MIC2811/2821 Digital Power Management IC 2MHz, 600mA DC/DC with Triple 300mA LDOs General Description The MIC2811/21 are high performance power management ICs, supporting four output voltage rails with maximum efficiency. The four rails are generated by a single 600mA DC/DC converter and three 300mA LDOs. LDO1 and LDO2 are capable of operating at a low input voltage down to 1.65V useful for post regulating the output voltage of the DC-DC converter. The MIC2811 supports the use of a bypass cap for improved noise performance on LDO1 & LDO2 while the MIC2821 offers a separate enable pin for LDO3. Featuring an operating frequency of 2MHz, the DC to DC converter uses small values of L and C to reduce board space but still retains operating efficiencies up to 86% at load currents up to 600mA. The MIC2811/21 feature a µCap design, operating with very small ceramic output capacitors and inductors for stability, reducing required board space and component cost and it is available in fixed output voltages in the 16pin 3mm × 3mm MLF® leadless package. Data sheets and support documentation can be found on Micrel’s web site at: www.micrel.com. Applications Features • • • • • 2MHz DC/DC converter and 3 LDOs Tiny 16-pin 3mm x 3mm MLF® package Thermal Shutdown Protection ±2% Output Voltage Accuracy on all outputs Current Limit Protection DC/DC Converter • • • • 2.7V to 5.5V input voltage range Output current to 600mA 2MHz PWM operation Up to 86% efficiency (1.2V output) LDO 1 & 2 • • • • • 1.65V to 5.5V input voltage range 300mA output current Fixed Output voltage as low as 0.8V Low 142mV dropout 70dB PSRR at 1kHz LDO 3 • • • 2.7V to 5.5V input voltage range 300mA output current Fixed Output voltage as low as 1.0V • Mobile phones / PDAs • Portable media players • Mobile Television Receivers ____________________________________________________________________________________________________________ Typical Application 1.2VOUT Efficiency 100 90 EFFICIENCY (%) 80 70 60 3V 3.6V 4.2V 50 40 30 20 10 0 0 L = 2.2µH C = 2.2µF 100 200 300 400 500 600 OUTPUT CURRENT (mA) MicroLeadFrame and MLF are registered trademarks of Amkor Technology, Inc. Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com April 2008 M9999-042208-A Micrel, Inc. MIC2811/2821 Ordering Information (1) Junction Temperature Range Package(2) Part Number Marking Code MIC2811-4GJLYML YHA4 1.2V/1.8V/2.5V/2.7V –40°C to +125°C 16-Pin 3x3 MLF® MIC2811-4GMSYML YHA3 1.2V/1.8V/2.8V/3.3V –40°C to +125°C 16-Pin 3x3 MLF® MIC2821-4GJLYML YJA2 1.2V/1.8V/2.5V/2.7V –40°C to +125°C 16-Pin 3x3 MLF® MIC2821-4GMSYML YJA3 1.2V/1.8V/2.8V/3.3V –40°C to +125°C 16-Pin 3x3 MLF® Voltage Note: 1. Output Voltage of DC/DC, LDO1, LDO2, LDO3 respectively For additional voltage options, contact Micrel Marketing. Available fixed output voltage range for each output is as follows: DC/DC LDO1 LDO2 LDO3 min 1.0 0.8 0.8 1.0 max 2.0 (Adjustable output also available) 3.6 3.6 3.9 2. MLF is a GREEN RoHS compliant package. Lead finish is NiPdAu. Mold compound is Halogen Free. April 2008 2 M9999-042208-A Micrel, Inc. MIC2811/2821 FB EN3 EN EN2 FB BYP EN EN2 Pin Configuration EN1 VIN1 EN1 VIN1 BIAS LDO1 BIAS LDO1 LDO3 LDO2 MIC2811 ® 16-Pin 3mm x 3mm MLF (ML) (Top View) LDO2 PGND VIN2 LDO3 DVIN PGND SW VIN VIN2 SGND DVIN VIN SW SGND MIC2821 ® 16-Pin 3mm x 3mm MLF (ML) (Top View) Pin Description Pin Number MIC2811 Pin Number MIC2821 Pin Name 1 1 EN1 Enable Input (LDO 1). Active High Input. Logic High = On; Logic Low = Off; Do not leave floating. 