MIC21000 Digital PWM Controller with PMBus® General Description Features The MIC21000 is a configurable, true-digital, PWM controller for high-current, non-isolated DC-to-DC power supplies in computing and telecom applications. The MIC21000 drives industry-standard DrMOS devices so that the current capability can be easily scaled. • • • • • The MIC21000 integrates a digital control loop, optimized for maximum flexibility and stability, as well as for load step and steady-state performance. In addition, a rich set of protection and monitoring functions is provided. On2 ® chip, nonvolatile memory (NVM) and an I C™/PMBus interface facilitate configuration. The PC-based Micrel Digital Designer graphical user interface (GUI) provides a user-friendly and easy-to-use interface to the device for communication and configuration. It can guide the user through the design of the digital compensator and offers intuitive configuration methods for additional features, such as protection and sequencing. • • • • • • The MIC21000 is offered in a compact and thermally efficient 24-pin 4mm × 4mm QFN package. Datasheets and support documentation are available on Micrel’s web site at: www.micrel.com. True digital engine, programmable, PWM control loop Ultra-fast transient response 2 I C/PMBus interface for configuration Single supply voltage 5V or 3.3V Input voltage, output voltage, output current, internal and external temperature telemetry Temperature-compensated inductor DCR current sensing with end-of-line calibration support Resistor or pin-strapping PMBus address setting Remote differential load voltage sense Embedded OTP NVM for user configuration storage Switching frequencies: 177kHz to 1MHz (12 options) Protection features: − Overcurrent protection − Overvoltage protection (VIN, VOUT) − Undervoltage protection (VIN, VOUT) − Overloaded startup − Restart and delay Applications • Datacom and telecom advanced high-current POL converters Typical Application I2C is a registered trademark of NXP. PMBus is a registered trademark of System Management Interface Forum, Inc. SMBus is a trademark of Intel Corporation. Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com February 11, 2014 Revision 1.1 Micrel, Inc. MIC21000 Ordering Information Part Number MIC21000YML Operating Ambient Temperature Range Package −40°C to +85°C 24-Pin QFN Note: This product is subject to a limited license from Power-One, Inc. related to digital power technology as set forth in U.S. Patent No. 7,000,125 and other related patents owned by Power-One, Inc. This license does not extend to standalone power supply products. Pin Configuration 24-Pin 4mm × 4mm QFN (Top View) Pin Description Pin Number Pin Name 1 AGND Analog Ground. 2 VREFP Reference Voltage Output. Bypass VREFP to AGND with a 4.7µF ceramic capacitor. 3 VFBP Positive Input of Differential Feedback Voltage Sensing 4 VFBN Negative Input of Differential Feedback Voltage Sensing 5 ISNSP Positive Input of Differential Current Sensing 6 ISNSN Negative Input of Differential Current Sensing 7 TEMP Connection to External Temperature Sensing Element 8 VIN 9 ADDR0 Address Selection 0 10 ADDR1 Address Selection 1 February 11, 2014 Pin Function Input Power Rail Voltage Sensing. Connect this pin to the input of the power stage through a resistor divider. 2 Revision 1.1 Micrel, Inc. MIC21000 Pin Description (Continued) Pin Number Pin Name 11 PWM High-side FET Control Signal 12 LSE Low-side FET Control Signal 13 PGOOD 14 CONTROL 15 GPIO0 16 SMBALERT 17 SDA Serial Data I/O 18 SCL Serial Clock Input 19 GND Digital Ground 20 VDD18 Internal 1.8V Digital Supply LDO Output. Locally decouple with a 4.7µF ceramic capacitor to ground. 21 VDD33 3.3V LDO Output. For operation from a single 3.3V rail, short VDD33 to VDD50 together and feed the 3.3V rail to both pins. Locally decouple with a 4.7µF ceramic capacitor to AGND. 22 VDD50 LDO Input Voltage Terminal. Used if a 5V supply rail is available in the system. If used, locally decouple with a 1µF ceramic capacitor to AGND. 23 AVDD18 Internal 1.8V Analog Supply LDO Output. Locally decouple with a 4.7µF ceramic capacitor to AGND. 24 ADCVREF EP EP February 11, 2014 Pin Function PGOOD Output Control Input General Purpose Input/Output Pin Alert Output Analog-to-Digital Converter (ADC) Reference Terminal. Connect to VREFP through an RC filter. Exposed Pad (connect to Analog Ground). 3 Revision 1.1 Micrel, Inc. MIC21000 Absolute Maximum Ratings(1) Operating Ratings(2) 5V Supply Voltage (VDD50)........................... −0.3V to 5.5V 5V Supply Voltage Maximum Slew Rate ............... 0.15V/µs 3.3V Supply Voltage (VDD33)........................ −0.3V to 3.6V 1.8V Supply Voltages (VDD18, AVDD18) ......... −0.3V to 2V Digital Pins (SDL, SDA, SMBALERT, GPIO0, CONTROL, PGOOD, LSE, PWM) ..................................... −0.3V to 5.5V ISNSP, ISNSN................................................ −0.3V to 5.5V VFBP, VFBN .................................................. −0.3V to 2.0V All Other Analog Pins (ADCVREF, VREFP, TEMP, VIN, ADDR0, ADDR1) ............................................ −0.3V to 2.0V Lead Temperature (soldering, 10s) ............................ 260°C Storage Temperature (TS) ............................ −40°C to150°C (3) ESD Rating .................................................................. 2kV 5V External Supply Voltage ......................... 4.75V to 5.25V 3.3V External Supply Voltage .......................... 3.0V to 3.6V 3.3V LDO Supply Current to external loads .......2mA (max.) 1.8V Analog LDO Supply Current to external loads ..... 0mA 1.8V Digital LDO Supply Current to external loads ....... 0mA Ambient Temperature (TA) ............................ −40°C to 85°C Junction Thermal Resistance QFN-24 (θJA) ...................................................... 44°C/W Electrical Characteristics(4) VDD50 = VDD33 = 3.3V unless otherwise noted; TJ = 25°C, bold values indicate −40°C ≤ TA ≤ 85°C, unless otherwise noted. Parameter Condition Min. Typ. Max. Units VDD50, VDD33, VDD18 and AVDD18 Supply Rails 5V Supply Current VDD50 = 5V, using internal 3.3V LDO 23 mA 3.3V Supply Current VDD50 = VDD33 = 3.3V, internal 3.3V LDO shorted 23 mA 3.3V LDO Output Voltage VDD50 = 5V, no external load at VDD33 3.0 3.3 3.6 V 1.8V Analog LDO Output Voltage VDD50 = 5V 1.72 1.80 1.88 V 1.8V Digital LDO Output Voltage VDD50 = 5V 1.72 1.80 1.88 V 3.3V POR Threshold – Rising 2.8 V 3.3V POR Threshold – Falling 2.6 V Digital I/O pins (GPIO0, CONTROL, PGOOD) 2.0 Input High Voltage V 0.8 V VDD33 V 0.5 V +1.0 µA Output Current High 2.0 mA Output Current Low 2.0 mA Input Low Voltage 2.4 Output High Voltage Output Low Voltage −1.0 Input Leakage Current Notes: 1. Exceeding the absolute maximum ratings may damage the device. 