MIC22200 2A Integrated Switch Synchronous Buck Regulator with Frequency Programmable from 800kHz to 4MHz General Description Features The Micrel MIC22200 is a high-efficiency, 2A integrated switch synchronous buck (step-down) regulator. The MIC22200 switching frequency is programmable from 800kHz to 4MHz, allowing the customer to optimize their designs either for efficiency or for the smallest footprint. The regulator achieves efficiencies as high as 95% while still switching at 1MHz over a broad load range. The ultra high-speed control loops keep the output voltage within regulation even under the 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. The MIC22200 offers a full range of sequencing and tracking options. The EN/DLY pin, combined with the Power-On-Reset (POR) pin, allows multiple outputs to be sequenced in many ways during turn on and turn off. The RC (ramp control) pin allows the device to be connected to another device in the MIC22X00 family of products to keep the output voltages within a certain delta V on start up. ® The MIC22200 is available in a 3mm × 3mm 12-pin MLF package with a junction operating 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 Adjustable output voltage option down to 0.7V Output load current to 2A Full sequencing and tracking capability Easy RC compensation Power-On-Reset (POR) output Efficiency >90% across a broad load range Operating frequency: Programmable from 800 kHz up to 4MHz Ultra-fast transient response 100% maximum duty cycle Fully integrated MOSFET switches Micropower shutdown Thermal-shutdown and current-limit protection Available in Pb-free 3mm × 3mm MLF-12-pin MLF® Package –40°C to +125°C junction temperature range Applications • • • • • • High power density point-of-load conversion Servers/routers DVD recorders and multimedia players Computing peripherals Base stations FPGAs, DSP and low voltage ASIC devices _________________________________________________________________________________________________________________________ Typical Application Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com December 2010 M9999-120310-C Micrel, Inc. MIC22200 Ordering Information Part Number Nominal Output Voltage MIC22200YML Adjustable Junction Temperature Range(1) −40°C to +125°C Package Lead Finish ® 3mm × 3mm 12-Pin MLF Lead Free(1) Note: ® MLF is a green RoHS-compliant package. Lead finish is NiPdAu. Mold compound is halogen free. Pin Configuration 12-Pin MLF® (ML) Pin Description Pin Number Pin Name Pin Function 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. 1 POR 2 RC Ramp Control. Capacitor to GND from this pin determines the slew rate of output voltage during start-up. This can be used for tracking capability as well as for soft start. 3 CF External capacitor to adjust switching frequency. 4 SGND Signal Ground (signal): Ground (GND) 5 COMP Compensation Pin (input): Placing an RC to GND will compensate the device. See Applications section. 6 FB 7 SVIN Signal Power Supply Voltage (input): Requires bypass capacitor to GND. 8 PVIN Power Supply Voltage (input): Requires bypass capacitor to GND. 9 SW 10 PGND Power Ground (power): Ground (GND) 11 DELAY Delay (input) 12 EN/DLY Enable (Input): When this pin is pulled higher than the enable threshold, 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. ePad GND Exposed Pad (Power): You must make a full connection to a GND plane for full output power to be released. December 2010 Feedback (input): Input to the error amplifier; connected to the external resistor divider network to set the output voltage. Switch (output): From internal power MOSFET output switches. 2 M9999-120310-C Micrel, Inc. MIC22200 Absolute Maximum Ratings(1) Operating Ratings(2) Supply Voltage (PVIN, SVIN ) ............................................