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 Enable/Delay pin, combined with the 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 x 3mm 12-lead MLF(R) package with a junction operating range from -40C to +125C. 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 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 x 3mm MLF-12-lead MLF(R) Package -40C to +125C 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 Efficiency VOUT=3.3V U1 - MIC22200 VIN 2.6V - 5.5V PVIN SVIN EN RC DELAY SW VOUT 1.8V / 2A 100 POR 95 FB 90 COMP 85 CF EP PGND SGND CERAMIC 80 75 70 0 VIN = 5V 0.5 1 1.5 OUTPUT CURRENT (A) 2 Micrel Inc. * 2180 Fortune Drive * San Jose, CA 95131 * USA * tel +1 (408) 944-0800 * fax + 1 (408) 474-1000 * http://www.micrel.com June 2009 M9999-061909-B Micrel, Inc. MIC22200 Ordering Information Part Number Nominal Output Voltage Junction Temp. Range(1) Package Lead Finish MIC22200YML Adjustable -40C to +125C 3mmx3mm 12-Lead MLF(R) Lead Free(1) (R) Note. MLF is a green RoHS compliant package. Lead finish is NiPdAu. Mold compound is halogen free. Pin Configuration 12 EN POR 1 RC 2 11 DELAY CF 3 10 PGND SGND 4 9 SW COMP 5 8 PVIN FB 6 EP 7 SVIN Figure 2. 12-Lead MLF(R) (ML) Pin Description Pin Number Pin Name Pin Function 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. 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. 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 EPad GND June 2009 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. 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 1A 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. Exposed Pad (Power): You must make a full connection to a GND plane for full output power to be released. 2 M9999-061909-B Micrel, Inc. MIC22200 Absolute Maximum Ratings(1) Operating Ratings(2) Supply Voltage (PVIN, SVIN ) ............................................+6V Output Switch (SW)..........................................................6V Logic Voltage (EN, POR, DELAY) ....................VIN to -0.3V Control Voltage (CF, RC, COMP, FB) ..............VIN to -0.3V Lead Temperature (soldering 10s)............................. 260C Storage Temperature Range (Ts) ..............-65C to +150C EDS Rating(3) .................................................................. 2kV Supply Voltage (VIN)..................................... +2.6V to +5.5V Junction Temperature Range (TJ)....... -40C TJ +125C Thermal Resistance 3mm x 3mm MLF-12L (JA) ...............................40C/W Electrical Characteristics(4) TA = 25C with VIN = VEN = 3.3V, unless otherwise specified. Bold values indicate -40C TJ +125C 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 A 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 threshold voltage VIN=3.3V 2 5.5 8 100 % 0.18 0.10 1.14 EN hysteresis A 1.24 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 A RC source current Ramp Control Current 0.7 1 1.3 A Power On Reset IPG(LEAK) VPORH = 5.5V; POR = High 1 A 2 A DLY threshold voltage DLY hysteresis 1.24 1.34 6 Power On Reset VPG(LO) Output Logic-Low Voltage (undervoltage condition), IPOR = 5mA Power On Reset VPG Threshold, % of Vout below nominal Hysteresis mV 135 7.5 10 V mV 12.5 % 1 % Over-temperature Shutdown 160 C Over-temperature Shutdown Hysteresis 25 C June 2009 3 M9999-061909-B Micrel, Inc. MIC22200 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. June 2009 4 M9999-061909-B 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 1200 0 2.5 1300 TA = 25C 3 3.5 4 4.5 5 INPUT VOLTAGE (V) No Switching FB = 0.9V TA = 25C 1100 5.5 Quiscent Current vs. Temperature 1250 0 0.71 0 25 50 75 100 125 TEMPERATURE (C) Reference Voltage vs. Input Voltage 1000 