΔIL(PP) = The peak-to-peak value of the inductor current ripple R FB1//R FB2 R INJ + R FB1//R FB2 Eq.18 Where: 2. There is virtually no or inadequate ripple at the FB pin voltage due to the very-low ESR of the output capacitors; such is the case with ceramic output capacitor. In this case, the VFB ripple waveform needs to be generated by injecting suitable signal. MIC45208 has provisions to enable an internal series RC injection network, RINJ and CINJ as shown in Figure 10 by connecting RIB to FB pin. This network injects a square-wave current waveform into FB pin, which by means of integration across the capacitor (C14) generates an appropriate saw-tooth FB ripple waveform. VIN = Power stage input voltage D = Duty cycle fSW = Switching frequency τ = (RFB1//RFB2//RINJ) × C14 RINJ= 10kΩ CINJ = 0.1µF In Equations 18 and 19, it is assumed that the time constant associated with C14 must be much greater than the switching period: 1 fSW × τ = T << 1 τ Eq. 19 If the voltage divider resistors RFB1 and RFB2 are in the kΩ range, then a C14 of 1nF to 100nF can easily satisfy the large time constant requirements. Figure 10. Internal Ripple Injection at FB via RIB Pin February 6, 2015 20 Revision 2.0 Micrel, Inc. MIC45208 Thermal Measurements and Safe Operating Area (SOA) 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. The safe operating area (SOA) of the MIC45208 is shown in Figure 11, Figure 12, Figure 13, Figure 14, and Figure 15. These thermal measurements were taken on MIC45208 evaluation board. Since the MIC45208 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 MIC45208. SOA curves should only be used as a point of reference. SOA data was acquired using the MIC45208 evaluation board. Thermal performance depends on the PCB layout, board size, copper thickness, number of thermal vias, and actual airflow. February 6, 2015 21 Revision 2.0 MIC45208 11 MAXIMUM OUTPUT CURRENT (A) MAXIMUM OUTPUT CURRENT (A) Micrel, Inc. 10 9 8 7 6 0 LFM 200 LFM 5 400 LFM 4 80 85 90 95 100 105 110 115 11 10 9 8 7 6 400 LFM 120 70 MAXIMUM OUTPUT CURRENT (A) MAXIMUM OUTPUT CURRENT (A) 10 9 8 7 0 LFM 200 LFM 400 LFM 4 75 80 85 90 85 90 95 100 105 110 115 120 11 10 9 8 7 6 5 0 LFM 200 LFM 400 LFM 4 40 45 50 55 60 65 70 75 80 85 90 95 100105110 95 100 105 110 115 120 AMBIENT TEMPERATURE (°C) AMBIENT TEMPERATURE (°C) Figure 13. MIC45208 Power Derating vs. Airflow (12VIN to 3.3VOUT) MAXIMUM OUTPUT CURRENT (A) 80 Figure 12. MIC45208 Power Derating vs. Airflow (12VIN to 1.5VOUT 11 70 75 AMBIENT TEMPERATURE (°C) Figure 11. MIC45208 Power Derating vs. Airflow (5VIN to 1.5VOUT) 5 200 LFM 4 AMBIENT TEMPERATURE (°C) 6 0 LFM 5 Figure 14. MIC45208 Power Derating vs. Airflow (24VIN to 1.5VOUT) 11 10 9 8 7 6 0 LFM 200 LFM 5 400 LFM 4 40 45 50 55 60 65 70 75 80 85 90 95 100105110 AMBIENT TEMPERATURE (°C) Figure 15. MIC45208 Power Derating vs. Airflow (24VIN to 3.3VOUT) February 6, 2015 22 Revision 2.0 Micrel, Inc. MIC45208 PCB Layout Guidelines Warning: To minimize EMI and output noise, follow these layout recommendations. Input Capacitor • 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. 