+6V Output Switch (SW)..........................................................6V Logic Voltage (EN/DLY, POR, DELAY) ............VIN to -0.3V Control Voltage (CF, RC, COMP, FB) ..............VIN to -0.3V Lead Temperature (soldering 10s)............................. 260°C Storage Temperature Range (Ts) .............−65°C to +150°C EDS Rating(3) .................................................................. 2kV Supply Voltage (VIN)..................................... +2.6V to +5.5V Junction Temperature Range (TJ).......−40°C ≤ TJ ≤ +125°C Thermal Resistance 3mm × 3mm MLF-12L (θJA) ...............................40°C/W Electrical Characteristics(4) TA = 25°C with VIN = VEN = 3.3V, unless otherwise specified. Bold values indicate −40°C ≤ TJ ≤ +125°C Parameter Condition Min. Supply Voltage Range Under-Voltage Lockout Threshold Typ. 2.6 (turn-on) 2.4 UVLO Hysteresis 2.5 Max. Units 5.5 V 2.6 V 280 mV Quiescent Current, PWM mode VEN ≥ 1.34V; VFB = 0.9V 1.2 2 mA Shutdown Current VEN = 0V 3.7 10 µA Feedback Voltage ± 2% (over temperature) 0.686 0.7 0.714 V 0.8 1 1.2 MHz Oscillator Frequency FB Pin Input Current 1 nA Current Limit VFB = 0.9*VNOM Output Voltage Line Regulation VIN = 2.6V to 5.5V 0.2 % Output Voltage Load Regulation 100mA < ILOAD < 2A, VIN = 3.3V 0.2 % Maximum Duty Cycle VFB ≤ 0.5V Switch ON-Resistance PFET Switch ON-Resistance NFET ISW = 1000mA VFB=0.5V ISW = -1000mA VFB=0.9V EN/DLY Threshold Voltage VIN=3.3V 2 5.5 8 100 % 0.18 0.10 1.14 EN/DLY Hysteresis A 1.24 Ω 1.34 12 V mV VIN=3.3V 1.14 EN/DLY Source Current VIN = 2.6 to VIN = 5.5V 0.7 1 1.3 µA RC Source Current Ramp Control Current 0.7 1 1.3 µA POR IPG(LEAK) VPORH = 5.5V; POR = High POR VPG(LO) Output Logic-Low Voltage (undervoltage condition), IPOR = 5mA DELAY Threshold Voltage DELAY Hysteresis 1.24 1.34 6 mV 1 2 135 V µA mV 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. Human body model, 1.5k in series with 100pF. 4. Specification for packaged product only. December 2010 3 M9999-120310-C Micrel, Inc. MIC22200 Electrical Characteristics(4) (Continued) TA = 25°C with VIN = VEN = 3.3V, unless otherwise specified. Bold values indicate −40°C ≤ TJ ≤ +125°C Parameter POR VPG Condition Threshold, % of VOUT below nominal Typ. Max. Units 7.5 10 12.5 % 1 % Over-Temperature Shutdown 160 °C Over-Temperature Shutdown Hysteresis 25 °C December 2010 Hysteresis Min. 4 M9999-120310-C Micrel, Inc. MIC22200 Typical Characteristics 10 Shutdown Current vs. Input Voltage 10 8 8 6 6 4 4 2 2 Shutdown Current vs. Temperature 1600 Quiescent Current vs. Input Voltage 1500 1400 1300 0 2.5 1300 1200 TA = 25°C 3 3.5 4 4.5 5 INPUT VOLTAGE (V) 5.5 Quiscent Current vs. Temperature 0 0.71 No Switching FB = 0.9V TA = 25°C 1100 02 55 07 5 100 125 TEMPERATURE (°C) Reference Voltage vs. Input Voltage 1000 2.5 0.71 3 3.5 4 4.5 5 INPUT VOLTAGE (V) 5.5 Reference Voltage vs. Temperature 1250 0.705 0.705 1200 0.7 1150 1100 VIN = 3.3V No Switching FB = 0.9V TA = 25°C 1050 1000 1.3 0.7 TA = 25°C 02 55 07 5 100 125 TEMPERATURE (°C) Enable Voltage vs. Temperature 0.695 0.69 2.5 16 0.695 VIN = 3.3V 3 3.5 4 4.5 5 INPUT VOLTAGE (V) 5.5 Enable Hysterisis vs. Temperature 15 1.26 1100 02 55 07 5 100 125 TEMPERATURE (°C) Frequency vs. Temperature 1075 14 1050 13 1.22 1025 12 1.18 11 1000 10 1.14 1.1 0.69 VIN = 3.3V 02 55 07 5 100 125 TEMPERATURE (°C) December 2010 975 9 8 VIN = 3.3V 02 55 07 5 100 125 TEMPERATURE (°C) 5 950 CF = 220pF VIN = 3.3V 02 55 07 5 100 125 TEMPERATURE (°C) M9999-120310-C Micrel, Inc. MIC22200 Typical Characteristics (Continued) Channel RDSON vs. Temperature 225 215 205 140 100 135 130 95 125 90 195 120 185 115 110 175 Efficiency VOUT=3.3V Channel RDSON vs. Temperature 85 80 105 165 155 100 95 75 145 90 70 0 02 55 07 5 100 125 TEMPERATURE (°C) Frequency vs. CF 5 4.5 Efficiency VOUT=1.8V 95 90 3 85 2.5 80 2 75 75 70 70 65 65 1 0.5 60 0 50 0 CF CAPICITOR (pF) December 2010 2 100 VIN = 