2. The device is not guaranteed to function outside its operating ratings. 3. Devices are ESD sensitive. Handling precautions are recommended. Human body model, 1.5kΩ in series with 100pF. 4. Specification for packaged product only. February 11, 2014 4 Revision 1.1 Micrel, Inc. MIC21000 Electrical Characteristics(4) (Continued) VDD50 = VDD33 = 3.3V unless otherwise noted; TJ = 25°C, bold values indicate −40°C ≤ TA ≤ 85°C, unless otherwise noted. Parameter Condition Min. Typ. Max. Units VDD33 V Output Low Voltage 0.5 V Output Current High 2.0 mA 2.0 mA +1.0 µA Digital IO pins with Tri-State Capability (LSE, PWM) 2.4 Output High Voltage Output Current Low Leakage Current −1.0 Tri-stated PMBus Pins (SCL, SDA, SMBALERT) 2.0 Input High voltage V Input Low voltage 0.8 V Maximum Bus Voltage 5.25 V 2.0 mA 1.4 V Output Current Low SDA, SMBALERT Output Voltage Setting Setpoint Voltage Range No external divider 0 Setpoint Resolution No external divider 1.4 mV Setpoint Accuracy No external divider 1 % Inductor Current Sensing Common Mode Voltage Range ISNSP, ISNSN Differential Mode Voltage Range V(ISNSP, ISNSN) 0 5.0 V −100 +100 mV Accuracy 5 Recommended DCR Sense Voltage for Maximum Output Current % 10 mV Digital Pulse Width Modulator (DPWM) Switching Frequency 177 1000 kHz Resolution 163 ps Frequency Accuracy 2.0 % Overvoltage Protection (OVP) OVP DAC Setpoint Voltage 0 1.575 V OVP DAC Resolution 25 mV OVP DAC Setpoint Accuracy 2 % OVP Comparator Hysteresis 35 mV Housekeeping ADC (HKADC) Input Pins (TEMP, VIN, ADDR0, ADDR1) Input Voltage Range TEMP, VIN, ADDR0, ADDR1 Recommended Source Impedance on VIN Sensing VIN ADC Resolution February 11, 2014 0 0.7 5 1.44 V 3 kΩ mV Revision 1.1 Micrel, Inc. MIC21000 Electrical Characteristics(4) (Continued) VDD50 = VDD33 = 3.3V unless otherwise noted; TJ = 25°C, bold values indicate −40°C ≤ TA ≤ 85°C, unless otherwise noted. Parameter Condition Min. Typ. Max. Units External PN-Junction Temperature Measurement (TEMP) Ext. PN-Junction Bias Current 60 µA Resolution 0.32 K Accuracy ±5.0 K Resolution 0.22 K Accuracy ±5.0 K Internal Temperature Measurement February 11, 2014 6 Revision 1.1 Micrel, Inc. MIC21000 Typical Application Circuit Typical Application Circuit with 5V Bias February 11, 2014 7 Revision 1.1 Micrel, Inc. MIC21000 Functional Characteristics VIN = 12V, unless otherwise noted. Refer to the circuit configuration shown in the “Typical Application Schematic” section (with L1 = Wuerth 7443320047). February 11, 2014 8 Revision 1.1 Micrel, Inc. MIC21000 Functional Block Diagram February 11, 2014 9 Revision 1.1 Micrel, Inc. MIC21000 Functional Description Output Voltage Feedback The voltage feedback signal is sampled with a highspeed analog front-end. The feedback voltage is differentially measured and subtracted from the voltage reference provided by a reference digital-to-analog converter (DAC) using an error amplifier. A flash ADC is then used to convert the voltage to its digital equivalent. This is followed by internal digital filtering to improve the system’s noise rejection. The MIC21000 is a configurable true-digital single-phase PWM controller designed for high-current, non-isolated DC-to-DC supplies and supporting switching frequencies up to 1MHz. It offers a PMBus configurable digital power control loop incorporating output voltage sensing, average inductor current sensing bundled with extensive telemetry, fault monitoring, and handling options. Several different functional units are incorporated in the device. A dedicated digital control loop is used to provide fast loop response and optimal output voltage regulation. This includes output voltage sensing, average inductor current sensing, a digital control law, and a digital pulsewidth modulator (DPWM). In parallel, a dedicated, configurable error handler allows for fast and flexible detection of error signals and their appropriate handling. A housekeeping analog-to-digital converter (HKADC) ensures the reliable and efficient measurement of environmental signals such as input voltage and temperature. An application-specific, low-energy microcontroller controls the overall system. Among other things, it manages configuration of the various logic units and handles the PMBus communication protocol. A PMBus/I²C interface is incorporated to connect with the outside world, supported by control (CONTROL), alert (SMBALERT) and power-good (PGOOD) signals. Although the reference DAC generates a voltage up to 1.44V, keeping the voltage on the feedback pin (VFBP) around 1.20V is recommended to guarantee sufficient head room. If a larger output voltage is desired, an external feedback divider is required. Digital Compensator The sampled output voltage is processed by a digital control loop to modulate the DPWM output signals controlling the power stage. This digital control loop works as a voltage-mode controller using PID-type compensation. The basic structure of the controller is shown in Figure 1. The Adaptive PID Management concept features two parallel compensators for steadystate operation, and fast transient operation. The coefficients for the two modes can be derived using the Micrel Digital Designer PC-based graphical user interface. The MIC21000 implements fast, reliable switching between the different compensation modes to ensure good transient performance and quiet steady state. This allows each compensator to be tuned individually for its respective needs; that is, quiet steadystate and fast transient performance. A high-reliability, high-temperature one-time programmable memory (OTP) is used to store user configuration parameters. Digital Power Control Overview The digital power control loop consists of the integral parts required for the control functionality of the MIC21000. A high-speed analog front-end digitizes the output voltage. A digital control core uses the acquired information to provide duty-cycle information to the PWM, which