MIC22601 4 MHz, 6A Integrated Switch Synchronous Buck Regulator General Description Features The Micrel MIC22601 is a high efficiency 6A Integrated switch synchronous buck (step-down) regulator. The MIC22601 is optimized for highest efficiency (greater than 90%), while still switching at 4MHz over a broad load range with only 0.22µH inductor and down to 22µF output capacitor. The ultra-high speed control loop keeps the output voltage within regulation even under extreme transient load swings commonly found in FPGAs and low voltage ASICs. The output voltage can be adjusted down to 0.7V to address all low voltage power needs. A full range of sequencing and tracking options is available with the MIC22601. The enable/delay pin, combined with the power good PG/POR pin, allows multiple outputs to be sequenced in any way during turn on and turn off. The RC (Ramp Control™) pin allows the device to be connected to another product in the MIC22xxx and/or MIC68xxx family, to keep the output voltages within a certain ΔV on start up. The MIC22601 is available in a 24-pin 4mm x 4mm MLF® package with a junction operating temperature range from –40°C to +125°C. Data sheets and support documentation can be found on Micrel’s web site at: www.micrel.com. • • • • • • • • • • • • • • Input voltage range: 2.6V to 5.5V 4MHz PWM frequency Adjustable output voltage option down to 0.7V Output current to 6A Small Passive components: 0.22µH and 22µF Full sequence and tracking ability Power On Reset/Power Good Ultra fast transient response – Easy RC compensation 100% maximum duty cycle Fully integrated MOSFET switches Micro power shutdown Thermal shutdown and current limit protection 24-pin 4mmx4mm MLF® package –40°C to +125°C junction temperature range Applications • • • • • • High power density point of load conversion Servers and routers Blu-ray/DVD players and recorders Computer peripherals Base stations FPGA, DSP and low voltage ASIC power _____________________________________________________________________________________________________________________________________ Typical Application 100 Efficiency vs. Load Current 90 80 VIN = 3.6V VIN = 5V 70 60 50 40 0 VOUT = 3.3V TA = 25°C L = 470nF 1 2 3 4 5 OUTPUT CURRENT (A) 6 Figure 1. Typical Application Circuit, 6A 4MHz Synchronous Output Converter Sequencing & Tracking Ramp Control is a trademark 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 May 2009 M9999-050509-A Micrel, Inc. MIC22601 Ordering Information Part Number Voltage Junction Temp. Range Package Lead Finish MIC22601YML Adj. –40° to +125°C 24-Pin 4x4 MLF® Pb-Free ® Note: MLF is a GREEN RoHS compliant package. Lead finish is NiPdAu. Mold compound is Halogen Free. PGND SW SW SW SW PGND Pin Configuration PVIN PVIN EN SVIN DELAY SGND EP RC COMP PGND SW SW SW PVIN SW FB PGND POR PVIN 24-Pin 4mm x 4mm MLF® (ML) Pin Description May 2009 Pin Number Pin Name 1, 6, 13, 18 PVIN Power Supply Voltage (Input): Requires bypass capacitor to GND. Pin Name 17 SVIN Signal Power Supply Voltage (Input): Requires bypass capacitor-toGND. 2 EN Enable/Delay (Input): This pin has a 1.24V band gap reference. When the pin is pulled higher than this the part will start up. Below this voltage the device is in its low quiescent current mode. The pin has a 1µA current source charging it to VIN. By adding a capacitor to this pin a delay may easily be generated. The enable function will not operate with an input voltage lower than the min specified. 4 RC Ramp Control: A capacitor-to-ground from this pin determines the slew rate of the output voltage during start-up. This can be used for tracking capability as well as soft start. 14 FB Feedback: Input to the error amplifier, connect to the external resistor divider network to set the output voltage. 