MIC General Description. Features. Applications. Typical Application. 1.5A Low Voltage LDO Regulator w/dual Input Voltages

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1 MIC A Low oltage LDO Regulator w/dual Input oltages General Description The MIC4915 is a high-bandwidth, low-dropout, 1.5A voltage regulator ideal for powering core voltages of lowpower microprocessors. The MIC4915 implements a dual supply configuration allowing for very low output impedance and very fast transient response. The MIC4915 requires a bias input supply and a main input supply, allowing for ultra-low input voltages on the main supply rail. The input supply operates from 1.4 to 6.5 and the bias supply requires between 3 and 6.5 for proper operation. The MIC4915 offers fixed output voltages from.9 to 1.8 and adjustable output voltages down to.9. The MIC4915 requires a minimum of output capacitance for stability, working optimally with small ceramic capacitors. The MIC4915 is available in an 8-pin power MSOP package and a 5-pin S-Pak. Its operating temperature range is 4 C to +125 C. Data sheets and support documentation can be found on Micrel s web site at Features Input oltage Range: IN : 1.4 to 6.5 BIAS : 3. to 6.5 Stable with 1µF ceramic capacitor ±1% initial tolerance Maximum dropout voltage ( IN OUT ) of 5m over temperature Adjustable output voltage down to.9 Ultra fast transient response (Up to 1MHz bandwidth) Excellent line and load regulation specifications Logic controlled shutdown option Thermal shutdown and current limit protection Power MSOP-8 and S-Pak packages Junction temperature range: 4 C to 125 C Applications Graphics processors PC add-in cards Microprocessor core voltage supply Low voltage digital ICs High efficiency linear power supplies SMPS post regulators Typical Application BIAS = 3.3 IN = 1.8 C BIAS = 1µF Ceramic MIC4915BR IN OUT BIAS ADJ GND OUT = 1. R1 R2 C OUT = 1µF Ceramic C IN = 1µF Ceramic Low oltage, Fast Transient Response Regulator Micrel Inc. 218 Fortune Drive San Jose, CA USA tel +1 (48) fax + 1 (48) November 26 1 M

2 MIC4915 Ordering Information Part Number Standard Pb-Free / RoHS Compliant Output Current oltage Junction Temp. Range Package MIC BMM MIC YMM 1.5A.9 4 to +125 C 8-Pin Power MSOP MIC BMM MIC YMM 1.5A to +125 C 8-Pin Power MSOP MIC BMM MIC YMM 1.5A to +125 C 8-Pin Power MSOP MIC BMM MIC YMM 1.5A to +125 C 8-Pin Power MSOP MIC4915BMM MIC4915YMM 1.5A Adj. 4 to +125 C 8-Pin Power MSOP MIC BR MIC WR* 1.5A.9 4 to +125 C 5-Pin S-PAK MIC BR MIC WR* 1.5A to +125 C 5-Pin S-PAK MIC BR MIC WR* 1.5A to +125 C 5-Pin S-PAK MIC BR MIC WR* 1.5A to +125 C 5-Pin S-PAK MIC4915BR MIC4915WR* 1.5A Adj. 4 to +125 C 5-Pin S-PAK * RoHS Compliant with high-melting solder exemption. Pin Configuration EN/ADJ. BIAS IN OUT GND GND GND GND TAB 5 OUT 4 IN 3 GND 2 BIAS 1 EN/ADJ. 8-Pin Power MSPO (MM) 5-Pin S-Pak (R) Pin Description Pin Number Pin Number 8-MSOP 5-SPak 1 1 Pin Name EN Pin Name Enable (Input): CMOS compatible input. Logic high = enable, logic low = shutdown. ADJ Adjustable regulator feedback input. Connect to resistor voltage divider. 2 2 BIAS Input Bias oltage for powering all circuitry on the regulator with the exception of the output power device. 3 4 IN Input voltage which supplies current to the output power device. 4 5 OUT Regulator Output. 5/6/7/8 3 GND Ground (TAB is connected to ground on S-Pak). November 26 2 M