controls the drive signals to the power stage. Switching Frequency The MIC21000 supports the switching frequencies listed in Table 1. Table 1. Supported Switching Frequencies 1000kHz 400.0kHz 800.0kHz 333.3kHz 666.6kHz 285.7kHz 571.4kHz 266.6kHz 500.0kHz 222.0kHz 444.4kHz 177.0kHz February 11, 2014 Figure 1. Simplified Block Diagram of the Digital Compensation with Adaptive PID Management 10 Revision 1.1 Micrel, Inc. MIC21000 Power Sequencing and the CONTROL Pin The MIC21000 supports power sequencing features such as programmable ramp up/down and delays. The typical sequence of events is shown in Figure 3 and follows the PMBus standard. The individual values can be configured using the appropriate setting. Three different configuration options are supported to turn the device on. The device can be configured to turn on immediately after POR, on an OPERATION_ON command, or on an edge of the CONTROL pin. Additionally, three techniques are used to improve transient performance further. Optimal Sampling Technology is used to acquire fast, accurate, and continuous information about the output voltage so that the device can react quickly to any change in output voltage. Optimal Sampling Technology reduces phaselag caused by sampling delays, reduces noise sensitivity, and improves transient performance. Second, the Ultra-Fast Transient Response (UFTR) technique, a method to drive the DPWM asynchronously during load transients, allows limiting the maximum deviation of the output voltage and recharging the output capacitors faster. Third, a nonlinear gain adjustment is used during large load transients to boost the loop gain and reduce the settling time. The DPWM supports switching frequencies up to 1MHz with a resolution of 165ps. The PWM and LSE signals are modulated by the DPWM according to the pattern shown in Figure 2. Note that the physical output of the MIC21000, that is, the signals on the respective pins, may be different depending on the selected pin configuration options. For example, if a tri-state output functionality is chosen for the PWM, the PWM signal will be in one of three states: active high, high impedance, or active low. In this case, the LSE pin can be configured for an alternative function. For detailed information, refer to the “Pin Functionality Configuration” section. The minimum on-time and the maximum off-time of the modulation signal can be configured so that the MIC21000 can match the requirements of the selected driver optimally. Figure 3. Power Sequencing Pre-Biased Start-Up and Soft Stop Dedicated pre-biased start-up logic ensures that the power converter will start up correctly when the output capacitors are precharged to a nonzero output voltage (Vpre-bias). This is shown in Figure 4. Closed-loop stability is ensured during this phase. The MIC21000 also supports pre-biased off, that is, the output voltage is not ramped down to zero and instead remains at a predefined level (VOFFnom). This value can be configured using the Micrel Digital Designer. After receiving the shutdown command, from PMBus or the CONTROL pin, the MIC21000 ramps down the voltage to the predefined value. Once the value is reached, PWM and LSE will be turned off to put the output driver into tristate mode. Figure 2. LSE and PWM Signals during Synchronous Operation Figure 4. Power Sequencing with Nonzero Off Voltage February 11, 2014 11 Revision 1.1 Micrel, Inc. MIC21000 Current Sensing The MIC21000 offers cycle-by-cycle average current sensing with configurable overcurrent protection. A dedicated ADC provides fast and accurate current information over the switching period. The acquired information is compared with configurable current thresholds to report warning and error levels to the user. Inductor DCR current sensing and dedicated sense resistors are supported. Additionally, the device uses DCR temperature compensation using the external temperature sense element. This increases the accuracy of the current sense method by counteracting the significant change of the DCR over temperature. End-of-line calibration is supported so that the MIC21000 can achieve improved accuracy over the full output current range. The full calibration method is detailed in the relevant application note. This allows the user to correct mismatches between the nominal DCR value used to configure the device and the actual DCR value in the application caused by effects such as manufacturing variations. The calibration range is limited to ±50% of the nominal DCR. Additionally, in order to improve the accuracy of the current measurement challenged by the temperature coefficient of the inductor’s DCR, the MIC21000 features temperature compensation using the external temperature sensing. Therefore, the temperature of the inductors is measured with an external temperature sense element placed close to the inductor. This information is used to adapt the gain of the current sense path to compensate for the increase in actual DCR. To get accurate current information, the selection of the current sensing circuit is of critical importance. The schematic of the required current sensing circuitry is shown in Figure 5 for the widely-used DCR currentsensing method, which uses the parasitic resistance of the inductor to get the current information. The principle is based on a matched time-constant between the inductor and the low-pass filter built from R7 and C8. The two resistors R6 and R7 should be matched fairly well in order to provide good DC voltage rejection, that is, reduce the influence of the output voltage level in the current measurement. Temperature Measurement The MIC21000 features two independent temperature measurement units. The internal temperature sensing measures the temperatures inside the IC; the external temperature sense element should be placed close to the inductor to measure its temperature. A PN-junction is used as an external temperature sense element. Smallsignal transistors, such the 3904, are widely used for this application. The configuration of the sensitivity and the offset is required in the Micrel Digital Designer. A temperature calibration is highly recommended. Fault Monitoring and Response Generation The MIC21000 monitors various signals during operation. It can respond to events generated by these signals based on the selected configuration. A