2 2 BIAS Internal circuit bias supply. It must be de-coupled to signal ground with a 0.1µF capacitor and should not be loaded. 3 3 SGND Signal ground. 4 4 PGND Power ground. 5 5 SW Switch (Output): Internal power MOSFET output switches. 6 6 DVIN Power Supply for DC/DC converter. Must be tied to VIN. 7 7 VIN2 Power Supply to LDO2. 8 8 LDO2 Output of LDO2. 9 9 LDO3 Output of LDO3. 10 10 VIN 11 11 LDO1 12 12 VIN1 13 13 FB 14 N/A BYP Reference Bypass. Connect external 0.1µF to GND to reduce output noise. May be left open. Do not connect directly to GND. N/A 14 EN3 Enable Input (LDO3). Active High Input. Logic High = On; Logic Low = Off; Do not leave floating. 15 N/A EN Enable Input (DC/DC and LDO3). Active High Input. Logic High = On; Logic Low = Off; Do not leave floating. N/A 15 EN Enable Input (DC/DC). Active High Input. Logic High = On; Logic Low = Off; Do not leave floating. 16 16 EN2 Enable Input (LDO2). Active High Input. Logic High = On; Logic Low = Off; Do not leave floating. April 2008 Pin Name Supply to bias circuitry and power to LDO3, must be tied to DVIN. Output of LDO1. Power Supply to LDO1. Feedback input to the error amplifier of the DC/DC converter. Adjust version: Use external resistor divider from DC/DC output to set VOUT. Fixed voltage version: Connect directly to VOUT of the DC/DC converter. 3 M9999-042208-A Micrel, Inc. MIC2811/2821 Absolute Maximum Ratings(1) Operating Ratings(2) Supply Voltage (DVIN, VIN, VIN1, VIN2) ................... 0V to +6V Enable Voltage (VEN, VEN1, VEN2, VEN3) ................ 0V to +6V Power Dissipation ................................. Internally Limited(3) Lead Temperature (Soldering, 10 sec.) ..................... 260°C Storage Temperature (TS)...................–65°C ≤ TJ ≤ +150°C ESD Rating(4) ................................................................. 2kV Supply voltage (DVIN, VIN) ......................... +2.7V to +5.5V Supply voltage (VIN1, VIN2) ............................+1.65V to VIN Enable Input Voltage (VEN, VEN1, VEN2, VEN3) ...... 0V to VIN Junction Temperature Range (TJ) .........–40°C to +125°C Package Thermal Resistance 3mm x 3mm MLF-16 (θJA) .............................56°C/W Electrical Characteristics(5) DVIN = VIN = VIN1 = VIN2 = VOUTMAX + 1V, L = 2.2µH; COUTDC/DC = 2.2µF, COUT1 = COUT2 = COUT3 = 2.2µF; IOUTDC/DC = 20mA; IOUTLDO1 = IOUTLDO2 = IOUTLDO2 = 100µA; TJ = 25°C, bold values indicate –40°C < TJ < +125°C; unless noted. Parameter Conditions Min Typ Max Units UVLO Threshold Rising input voltage during turn-on (DVIN & VIN Only) 2.45 2.55 2.65 V UVLO Hysteresis Ground Pin Current Ground Pin Current in Shutdown 100 mV VFB = 1.1*VFBNOM (not switching); 800 1100 µA LDO2 or LDO1 Only (VEN = VEN3 = GND) 55 85 95 LDO3 only (VEN = VEN1 = VEN2 = GND / MIC2821 only) All 3 LDOs 40 120 µA µA µA µA All EN = 0V 0.2 5 µA Over-temperature Shutdown 160 °C Over-temperature