3 Absolute Maximum Ratings (1) Supply oltage ( IN )...8 Bias Supply oltage ( BIAS )...8 Enable Input oltage ( EN )...8 Power Dissipation...Internally Limited ESD Rating (3)... 4k Operating Ratings (2) MIC4915 Supply oltage ( IN ) to 6.5 Bias Supply oltage ( BIAS )... 3 to 6.5 Enable Input oltage ( EN )... to 6.5 Junction Temperature (T J )... 4 C T J +125 C Package Thermal Resistance MSOP-8 (θ JA )...8 C/W S-Pak (θ JC )...2 C/W Electrical Characteristics (4) T A = 25 C with BIAS = OUT + 2.1; IN = OUT + 1; bold values indicate 4 C< T J < +125 C, unless noted (5). Parameter Condition Min Typ Max Units Output oltage Accuracy At 25 C Over temperature range Line Regulation IN = OUT +1 to %/ Load Regulation I L = ma to 1.5A Dropout oltage ( IN - OUT ) Dropout oltage ( BIAS - OUT ), Note 5 Ground Pin Current, Note 6 Ground Pin Current in Shutdown Current thru BIAS I L = 75mA I L = 1.5A I L = 75mA I L = 1.5A I L = ma I L = 1.5A EN.6, (I BIAS + I CC ), Note I L = ma I L = 1.5A Current Limit MIC Enable Input (Note 7) Enable Input Threshold Regulator enable (Fixed oltage only) Regulator shutdown.6 Enable Pin Input Current Independent of state.1 1 µa Reference Reference oltage 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, 1.5kΩ in series with 1pF. 4. Specification for packaged product only. 5. For OUT 1, BIAS dropout specification does not apply due to a minimum 3 BIAS input. 6. I GND = I BIAS + (I IN I OUT ). At high loads, input current on IN will be less than the output current, due to drive current being supplied by BIAS. 7. Fixed output voltage versions only. % % % % m m m m ma ma ma µa µa ma ma ma A A November 26 3 M

4 MIC4915 Typical Characteristics Power Supply Rejection Ratio (Input Suppl ) 8 Power Supply Rejection Ratio (Bias Suppl ) 8 3 Dropout oltage (Input Suppl ) PSRR (db) BIAS =3.3 3 IN =1.8 2 OUT =1. 1 I OUT =1.5A C OUT =1µF ceramic FREQUENCY (khz) PSRR (db) BIAS =3.3 3 IN =1.8 2 OUT =1. 1 I OUT =1.5A C OUT =1µF ceramic FREQUENCY (khz) DROPOUT OLTAGE (m) OUT = OUTPUT CURRENT (ma) DROPOUT OLTAGE () Dropout oltage (Bias Supply) OUTPUT CURRENT (ma) DROPOUT OLTAGE (m) Dropout oltage (Input Supply) BIAS =5 I OUT =1.5A TEMPERATURE( C) DROPOUT OLTAGE () Dropout oltage (Bias Supply) I OUT =1.5A TEMPERATURE( C) OUTPUT OLTAGE () BIAS CURRENT (ma) Dropout Characteristics (Input oltage) I OUT =1mA I OUT =1.5A INPUT OLTAGE () Maximum vs. Bias oltage ADJ = I OUT =1.5A 5 *Note: Maximum bias current is bias current with input in dropout BIAS OLTAGE () OUTPUT OLTAGE () BIAS CURRENT (ma) Dropout Characteristics (Bias oltage) I OUT =1mA 1..8 I OUT =1.5A IN = BIAS OLTAGE () Maximum ADJ = TEMPERATURE( C) OUTPUT OLTAGE () BIAS CURRENT (ma) Load Regulation OUTPUT CURRENT (ma) I = 75mA OUT 25 I = 15mA OUT 2 I 15 OUT = 1mA 1 5 I =1mA OUT TEMPERATURE ( C) November 26 4 M

5 MIC4915 Typical Characteristics (cont.) CURRENT (ma) GROUND CURRENT (ma) BIAS CURRENT (ma) OUTPUT OLTAGE () vs. Output Current I BIAS OUTPUT CURRENT (ma) vs. Bias oltage I BIAS I OUT = 75mA BIAS OLTAGE () vs. Input oltage 75mA 15mA INPUT OLTAGE () Output oltage BIAS = IN = TEMPERATURE ( C) GROUND CURRENT (ma) GROUND CURRENT (ma) REFERENCE OLTAGE () SHORT CIRCUIT CURRENT (A) Ground Current vs. Bias oltage I OUT =ma BIAS OLTAGE () vs. Bias oltage I BIAS 2 I OUT = 15mA 1 BIAS OLTAGE ().91.9 Reference oltage vs. Input oltage INPUT OLTAGE () Short Circuit Current 1..5 OUT = TEMPERATURE ( C) GROUND CURRENT (ma) BIAS CURRENT (ma) REFERENCE OLTAGE () ENABLE THRESHOLD () vs. Bias oltage I BIAS I OUT = 1mA BIAS OLTAGE () vs. Input oltage I OUT = 1mA I OUT =ma INPUT OLTAGE ().91.9 Reference oltage vs. Bias oltage.899 BIAS OLTAGE () Enable Threshold vs. Bias oltage 1.4 ON OFF BIAS OLTAGE () November 26 5 M