15 COMP 5 POR/PG 7, 12, 19, 24 PGND Compensation pin (Input): Place a RC-to-GND to compensate the device, refer to the applications section. Power On Reset (Output): Open-drain output device indicates when the output is out of regulation and is active after the delay set by the delay pin. High when the Power is Good Power Ground (Signal): Ground 16 SGND Signal Ground (Signal): Ground 3 DELAY Delay (Input): Add a capacitor to set the delay from FB reaching 90% nominal to POR asserting high. 8, 9, 10, 11, 20, 21, 22, 23 SW EP GND Switch (Output): Internal power MOSFET output switches. Exposed Pad (Power): Must make a full connection to a GND plane for full output power to be realized. 2 M9999-050509-A Micrel, Inc. MIC22601 Absolute Maximum Ratings(1) Operating Ratings(2) Supply Voltage (VIN) .........................................................6V Output Switch Voltage (VSW) ............................................6V Output Switch Current (ISW).......................Internally Limited Logic Input Voltage (VEN, VLQ)........................... VIN to –0.3V Storage Temperature (Ts) .........................–65°C to +150°C Lead Temperature (soldering 10sec.)........................ 260°C EDS Rating(3) ................................................................+2kV Supply Voltage (VIN)......................................... 2.6V to 5.5V Junction Temperature (TJ) ..................–40°C ≤ TJ ≤ +125°C Thermal Resistance 4mm x 4mm MLF-24 (θJC) ................................. 14ºC/W 4mm x 4mm MLF-24 (θJA) .................................40°C/W Electrical Characteristics(4) TA = 25°C with VIN = VEN = 3.3V; VOUT = 1.8V, unless otherwise specified. Bold values indicate –40°C≤ TJ ≤ +125°C. Parameter Supply Voltage Range Under-Voltage Lockout Threshold UVLO Hysteresis Quiescent Current, PWM Mode Shutdown Current [Adjustable] Feedback Voltage FB Pin Input Current Current Limit Output Voltage Line Regulation Output Voltage Load Regulation Maximum Duty Cycle Switch ON-Resistance PFET Switch ON-Resistance NFET Oscillator Frequency 22601 EN/DLY Threshold Voltage EN/DLY Source Current Condition Min (turn-on) 2.6 2.4 VEN =>1.34V; VFB = 0.9V (not switching) VEN = 0V ± 2% (over temperature) VFB = 0.9*VNOM VOUT 1.8V; VIN = 2.6 to 5.5V, ILOAD= 100mA 100mA < ILOAD < 6000mA, Vin = 3.3V VFB ≤ 0.5V ISW = 1000mA; VFB=0.5V ISW = -1000mA; VFB=0.9V 6 VIN = 2.6 to VIN = 5.5V Ramp Control Current 0.7 Power On Reset IPG(LEAK) VPORH = 5.5V; POR = High Power On Reset VPG(LO) Output Logic-Low Voltage (undervoltage condition), IPOR = 5mA Threshold, % of VOUT below nominal Over-Temperature Shutdown Over-Temperature Shutdown Hysteresis Units 5.5 2.6 0.03 0.025 4 1.24 1 4.8 1.34 1.3 1 1.3 µA 1 2 µA µA 1 10 0.2 0.2 1300 10 0.714 14 100 RC Pin IRAMP Hysteresis Max V V mV µA µA V nA A % % % Ω Ω MHz V µA 2.5 280 850 5 0.686 3.2 1.14 0.7 Power On Reset VPG Typ 130 7.5 10 mV 12.5 % 2 % 160 20 °C °C Notes: 1. Exceeding the absolute maximum rating may damage the device. 2. The device is not guaranteed to function outside its operating rating. 3. Devices are ESD sensitive. Handling precautions recommended. 4. Specification for packaged product only. May 2009 3 M9999-050509-A Micrel, Inc. MIC22601 Typical Characteristics RDSON (mO) 3.8 3.6 120 80 100 60 40 REFERENCE VOLTAGE (V) 120 25 20 15 5 120 100 40 20 0 4.2 4 3.8 3.6 2.0 30 0 2.5 Switching Frequency vs. Input Voltage 4.4 3.2 2.5 vs. Input Voltage 10 VIN = 3.3V VIN = 3.3V 3.4 OUTPUT VOLTAGE (V) 45 4.0 -20 0.690 P-Channel RDSON 4.2 -40 0.692 VIN = 5.5V TEMPERATURE (°C) 35 May 2009 0.696 0.694 FREQUENCY (MHz) 1.14 1.12 4.4 TEMPERATURE (°C) 0.698 4.6 1.18 1.16 40 3.4 0.702 0.700 4.8 1.20 Switching Frequency vs. Temperature Reference Voltage vs. Temperature TEMPERATURE (°C) 1.24 1.22 1.10 5.5 0.704 Enable Voltage vs. Temperature 80 5.5 6 1.28 1.26 4.6 3.2 3.5 4 4.5 5 5.5 INPUT VOLTAGE (V) 100 3.5 4 4.5 5 INPUT VOLTAGE (V) 80 FREQUENCY (MHz) 4.8 TA = 25°C 3 3 TA = 25°C 3.0 3.5 4.0 4.5 5.0 INPUT VOLTAGE (V) 