2.5 0.71 0.705 3 3.5 4 4.5 5 INPUT VOLTAGE (V) 5.5 Reference Voltage vs. Temperature 0.705 1200 0.7 1150 1100 1050 1000 1.3 VIN = 3.3V No Switching FB = 0.9V TA = 25C 0 25 50 75 100 125 TEMPERATURE (C) Enable Voltage vs. Temperature 3.5 4 4.5 5 INPUT VOLTAGE (V) 5.5 Enable Hysterisis vs. Temperature VIN = 3.3V 0.69 1100 0 25 50 75 100 125 TEMPERATURE (C) Frequency vs. Temperature 1075 1050 1025 12 11 1000 10 1.14 VIN = 3.3V 0 25 50 75 100 125 TEMPERATURE (C) Channel RDSON vs. Temperature 215 975 9 8 140 135 VIN = 3.3V 0 25 50 75 100 125 TEMPERATURE (C) Channel RDSON vs. Temperature 195 185 175 165 155 0 25 50 75 100 125 TEMPERATURE (C) 105 100 95 90 950 CF = 220pF VIN = 3.3V 0 25 50 75 100 125 TEMPERATURE (C) Efficiency VOUT=3.3V 100 95 130 125 120 115 110 205 June 2009 16 3 13 1.18 145 0.69 2.5 0.695 14 1.22 225 0.695 15 1.26 1.1 0.7 TA = 25C 90 85 80 75 0 25 50 75 100 125 TEMPERATURE (C) 5 70 0 VIN = 5V 0.5 1 1.5 OUTPUT CURRENT (A) 2 M9999-061909-B Micrel, Inc. MIC22200 Typical Characteristics Frequency vs. CF 5 4.5 4 Efficiency VOUT=1.8V Efficiency VOUT=1.2V 100 95 100 VIN = 3.3V 95 90 3.5 90 3 85 2.5 80 2 75 75 70 70 65 65 1.5 1 0.5 60 0 50 0 CF CAPICITOR (pF) June 2009 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 M9999-061909-B OUTPUT CURRENT OUTPUT VOLTAGE INPUT VOLTAGE (1A/div) (100mV/div) (1V/div) June 2009 5.5V 1.2V 2A 100mA Time (100s/div) OUTPUT CURRENT OUTPUT VOLTAGE INPUT VOLTAGE (1A/div) (100mV/div) (500mV/div) ENABLE (1V/div) SW (2V/div) Enable On OUTPUT CURRENT (500mA/div) INPUT VOLTAGE OUTPUT VOLTAGE (1V/div) (200mV/div) OUTPUT VOLTAGE (500mV/div) Micrel, Inc. MIC22200 Functional Characteristics Time (100s/div) Load Transient Response 7 Line Transient Response VIN = 5V VIN = 2.6V Time (100s/div) Load Transient Response 3V 1.2V 2A 100mA Time (100s/div) M9999-061909-B Micrel, Inc. MIC22200 Functional Diagram Figure 1. MIC22200 Functional Diagram June 2009 8 M9999-061909-B Micrel, Inc. MIC22200 Functional Description PVIN, SVIN PVIN is the input supply to the internal 180m 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 10F 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 This pin is internally fed with a 1A 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 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 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 1A current source and VOUT slew rate is proportional to the capacitor and the 1A 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 (1A) 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. June 2009 SGND Internal signal ground for all low power sections. PGND Internal ground connection to the source of the internal N-Channel MOSFETs. 9 M9999-061909-B Micrel, Inc. MIC22200 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, power on reset. Component Selection Input Capacitor A minimum 10F 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 Capacitor Enable sources 1A out of the IC to allow a startup delay to be implemented. The delay time is simply the time it takes 1A to charge CDLY to 1.25V. Therefore: Output Capacitor The MIC22200 was designed specifically for the use of ceramic output capacitors and 22F is optimum output capacitor. 