SC251MLTRT

SC251 SEMTECH | Alldatasheet

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Features

The SC251 is a synchronous step-down converter designed for use as an adaptive voltage supply for WCDMA RF power amplifi ers (PAs). An analog control input is used to adjust the output voltage dynamically between 0.5V and 3.4V using a non-linear transfer function. The non-linear relationship maximizes total system effi ciency by providing the PA with the minimum voltage it needs to maintain linearity. For output voltages greater than 3.4V the input is connected directly to the output via an internal PMOS switch. An optional gate drive (GD) output to control an external low on-resistance PMOS switch is also provided for systems applications that require minimal voltage drop. The SC251 also provides a 2.85V LDO reference output that can be used to supply a PA bias input. Low power and high power modes are provided to match performance with dual mode PAs. In low power mode the output voltage follows an exponential relationship with the VDAC input until it reaches 3.4V. When the VMODE pin changes state, V OUT follows an alternate exponential relationship. The SC251 is capable of supplying output current up to 800mA. Standby current is <1 μA when the device is disabled. The internal clock runs at 1MHz so that small surface mount inductors and capacitors can be used. V OUT exponentially proportional to VDAC for maximum effi ciency (patent pending) Output range and pass-through mode - 0.5V to 3.4V Output current - 800mA Shutdown current - < 1μA LDO PA bias supply - 2.85V, 10mA Internal clock - 1MHz Continuous short circuit protection on VOUT Duty cycle mode - 100% Internal PMOS bypass transistor Gate drive available for external bypass transistor Over 90% effi ciency Low and high power modes for optimum dual-mode PA effi ciency Switching time (lowest to highest output) < 40μs Micro-lead frame package MLPD-10, 3mm x 3mm 3G mobile phones - RF PA power supply WCDMA power amplifi er modules Wireless modems PA 4.7μH CIN 10μF VIN VOUT VREF GND LX VDAC PGND CREF 1μF EN COUT 4.7μF VIN 2.7 to 5V RF OutputRF Input Vcc GND BIAS ENABLE VDAC SC251 VMODE5VMODE GD 3 VOUT 0.5V to VIN Optional External Pass-through MOSFET Patent PendingTypical Application Circuit

2© 2006 Semtech Corp. www.semtech.com SC251 POWER MANAGEMENT Exceeding the specifi cations below may result in permanent damage to the device or device malfunction. Operation outside of the parameters specifed in the Electrical Characteristics section is not recommended. Parameter Symbol Maximum Units Input Supply Voltage V IN -0.3 to 7 V Logic Inputs/Outputs (EN, VMODE, VDAC, GD) VN -0.3 to VIN +0.3 ,7V Max V Output Voltage V OUT -0.3 to VIN +0.3 ,7V Max V LX Voltage V LX -1 to VIN +1, 7V Max V Thermal Impedance Junction to Ambient(1) θJA 49 °C/W VOUT Short-Circuit to GND t SC Continuous s Operating Ambient Temperature Range T A -40 to +85 °C Storage Temperature T S -60 to +160 °C Maximum Junction Temperature T J -40 to +150 °C Peak IR Refl ow Temperature T LEAD 260 °C ESD Protection Level(2) VESD 2k V Notes: Calculated from package in still air, mounted to 3” x 4.5”, 4 layer FR4 PCB with thermal vias under exposed pad pre JESD51 standards. Tested according JEDEC standard JESD22-A114-B Unless otherwise noted: VIN = 4V, EN = VIN, VMODE = GND (High Power), VDAC = 1.1V, TA = -40 to 85°C. Typical values are at TA = +25°C. Parameter Symbol Conditions Min Typ Max Units Input Voltage Range V IN 2.7 5 V VOUT Accuracy V OUT VDAC = 0.3V, VMODE = VIN, IOUT = 20mA 0.44 0.48 0.52 VVMODE = VIN, IOUT = 60mA 3.16 3.40 3.64 IOUT = 200mA 1.38 1.62 1.86 Line Regulation V OUT LINE VIN = 2.7V to 5V, IOUT = 200mA, TA = -40 to 85°C ±1.2 % Load Regulation (PWM) V OUT LOAD IOUT = 0A to 800mA, TA = -40 to 85°C ±0.5 % Peak Inductor Current I LX PK 1 1.7 A Bypass FET current limit I PASS 1 2.5 A Quiescent Current IQ NORM 2.5 mA IQ PASS VDAC = 1.3V 1.5 Absolute Maximum Ratings