0.708 0.706 -40 0.690 2.5 60 1.1 2.5 TA = 25°C 0.692 40 1.14 120 0.694 0 1.16 80 0.696 -40 1.2 1.18 60 0.698 ENABLE VOLTAGE (V) 1.22 60 ENABLE VOLTAGE (V) 1.24 40 0.700 1.30 1.26 20 0.702 1.28 1.12 0 0.704 Enable Level vs. Input Voltage 1.3 0.710 0.706 -20 TEMPERATURE (°C) 120 80 40 20 0 -20 -40 0 100 VIN = 3.3V 0.1 0.2 0 2.5 Reference Voltage vs. Input Voltage 20 REFERENCE VOLTAGE (V) 0.708 60 INPUT CURRENT (mA) 0.710 0.3 0.2 0.4 TEMPERATURE (°C) 0.9 Not Switching FB = 1V 0.8 0.4 -20 -40 0 VIN = 3.3V 0.6 20 3 2 0.8 0 4 1.0 -20 6 5 1.0 0.6 0.5 INPUT CURRENT (mA) 7 Quiescent Current vs. Temperature 0.7 Not Switching FB = 1V 1 1 TA = 25°C 0 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 INPUT VOLTAGE (V) 1.2 9 8 100 5 4 3 2 Quiescent Current vs. Input Voltage Shutdown Current vs. Temperature 10 9 8 7 6 INPUT CURRENT (µA) INPUT CURRENT (µA) 10 Shutdown Current vs. Input Voltage TCASE = 90°C 3 3.5 4 4.5 5 INPUT VOLTAGE (V) 4 5.5 TCASE = 25°C 3 3.5 4 4.5 5 INPUT VOLTAGE (V) 5.5 Output Voltage vs VRC 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0 0 V 0.2 0.4 0.6 VRC (V) OUT = 1.8V 0.8 1 M9999-050509-A Micrel, Inc. MIC22601 Typical Characteristics (continued) 100 Efficiency vs. Output Current VIN = 2.5V 90 80 60 60 VOUT = 3.3V TA = 25°C L = 470nF Bode (5V to 1.8V - 6A) 470nH and 47µF 40 30 Phase 20 10 Gain 0 40 0 6 180 50 144 40 30 108 72 36 0 20 10 0 100µF OSCON on VIN 1 May 2009 10 100 1000 10000 FREQUENCY (kHz) 70 VIN = 3.3V VIN = 5V 60 VOUT = 1.8V TA = 25°C L = 470nF 1 2 3 4 5 OUTPUT CURRENT (A) Bode (3.3V to 1.8V - 6A) 470nH and 47µF Phase 50 180 50 144 40 30 108 72 36 0 Gain 40 0 6 20 10 0 100µF OSCON on VIN 1 Efficiency vs. Output Current 80 VIN = 5V 50 GAIN (dB) 50 1 2 3 4 5 OUTPUT CURRENT (A) 90 80 70 50 GAIN (dB) VIN = 5V 70 40 0 VIN = 3.6V 90 VIN = 3.6V 100 GAIN (dB) 100 Efficiency vs. Load Current 10 100 1000 10000 FREQUENCY (kHz) 5 VOUT = 1V L = 470nF 1 2 3 4 5 OUTPUT CURRENT (A) Bode (5V to 3.3V - 6A) 470nH and 47µF 6 180 144 Phase 108 72 36 Gain 0 100µF OSCON on VIN 1 10 100 1000 10000 FREQUENCY (kHz) M9999-050509-A Micrel, Inc. MIC22601 Functional Characteristics May 2009 6 M9999-050509-A Micrel, Inc. MIC22601 Typical Circuits and Waveforms Sequencing Circuit and Waveform Tracking Circuit and Waveform May 2009 7 M9999-050509-A Micrel, Inc. MIC22601 Functional Diagram Figure 2. IC Block Diagram May 2009 8 M9999-050509-A Micrel, Inc. MIC22601 FB The feedback pin provides a control path to control the output. A resistor divider connecting the feedback to the output is used to adjust the desired output voltage. Refer to the feedback section in the “Applications Information” for more detail. Functional Description PVIN PVIN is the input supply to the internal 30mΩ P Channel Power MOSFET. This should be connected externally to the SVIN pin. The supply voltage range is from 2.6V to 5.5V. A 10µF ceramic is recommended for bypassing each PVIN supply. POR This is an open drain output. A 47k resistor can be used for a pull up to this pin. POR is asserted high when output voltage reaches 90% of nominal set voltage and after the delay set by CDELAY. POR is asserted low without delay when enable is set low or when the output goes below the -10% threshold. For a Power Good (PG) function, the delay can be set to a minimum. This can be done by removing the Delay capacitor. EN/DLY This pin is internally fed with a 1µA current source to VIN. A delayed turn on is implemented by adding a capacitor to this pin. The delay is proportional to the capacitor value. The internal circuits are held off until EN/DLY reaches the enable threshold of 1.24V. RC RC allows the slew rate of the output voltage to be programmed by the addition of a capacitor from RC-toground. RC is internally fed with a 1µA current source and VOUT slew rate is proportional to the capacitor and the 1µA source. SW This is the connection to the source