3.3V 90 1.5 0.5 1 1.5 OUTPUT CURRENT (A) Efficiency VOUT=1.2V 100 95 4 3.5 02 55 07 5 100 125 TEMPERATURE (°C) VIN = 5V VIN = 3.3V 85 VIN = 5.0V 80 0.5 1 1.5 OUTPUT CURRENT (A) 6 2 60 0 VIN = 5.0V 0.5 1 1.5 OUTPUT CURRENT (A) 2 M9999-120310-C Micrel, Inc. MIC22200 Functional Characteristics December 2010 7 M9999-120310-C Micrel, Inc. MIC22200 Functional Diagram Figure 1. MIC22200 Functional Diagram December 2010 8 M9999-120310-C Micrel, Inc. MIC22200 Functional Description PVIN, SVIN PVIN is the input supply to the internal 180mΩ 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 the PVIN supply. FB The feedback pin provides the 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 section for more detail. 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. 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 pin capacitor. RC RC allows the slew rate of the output voltage to be programmed by the addition of a capacitor from RC to ground. 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 drain of the internal P-Channel 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. 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. CF Adding a capacitor to this pin can adjust switching frequency from 800kHz to 4MHz. The CF capacitor must be connected between the CF pin and power ground. COMP The MIC22200 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 using low-value, low-ESR ceramic capacitors. December 2010 SGND Internal signal ground for all low-power sections. PGND Internal ground connection to the source of the internal N-Channel MOSFETs. 9 M9999-120310-C Micrel, Inc. MIC22200 in a fault condition. For best electrical 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, so it 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 MIC22200 is a 2A Synchronous step-down regulator IC with an adjustable switching frequency from 800kHz to 4MHz, voltage mode PWM control scheme. The other features include tracking and sequencing control for controlling multiple output power systems, POR. 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 highfrequency noise. EN/DLY Capacitor EN/DLY pin sources 1µA out of the IC to allow a startup delay to be implemented. The delay time is simply the time it takes 1µA to charge CEN/DLY to 1.25V. Therefore: Output Capacitor The MIC22200 was designed specifically for the use of ceramic output capacitors and 22µF is optimum output capacitor. 22µF can be increased to 100µF to improve transient performance. Since the MIC22200 is in 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 MIC22200. TEN/DLY = 1.24 × CEN/DLY 1.10 − 6 CF Capacitor Adding a capacitor to this pin can adjust switching frequency from 800kHz to 4MHz. CF sources 400µA out of the IC to charge the CF capacitor to set up the switching frequency. The switch period is simply the time it takes 400µA to charge CF to 1.0V (±2%). Therefore: Inductor Selection Inductor selection will be determined by the following (not necessarily in the order of importance): Capacitor CF Frequency 56pF 4.4MHz 68pF 4MHz Size requirements 82pF 3.4MHz DC resistance (DCR) 100pF 2.8MHz 150pF 2.1MHz 180pF 1.7MHz 220pF 1.4MHz 270pF 1.2MHz 330pF 1.1MHz 390pF 1.05MHz 470pF 1MHz • Inductance • Rated current value • • The MIC22200 is designed for use with a 0.47µH 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 1.2A to the output current level. The RMS rating should be chosen to be equal or greater than the current limit of the MIC22200 to prevent overheating December 2010 Table 1. CF vs. Frequency It is necessary to connect the CF capacitor between the CF pin and power ground. 10 M9999-120310-C Micrel, Inc. MIC22200 The region, 0.2A to 2A, efficiency loss is dominated by MOSFET RDSON and inductor DC losses. Higher input supply voltages will increase the gate-to-source voltage on the internal MOSFETs, reducing the internal RDSON. 