22F can be increased to 100F 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. TDLY = 1.10 - 6 CF Capacitor Adding a capacitor to this pin can adjust switching frequency from 800kHz to 4MHz. CF sources 400A out of the IC to charge the CF capacitor to set up the switching frequency. The switch period is simply the time it takes 400A to charge CF to 1.0V (2%). Therefore: Capacitor CF 56pF 68pF 82pF 100pF 150pF 180pF 220pF 270pF 330pF 390pF 470pF Inductor Selection Inductor selection will be determined by the following (not necessarily in the order of importance): Inductance Rated current value Size requirements DC resistance (DCR) The MIC22200 is designed for use with a 0.47H to 4.7H 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 40C 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 in a fault condition. For best electrical June 2009 1.24 C DLY Frequency 4.4MHz 4MHz 3.4MHz 2.8MHz 2.1MHz 1.7MHz 1.4MHz 1.2MHz 1.1MHz 1.05MHz 1MHz Table 1. CF vs. Frequency It is necessary to connect the CF capacitor between the CF pin and power ground. Efficiency Considerations Efficiency is defined as the amount of useful output power, divided by the amount of power consumed. VOUT x I OUT x 100 VIN x I IN Efficiency % = Maintaining high efficiency serves two purposes. It 10 M9999-061909-B Micrel, Inc. MIC22200 resistance can be calculated as follows: 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. VOUT I OUT x 100 1 - (VOUT I OUT ) + LPD Efficiency Loss = 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 88 84 82 80 78 76 0 75 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 1H inductor and a 47F ceramic (X5R) output capacitor. These values can be varied dependant upon the tradeoff between size, cost and efficiency, keeping the LC natural frequency VIN = 3.3V VIN = 5.0V 70 65 60 0 0.5 1 1.5 OUTPUT CURRENT (A) 2 Figure 2. Efficiency Curve 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; LPD = IOUT2 x DCR From that, the loss in efficiency due to inductor June 2009 0.2 0.4 0.6 0.8 1 1.2 OUTPUT CURRENT (A) Figure 3. Efficiency vs. Inductance 85 80 1H 86 100 90 4.7H 90 Efficiency VOUT=1.2V 95 Efficiency vs. Inductance 1 ( 2 L C ) ideally less than 26kHz to ensure stability can be achieved. The minimum recommended inductor value is 0.47H and minimum recommended output capacitor value is 22F. 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 11 M9999-061909-B Micrel, Inc. MIC22200 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. 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. CAE 22-47F 47F100F 100F470F 0.47H 0*-10pF 22pF 33pF 1H 0-15pF 15-22pF 33pF 2.2H 15-33pF 33-47pF 100-220pF LE Sequencing and Tracking The MIC22200 provides additional pins to provide up/down sequencing and tracking capability for connecting multiple voltage regulators together. * VOUT > 1.2V, VOUT > 1V Enable Pin The Enable pin contains a trimmed, 1A 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. Table 2. Compensation Capacitor Selection 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. The resistor divider network for a desired VOUT is given by: R2 = Delay Pin The Delay pin also has a 1A trimmed current source and a 1A 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 first up, last down power sequence. 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 1A 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 1A 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 DLY TPOR = 1.10 -6 matched at R1 VOUT - 1 VREF where VREF is 0.7V and VOUT is the desired output voltage. A 10k 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. 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 180m high-side PChannel MOSFET from the input supply to the switch pin and a 100m 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 June 2009 RC Pin The RC pin provides a trimmed 1A 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 12 M9999-061909-B Micrel, Inc. MIC22200 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 time of the output voltage. The time 0.7 C RC TRAMP = 1.10 -6 where TRAMP is the time is given by 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. The following diagrams illustrate methods for connecting two MIC22200's to achieve these requirements. Sequencing: Figure 6. Delayed Sequencing Example Figure 4. Sequencing MIC22200 Circuit Figure 7. Normal Tracking Circuit Figure 5. Window Sequencing Example June 2009 Figure 8. Normal Tracking Example 13 M9999-061909-B Micrel, Inc. MIC22200 Figure 12. DDR Memory Tracking Example Figure 9. Radio Metric Tracking Circuit 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. 