Shutdown Hysteresis 23 °C Enable Input Voltage Logic Low Logic High 0.2 V 1 µA V 1.1 Enable Input Current 0.1 Electrical Characteristics - DC/DC Converter DVIN = VIN = VEN = VOUTDC/DC + 1V, L = 2.2µH; COUTDC/DC = 2.2µF, COUT1 = COUT2 = COUT3 = 2.2µF; IOUTDC/DC = 20mA; TJ = 25°C, bold values indicate –40°C to + 125°C; unless noted. Parameter Output Voltage Accuracy Current Limit in PWM Mode Conditions Min Fixed Output Voltages Typ -2 -3 VFB = 0.9*VFBNOM 0.75 FB pin input current (ADJ only) 1.2 Max Units +2 +3 % % 1.8 A 1 nA Output Voltage Line Regulation VOUT > 2.4V; VIN = VOUT + 300mV to 5.5V, ILOAD= 20mA VOUT < 2.4V; VIN = 2.7V to 5.5V, ILOAD= 20mA 0.2 %/V %/V Output Voltage Load Regulation 20mA < ILOAD < 300mA 0.2 Maximum Duty Cycle VFB ≤ 0.4V Switch ON-Resistance PMOS (0.7*VFBNOM) NMOS (1.1*VFBNOM) 1.5 100 % Ω Ω 0.5 0.55 Oscillator Frequency 1.8 % 2 2.2 MHz 83 350 µs Turn-on Time Turn-on Time (DC/DC) April 2008 ILOAD = 300mA; CBYP = 0.1µF 4 M9999-042208-A Micrel, Inc. MIC2811/2821 Electrical Characteristics - LDO1 and LDO2 VIN = DVIN = VOUTMAX + 1V, VIN1 = VEN1 = VLDO1 + 1V; VIN2 = VEN2 = VLDO2 + 1V ; COUTLDO1 = COUTLDO2 = 2.2µF, ILDO1 = ILDO2 = 100µA; TJ = 25°C, VEN = VEN3 = GND, bold values indicate –40°C< TJ < +125°C; unless noted. Parameter Conditions Min Output Voltage Accuracy Typ -2.0 -3.0 Max Units +2.0 +3.0 % % Output Current Capability VIN > 1.8V 300 Load Regulation IOUT = 100µA to 300mA 0.3 1.5 % Line Regulation VIN1(2) = VLDO1(2) +1V to 5.5V 0.02 0.3 %/V Dropout Voltage IOUT = 300mA @ Vout > 1.5V 142 300 mV Current Limit VOUT = 0V 650 900 mA Ripple Rejection f = up to 1kHz; COUT = 2.2µF; CBYP = 0.1µF f = 20kHz; COUT = 2.2µF; CBYP = 0.1µF 70 44 dB dB Output Voltage Noise COUT = 2.2µF; CBYP = 0.1µF; 10Hz to 100KHz 30 µVRMS 350 mA Electrical Characteristics – LDO3 VIN = DVIN = VEN3 = VLDO3 +1 V; COUT3 = 2.2µF; IOUTLDO3 = 100µA; TJ = 25°C, VEN1 = VEN2 = GND bold values indicate –40°C< TJ < +125°C; unless noted. Parameter Conditions Min Output Voltage Accuracy Typ -2.0 -3.0 Max Units +2.0 +3.0 % % 0.5 %/V Line Regulation VIN = VOUT +1V to 5.5V; IOUT = 100µA 0.03 Load Regulation IOUT = 100µA to 300mA @ 3.3V 0.50 1.5 % Dropout Voltage IOUT = 300mA @ Vin = 2.7V 210 350 mV Ripple Rejection f = up to 1kHz; COUT = 2.2µF f = 20kHz; COUT = 2.2µF 45 20 Current Limit VOUT = 0V Output Voltage Noise COUT = 2.2µF, 10Hz to 100kHz 350 600 470 dB dB 980 mA µVRMS Notes: 1. Exceeding the absolute maximum rating may damage the device. 2. The device is not guaranteed to function outside its operating rating. 3. The maximum allowable power dissipation of any TA (ambient temperature) is PD(max) = (TJ(max) – TA) / θJA. Exceeding the maximum allowable power dissipation will result in excessive die temperature, and the regulator will go into thermal shutdown. 