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: Efficiency Considerations Efficiency is defined as the amount of useful output power, divided by the amount of power consumed: ⎛ VOUT × IOUT ⎞ Efficiency % = ⎜ ⎟ × 100 ⎝ VIN × IIN ⎠ Maintaining high efficiency serves two purposes. It decreases power dissipation in the power supply, reducing the need for heat sinks and thermal design considerations and it decreases 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 VI or I2R. 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 in the frequency range from 800kHz to 4MHz and the switching transitions make up the switching losses. Figure 2 shows an efficiency curve. The portion, from 0A to 0.2A, 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. LPD = IOUT 2 × DCR From that, the loss in efficiency due to inductor resistance can be calculated as follows: ⎡ ⎛ ⎞⎤ VOUT × IOUT ⎟⎟⎥ × 100 Efficiency % = ⎢1 − ⎜⎜ ⎣ ⎝ (VOUT × IOUT ) + LPD ⎠⎦ 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 may be desired. Larger inductances reduce the peak-to-peak inductor ripple current, which minimize losses. The following graph in Figure 3 illustrates the effects of inductance value at light load: 94 92 Efficiency vs. Inductance 4.7µH 90 88 1µH 86 84 82 80 78 76 0 0.2 0.4 0.6 0.8 1 1.2 OUTPUT CURRENT (A) Figure 3. Efficiency vs. Inductance Figure 2. Efficiency Curve December 2010 11 M9999-120310-C Micrel, Inc. MIC22200 The resistor divider network for a desired VOUT is given by: Compensation The MIC22200 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 1MHz ramp signal and using the output of the error amplifier to modulate the pulse width of the switch node, thereby maintaining output voltage regulation. With a typical gain bandwidth of 100 − 200kHz, the MIC22200 is capable of extremely fast transient responses. The MIC22200 is designed to be stable with a typical application using a 1µH inductor and a 47µF ceramic (X5R) output capacitor. These values can be varied dependant upon the tradeoff between size, cost and efficiency, keeping the LC natural frequency 1 ( ) ideally less than 26kHz to ensure 2×Π× L × C stability can be achieved. The minimum recommended inductor value is 0.47µH 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 in Table 2: ( R2 = where VREF is 0.7V 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 capacitor (50pF – 100pF) across the lower resistor can reduce noise pick-up by providing a low impedance path to ground. ) CÆ LÈ 0.47µH 22-47µF 47µF100µF 100µF470µF 0*-10pF 22pF 33pF † 1µH 0 -15pF 15-22pF 33pF 2.2µH 15-33pF 33-47pF 100-220pF PWM Operation The MIC22200 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 MIC22200 will run at 100% duty cycle. The MIC22200 provides constant switching from 800kHz to 4MHz with synchronous internal MOSFETs. The internal MOSFETs include a 180mΩ high-side PChannel MOSFET from the input supply to the switch pin and a 100mΩ N-Channel MOSFET from the switch pinto-ground. Since the low-side 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. * VOUT > 1.2V, † VOUT > 1V Table 2. Compensation Capacitor Selection Sequencing and Tracking The MIC22200 provides additional pins to provide up/down sequencing and tracking capability for connecting multiple voltage regulators together. Note: For compensation values for various output voltages and inductor values refer to Table 4. Feedback The MIC22200 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. December 2010 R1 ⎛ VOUT ⎞ − 1⎟ ⎜ ⎝ VREF ⎠ EN/DLY Pin The EN/DLY 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. 