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. Figure 10. Radio Metric Tracking Example 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 > 0.9VREF. In this example, FB2 is regulated to 1/2VREF. Figure 13. Current Limit Detail Thermal Considerations The MIC22200 is packaged in the MLF(R) 3mm x 3mm, a package that has excellent thermal performance Figure 11. DDR Memory Tracking Circuit June 2009 14 M9999-061909-B Micrel, Inc. MIC22200 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 * RJA Where PD is the power dissipated within the MLF(R) package and is typically 0.8W at 2A for VIN = 5V and VOUT = 1.8V load. This has been calculated for a 1H inductor and details can be found in table 1 below for reference. RJA is a combination of junction to case thermal resistance (RJC) and Case-to-Ambient thermal resistance (RCA), since thermal resistance of the solder connection from the ePAD to the PCB is negligible; RCA is the thermal resistance of the ground plane to ambient, so RJA = RJC + RCA. June 2009 VOUT @2A 1 1.2 1.8 2.5 3.3 VIN 3V 0.86822 0.87796 0.93972 0.91848 -- VIN 3.5V 0.81512 0.8247 0.86722 0.90504 -- VIN 4V 0.7836 0.79362 0.82568 0.85466 0.8764 VIN 4.5V 0.77014 0.77956 0.8095 0.83296 0.842 VIN 5V 0.76194 0.76842 0.80076 0.81846 0.8326 Table 3. Power Dissipation (W) for 4A Output TA is the Operating Ambient temperature. Example: To calculate the junction temperature for a 50C ambient: TJ = TA + PDI . RJA TJ = 50 + 0.8 x 40 TJ = 82C This is below the maximum of 125C. 15 M9999-061909-B Micrel, Inc. MIC22200 Design Example C1 10F C2 1F VIN IC1 MIC22200YML VIN 8 PVIN 7 SVIN EN 12 EN RC 2 RC DLY 11 DLY C7 1nF C3 1nF C4 3.3nF C5 47pF R4 5 20k COMP 3 CF 4 SGND C6 220pF SW 9 POR 1 L1 1H VOUT R3 10k POR R1 16k FB 6 PGND 10 C9 100pF R2 10k C8 100F EP EPad GND GND MIC22200YML Evaluation Board Schematic Bill of Materials Item Part Number C2012X5R0J106K C1 VJ0805G106KXYAT C2 C3, C7 C4 C5 C6 C8 Manufacturer TDK Vishay(2) C1608X7R1C105K TDK VJ0603Y105KXYAT Vishay C1608C0G1H102J TDK VJ0603A102KXXAT Vishay C1608C0G1H332J TDK VJ0603A332KXXAT Vishay C1608C0G1H470J TDK VJ0603A470KXXAT Vishay C1608C0G1H221J. TDK VJ0603A221KXXAT Vishay C3225X7R0J107M TDK GRM32ER60J17ME20L Description Qty (1) (3) Murata 10F, 6.3V, 0805, XR5 1 1F, 6.3V, 0603, X7R 1 1nF, 50V, 0603, NPO 2 3.3nF, 50V, 0603, NPO 1 47pF, 50V, 0603, NPO 1 220pF, 50V, 0603, NPO 1 1 100F, 6.3V, 1210, X7R C1608COG1H101J TDK VJ0603Y101KXAAT Vishay L1 IHLP1616BZER1R0M11 R1 CRCW06031602FKEA R2, R3 CRCW06031002FKEA Vishay 10K, 1/16W , 0603, 1% 2 R4 CRCW060320K0FKEA Vishay 20K, 1/16W , 0603, 1% 1 U1 MIC22200YML Integrated 2A Synchronous Buck Regulator 1 C9 100pF, 50V, 0603 1 Vishay 1H, 3A Inductor 1 Vishay 16K, 1/16W , 0603, 1% 1 Micrel(4) Notes: 1. TDK: www.tdk.com 2. Murata: www.murata.com 3. Vishay: www.vishay.com 4. Micrel, Inc.: www.micrel.com June 2009 16 M9999-061909-B Micrel, Inc. MIC22200 PCB Layout Recommendations Top Layer Top Silk June 2009 17 M9999-061909-B Micrel, Inc. MIC22200 Bottom Layer Bottom Silk June 2009 18 M9999-061909-B Micrel, Inc. MIC22200 Package Information 12-Pin MLF(R) (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. (c) 2008 Micrel, Incorporated. June 2009 19 M9999-061909-B