4. Devices are ESD sensitive. Handling precautions recommended. Human body model, 1.5k in series with 100pF. 5. Specification for packaged product only. April 2008 5 M9999-042208-A Micrel, Inc. MIC2811/2821 Typical Characteristics (DC/DC Converter) Disable 780 760 740 720 700 2.7 2.8 3.4 4.1 4.8 SUPPLY VOLTAGE (V) 5.5 EFFICIENCY (%) 40 30 20 10 0 0 120 80 100 60 -40 60 50 1.2033 1.203 L = 2.2µH COUT = 2.2µF 1.2027 1.2024 1.2021 1.2018 3.4 4.1 4.8 INPUT VOLTAGE (V) L = 2.2µH C = 2.2µF 100 200 300 400 500 600 OUTPUT CURRENT (mA) Load Regulation IOUT = 300mA 1.2015 2.7 3.6V 4.2V 5.5 1.205 V = 3.6V 1.2045 IN L = 2.2µH 1.204 C = 2.2µF 1.2035 1.203 1.2025 1.202 1.2015 1.201 1.2005 1.2 0 100 200 300 400 500 600 OUTPUT CURRENT (mA) 1.5 L = 2.2µH 1.45 C = 2.2µF CURRENT LIMIT (A) 2 1.8 1.6 April 2008 TEMPERATURE (°C) 80 70 3V Current Limit vs. Input Voltage 2.2 3.4 4.1 4.8 INPUT VOLTAGE (V) 1.18 1.2036 Switching Frequency vs. Input Voltage IOUT = 300mA 2.6 L = 2.2µH C = 2.2µF 2.4 1.4 2.7 1.19 OUTPUT VOLTAGE (V) 820 800 = 300mA 1.2 1.2039 Enable OUTPUT VOLTAGE (V) ILOAD = 100mA L = 2.2µH 840 C = 2.2µF OUT OUT Line Regulation DC/DC Enable Threshold vs. Supply Voltage 860 I 1.17 120 100 80 60 40 0 20 -40 ENABLE THRESHOLD (mV) 880 TEMPERATURE (°C) 90 40 2 1.9 1.8 1.21 20 2.2 2.1 100 1.22 C = 4.7µF OUT 0 2.4 2.3 IOUT = 300mA 1.2VOUT Efficiency VIN = 4V -20 VOUT = 1.2V 1.7 1.6 SWITCHING FREQUENCY (MHz) 1.23 VIN = 4V -20 FRQUENCY (MHz) 2.5 OUTPUT VOLTAGE (V) 2.6 Output Voltage vs. Temperature SW Frequency vs. Temperature 5.5 1.4 1.35 1.3 1.25 1.2 1.15 1.1 1.05 1 2.7 3.4 4.1 4.8 INPUT VOLTAGE (V) 6 5.5 M9999-042208-A Micrel, Inc. MIC2811/2821 Typical Characteristics (LDO) MIC2811 LDO2 PSRR 10 0 10 1E+2 1k 1E+4 10k 100k 1M 100 1E+3 1E+1 1E+5 1E+6 FREQUENCY (Hz) MIC2811 LDO1 Output Noise Spectral Density MIC2811 LDO2 Output Noise Spectral Density 0 1k 1E+4 100k 1E+6 10k 1E+5 10 1E+2 100 1E+3 1M 1E+1 FREQUENCY (Hz) MIC2811 LDO3 Output Noise Spectral Density 10 10 1 1 1 0.1 VIN = 4V COUT = 2.2µF Noise(10Hz to 100kHz) = 46.75µV 2.6 COUT = 2.2µF 2.5 2.45 April 2008 50 100 150 200 250 300 OUTPUT CURRENT (mA) 1.84 -40 120 80 2.53 VIN = 5.5V 2.525 = 150mA I 1.83 LOAD C = 2.2µF 1.82 1.81 1.8 1.79 1.78 1.77 1.76 1.75 2 2.5 3 3.5 4 4.5 5 5.5 VIN1 INPUT VOLTAGE (V) 7 TEMPERATURE (°C) LDO2 Line Regulation 2.52 2.515 ILOAD = 150mA C = 2.2µF 2.51 2.505 2.5 2.495 2.49 2.485 2.48 2.8 1.76 1.75 0 100 2.55 OUTPUT VOLTAGE (V) 1.78 1.77 2.65 2.35 1.85 OUTPUT VOLTAGE (V) 1.79 2.7 2.6 TEMPERATURE (°C) IOUT = 150mA LDO1 Line Regulation 1.85 1.82 C = 2.2µF 1.81 1.8 2.75 2.4 LDO1 Load Regulation 1.84 VIN = 5.5V 1.83 VIN1 = 3.6V LDO3 OUT (V) IOUT = 150mA 60 120 80 TEMPERATURE (°C) 100 60 40 20 0 -40 -20 1.76 1.74 VIN = 4V 2.8 COUT = 2.2µF 40 1.78 2.55 20 1.82 1.8 1.72 1.7 2.85 VIN = 4V -20 COUT = 2.2µF RMS 1k 10k 100k 1M 10M FREQUENCY (Hz) LDO3 vs. Temperature -20 2.65 VIN = 4V -40 1.86 1.84 LDO2 vs. Temperature LDO2 OUT (V) 1.9 0.001 10 100 1k 10k 100k 1M 10M FREQUENCY (Hz) 120 0.001 10 100 VOUT = 2.7V Noise(10Hz to 100kHz) = 91.93µV RMS 5.5 1k 10k 100k 1M 10M FREQUENCY (Hz) CBYP = 0.1µF 80 RMS LDO1 vs. Temperature 1.88 0.01 VOUT = 2.5V 0 0.001 10 100 CBYP = 0.1µF 100 0.01 VOUT = 1.8V 0.1 VIN = 4V COUT = 2.2µF 5.2 CBYP = 0.1µF Noise(10Hz to 100kHz) = 35.88µV LDO1 OUT (V) 10 10 0.01 OUTPUT VOLTAGE (V) 20 010 1k 1E+4 1M 100 1E+3 10k 1E+5 100k 1E+6 1E+1 1E+2 FREQUENCY (Hz) 0.1 VIN = 4V COUT = 2.2µF 300mA 30 4.9 10 30 300mA 20 40 60 20 40 50 3.1 30 150mA 60 50 4.6 300mA 150mA 60 40 150mA 40 80 70 4.3 50 10mA 70 4.0 60 PSRR (dB) PSRR (dB) 70 10mA PSRR (dB) 10mA 80 0 90 