of the internal PChannel MOSFET and drain of the N-Channel MOSFET. This is a high frequency high power connection; therefore traces should be kept as short and as wide as practical. In order to achieve the highest efficiency and reduce internal losses, connect a Schottky diode directly from this pin-to-ground as close to the package as possible. Delay Adding a capacitor to this pin allows the delay of the POR signal. When VOUT reaches 90% of its nominal voltage, the Delay pin current source (1µA) starts to charge the external capacitor. At 1.24V, POR is asserted high. SGND Internal signal ground for all low power sections. PGND Internal ground connection to the source of the internal N-Channel MOSFETs. Comp The MIC22601 uses an internal compensation network containing a fixed frequency zero (phase lead response) and pole (phase lag response) which allows the external compensation network to be much simplified for stability. The addition of a single capacitor and resistor will add the necessary pole and zero for voltage mode loop stability when using low value, low ESR ceramic capacitors. May 2009 9 M9999-050509-A Micrel, Inc. MIC22601 performance, the inductor should be placed very close to the SW nodes of the IC. For this reason, the heat of the inductor is somewhat coupled to the IC, which offers some level of protection if the inductor gets too hot. It is important to test all operating limits before settling on the final inductor choice. The size requirements refer to the area and height requirements that are necessary to fit a particular design. Please refer to the inductor dimensions on their datasheet. DC resistance is also important. While DCR is inversely proportional to size, DCR can represent a significant efficiency loss. Refer to the “Efficiency Considerations” below for a more detailed description. Application Information The MIC22601 is a 6A Synchronous step down regulator IC with a fixed 4MHz, voltage mode PWM control scheme. The other features include tracking and sequencing control for controlling multiple output power systems. Power-on-reset and easy RC compensation are other features as well. Component selection Input Capacitor A minimum 10µF ceramic is recommended on each of the PVIN pins for bypassing. X5R or X7R dielectrics are recommended for the input capacitor. Y5V dielectrics, aside from losing most of their capacitance over temperature, they also become resistive at high frequencies. This reduces their ability to filter out high frequency noise. Enable/DLY Capacitor Enable/DLY sources 1uA out of the IC to allow a startup delay to be implemented. The delay time is simply the time it takes 1uA to charge CDLY to 1.24V. Therefore: Output Capacitor The MIC22601 was designed specifically for the use of ceramic output capacitors. 47µF can be increased to improve transient performance. Since the MIC22601 is voltage mode, the control loop relies on the inductor and output capacitor for compensation. For this reason, do not use excessively large output capacitors. The output capacitor requires either an X7R or X5R dielectric. Y5V and Z5U dielectric capacitors, aside from the undesirable effect of their wide variation in capacitance over temperature, become resistive at high frequencies. Using Y5V or Z5U capacitors can cause instability in the MIC22601. TDLY = Inductance • Rated current value • Size requirements ⎛V ×I Efficiency % = ⎜⎜ OUT OUT ⎝ VIN × IIN ⎞ ⎟⎟ × 100 ⎠ Maintaining high efficiency serves two purposes. It reduces power dissipation in the power supply, reducing the need for heat sinks and thermal design considerations and it reduces consumption of current for battery powered applications. Reduced current draw from a battery increases the devices operating time, critical in hand held devices. There are mainly two loss terms in switching converters: Static losses and switching losses. Static