wide range of options is configurable using the Micrel Digital Designer. Typical monitoring within the MIC21000 is a three-step process. First, an event is generated by a configurable set of thresholds. This event is then digitally filtered before the MIC21000 reacts with a configurable response. For most monitored signals, a warning and a fault threshold can be configured. A warning typically sets a status flag, but does not trigger a response, whereas a fault also generates a response. Figure 5. Inductor Current Sensing Using the DCR Method Alternatively, a simple shunt resistor can be used to measure the inductor current. The value of this resistor should be selected so that the voltage range between the pins is within the specifications given in the “Electrical Characteristics” section. February 11, 2014 Each warning and fault event can be individually enabled. The assertion of the SMBALERT signal can also be configured to individual needs. An overview of the options and configuration is given in Table 2. 12 Revision 1.1 Micrel, Inc. MIC21000 Table 2. Fault Configuration Overview Signal Output Overvoltage Output Undervoltage Input Overvoltage Input Undervoltage Overcurrent External Overtemperature Internal Overtemperature Fault Level Response Type Delay Resolution Maximum Delay Low impedance 500 µs 90 ms Low-impedance 500 µs 90 ms Off 500 µs 90 ms Off 500 µs 90 ms Low-impedance 500 µs 90 ms Off 5 ms 900 ms Off 5 ms 900 ms Warning Fault Warning Fault Warning Fault Warning Fault Warning Fault Warning Fault Warning Fault The MIC21000 supports different response types depending on the fault detected. An “Off” response ramps the output voltage down using the falling-edge sequencer settings. The final state of the output signals depends on the value selected for VOFFnom. The “low-impedance” response turns off the top MOSFET and enables the lowside MOSFET, that is, PWM = 0 and LSE = 1. Additionally, the output voltage is sampled using the HKADC and continuously compared to an output overvoltage warning threshold. If the output voltage exceeds this threshold, a warning is generated and the preconfigured actions are triggered. The MIC21000 also monitors the output voltage with two lower thresholds. If the output voltage is below the undervoltage warning level and above the undervoltage fault level, an output voltage undervoltage warning is triggered. If the output voltage falls below the fault level, a fault event is generated. For each fault response, a delay and a retry setting can be configured. If the delay value is set to nonzero, the MIC21000 will not respond to a fault immediately. Instead it delays the response by the configured value and then reassesses the signal. If the fault is still present, the appropriate response is triggered. If the fault is no longer present, the previous detection is disregarded. With the retry setting, the number of retries, that is, the number of restarts of the power converter after a fault event can be configured. This number can be between zero and seven, where a setting of seven represents an infinite retry operation. In analog controllers, this feature is also known as “hiccup mode.” Output Current Protection and Limiting The MIC21000 continuously monitors the average inductor current and uses this information to protect the power supply against excessive output current. Two different types of protection are independently configurable. Output current limiting to a configured value is supported by reducing the output voltage. Additionally, the maximum output current warning and fault threshold can be used to shut down the MIC21000. Both features can be enabled independently. If the overcurrent fault threshold is chosen below the limiting threshold, the MIC21000 will shut down without going into current limiting mode. Output Over/Undervoltage To prevent damage to the load, the MIC21000 uses an output overvoltage protection circuit. The voltage at VFBP is continuously compared to a configurable threshold using a high-speed analog comparator. If the voltage exceeds the configured threshold, the fault response is generated and the PWM outputs are turned off. The voltage fault level is generated by a 6-bit DAC with a reference voltage of 1.60V, resulting in 25mV resolution. February 11, 2014 Overtemperature Protection The MIC21000 monitors internal and external temperature. For each, a warning and a fault level can be configured and an appropriate response can be enabled. 13 Revision 1.1 Micrel, Inc. MIC21000 Pin Functionality Configuration The MIC21000 offers a flexible configuration scheme for its digital output pins. This enables using the LSE and GPIO pins with different functions depending on the application requirements. Configuration The MIC21000 incorporates two different sets of configuration parameters. The first set of parameters can be configured during design time and cannot be changed during runtime. The second set of configuration parameters can be configured during design time, but can also be reconfigured during runtime using the appropriate PMBus command. Note that these reconfigured values are not stored in the OTP memory, so they are lost when power cycling the device. The configuration options are listed in Table 3. Table 3. Pin Configuration Overview Pin LSE LSE Active high GPIO0 Thermal Shutdown High and low active Driver Disable Hardwire Option High and low active High and low active High and low active High and low active To evaluate the device and its configuration on the bench, a special engineering mode is supported by the device and Micrel Digital Designer; that is, the device can be reconfigured multiple times without writing the configuration into the OTP. During this “engineering mode,” the device starts up after power-on reset in an unconfigured state. The Micrel Digital Designer then provides the configuration to the MIC21000, enabling full operation without actually configuring the OTP. The engineer can use this mode to evaluate the configuration on the bench. However, the configuration will be lost upon power-on-reset. The PWM pin can be configured as a push/pull or tri-state output. In push/pull mode, the PWM signal can be only high or low at low impedance and is used by the MOSFET driver/DrMOS in conjunction with the LSE signal to determine the gate drive for the high- and