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 ceramic input capacitor. • If a non-ceramic input capacitor is placed in parallel with the input capacitor, it must be recommended for switching regulator applications and the operating voltage. • In “Hot-Plug” applications, an electrolytic bypass capacitor must be used to limit the over-voltage spike seen on the input supply with power is suddenly applied. If hot-plugging is the normal operation of the system, using an appropriate hot-swap IC is recommended. Figure 16 is optimized from a 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 (Optional) • Depending on the operating conditions, a RC snubber on the same side of the board can be used. Place the RC and as close to the SW pin as possible if needed. 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. Output Capacitor • Use a wide trace to connect the output capacitor ground terminal to the input capacitor ground terminal. Figure 16. Top And Bottom Layer of a Four-Layer Board • Phase margin will change as the output capacitor value and ESR changes. The following guidelines should be followed to insure proper operation of the MIC45208 module: • 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. Place the IC close to the point-of-load (POL). • Use thick traces to route the input and output power lines. • Analog and power grounds should be kept separate and connected at only one location with low impedance. February 6, 2015 23 Revision 2.0 Micrel, Inc. MIC45208 PCB Layout Recommendations Top − Copper Layer 1 Copper Layer 2 February 6, 2015 24 Revision 2.0 Micrel, Inc. MIC45208 PCB Layout Recommendations (Continued) Copper Layer 3 Bottom Copper Layer 4 February 6, 2015 25 Revision 2.0 Micrel, Inc. MIC45208 Simplified PCB Design Recommendations After completion of the periphery pad design, the larger exposed pads will be designed to create the mounting surface of the QFN exposed heatsink. The primary transfer of heat out of the QFN will be directly through the bottom surface of the exposed heatsink. To aid in the transfer of generated heat into the PCB, the use of an array of plated through-hole vias beneath the mounted part is recommended. The typical via hole diameter is 0.30mm to 0.35mm, with center-to-center pitch of 0.80 to 1.20mm. Periphery I/O Pad Layout and Large Pad for Exposed Heatsink The board design should begin with copper/metal pads that sit beneath the periphery leads of a mounted QFN. The board pads should extend outside the QFN package edge a distance of approximately 0.20mm per side: Total pad length = 10.00mm + (0.20mm per side x 2 sides) = 10.40mm . Note: Exposed metal trace is “mirror image” of package bottom view. Figure 17. Package Bottom View vs. PCB Recommended Exposed Metal Trace February 6, 2015 26 Revision 2.0 Micrel, Inc. MIC45208 Solder Paste Stencil Design (Recommend stencil thickness is 125 ±25µm) The solder stencil aperture openings should be smaller than the periphery or large PCB exposed pads to reduce any chance of build-up of excess solder at the large exposed pad area which can result to solder bridging. The suggested reduction of the stencil aperture opening is typically 0.20mm smaller than exposed metal trace. The suggested reduction of the stencil aperture opening is typically 0.20mm smaller than exposed metal trace. Note: A critical requirement is to not duplicate land pattern of the exposed metal trace as solder stencil opening as the design and dimension