losses are simply the power losses due to V.I (during flywheel diode conduction time) or I2R (during MOSFET conduction time). For example, power is dissipated in the high side switch during the on cycle. Power loss is equal to the high side MOSFET RDS(ON) multiplied by the RMS Switch Current squared (ISW2). During the off cycle, the low side N-Channel MOSFET conducts, also dissipating power. Similarly, the inductor’s DCR and capacitor’s ESR also contribute to the I2R losses. Device operating current also reduces efficiency by the product of the quiescent (operating) current and the supply voltage. The current required to drive the gates on and off at a constant 4Mhz frequency and the switching transitions make up the switching losses. Although one is not required, a Schottky diode rated for 2A continuous current, connected between SW and GND can add up to 5% to efficiency. This is achieved by preventing forward biasing of the internal MOSFET body • DC resistance (DCR) The MIC22601 is designed for use with a 0.22µH to 4.7µH inductor. Maximum current ratings of the inductor are generally given in two methods: permissible DC current and saturation current. Permissible DC current can be rated either for a 40°C temperature rise or a 10% loss in inductance. Ensure the inductor selected can handle the maximum operating current. When saturation current is specified, make sure that there is enough margin that the peak current will not saturate the inductor. The ripple can add as much as 1A to the output current level. The RMS rating should be chosen to be equal or greater than the Current Limit of the MIC22601 to prevent overheating in a fault condition. For best electrical May 2009 1 ⋅ 10 -6 Efficiency considerations Efficiency is defined as the amount of useful output power, divided by the amount of power consumed. Inductor Selection Inductor selection will be determined by the following (not necessarily in the order of importance): • 1.24 ⋅ C DLY 10 M9999-050509-A Micrel, Inc. MIC22601 diodes between switching transitions. The MOSFET body diode is less efficient for these short current pulses. Figure 3 shows an efficiency curve. The non-shaded portion, from 0A to 1A, efficiency losses are dominated by quiescent current losses, gate drive and transition losses. In this case, lower supply voltages yield greater efficiency in that they require less current to drive the MOSFETs and have reduced input power consumption. Compensation The MIC22601 has a combination of internal and external stability compensation to simplify the circuit for small, high efficiency designs. In such designs, voltage mode conversion is often the optimum solution. Voltage mode is achieved by creating an internal 4Mhz ramp signal and using the output of the error amplifier to modulate the pulse width of the switch node, maintaining output voltage regulation. With a typical gain bandwidth of 100-200 kHz, the MIC22601 is capable of extremely fast transient responses. The MIC22601 is designed to be stable with a typical application using a 0.22µH inductor and a 47µF ceramic (X5R) output capacitor. These values can be varied dependant on the tradeoff between size, cost and efficiency, keeping the LC natural frequency 1 ( ) ideally less than 34kHz to ensure stability 2⋅Π ⋅ L⋅C can be achieved. The minimum recommended inductor value is 0.22µH and minimum recommended output capacitor value is 22µF. The tradeoff between changing these values is that with a larger inductor, there is a reduced peak-to-peak current which yields a greater efficiency at lighter loads. A larger output capacitor will improve transient response by providing a larger hold up reservoir of energy to the output. The integration of one pole-zero pair within the control loop greatly simplifies compensation. The optimum values for CCOMP (in series with a 20k resistor) are shown