lowside MOSFETs. Alternatively, the PWM signal can be configured as a tri-state output, and it is allowed to also assume a high-impedance state in addition to logic high or logic low. When PWM is in high-impedance, the DrMOS disables both gate drivers for the high- and lowside MOSFETs, regardless of the status of the LSE pin. In this case, the LSE pin can be configured for an alternative function After the design engineer has determined the final configuration options, an OTP image can be created that is then written into the MIC21000. This can be either on the bench using the Micrel Digital Designer or in end–ofline testing during mass production. In LSE mode, the LSE pin is used by the DrMOS as an SMOD# signal to actively modulate the low-side FET of the power stage. Alternatively, it can be used as a control signal to enable/disable the driver. This signal is deasserted before the first switching on the PWM pin and asserted shortly after the last switching event. If the pin is not used in the application, a hardwire option can be used to set the pin to a defined level. The GPIO0 pin supports the driver disable feature and the hardwire option, but it can also be used as a thermal shutdown input. If the pin is asserted by an external source, for example, the thermal shutdown flag of a DrMOS, the controller flags an external overtemperature fault and reacts accordingly. February 11, 2014 14 Revision 1.1 Micrel, Inc. MIC21000 Application Information Power Supplies, Reference Decoupling, and Grounding The MIC21000 incorporates several internal power regulators so that it can derive all required supply and bias voltages from a single external supply voltage. This supply voltage can be either 5V or 3.3V, depending on whether the internal 3.3V regulator is used. If the internal 3.3V regulator is not used, then 3.3V must be supplied to the 3.3V and 5V supply pins. Decoupling capacitors are required at the VDD33, VDD18, and AVDD18 pins (1.0µF minimum; 4.7µF recommended). If the 5V supply voltage is used, that is, the internal 3.3V regulator is used, a small load current (2mA max.) can be drawn from the VDD33 pin. This can be used to supply pull-up resistors, for example. The reference voltages required for the analog-to-digital converters are generated within the MIC21000. External decoupling must be provided between the VREFP and ADCVREF pins. Therefore, a 4.7µF capacitor is required at the VREFP pin and a 100nF capacitor at the ADCVREF pin. The two pins should be connected with approximately 50Ω resistance in order to provide sufficient decoupling between the pins. Figure 6. Output Voltage Sense Circuitry Table 4. Output Voltage Feedback Component Overview Output Voltage Feedback Components The MIC21000 supports direct output voltage feedback without external components up to an output voltage of 1.4V. However, adding a high-frequency low-pass filter in the sense path is highly recommended to remove highfrequency disturbances from the sense signals. Placing these components as close as possible to the MIC21000 is recommended. For larger output voltages, a feedback divider is required, as shown in Figure 6. Using resistors with small tolerances is recommended to guarantee output voltage accuracy. Table 4 lists the required component values as a function of the maximum supportable output voltage. The selected resistors values must be configured in the Micrel Digital Designer so that they can be taken into account for the configuration of the device. Nominal Output Voltage Maximum Output Voltage R4 R5 C7 1.30V 1.40V open 1.0kΩ 22pF 1.80V 2.10V 1.5kΩ 750Ω 47pF 2.50V 2.80V 1.0kΩ 1.0kΩ 47pF 3.30V 4.25V 1.0kΩ 2.2kΩ 33pF 5.00V 5.00V 1.0kΩ 3.3kΩ 33pF DCR Current Sensing Components The MIC21000 supports the lossless DCR current sense method shown in Figure 5. The equivalent DC resistance of the inductor is used to measure the inductor current without adding any additional components into the power path. This technique is based on matching the time constant of the inductor and the parallel low-pass filter. Therefore the components R6, R7, and C8 must be selected depending on the selected inductor. The following procedure is recommended: 1. Set R7’ = 1kΩ 2. Calculate C8’ = L ÷ (DCR × R7). 3. Pick capacitor C8 from the appropriate E-series close to C8. 4. Recalculate R6 = R7 = L ÷ (DCR × C8) based on the capacitor selected for C8. February 11, 2014 15 Revision 1.1 Micrel, Inc. MIC21000 Input Voltage Sensing The MIC21000 supports input voltage sensing for protection and monitoring. Therefore, a voltage divider between the input power rail (VBUS) and the VIN pin is required, as shown in Figure 7. The recommended resistors values for different input voltage ranges can be found in Table 5. To ensure proper operation and high accuracy, a capacitor must not be connected to the VIN pin. Digital filtering is provided inside the ICs. Figure 7. Input Voltage Sense Circuitry Table 5. Input Voltage Sense Component Overview Nominal Input Voltage Maximum Input Voltage R9 R8 12V 14.5V 20kΩ 2.2kΩ 8.0V 9.0V 12kΩ 2.2kΩ 5.0 V 6.5V 8.2kΩ 2.2kΩ February 11, 2014 16 Revision 1.1 Micrel, Inc. MIC21000 PMBus Functionality Introduction The MIC21000 supports the PMBus protocol to enable the use of configuration, monitoring, and fault management during runtime. The PMBus host controller is connected to the MIC21000 using the PMBus pins. A dedicated SMBALERT pin is provided to notify the host that new status information is present. The MIC21000 supports packet error correction (PEC) according to the PMBus specification. The MIC21000 complies with PMBus specification rev. 1.1. Timing and Bus Specification Figure 8. PMBus Timing Diagram Table 6. PMBus Timing Specifications Symbol fSMB Parameter Conditions PMBus Operation Frequency Min. Typ. Max. Units 10 400 500 kHz tBUF Bus Free Time between Start and Stop 1.3 µs tHD:STA Hold Time after Start Condition 0.6 µs tSU:STA Repeat Start Condition Setup Time 0.6 µs tSU:STO Stop Condition Setup Time 0.6 µs tHD:DAT Data Hold Time 300 ns tSU:DAT Data Setup Time 100 ns tTIMEOUT Clock Low Timeout 25 tLOW Clock Low Period 1.3 µs tHIGH Clock High Period 0.6 µs tLOW:SEXT Cumulative Clock Low Extend Time 25 ms tF Clock or Data Fall Time 300 ns tR Clock or Data Rise Time 300 ns February 11, 2014 17 35 ms Revision 1.1 Micrel, Inc. MIC21000 Address Selection