20 100 80 3.7 90 MIC2811 LDO3 PSRR 3.4 MIC2811 LDO1 PSRR VIN2 INPUT VOLTAGE (V) M9999-042208-A Micrel, Inc. MIC2811/2821 Typical Characteristics (LDO cont.) LDO2 Dropout Voltage vs. Load Current 2.5025 120 V = 1.2V OUT 100 C = 2.2µF 80 60 40 20 0 0 50 100 150 200 250 300 OUTPUT CURRENT (mA) 2.502 2.5005 2.5 2.4995 2.499 2.4985 2.498 2.4975 0 2.704 2.702 2.7 2.698 2.696 2.694 2.692 2.69 0 April 2008 50 100 150 200 250 300 OUTPUT CURRENT (mA) 65 GND CURRENT (µA) OUTPUT VOLTAGE (mV) 2.71 V = 3.6V 2.708 IN C = 2.2µF 2.706 2.74 V = 3.6V 2.5015 IN2 C = 2.2µF 2.501 LDO3 Load Regulation 2.75 VIN = 5.5V OUTPUT VOLTAGE (V) VIN = 5.5V OUTPUT VOLTAGE (V) DROPOUT VOLTAGE (mV) 140 LDO2 Load Regulation 50 100 150 200 250 300 OUTPUT CURRENT (mA) 2.73 2.72 LDO3 Line Regulation ILOAD = 150mA C = 2.2µF 2.71 2.7 2.69 2.68 2.67 2.66 2.65 3.1 3.7 4.3 4.9 5.5 VIN3 INPUT VOLTAGE (V) LDO2 GND Current vs. Output Current V = 3.6V 64 IN C = 2.2µF 63 62 61 60 59 58 57 56 55 0 50 100 150 200 250 300 OUTPUT CURRENT (mA) 8 M9999-042208-A Micrel, Inc. MIC2811/2821 Functional Characteristics (DC/DC Converter) April 2008 9 M9999-042208-A Micrel, Inc. MIC2811/2821 Functional Characteristics (LDO) April 2008 10 M9999-042208-A Micrel, Inc. MIC2811/2821 Functional Diagram DVIN VIN P-Channel Current Limit 6 BIAS HSD CBIAS PWM Control SW VOUT Anti-Shoot Through COUT LSD N-Channel Current Limit PGND R1 EN Bias, UVLO, Thermal Shutdown Enable and Control Logic Internal for Fixed Output Options Connect VOUT R2 directly to FB FB Soft Start EA 1.0V BIAS EN3 (MIC2821) LDO Current Limit EA BIAS LDO3 VIN1 CLDO3 LDO Current Limit EN1 EA LDO1 VIN2 CLDO1 LDO Current Limit EN2 EA LDO2 BIAS CLDO2 0.8V LDO1 & 2 Quick Start Ref Voltage BYP 750k 0.8V CBYP (MIC2811) SGND Block Diagram April 2008 11 M9999-042208-A Micrel, Inc. MIC2811/2821 performance. X7R-type capacitors change capacitance by 15% over their operating temperature range and are the most stable type of ceramic capacitors. Z5U and Y5V dielectric capacitors change value by as much as 50% to 60% respectively over their operating temperature ranges and for that reason are not recommended. Larger output capacitances can be achieved by placing tantalum or aluminum electrolytics in parallel with the ceramic capacitor. For example, a 100µF electrolytic in parallel with a 10µF ceramic can provide the transient and high frequency noise performance of a 100µF ceramic at a significantly lower cost. Specific undershoot/overshoot performance will depend on both the values and ESR/ESL of the capacitors. Applications Information The MIC2811 and MIC2821 are power management ICs with a single integrated step-down regulator and three low dropout regulators. LDO1, LDO2, and LDO3 are 300mA low dropout regulators supplied by their own independent input voltage pins. The supply to LDO3 (VIN) also powers the bias circuitry and must be available for any output to be operational. This supply requires an external connection to DVIN. The step-down regulator is a 2MHz 600mA PWM power supply, using small values of L and C operating at over 90% efficiency. DVIN/VIN/VIN1/VIN2 All four regulators, the switch mode regulator, LDO1, LDO2, and LDO3 have their own