12 M9999-120310-C Micrel, Inc. MIC22200 Sequencing: 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 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 first up, last down power sequence. After EN/DLY pin 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 pin 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 pin continues to charge to a voltage VDD. When FB falls below 90% of nominal, POR is asserted low immediately. However, if EN/DLY pin is driven low, POR will fall immediately to the low state and DELAY pin will begin to fall as the external capacitor is discharged by the 1µA current sink. When the threshold of VDD -1.24V 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 × CDELAY matched at TPOR = . 1.10 − 6 Figure 4. Sequencing MIC22200 Circuit 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 MIC22200 to be used in systems requiring voltage tracking or ratio-metric voltage tracking at startup. There are two ways of using the RC pin: • Externally driven from a voltage source • Externally attached capacitor sets output ramp up/down rate Figure 5. Window Sequencing Example 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 time of the output voltage. The time 0.7 × CRC is given by TRAMP = where TRAMP is the time 1.10 − 6 from 0 to 100% nominal output voltage. Sequencing and Tracking Examples There are four distinct variations which are easily implemented using the MIC22200. The two sequencing variations are Windowed and Delayed. The two tracking variants are Normal and Ratio Metric. Figures 5 thru 10 illustrate methods for connecting two MIC22200’s to achieve these requirements. December 2010 Figure 6. Delayed Sequencing Example 13 M9999-120310-C Micrel, Inc. MIC22200 Normal Tracking: Radio Metric Tracking: Figure 7. Normal Tracking Circuit Figure 9. Radio Metric Tracking Circuit Figure 8. Normal Tracking Example Figure 10. Radio Metric Tracking Example December 2010 14 M9999-120310-C Micrel, Inc. MIC22200 Figure 13 describes the operation of the current-limit circuit. Since the actual RDSON of the P-Channel MOSFET varies part-to-part, over temperature and with input voltage, simple IR 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 upon the RDSON value. Current limit is set to 5.5A 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. An alternative method here shows an example of a VDDQ and 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. Figure 11. DDR Memory Tracking Circuit Figure 13. Current-Limit Detail Thermal Considerations The MIC22200 is packaged in the MLF® 3mm x 3mm, 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: TJ = TA + PD × RθJA Figure 12. DDR Memory Tracking Example where: PD is the power dissipated within the MLF® package and is typically 0.8W at 2A for VIN = 5V and VOUT = 1.8V load. This has been calculated for a 1µH inductor and details can be found in Table 3. Current Limit The MIC22200 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. December 2010 15 M9999-120310-C Micrel, Inc. MIC22200 TA is the Operating Ambient temperature. Example: To calculate the junction temperature for a 50°C ambient: TJ = TA + PDI . RθJA TJ = 50 + 0.8 x 40 TJ = 82°C This is below the maximum of 125°C. 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. VOUT @2A VIN 3V VIN 3.5V VIN 4V VIN 4.5V VIN 5V 1 0.86822 0.81512 0.7836 0.77014 0.76194 1.2 0.87796 0.8247 0.79362 0.77956 0.76842 1.8 0.93972 0.86722 0.82568 0.8095 0.80076 2.5 0.91848 0.90504 0.85466 0.83296 0.81846 3.3 — — 0.8764 0.842 0.8326 Table 3. Power Dissipation (W) for 2A Output VIN = 5V VOUT L COUT CCOMP RCOMP CFF RFF CFB RFB 1.1V 3.3µH 2 x 47µF 100pF 5k Ω N.U. 4.7k Ω 100pF 8.2k Ω 1.3V 1.5µH 2 x 47µF 100pF 5k Ω 1nF 4.7k Ω 100pF 5.49k Ω 1.8V 2.2µH 2 x 47µF 100pF 5k Ω 1nF 4.7k Ω 100pF 3.0k Ω 4.2V 1.5µH 2 x 47µF 100pF 20k Ω 1nF 4.7k Ω 100pF 953 Ω Table 4. Compensation Selection Figure 14. Table 4 Schematic Reference December 2010 16 M9999-120310-C Micrel, Inc. MIC22200 Design Example MIC22200YML Evaluation Board Schematic Bill of Materials Item Part Number C2012X5R0J106K C1 GRM2196R60J106K C2 C4 