Using External Resistors PMBus uses a 7-bit device address to identify different devices connected to the bus. This address can be selected using the external resistors connected to the ADDRx pins. The resistor values are sensed using the internal ADC during the initialization phase; then, the appropriate PMBus address is selected. Note that the respective circuitry is active only during the initialization phase; so, DC voltage cannot be measured at the pins. The supported PMBus addresses and the values of the respective required resistors are listed in Table 7. Table 7. Supported Resistor Values for PMBus Address Selection Address (Hex) ADDR1 Ω ADDR0 Ω Address (Hex) ADDR1 Ω ADDR0 Ω Address (Hex) ADDR1 Ω ADDR0 Ω Address (Hex) ADDR1 Ω ADDR0 Ω 0 0 0 32 1.2k 0 64 2.7k 0 96 4.7k 0 (5) 1 0 680 33 1.2k 680 65 2.7k 680 4.7k 680 2(5) 0 1.2k 34 1.2k 1.2k 66 2.7k 1.2k 98 4.7k 1.2k 3(5) 0 1.8k 35 1.2k 1.8k 67 2.7k 1.8k 99 4.7k 1.8k (5) 0 2.7k 36 1.2k 2.7k 68 2.7k 2.7k 100 4.7k 2.7k (5) 0 3.9k 37 1.2k 3.9k 69 2.7k 3.9k 101 4.7k 3.9k (5) 0 4.7k 38 1.2k 4.7k 70 2.7k 4.7k 102 4.7k 4.7k (5) 0 5.6k 39 1.2k 5.6k 71 2.7k 5.6k 103 4.7k 5.6k (5) 0 6.8k 40* 1.2k 6.8k 72 2.7k 6.8k 104 4.7k 6.8k 9 0 8.2k 41 1.2k 8.2k 73 2.7k 8.2k 105 4.7k 8.2k 10 0 10k 42 1.2k 10k 74 2.7k 10k 106 4.7k 10k 11 0 12k 43 1.2k 12k 75 2.7k 12k 107 4.7k 12k 0 15k 44 1.2k 15k 76 2.7k 15k 108 4.7k 15k 13 0 18k 45 1.2k 18k 77 2.7k 18k 109 4.7k 18k 14 0 22k 46 1.2k 22k 78 2.7k 22k 110 4.7k 22k 15 0 27k 47 1.2k 27k 79 2.7k 27k 111 4.7k 27k 16 680 0 48 1.8k 0 80 3.9k 0 112 5.6k 0 17 680 680 49 1.8k 680 81 3.9k 680 113 5.6k 680 18 680 1.2k 50 1.8k 1.2k 82 3.9k 1.2k 114 5.6k 1.2k 19 680 1.8k 51 1.8k 1.8k 83 3.9k 1.8k 115 5.6k 1.8k 20 680 2.7k 52 1.8k 2.7k 84 3.9k 2.7k 116 5.6k 2.7k 21 680 3.9k 53 1.8k 3.9k 85 3.9k 3.9k 117 5.6k 3.9k 22 680 4.7k 54 1.8k 4.7k 86 3.9k 4.7k 118 5.6k 4.7k 23 680 5.6k 55* 1.8k 5.6k 87 3.9k 5.6k 119 4 5 6 7 8 (5) 12 24 25 680 680 6.8k 8.2k 56 57 1.8k 1.8k 6.8k 88 8.2k 89 3.9k 3.9k 6.8k 8.2k (5) 97 5.6k 5.6k (5) 5.6k 6.8k (5) 5.6k 8.2k (5) 120 121 26 680 10k 58 1.8k 10k 90 3.9k 10k 122 5.6k 10k 27 680 12k 59 1.8k 12k 91 3.9k 12k 123(5) 5.6k 12k 15k (5) 5.6k 15k (5) 5.6k 18k (5) 5.6k 22k (5) 5.6k 27k 28 29 30 31 680 680 680 680 15k 18k 22k 27k 60 61 62 63 1.8k 1.8k 1.8k 1.8k 15k 92 18k 93 22k 94 27k 95 3.9k 3.9k 3.9k 3.9k 18k 22k 27k 124 125 126 127 Note: 5. These addresses are reserved by the SMBus™ specification. February 11, 2014 18 Revision 1.1 Micrel, Inc. MIC21000 Configuration Two sets of configuration parameters are supported by the MIC21000. The first set of parameters can only be set during the configuration phase of the MIC21000. These values are written into the OTP memory and cannot be changed using PMBus commands during runtime. A second set of parameters can also be configured, also during runtime, using the appropriate PMBus commands. The two groups are classified in the PMBus configuration table (Table 9). If only four devices are used in a system, their respective addresses can alternatively be configured without resistors by connecting the pins to GND or AVDD18 pin. The PMBus addresses selectable in this fashion are listed in Table 8. Table 8. PMBus Address Selection without Resistors Address ADDR1 ADDR0 15 GND AVDD18 48 AVDD18 GND 63 AVDD18 AVDD18 64 GND GND Table 9. List of Supported PMBus Configuration Registers PMBus Parameter Description Data Format Classification On/off configuration N/A OTP Exponent of the VOUT_COMMAND value N/A Output Voltage ON_OFF_CONFIG (6, 7) VOUT_MODE Read only (8) VOUT_COMMAND Set output voltage LINEAR PMBus VOUT_OV_FAULT_LIMIT Overvoltage fault limit N/A OTP VOUT_OV_FAULT_RESPONSE Overvoltage fault response N/A OTP VOUT_OV_WARN_LIMIT Overvoltage warning level N/A OTP VOUT_UV_WARN_LIMIT Undervoltage warning level N/A OTP VOUT_UV_FAULT_LIMIT Undervoltage fault level N/A OTP VOUT_UV_FAULT_RESPONSE Undervoltage fault response N/A OTP IOUT_OC_FAULT_LIMIT Overcurrent fault limit N/A OTP IOUT_OC_FAULT_RESPONSE Overcurrent fault response N/A OTP IOUT_OC_LV_FAULT_LIMIT Voltage threshold during constant-current mode N/A OTP IOUT_OC_WARN_LIMIT Overcurrent warning level N/A OTP OT_FAULT_LIMIT Overtemperature fault level N/A OTP OT_FAULT_RESPONSE Overtemperature fault response N/A OTP OT_WARN_LIMIT Overtemperature warning level N/A OTP IOT_FAULT_LIMIT Overtemperature fault level N/A OTP IOT_FAULT_RESPONSE Overtemperature fault response N/A OTP IOT_WARN_LIMIT Overtemperature warning level N/A OTP Output Current Temperature - External Temperature - Internal Notes: 6. VOUT_MODE is read-only for the MIC21000. 7. In accordance with the PMBus specification, all commands related to the output voltage are subject to the VOUT_MODE settings. 8. The MIC21000 supports the LINEAR data format according to the PMBus specification. February 11, 2014 19 Revision 1.1 Micrel, Inc. MIC21000 Table 9. List of Supported PMBus Configuration Registers (Continued) PMBus Parameter Description Data Format Classification VIN_OV_FAULT_LIMIT Overvoltage fault limit N/A OTP VIN_OV_FAULT_RESPONSE Overvoltage fault response N/A OTP VIN_OV_WARN_LIMIT Overvoltage warning level N/A OTP VIN_UV_WARN_LIMIT Undervoltage warning level N/A OTP VIN_UV_FAULT_LIMIT Undervoltage fault level N/A OTP VIN_UV_FAULT_RESPONSE Undervoltage fault response N/A OTP POWER_GOOD_ON Power good on threshold N/A OTP POWER_GOOD_OFF Power good off threshold N/A OTP TON_DELAY Turn-on delay N/A OTP TON_RISE Turn-on rise time N/A OTP TON_FAULT_MAX Turn-on maximum fault time N/A OTP TOFF_DELAY Turn-off delay N/A OTP TOFF_FALL Turn-off fall time N/A OTP TOFF_WARN_MAX Turn-off maximum warning time N/A OTP VOFF_NOM Soft-stop off value N/A OTP Input Voltage Start-Up Behavior / Power Sequencing Output Voltage Sequencing Monitoring The MIC21000 has a dedicated set of PMBus status registers to enable advanced power management using extensive monitoring features, as described in Table 10. Different warning and error flags can be read by the PMBus master to ensure proper operation of the power converter or monitor the converter over its lifetime. Table 10. List of Supported PMBus Status Registers PMBus Command Description CLEAR_FAULTS Clear status information STATUS_BYTE Unit status byte STATUS_WORD Unit status word STATUS_VOUT Output voltage status STATUS_IOUT Output current status STATUS_INPUT Input status