below. Efficiency 3.6V to 1.8V L = 470nH (3mm x 3mm) 100 90 80 70 60 50 40 0 1 2 3 4 5 OUTPUT CURRENT (A) 6 Figure 3. Efficiency Curve The dashed region, 1A to 6A, efficiency loss is dominated by MOSFET RDS(ON) and inductor DC losses. Higher input supply voltages will increase the Gate-toSource threshold on the internal MOSFETs, reducing the internal RDS(ON). This improves efficiency by reducing DC losses in the device. All but the inductor losses are inherent to the device. In which case, inductor selection becomes increasingly critical in efficiency calculations. As the inductors are reduced in size, the DC resistance (DCR) can become quite significant. The DCR losses can be calculated as follows; LPD = IOUT2 × DCR From that, the loss in efficiency due to inductor resistance can be calculated as follows: ⎡ CÆ 22-47µF 47µF100µF 100µF470µF 4.7pF 0*-10pF 0†-15pF 15-33pF 10pF 22pF 15-22pF 33-47pF 15pF 33pF 33pF 100-220pF LÈ 0.22µH 0.47µH 1µH 2.2µH ⎞⎤ VOUT ⋅ IOUT ⎟⎥ × 100 ⎟ ⎝ (VOUT ⋅ IOUT ) + LPD ⎠⎦⎥ ⎛ Efficiency Loss = ⎢1 − ⎜⎜ * VOUT > 1.2V, VOUT > 1V Efficiency loss due to DCR is minimal at light loads and gains significance as the load is increased. Inductor selection becomes a trade-off between efficiency and size in this case. Alternatively, under lighter loads, the ripple current due to the inductance becomes a significant factor. When light load efficiencies become more critical, a larger inductor value maybe desired. Larger inductances reduce the peak-to-peak inductor ripple current, which minimize losses. Feedback The MIC22601 provides a feedback pin to adjust the output voltage to the desired level. This pin connects internally to an error amplifier. The error amplifier then compares the voltage at the feedback to the internal 0.7V reference voltage and adjusts the output voltage to maintain regulation. To calculate the resistor divider network for the desired output is as follows: ⎣⎢ May 2009 † R2 = 11 R1 ⎛ VOUT ⎞ ⎜⎜ − 1⎟⎟ ⎝ VREF ⎠ M9999-050509-A Micrel, Inc. MIC22601 After Enable is driven high, VOUT will start to rise (rate determined by RC capacitor). As the FB voltage goes above 90% of its nominal set voltage, Delay begins to rise as the 1µA source charges the external capacitor. When the threshold of 1.24V is crossed, POR is asserted high and Delay continues to charge to a voltage VDD. When FB falls below 90% of nominal, POR is asserted low immediately. However, if enable is driven low, POR will fall immediately to the low state and Delay will begin to fall as the external capacitor is discharged by the 1µA current sink. When the threshold of VDD1.24V is crossed, Vout will begin to fall at a rate determined by the RC capacitor. As the voltage change in both cases is 1.24V, both rising and falling delays are 1.24 ⋅ C DELAY matched at TPOR = 1 ⋅ 10 - 6 Where VREF is 0.7V, R1 is the upper resistor, R2 is the lower resistor and VOUT is the desired output voltage. A 10kΩ or lower resistor value from the output to the feedback is recommended since large feedback resistor values increase the impedance at the feedback pin, making the feedback node more susceptible to noise pick-up. A small decoupling capacitor (50pF – 100pF) across the lower resistor (R2) can reduce noise pick-up by providing a low impedance path to the ground. PWM Operation The MIC22601 is a voltage mode, pulse width modulation (PWM) controller. By controlling the ratio of on-to-off time, or duty cycle, a regulated DC output voltage is achieved. As load or supply voltage changes, so does the duty cycle to maintain a constant output voltage. In cases where the input supply runs into a dropout condition, the MIC22601 will run at 100% duty cycle. The MIC22601 provides constant switching at 4MHz with synchronous internal MOSFETs. The internal 30mΩ MOSFETs include a high-side P-Channel MOSFET from the input supply to the switch pin and an N-Channel MOSFET