unique input voltage supply pin. VIN provides power to LDO3 and internal circuitry shared by all the regulators and therefore must be available for any of the regulators to operate properly. DVIN and VIN must be tied together and have a minimum input voltage of 2.7V. Inputs to LDO1 (VIN1) and LDO2 (VIN2) can go as low as 1.65V, but should never exceed the VIN and DVIN input voltage. Due to the high switching speeds, a 1µF input capacitor is recommended close to the DVIN, decoupled to the PGND pin. 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 MIC2811 and MIC2821 are designed for use with a 2.2µH 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% to 20% 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. Peak inductor current can be calculated as follows: LDO1 Regulated output voltage of LDO1. Power is provided by VIN1 and enabled through EN1. Recommended output capacitance is 2.2µF, decoupled to the SGND pin. LDO2 Regulated output voltage of LDO2. Power is provided by VIN2 and enabled through EN2. Recommended output capacitance is 2.2µF, decoupled to the SGND pin. I PK = IOUT + LDO3 Regulated output voltage of LDO3. Power is provided by VIN and enabled through EN (MIC2811) or EN3 (MIC2821). Recommended output capacitance is 2.2µF, decoupled to the SGND pin. VOUT VIN ) 2×f ×L 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. SW The switch (SW) pin connects directly to the inductor and provides the switching current necessary to operate in PWM mode. Due to the high speed switching on this pin, the switch node should be routed away from sensitive nodes. Efficiency Considerations Efficiency is defined as the amount of useful output power, divided by the amount of power supplied. DC/DC Output Capacitor The DC/DC regulator requires an output capacitor for proper operation. Values of greater than 2.2µF improve transient response and noise reduction at high frequency. X7R/X5R dielectric-type ceramic capacitors are recommended because of their superior temperature April 2008 VOUT (1 − ⎛ Vout × Iout ⎞ Efficiency _ % = ⎜ ⎟ × 100 ⎝ Vin × Iin ⎠ Maintaining high efficiency serves two purposes. It reduces power dissipation in the power supply, reducing the need for heat sinks and thermal design 12 M9999-042208-A Micrel, Inc. MIC2811/2821 considerations and it reduces consumption of current for battery powered applications. Reduced current draw from a battery increases the devices operating time and is critical in hand held devices. There are two types of losses in switching converters; DC losses and switching losses. DC losses are simply the power dissipation of I2R. Power is dissipated in the high side switch during the on cycle. Power loss is equal to the high side MOSFET RDSON multiplied by the Switch Current2. During the off cycle, the low side N-channel MOSFET conducts, also dissipating power. Device operating current also reduces efficiency. The product of the quiescent (operating) current and the supply voltage is another DC loss. Over 100mA, efficiency loss is dominated by MOSFET RDSON and inductor losses. Higher input supply voltages will increase the Gate to Source threshold 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: MIC2811 Layout Recommendations A poor layout of the MIC2811 may cause unwanted voltage and current spikes. This can lead to noise on DC voltages and EMI radiating to nearby devices. The following are recommendations for the MIC2811/21 layout. The evaluation board layout is included as an example. 