STATUS_TEMPERATURE Temperature status STATUS_CML Communication and memory status READ_VIN Input voltage read back LINEAR READ_VOUT Output voltage read back LINEAR READ_IOUT Output current read back LINEAR READ_TEMPERATURE_1 External temperature read back LINEAR READ_TEMPERATURE_2 Internal temperature read back LINEAR February 11, 2014 Data Format 20 Revision 1.1 Micrel, Inc. MIC21000 Miscellaneous Table 11. Additional Supported PMBus Registers PMBus Command Description Data Length (Byte) Values PMBUS_REVISION PMBus revision 1 0x11 MFR_ID Manufacturer ID 4 “MCRL” MFR_MODEL Manufacturer model identifier 4 “210A” MFR_REVISION Manufacturer product revision 4 MFR_SERIAL Serial number 12 Detailed Description of the Supported PMBus Commands OPERATION The OPERATION command is used to turn the unit on and off in conjunction with the input from the CONTROL pin. The unit stays in the commanded operating mode until a subsequent OPERATION command or a change in the state of the CONTROL pin tells the device to change to another mode. The supported operation modes are listed in Table 12. Table 12. Supported PMBus Operation Modes OPERATION (read/write) Bits[7:6] Bits[5:4] Bits[3:2] Bits[1:0] Unit On or Off Margin State 01 XX XX XX Soft Off (With Sequencing) N/A 10 00 XX XX On Off CLEAR_FAULTS The CLEAR_FAULTS command is used to clear any fault bits that have been set in the status registers. Additionally, the SMBALERT signal is cleared if it was previously asserted. The device resumes operation with the currently configured state after a CLEAR_FAULTS command has been issued. If a fault/warning is still present, the respective bit is set again immediately. VOUT_MODE The VOUT_MODE command is used to retrieve information about the data format for all output voltage related commands. Note that this is a read-only value. VOUT_MODE (read only) Bits Name Description [4:0] PARAMETER 2’s complement of the exponent [7:5] MODE 000: Linear data format VOUT_COMMAND The VOUT_COMMAND is used to set the output voltage during runtime. VOUT_COMMAND (read/write) Bits [15:0] February 11, 2014 Name Description MANTISSA Unsigned mantissa of output voltage in V. Exponent can be retrieved via VOUT_MODE command. 21 Revision 1.1 Micrel, Inc. MIC21000 STATUS_BYTE The STATUS_BYTE command returns a summary of the most critical faults in one byte. STATUS_BYTE (read only) Bits Name Description [0] NONE OF THE ABOVE A fault not listed in bits [7:1] has occurred. [1] CML A communication fault as occurred. [2] TEMPERATURE A temperature fault or warning has occurred. [3] VIN_UV An input undervoltage fault has occurred. [4] IOUT_OC An output overcurrent fault has occurred. [5] VOUT_OV An output overvoltage fault has occurred. [6] OFF This bit is asserted if the unit is not providing power to the output, regardless of the reason, including simply not being enabled. [7] BUSY Not supported. STATUS_WORD The STATUS_WORD command returns a summary of the device status information in two data bytes. STATUS_WORD (read only) Bits Name Description [7:0] STATUS_BYTE See STATUS_BYTE [8] UNKNOWN Not supported [9] OTHER Not supported [10] FANS No supported [11] POWER_GOOD# The POWER_GOOD signal, if present, is negated. [12] MFR A manufacturer specific fault or warning has occurred. [13] INPUT An input related warning or fault has occurred. [14] IOUT/POUT An output current or output power warning or fault has occurred. [15] VOUT An output voltage related warning or fault has occurred. STATUS_VOUT STATUS_VOUT (read only) Bits Name Description [0] Not supported. [1] Not supported. [2] Not supported. [3] Not supported. [4] VOUT_UV_FLT An output voltage undervoltage fault has occurred. [5] VOUT_UV_WARN An output voltage undervoltage warning has occurred. [6] VOUT_OV_WARN An output voltage overvoltage warning has occurred. [7] VOUT_OV_FLT An output voltage overvoltage fault has occurred. February 11, 2014 22 Revision 1.1 Micrel, Inc. MIC21000 STATUS_IOUT STATUS_IOUT (read only) Bits Name Description [0] Not supported. [1] Not supported. [2] Not supported. [3] Not supported. [4] Not supported. [5] IOUT_OC_WARN An overcurrent warning has occurred. [6] ICOUT_OC_LV_FLT An overcurrent low-voltage shutdown fault has occurred. [7] IOUT_OC_FLT An overcurrent fault has occurred. STATUS_INPUT STATUS_INPUT (read only) Bits Name Description [0] Not supported. [1] Not supported. [2] Not supported. [3] Not supported. [4] VIN_UV_FLT An input voltage undervoltage fault has occurred. [5] VIN_UV_WARN An input voltage undervoltage warning has occurred. [6] VIN_OV_WARN An input voltage overvoltage warning has occurred. [7] VIN_OV_FLT An input voltage overvoltage fault has occurred. STATUS_TEMPERATURE STATUS_TEMPERATURE (read only) Bits Name Description [0] Not supported. [1] Not supported. [2] Not supported. [3] Not supported. [4] Not supported. [5] Not supported. [6] TEMP_OV_WARN An (external) overtemperature warning has occurred. [7] TEMP_OV_FLT An (external) overtemperature fault has occurred. February 11, 2014 23 Revision 1.1 Micrel, Inc. MIC21000 STATUS_CML STATUS_CML (read only) Bits Name [0] [1] Description Not supported. SMBUS_FLT SMBus timeout or a format error has occurred. [2] Not supported. [3] Not supported. [4] Not supported. [5] PEC_FLT [6] [7] A packet error check fault has occurred. Not supported. CMD_FLT An invalid or an unsupported command has been received. STATUS_MFR_SPECIFIC STATUS_MFR_SPECIFIC (read only) Bits Name Description [0] Not supported. [1] Not supported. [2] Not supported. [3] Not supported. [4] Not supported. [5] Not supported. [6] ITEMP_OV_WARN An (internal) overtemperature warning has occurred. [7] ITEMP_OV_FLT An (internal) overtemperature fault has occurred. READ_VIN READ_VIN (read only) Bits [15:0] Name Description VIN Input voltage in V (linear data format). READ_VOUT READ_VOUT (read only) Bits Name Description [15:0] VOUT Output voltage in V (linear data format). Note that this command is mantissa only. READ_IOUT READ_IOUT (read only) Bits Name Description [15:0] IOUT Output current in A (linear data format). February 11, 2014 24 Revision 1.1 Micrel, Inc. MIC21000 READ_TEMPERATURE1 READ_TEMPERATURE1 (read only) Bits Name Description [15:0] TEMP1 External temperature in °C (linear data format). READ_TEMPERATURE2 READ_TEMPERATURE2 (read only) Bits Name Description [15:0] TEMP2 Internal temperature