from the switch pin-to-ground. Since the lowside N-Channel MOSFET provides the current during the off cycle, a freewheeling Schottky diode from the switch node to ground is not required. PWM control provides fixed frequency operation. By maintaining a constant switching frequency, predictable fundamental and harmonic frequencies are achieved. Other methods of regulation, such as burst and skip modes, have frequency spectrums that change with load that can interfere with sensitive communication equipment. RC pin The RC pin provides a trimmed 1µA current source/sink similar to the Delay Pin for accurate ramp up (soft start) and ramp down control. This allows the MIC22601 to be used in systems requiring voltage tracking or ratio-metric voltage tracking at startup. There are two ways of using the RC pin: 1. Externally driven from a voltage source 2. Externally attached capacitor sets output ramp up/down rate In the first case, driving RC with a voltage from 0V to VREF will program the output voltage between 0% and 100% of the nominal set voltage. In the second case, the external capacitor sets the ramp up and ramp down rate of the output voltage. The rate is 0.7 ⋅ C RC where TRAMP is the time given by TRAMP = 1 ⋅ 10 -6 from 0% to 100% nominal output voltage. Sequencing and tracking The MIC22601 provides additional pins to provide up/down sequencing and tracking capability for connecting multiple voltage regulators together. Tracking & Sequencing examples There 4 distinct variations which are easily implemented using the MIC22601. The 2 Sequencing variations are Delayed and windowed. The 2 tracking variants are ratio metric and Normal. The following diagrams illustrate methods for connecting two MIC22601’s to achieve these requirements. Enable/DLY pin The Enable pin contains a trimmed, 1µA current source which can be used with a capacitor to implement a fixed desired delay in some sequenced power systems. The threshold level for power on is 1.24V with a hysteresis of 20mV. Delay Pin The Delay pin also has a 1µA trimmed current source and a 1µA current sink which acts with an external capacitor to delay the operation of the Power On Reset (POR) output. This can be used also in sequencing outputs in a sequenced system, but with the addition of a conditional delay between supplies; allowing a 1st up, last down power sequence. May 2009 12 M9999-050509-A Micrel, Inc. MIC22601 Normal Tracking Sequencing May 2009 13 M9999-050509-A Micrel, Inc. MIC22601 An alternative method here shows an example of a VDDQ & VTT solution for a DDR memory power supply. Note that POR is taken from VO1 as POR2 will not go high. This is because, POR is set high when FB > 0.9⋅Vref. In this example, FB2 is regulated to ½⋅VREF. Ratio Metric Tracking May 2009 14 M9999-050509-A Micrel, Inc. MIC22601 Where Current limit The MIC22601 is protected against overload in two stages. The first is to limit the current in the P-Channel switch; the second is over temperature shutdown. Current is limited by measuring the current through the high side MOSFET during its power stroke and immediately switching off the driver when the preset limit is exceeded. The circuit in Figure 4 describes the operation of the current limit circuit. Since the actual RDSON of the PChannel MOSFET varies part-to-part, over temperature and with input voltage, simple I.R voltage detection is not employed. Instead, a smaller copy of the Power MOSFET (Reference FET) is fed with a constant current which is a directly proportional to the factory set current limit. This sets the current limit as a current ratio and thus, is not dependant on the RDSON value. Current limit is set to 9A nominal. Variations in the scale factor K between the Power PFET and the reference PFET used to generate the limit threshold account for a relatively small inaccuracy. • PDISS is the power dissipated within the