1. Place the MIC2811/21 with the pad size designated in the “Recommended Land Patterns” page of the Micrel website. 2. When laying out the components, keep the MIC2811, inductor, and filter capacitors physically close to keep traces as short as possible. The traces between these components carry relatively high switching currents and can affect adjacent signals. 3. The input capacitor between DVIN and PGND should be placed right next to the MIC2811/21. This will eliminate trace inductance effects and reduce internal noise for the MIC2811/21 control circuitry. The trace from the DVIN filter capacitor to the MIC2811/21 device should not be routed through any vias. This lessens the chance of noise coupling by the effective antenna of the via. 4. Monitoring the path of the switching currents will help minimize the radiated noise. In the first half of the switching cycle, current flows from the input filter capacitor through the high side switch within the MIC2811, then through the inductor to the output filter capacitor and lastly through ground. In the second half of the switching cycle, current is pulled up from ground through the low side synchronous switch within the MIC2807 by the inductor, to the output filter capacitor and then back through ground, forming a second current loop. Route these loops to ensure the current curls in the same direction, preventing magnetic field reversal between the switching cycles. 5. Connect the Bypass capacitor (MIC2811 Only) to the BYP pin and the AGND pin. AGND and PGND should be connected close to the chip at a single point in order to minimize undesirable behavior due to ground bounce. Input and output filter capacitors should be connected to PGND. 6. Connections between power components and the MIC2811 should have wide traces. It is good practice to use a minimum of 30mils (0.762mm) per Ampere for 1oz copper weight. 7. Route noise sensitive traces such as Feedback (FB), BIAS, and BYP away from the switching traces and the inductor. Noise coupled into these pins can affect the accuracy of the output. The Feedback pin should be connected at point of load for an accurate load regulation. L _ Pd = Iout 2 × DCR From that, the loss in efficiency due to inductor resistance can be calculated as follows; ⎡ ⎛ ⎞⎤ Vout × Iout ⎟⎟⎥ × 100 Efficiency _ Loss = ⎢1 − ⎜⎜ ⎣ ⎝ Vout × Iout + L _ Pd ⎠⎦ 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. PGND Power ground (PGND) is the ground path for the high current PWM mode. The current loop area for the power ground should be as small as possible. SGND Signal ground (SGND) is the ground path for the biasing and control circuitry. The current loop for the signal ground should be as small as possible. BYP (MIC2811 only) For enhanced noise and PSRR performance on LDO1 & LDO2, the internal reference of the MIC2811 can be bypassed with a capacitor to ground. A quick-start