values are different. Note: Cyan-colored shaded pad indicate exposed trace keep out area. Figure 18. Solder Stencil Opening Figure 19. Stack-Up of Pad Layout and Solder Paste Stencil February 6, 2015 27 Revision 2.0 Micrel, Inc. MIC45208 Evaluation Board Schematic Bill of Materials Item C1 C2, C3 Part Number EEE-FK1V221P C3216X5R1H106M160AB Manufacturer Panasonic (6) (7) TDK C2X, C9, C10, C7, C7X, C13 (8) Description Qty. 220µF/35V, ALE Capacitor (optional) 1 10µF/50V, 1206, X5R, 10%, MLCC 2 Open 6 0.1µF/50V, X7R, 0603, 10%, MLCC 3 100µF/6.3V, X5R, 1206, 20%, MLCC 2 C4, C8, C14 GRM188R71H104KA93D Murata C5, C6 C3216X5R0J107M160AB TDK C11 GRM1885C1H150JA01D Murata 15pF/50V, NP0, 0603, 5%, MLCC 3 C12 C1608C0G1H222JT TDK 2.2nF/50V, NP0, 0603, 5%, MLCC 1 CON1, CON2, CON3, CON4 8191k 15A, 4-Prong Through-Hole Screw Terminal 4 (9) Keystone Notes: 6. Panasonic: www.panasonic.com. 7. TDK: www.TDK.com. 8. Murata: www.murata.com. 9. Keystone: www.keyelco.com. February 6, 2015 28 Revision 2.0 Micrel, Inc. MIC45208 Bill of Materials (Continued) Item J1 J2, J3, J4, TP3 − TP5 R1, R10 Part Number M50-3500742 90120-0122 CRCW0603100K0FKEA Manufacturer Harwin (10) (11) Molex Vishay Dale (12) R2, R12, R13, R16 Description Qty. Header 2x7 1 Header 2 6 100kΩ, 1%, 1/10W, 0603, Thick Film 2 Open 4 R3 CRCW060340K2FKEA Vishay Dale 40.2kΩ, 1%, 1/10W, 0603, Thick Film 1 R4 CRCW06020K0FKEA Vishay Dale 20kΩ, 1%, 1/10W, 0603, Thick Film 1 R5 CRCW060311K5FKEA Vishay Dale 11.5kΩ, 1%, 1/10W, 0603, Thick Film 1 R6 CRCW06038K06FKEA Vishay Dale 8.06kΩ, 1%, 1/10W, 0603, Thick Film 1 R7 CRCW06034K75FKEA Vishay Dale 4.75kΩ, 1%, 1/10W, 0603, Thick Film 1 R8 CRCW06033K24FKEA Vishay Dale 3.24kΩ, 1%, 1/10W, 0603, Thick Film 1 R9 CRCW06031K91FKEA Vishay Dale 1.91kΩ, 1%, 1/10W, 0603, Thick Film 1 R11 CRCW060349K9FKEA Vishay Dale 49.9kΩ, 1%, 1/10W, 0603, Thick Film 1 R14 CRCW060310K0FKEA Vishay Dale 10kΩ, 1%, 1/10W, 0603, Thick Film 1 R15 CRCW06031K37FKEA Vishay Dale 1.37kΩ, 1%, 1/10W, 0603, Thick Film 1 R17, R18, R19 RCG06030000Z0EA Vishay Dale 0Ω Resistor, 1%, 1/10W, 0603, Thick Film 3 TP7 − TP14 1502-2 Single-End, Through-Hole Terminal 8 26V/10A DC-to-DC Power Module 1 U1 MIC45208-1YMP MIC45208-2YMP Keystone (13) Micrel, Inc. Notes: 10. Harwin: http://www.harwin.com 11. Molex: www.molex.com. 12. Vishay-Dale: www.vishay.com. 13. Micrel: www.micrel.com. February 6, 2015 29 Revision 2.0 Micrel, Inc. MIC45208 Package Information and Recommended Landing Pattern(14) 52-Pin 10mm × 10mm QFN (MP) Note: 14. Package information is correct as of the publication date. For updates and most current information, go to www.micrel.com. February 6, 2015 30 Revision 2.0 Micrel, Inc. MIC45208 Package Information and Recommended Landing Pattern(14) (Continued) February 6, 2015 31 Revision 2.0 Micrel, Inc. MIC45208 Package Information and Recommended Landing Pattern(14) (Continued) February 6, 2015 32 Revision 2.0 Micrel, Inc. MIC45208 Thermally-Enhanced Landing Pattern February 6, 2015 33 Revision 2.0 Micrel, Inc. MIC45208 Thermally-Enhanced Landing Pattern (Continued) February 6, 2015 34 Revision 2.0 Micrel, Inc. MIC45208 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. 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. © 2014 Micrel, Incorporated. February 6, 2015 35 Revision 2.0