C1608X5R0J105K TDK(1) Murata(2) 06036D105KAT2A AVX (3) C1608C0G1H102J TDK(1) GRM1885C1H102JA01D Murata(2) AVX C1608X7R1H332K TDK(1) Murata(2) AVX C1608C0G1H470J TDK(1) Murata(2) AVX C1608C0G1H221J TDK(1) Murata(2) AVX 1 Capacitor, 1µF, 6.3V, X5R, Size 0603 1 Capacitor, 1nF, 50V, NPO, Size 0603 3 Capacitor, 3.3nF, 50V, X7R, Size 0603 1 Capacitor, 47pF, 50V, NPO, Size 0603 1 Capacitor, 220pF, 50V, NPO, Size 0603 1 (3) 06035A470JAT2A 06035A221JAT2A Capacitor, 10µF, 6.3V, X5R, Size 0805 (3) 06035C332KAT2A GRM1885C1H221JA01D Qty. (3) 06035A102KAT2A GQM1885C1H470JB01D C6 Murata(2) AVX(3) GRM188R71H332KA01D C5 TDK Description (1) 08056D106KAT2A GRM188R60J105KA01D C3, C7, C8 Manufacturer (3) Notes: 1. TDK: www.tdk.com. 2. Murata: www.murata.com. 3. AVX: www.avx.com. 4. Vishay: www.vishay.com 5. Micrel, Inc.: www.micrel.com. December 2010 17 M9999-120310-C Micrel, Inc. MIC22200 Bill of Materials (Continued) Item Part Number C3216X5R0J476M C9, C10 C11 GRM31CR60J476ME19L Manufacturer Murata(2) AVX C1608C0G1H101J TDK(1) 06035A101JAT2A Qty. Murata(2) AVX Capacitor, 47µF, 6.3V, X5R, Size 1206 2 Capacitor, 100pF, 50V, NPO Size 0603 1 (3) 1206D476MAT2A GRM1885C1H101JA01D Description TDK(1) (3) Vishay (4) L1 IHLP1616BZER1R0M11 Inductor , 1µH, 5A 1 R1 CRCW06031602FKEA AVX (3) Resistor, 16K, 1%, Size 0603 1 CRCW06031002FKEA AVX (3) Resistor, 10K, 1%, Size 0603 2 AVX (3) Resistor, 20K, 1%, Size 0603 1 (3) R2, R3 R4 CRCW060320K0FKEA R5 CRCW06032R20FKEA AVX R6 CRCW060349R9FKEA AVX (3) U1 MIC22200YML Micrel(5) Resistor, 2.2Ω, 1%, Size 0603 1 Resistor, 49.9Ω, 1%, Size 0603 1 Integrated 2A Synchronous Buck Regulator 1 Notes: 1. TDK: www.tdk.com. 2. Murata: www.murata.com. 3. AVX: www.avx.com. 4. Vishay: www.vishay.com 5. Micrel, Inc.: www.micrel.com. December 2010 18 M9999-120310-C Micrel, Inc. MIC22200 PCB Layout Recommendations Top Silk Top Layer December 2010 19 M9999-120310-C Micrel, Inc. MIC22200 PCB Layout Recommendations (Continued) Bottom Layer December 2010 20 M9999-120310-C Micrel, Inc. MIC22200 Package Information 12-Pin MLF® (ML) December 2010 21 M9999-120310-C Micrel, Inc. MIC22200 Recommended Land Pattern for 32-Pin 3mm x 3mm MLF® MICREL, INC. 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA TEL +1 (408) 944-0800 FAX +1 (408) 474-1000 WEB http://www.micrel.com Micrel makes no representations or warranties with respect to the accuracy or completeness of the information furnished in this data sheet. This information is not intended as a warranty and Micrel does not assume responsibility for its use. Micrel reserves the right to change circuitry, specifications and descriptions at any time without notice. No license, whether express, implied, arising by estoppel or otherwise, to any intellectual property rights is granted by this document. Except as provided in Micrel’s terms and conditions of sale for such products, Micrel assumes no liability whatsoever, and Micrel disclaims any express or implied warranty relating to the sale and/or use of Micrel products including liability or warranties relating to fitness for a particular purpose, merchantability, or infringement of any patent, copyright or other intellectual property right. Micrel Products are not designed or authorized for use as components in life support appliances, devices or systems where malfunction of a product can reasonably be expected to result in personal injury. Life support devices or systems are devices or systems that (a) are intended for surgical implant into the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significant injury to the user. A Purchaser’s use or sale of Micrel Products for use in life support appliances, devices or systems is a Purchaser’s own risk and Purchaser agrees to fully indemnify Micrel for any damages resulting from such use or sale. © 2008 Micrel, Incorporated. December 2010 22 M9999-120310-C