in °C (linear data format). February 11, 2014 25 Revision 1.1 Micrel, Inc. MIC21000 Typical Application Schematic Bill of Materials Item Part Number C1005C0G1H220J C7 GRM1555C1H220JA01D 04025U220JAT2A C1005X5R1C104K C6, C10 C17−18 GRM155R61C104KA88D C2−5 (10) 100nF Capacitor, 16V, X5R, 10%, Size 0402 2 100µF Capacitor, 6.3V, X5R, 20%, Size 1210 2 10µF Capacitor, 25V, X5R, 20%, Size 0805 4 1µF Capacitor, 10V, X5R, 20%, Size 0402 3 4.7µF Capacitor, 10V, X5R, 20%, Size 0603 4 TDK Murata AVX Murata TDK Murata TDK Murata LT02ZD105MAT2S AVX C1608X5R1A475M TDK 0603ZD475MAT2A AVX C0603C475M8PACTU 1 AVX 12106D107MAT2A GRM155R61A105ME15D 2.2pF Capacitor, 50V, C0G, 5%, Size 0402 (11) TDK C1005X5R1A105M C1, C11−12 Murata C3225X5R0J107M GRM21BR61E106MA73L Qty. TDK AVX C2012X5R1E106M Description (9) LD02YD104KAB2A GRM32ER60J107ME20K C13−16 Manufacturer (12) KEMET Notes: 9. TDK: www.tdk.com. 10. Murata: www.murata.com. 11. AVX: www.avx.com. 12. KEMET: www.kemet.com. February 11, 2014 26 Revision 1.1 Micrel, Inc. MIC21000 Bill of Materials (Continued) Item Part Number C3216X5R0J476M C19-22 C8 GRM31CR60J476ME19L Manufacturer Qty. TDK Murata 12066D476MAT2A AVX C1608X5R1C684K TDK 0603YD684KAT2A AVX C0603C684K4PACTU Description 47µF Capacitor, 6.3V, X5R, 20%, Size 1206 4 680nF Capacitor, 16V, X5R, 10%, size 0603 1 Inductor, SMD, 0.47µH, 26A 1 KEMET (13) L1 7443320047 R10 RC0402-1R0J ANY 1Ω Chip Resistor, Tolerance 5%, Size 0402 1 R8 RC0402-1001F ANY 1.0kΩ Chip Resistor, Tolerance 1%, Size 0402 1 R11 RC0402-10RJ ANY 10Ω Chip Resistor, Tolerance 5%, Size 0402 1 R12 RC0402-103J ANY 10kΩ Chip Resistor, Tolerance 5%, Size 0402 1 R5 RC0402-1001F ANY 1kΩ Chip Resistor, Tolerance 1%, Size 0402 1 R1 RC0402-51RJ ANY 51Ω Chip Resistor, Tolerance 5%, Size 0402 1 R9 RC0402-9101F ANY 9.10kΩ Chip Resistor, Tolerance 1%, Size 0402 1 R6-7 RC0402-953RF ANY 953Ω Chip Resistor, Tolerance 1%, Size 0402 2 MMBT3904 Q1 MMBT3904 MMBT3904 U2 U1 SiC780ACD-T1-GE3 MIC21000YML Wuerth Diodes, Inc. NXP (14) (15) 1 Transistor, NPN, SOT23 MMBT3904 (16) MCC (17) Vishay (18) Micrel, Inc. IC, PQFN-40, High Frequency DrMOS Module 1 MIC21000 Digital PWM Controller with PMBus 1 Notes: 13. Wuerth: www.we-online.com. 14. Diodes, Inc.: www.diodes.com. 15. NXP: www.nxp.com. 16. MCC: www.mccsemi.com. 17. Vishay: www.vishay.com. 18. Micrel, Inc.: www.micrel.com. February 11, 2014 27 Revision 1.1 Micrel, Inc. MIC21000 PCB Layout Recommendations 7. Carefully route the PWM signal to avoid switching noise pickup, which may in turn generate doublepulses at the DrMOS switching node. This also applies to signal LSE. PCB layout is critical to achieve reliable, stable and efficient performance. In the layer stack-up, at least one ground plane is required to control EMI and minimize the inductance in power, signal and return paths. Typically this is Layer 2. DrMOS and Power Stage The MIC21000 typically operates with a high-current power stage, so be careful connecting the power stage and controller grounds. Follow these guidelines to ensure proper MIC21000 controller operation. Please refer to the schematic shown in the “Typical Application Schematic” section. 1. Place input ceramic capacitors C13−C16 as close as possible to DrMOS U2. If different capacitor sizes are used, the smallest one (smallest ESL, highest SRF) should be closest to U2. This helps reduce the input pulsed current loop inductance. 2. Use a wide trace to connect the inductor to the DrMOS SW node to minimize impedance and copper losses, and maximize heatsinking of both inductor and DrMOS low-side MOSFET. Controller IC MIC21000 1. Create a separated ground area for the MIC21000 controller on the top and layer and on the internal GND plane. Connect this local controller ground to the highcurrent power stage ground at a single point to prevent possible power stage return currents through the controller ground. Best practice is to isolate the power and controller ground domains completely, and connect them with a single 0Ω resistor. 3. The SW node of the DrMOS is a high dV/dt node and a potential source of switching noise. Take care to minimize coupling of the SW node to adjacent noisesensitive traces. 4. The power stage output voltage should be sensed by the VFBP/VFBN differential-pair traces routed to the MIC21000 as close as possible to the actual point-ofload, to enable precise load regulation at the exact point of load power delivery. 2. Put capacitors C1, C2, C3 C4, C5, and C6 as close as possible to the IC (U1). Refer all capacitors C1−C6 to the local controller ground. In particular, capacitors refer C4, C5, and C6 as close as possible to the AGND pin (pin 1). In addition to these recommendations, please refer to the product literature of the chosen DrMOS device for additional layout guidelines. 3. Place R7 and C8 physically close to the inductor L1. The voltage sensed across C8 (ISNSP-ISNSN) should be routed as a differential pair to the MIC21000. Insert resistor R6 in the ISNSN path close to the MIC21000, with minimal disruption of the differential-pair routing style. 4. Locate the RC filter R5-C7 on the differential voltage sensing pins VFBP and VFBN in close proximity to the IC. This also applies to the attenuation resistor (R4 in Figure 6) needed for output voltages higher than 1.4V. The remotely sensed voltage signal should be routed from the sensing point to the IC as a differential pair. 5. The external temperature sensing BJT Q1 should be in close thermal coupling with the inductor. For example, it can be placed on the bottom layer right under the inductor. If the routing of the TEMP signal is long, it is recommended to place an optional, small noise filtering capacitor next to the IC between the TEMP pin and the IC ground. The return from the emitter of Q1 to IC ground should be routed together with the TEMP line as a differential pair. 6. Minimize the length of the connection from the midpoint of the VIN sensing divider R8−R9 to the IC pin to prevent noise coupling. February 11, 2014 28 Revision 1.1 Micrel, Inc. MIC21000 Package Information and Recommended Land Pattern(19) 24-Pin QFN44 Note: 19. Package information is correct as of the publication date. For updates and most current information, go to www.micrel.com. 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. © 2013 Micrel, Incorporated. February 11, 2014 29 Revision 1.1