MLF® package and is typically 1.8W at 6A load. This has been calculated for a 0.47µH inductor and details can be found in table 1 below for reference. VINÆ VOUT @5AÈ 1 1.2 1.8 2.5 3.3 3 3.5 4 4.5 5 1.67 1.68 1.70 1.72 1.71 1.72 1.74 1.76 1.78 1.76 1.77 1.79 1.80 1.82 1.81 1.81 1.74 1.85 1.86 1.85 1.86 1.84 1.89 1.91 Table 1. Power dissipation (W) for 5A output • RθJA is a combination of junction to case thermal resistance (RθJC) and Case to Ambient thermal resistance (RθCA), since thermal resistance of the solder connection from the ePAD to the PCB is negligible; RθCA is the thermal resistance of the ground plane to ambient. So RθJA = RθJC + RθCA. • TA is the Operating Ambient temperature. Example The Evaluation board has 2 copper planes contributing to an RθCA of approximately 25°C/W. The worst case RθJC of the MLF® 4x4 is 14°C/W. RθJA = RθJC + RθCA RθJA = 14 + 25 = 39°C/W Figure 4. Current Limit Detail Thermal considerations The MIC22601 is packaged in the MLF® 4mm x 4mm, a package that has excellent thermal performance equaling that of the larger TSSOP packages. This maximizes heat transfer from the junction to the exposed pad (ePAD) which connects to the ground plane. The size of the ground plane attached to the exposed pad determines the overall thermal resistance from the junction to the ambient air surrounding the printed circuit board. The junction temperature for a given ambient temperature can be calculated using: To calculate the junction temperature for a 50°C ambient: TJ = TAMB+PDISS. RθJA TJ = 50 + (1.8 x 39) TJ = 120°C This is below our maximum of 125°C. TJ = TA + PD · RθJA May 2009 15 M9999-050509-A Micrel, Inc. MIC22601 Schematic U1 MIC22601YML SVIN J1 +VIN C1 22µF C3 22µF/6.3V J2 GND C2 22µF C4 22µF SVIN C5 J3 EN 1 6 13 18 PVIN PVIN PVIN PVIN 17 SVIN 22µF/6.3V C6 1nF SVIN 7 12 19 SGND EP POR 5 PGND Delay C8 1nF PGND RC 3 PGND EN 4 PGND C7 10nF 2 24 16 SW SW SW SW SW SW SW SW 8 9 10 11 20 21 22 23 FB 14 Comp 15 L1 0.22µH D1 C10 C11 47µF/6.3V J7 +VOUT 1.8V@6A 47µF/6.3V R1 C9 15pF R4 20k R2 698 1.1k C12 100pF J8 GND R3 47.5k J11 POR Bill of Materials Item C1, C2, C3, C4, C5 Part Number C2012X5R0J226M 08056D226MAT GRM21BR60J226ME39L C6 Open Manufacturer TDK Description Qty 22µF/6.3V, 0805 Ceramic Capacitor 5 Open, 0603 Ceramic Capacitor NA (1) AVX(2) (3) Murata NA (3) C7 GRM188R71H103KA01D Murata 10nF, 0603 Ceramic Capacitor 1 C8 VJ0603Y102KXQCW1BC Vishay(4) 1nF, 0603 Ceramic Capacitor 1 C9 C1005COG1H150J TDK(1) 15pF, 0402 Ceramic Capacitor 1 C3216X5R0J476M (1) TDK GRM31CR60J476ME19 Murata 47µF/6.3V, 1206 Ceramic Capacitor 2 100pF, 0603 Ceramic Capacitor 1 2A, 20V Schottky Diode 1 0.22µH, 9.5A 1 1.1k, 0603 Resistor 1 C10, C11 C12 R1 (3) GRM31CC80G476ME19L Murata VJ0402A101KXQCW1BC Vishay(4) D1 L1 (3) (4) SS2P2L Visyay DFLS220 Diodes, Inc. IHLP1616ABERR22M01 CRCW06031101FKEYE3 (5) Vishay(4) (4) Vishay (4) R2 CRCW04026980FKEYE3 Vishay 698Ω, 0603 Resistor 1 R3 CRCW06034752FKEYE3 Vishay(4) 47.5k, 0603 Resistor 1 R4 CRCW04022002FKEYE3 Vishay(4) 20k, 0402 Resistor 1 Integrated 6A Synchronous Buck Regulator 1 U1 MIC22601YML Micrel (6) Notes: 1. TDK: www.tdk.com 2. AVX: www.avx.com 3. Murata: www.murata.com 4. Vishay: www.vishay.com 5. Diodes, Inc.: www.diodes.com 6. Micrel: www.micrel.com May 2009 16 M9999-050509-A Micrel, Inc. MIC22601 PCB Layout Recommendation Top Assembly Top Layer May 2009 17 M9999-050509-A Micrel, Inc. MIC22601 Package Information 24-Pin 4mm x 4mm MLF® (ML) 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 The information furnished by Micrel in this data sheet is believed to be accurate and reliable. However, no responsibility is assumed by Micrel for its use. Micrel reserves the right to change circuitry and specifications at any time without notification to the customer. 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. © 2009 Micrel, Incorporated. May 2009 18 M9999-050509-A