feature allows for quick turn-on of the output voltage. The recommended nominal bypass capacitor is 0.1µF, but it can be increased, which will also result in an increase to the start-up time. April 2008 13 M9999-042208-A Micrel, Inc. MIC2811/2821 MIC2811/2821-YML Schematic J1 DVIN U1 MIC2811/2821-YML DVIN 6 C1 4.7µF/6.3V J2 GND DVIN VO-LDO2 LDO2 10 VIN 12 VIN1 C2 4.7µF/6.3V J4 VIN2 VIN1 C3 4.7µF/6.3V C4 VIN2 4.7µF/6.3V LDO1 J6 EN R5 SGND PGND EN2 J12 VO_LDO1 J5 GND VO J13 VOUT C10 4.7µF/6.3V R2 OPTION 3 EN1 16 BYP/EN3 1 J11 VO_LDO2 J14 GND 13 EN 4 J7 EN1 15 J10 VO_LDO3 2.2µH R1 OPTION FB J6 EN L1 5 VIN2 14 J8 EN2 R4 10K R5 10K 11 C7 2.2µF/6.3V SW 7 8 C8 2.2µF/6.3V VIN1 VIN2 9 C9 2.2µF/6.3V DVIN J3 VIN1 VO-LDO3 LDO3 BIAS 2 C6 0.1µF/10V 10K (FOR MIC2821 ONLY) C5 0.1µF (FOR MIC2811 ONLY) April 2008 14 M9999-042208-A Micrel, Inc. MIC2811/2821 Bill of Materials Item Part Number C5, C6 JMK107BJ475MA-T Taiyo Yuden C1608X5R0J475K TDK GRM188R60J475KE19D muRATA C1608X5R0J225K TDK 06036D225KAT2A AVX GRM188R60J225KE19D muRata VJ0603G225KXYAT Vishay C1005X7R1A104K TDK R1 (3) 2.2µF, 6.3V, 0603, X5R Ceramic Capacitor 3 0.1µF, 10V, X5R Ceramic Capacitor (C5 for MIC2811 EV Board only) 2 (1) (2) (4) (3) (4) CDRH2D11HPNP Sumida (6) 2.2µH, 1.1A, 3.2x3.2x1.2mm Inductor (7) 2.2µH, 1.1A, 2.5x3.2x2mm Inductor ME3220-222-ML Coilcraft CRCW06030R00FRT1 Vishay CRCW06031002FRT1 Vishay MIC2811/21 5 (3) Vishay U1 4.7µF, 6.3V, 0603, X5R Ceramic Capacitor (2) 1 (4) 0Ω, 0603, 1% resistor 1 Open 0 (4) 10kΩ, 0603, 1% resistor R2 R3, R4, R5 Qty. (5) VJ0603Y104KXQCW1BC L1 Description (1) AVX C1, C2, C3, C4, C10 C7, C8, C9 Manufacturer 06036D475KAT2A Micrel, Inc. (8) 16-Pin 3mm x 3mm MLF 3 ® 1 Notes: 1. AVX: www.avx.com 2. Murata: www.murata.com 3. TDK: www.tdk.com 4. Vishay: www.vishay.com 5. Taiyo Yuden: www.t-yuden.com 6. Sumida: www.sumida.com 7. Coilcraft: www.coilcraft.com 8. Micrel, Inc.: www.micrel.com April 2008 15 M9999-042208-A Micrel, Inc. MIC2811/2821 PCB Layout Recommendations Top Layer Bottom Layer April 2008 16 M9999-042208-A Micrel, Inc. MIC2811/2821 Package Information 16-Pin 3mm x 3mm MLF® (ML) MICREL, INC. 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA TEL +1 (408) 944-0800 FAX +1 (408) 474-1000 WEB http://www.micrel.com The information furnished by Micrel in this data sheet is believed to be accurate and reliable. However, no responsibility is assumed by Micrel for its use. Micrel reserves the right to change circuitry and specifications at any time without notification to the customer. Micrel Products are not designed or authorized for use as components in life support appliances, devices or systems where malfunction of a product can reasonably be expected to result in personal injury. Life support devices or systems are devices or systems that (a) are intended for surgical implant into the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significant injury to the user. A Purchaser’s use or sale of Micrel Products for use in life support appliances, devices or systems is a Purchaser’s own risk and Purchaser agrees to fully indemnify Micrel for any damages resulting from such use or sale. © 2008 Micrel, Incorporated. April 2008 17 M9999-042208-A