6 MIC4915 Typical Characteristics (cont.) ENABLE THRESHOLD () Enable Threshold ON OFF TEMPERATURE ( C) November 26 6 M

7 MIC4915 Functional Characteristics November 26 7 M

8 MIC4915 Functional Diagram BIAS IN Ilimit EN / ADJ Fixed Enable Bandgap Adj. IN Open Circuit R1 OUT Fixed R2 November 26 8 M

9 Application Information The MIC4915 is an ultra-high performance, low-dropout linear regulator designed for high current applications requiring fast transient response. The MIC4915 utilizes two input supplies, significantly reducing dropout voltage, perfect for low-voltage, DC-to-DC conversion. The MIC4915 requires a minimum of external components and obtains a bandwidth of up to 1MHz. As a µcap regulator, the output is tolerant of virtually any type of capacitor including ceramic type and tantalum type capacitors. The MIC4915 regulator is fully protected from damage due to fault conditions, offering linear current limiting and thermal shutdown. Bias Supply oltage BIAS, requiring relatively light current, provides power to the control portion of the MIC4915. BIAS requires approximately 33mA for a 1.5A load current. Dropout conditions require higher currents. Most of the biasing current is used to supply the base current to the pass transistor. This allows the pass element to be driven into saturation, reducing the dropout to 3m at a 1.5A load current. Bypassing on the bias pin is recommended to improve performance of the regulator during line and load transients. Small ceramic capacitors from BIAS to ground help reduce high frequency noise from being injected into the control circuitry from the bias rail and are good design practice. Good bypass techniques typically include one larger capacitor such as 1µF ceramic and smaller valued capacitors such as.1µf or.1µf in parallel with that larger capacitor to decouple the bias supply. The BIAS input voltage must be above the output voltage with a minimum BIAS input voltage of 3 volts. Input Supply oltage IN provides the high current to the collector of the pass transistor. The minimum input voltage is 1.4, allowing con-version from low voltage supplies. Output Capacitor The MIC4915 requires a minimum of output capacitance to maintain stability. However, proper capacitor selection is important to ensure desired transient response. The MIC4915 is specifically designed to be stable with virtually any capacitance value and ESR. A 1µF ceramic chip capacitor should satisfy most applications. Output capacitance can be increased without bound. See Typical Characteristic for examples of load transient response. X7R dielectric ceramic capacitors are recommended because of their temperature performance. X7R-type capacitors change capacitance by 15% over their operating temperature range and are the most stable MIC4915 type of ceramic capacitors. Z5U and Y5 dielectric capacitors change value by as much as 5% and 6% respectively over their operating temperature ranges. To use a ceramic chip capacitor with Y5 dielectric, the value must be much higher than an X7R ceramic or a tantalum capacitor to ensure the same capacitance value over the operating temperature range. Tantalum capacitors have a very stable dielectric (1% over their operating temperature range) and can also be used with this device. Input Capacitor An input capacitor of 1µF or greater is recommended when the device is more than 4" away from the bulk supply capacitance, or when the supply is a battery. Small, surface-mount, ceramic chip capacitors can be used for the bypassing. The capacitor should be placed within 1" of the device for optimal performance. Larger values will help to improve ripple rejection by bypassing the input to the regulator, further improving the integrity of the output voltage. Thermal Design Linear regulators are simple to use. The most complicated design parameters to consider are thermal characteristics. Thermal design requires the following application-specific parameters: Maximum ambient temperature (T A ) Output current (I OUT ) Output voltage ( OUT ) Input voltage ( IN ) Ground current (I GND ) First, calculate the power dissipation of the regulator from these numbers and the device parameters from this datasheet. P D = IN I IN + BIAS I BIAS OUT I OUT The input current will be less than the output current at high output currents as the load increases. The bias current is a sum of base drive and ground current. Ground current is constant over load current. Then the heat sink thermal resistance is determined with this formula: TJ(MAX) TA θ SA = JC + P D ( θ θ ) The heat sink may be significantly reduced in applications where the maximum input voltage is known and large compared with the dropout voltage. Use a series input resistor to drop excessive voltage and distribute the heat between this resistor and the regulator. The low-dropout properties of the MIC4915 allow significant reductions in regulator power dissipation and the associated heat sink without compromising performance. When this technique is employed, a CS November 26 9 M

10 MIC4915 capacitor of at least 1µF is needed directly between the input and regulator ground. Refer to Application Note 9 for further details and examples on thermal design and heat sink specification. Minimum Load Current The MIC4915, unlike most other high current regulators, does not require a minimum load to maintain output voltage regulation. Power MSOP-8 Thermal Characteristics One of the secrets of the MIC4915 s performance is its power MSOP-8 package featuring half the thermal resistance of a standard MSOP-8 package. Lower thermal resistance means more output current or higher input voltage for a given package size. Lower thermal resistance is achieved by joining the four ground leads with the die attach paddle to create a single-piece electrical and thermal conductor. This concept has been used by MOSFET manufacturers for years, proving very reliable and cost effective for the user. Thermal resistance consists of two main elements, θ JC (junction-to-case thermal resistance) and θ CA (case-toambient thermal resistance). See Figure 1. θ JC is the resistance from the die to the leads of the package. θ CA is the resistance from the leads to the ambient air and it includes θ CS (case-to-sink thermal resistance) and θ SA (sink-to-ambient thermal resistance). Using the power MSOP-8 reduces the θ JC dramatically and allows the user to reduce θ CA. The total thermal resistance, θ JA (junction-to-ambient thermal resistance) is the limiting factor in calculating the maximum power dissipation capability of the device. Typically, the power MSOP-8 has a θ JA of 8 C/W, this is significantly lower than the standard MSOP-8 which is typically 16 C/W. θ CA is reduced because pins 5 through 8 can now be soldered directly to a ground plane which significantly reduces the case-to-sink thermal resistance and sink to ambient thermal resistance. Low-dropout linear regulators from Micrel are rated to a maximum junction temperature of 125 C. It is important not to exceed this maximum junction temperature during operation of the device. To prevent this maximum junction temperature from being exceeded, the appropriate ground plane heat sink must be used. MSOP-8 q JC q JA q CA AMBIENT printed circuit board Figure 1. Thermal Resistance ground plane heat sink area Figure 2 shows copper area versus power dissipation with each trace corresponding to a different temperature rise above ambient. From these curves, the minimum area of copper necessary for the part to operate safely can be determined. The maximum allowable temperature rise must be calculated to determine operation along which curve. COPPER AREA (mm 2 ) POWER DISSIPATION (W) Figure 2. Copper Area vs. Power-MSOP Power Dissipation ( T JA ) COPPER AREA (mm 2 ) T J =125 C 85 C 5 C 25 C POWER DISSIPATION (W) Figure 3. Copper Area vs. Power-MSOP Power Dissipation (T A ) November 26 1 M

11 T = T J(max) T A(max) T J(max) = 125 C T A(max) = maximum ambient operating temperature For example, the maximum ambient temperature is 5 C, the T is determined as follows: T = 125 C 5 C T = 75 C Using Figure 2, the minimum amount of required copper can be determined based on the required power dissipation. Power dissipation in a linear regulator is calculated as follows: P D = IN I IN + BIAS I BIAS OUT I OUT Using a typical application of 75mA output current, 1.2 output voltage, 1.8 input voltage and 3.3 bias voltage, the power dissipation is as follows: P D = (1.8) (73mA) + 3.3(3mA) 1.2(75mA) At full current, a small percentage of the output current is supplied from the bias supply, therefore the input current is less than the output current. P D = 513mW From Figure 2, the minimum current of copper required to operate this application at a T of 75 C is less than 1mm 2. MIC4915 The θ JA of this package is ideally 8 C/W, but it will vary depending upon the availability of copper ground plane to which it is attached. Adjustable Regulator Design The MIC4915 adjustable version allows programming the output voltage anywhere between.9and 5. Two resistors are used. The resistor value between OUT and the adjust pin should not exceed 1kΩ. Larger values can cause instability. The resistor values are calculated by: OUT R1 = R2 1.9 Where OUT is the desired output voltage. Enable The fixed output voltage versions of the MIC4915 feature an active high enable input (EN) that allows onoff control of the regulator. Current drain reduces to zero when the device is shutdown, with only microamperes of leakage current. The EN input has TTL/CMOS compatible thresholds for simple logic interfacing. EN may be directly tied to IN and pulled up to the maximum supply voltage. Quick Method Determine the power dissipation requirements for the design along with the maximum ambient temperature at which the device will be operated. Refer to Figure 3, which shows safe operating curves for three different ambient temperatures: 25 C, 5 C and 85 C. From these curves, the minimum amount of copper can be determined by knowing the maxi-mum power dissipation required. If the maximum ambient temperature is 5 C and the power dissipation is as above, 513mW, the curve in Figure 3 shows that the required area of copper is less than 1mm 2. November M

12 MIC4915 Package Information 8-Pin MSOP (MM) 5-Pin S-Pak (R) November M

13 MIC4915 MICREL, INC. 218 FORTUNE DRIE SAN JOSE, CA USA TEL +1 (48) FAX +1 (48) WEB 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. 23 Micrel, Incorporated. November M