Electrical Characteristics

3© 2006 Semtech Corp. www.semtech.com SC251 POWER MANAGEMENT Parameter Symbol Conditions Min Typ Max Units Shutdown Current I SD EN = GND 0.1 3 μA P-Channel Current Limit I LIM(P) 0.9 1.3 1.7 A VDAC Pass-through Mode Threshold VDAC PASS VDAC rising 1.24 1.28 1.32 V VDAC falling 1.2 1.245 VDAC Pass-through Mode Hysteresis VDAC HYST 40 mV VREF Output V REF IREF = 10mA 2.75 2.85 2.95 V VREF LDO Dropout V REF DO IREF = 10mA 100 mV VREF Load Current I REF 10 mA VREF Load Regulation V REF LDREG IREF = 0.1mA to 10mA 0.05 %/mA VREF Line Regulation V REF LNREG IREF = 1 mA 0.3 %/V GD Load Capacitance C GD 10 nF GD Source Current I GDH TA = 25°C 0.5 2m A GD Sink Current I GDL VDAC = 1.4V, TA = 25°C 75 150 mA RDSon of P-Channel FET R PFET VIN = 3V, IOUT = 100mA 0.4 Ω RDSon of N-Channel FET R NFET VIN = 3V, IOUT = 100mA 0.25 Ω RDSon of Bypass P-Channel FET RPASS IOUT = 600mA, VIN = 3V, VDAC = 1.4V 0.2 Ω LX Pin PMOS Leakage I LLXP EN=GND, VIN = 3.6V, LX = GND 0.1 μA VOUT Pin Bypass FET Leakage ILVOUT EN=GND, VIN = 3.6V, VOUT = GND 0.1 3 μA Oscillator Frequency f OSC VDAC > 0.95V 0.85 1 1.15 MHz VDAC < 0.95V 0.65 1.15 Logic Input High V IH EN / VMODE increasing 1.6 V Logic Input Low V IL EN / VMODE decreasing 0.6 V Logic Input Current High I IH EN / VMODE = 5.0V ±2 μA Logic Input Current Low I IL EN / VMODE = 0V ±2 μA Enable Transient Over/ Undershoot (1) OSEN 20 % Electrical Characteristics (Cont.)

4© 2006 Semtech Corp. www.semtech.com SC251 POWER MANAGEMENT Parameter Symbol Conditions Min Typ Max Units Enable Transient Settling Time (1) tEN-ST 40 μs VDAC Transient Over/Undershoot (1) OSVDAC 20 % VDAC Transient Settling Time (1) tVDAC-ST 40 μs Pass-Through Transition Over/Undershoot (1) OSPASS 20 % Pass-Through Transition Settling Time (1) tPASS-ST 40 μs Thermal Shutdown T SD 160 °C Thermal Shutdown Hysteresis T SDH 15 °C Notes: 1) Not tested - guaranteed by design. Electrical Characteristics (Cont.)

5© 2006 Semtech Corp. www.semtech.com SC251 POWER MANAGEMENT Pin Confi guration DEVICE PACKAGE SC251MLTRT (1) (2) MLP 3x3-10 SC251EVB Evaluation Board Notes: 1) Lead-free packaging only. This product is fully WEEE and RoHS compliant. 2) Available in tape and reel only. A reel contains 3000 devices.MLPD10: 3X3 10 LEAD TOP VIEW 56 T VIN VREF GD EN VMODE LX PGND VOUT GND VDAC Pin Confi guration Ordering Information Marking Information

6© 2006 Semtech Corp. www.semtech.com SC251 POWER MANAGEMENT Control Logic References GD VIN VREF EN GND VMODE VDAC PGND LX VOUT SENSE PWL Transfer Function Generator SENSE Error Amp. PWM Comparator Oscillator Slope Generator Current Sense Block Diagram

7© 2006 Semtech Corp. www.semtech.com SC251 POWER MANAGEMENT Pin# Pin Name Pin Function 1 VIN Input supply pin. 2 VREF A 2.85V LDO reference voltage supply - 10mA max load that can be used as a supply for power amplifi er bias inputs. 3G D A push pull external PFET Gate drive control output - connect to the gate of an external MOSFET to control a low resistance path between VIN and VOUT when low voltage drop is needed (optional - if not used leave fl oating). A low state turns on the MOSFET. 4 EN Enable pin - controls both the switching converter and the VREF output. Active high. 5 VMODE Input control to select the V DAC to VOUT profi le (high = low power, low = high power).

6 VDAC

Analog control voltage input - ranges between 0.3 and 1.2V for exponential control of VOUT , VDAC > 1.28 enables pass-through mode (using internal pass MOSFET or optional low RDSON MOSFET controlled by GD). 7 GND System and logic ground. 8 VOUT Output voltage pin. 9 PGND Ground reference for internal N-channel MOSFET. 10 LX Switch node connection to inductor. This pin connects to the drains of the internal main and synchronous power MOSFET switches. T Thermal Pad Pad for heatsinking purposes. Connect to ground plane using multiple vias. Not connected internally. Pin Description

10© 2006 Semtech Corp. www.semtech.com SC251 POWER MANAGEMENT Applications Information (Cont.) Inductor Selection The SC251 is designed for use with a 4.7μH inductor. The magnitude of the inductor current ripple is dependent on the inductor value and can be determined by the following equation: OSC N I OUT OUT L fL V V1V I × ⎞⎜⎝ ⎛ − The inductor should have a low DC Resistance (DCR) to minimize the conduction losses and maximize ef fi ciency. As a minimum requirement, the DC current rating of the inductor should be equal to the maximum load current plus half of the inductor current ripple as shown by the following equation: III L )MAX(OUTLPK Δ+= Final inductor selection will depend on various design considerations such as ef fi ciency, EMI, size and cost. Table 1 lists the manufacturers of practical inductor options. C IN Selection The source input current to a buck converter is non- continuous. To prevent large input voltage ripple a low ESR ceramic capacitor is required. A minimum value of 10μF should be used for suf fi cient input voltage fi ltering and a 22 μF should be used for improved input voltage fi ltering. C OUT Selection The internal compensation is designed to work with a certain output fi lter corner frequency de fi ned by the equation: OUT C CL2 This single pole fi lter is designed to operate with an output capacitor value of 4.7μF. Output voltage ripple is a combination of the voltage ripple from the inductor current charging and discharging the output capacitor and the voltage created from the inductor current ripple through the output capacitor ESR. Selecting an output capacitor with a low ESR reduces the bias supply for power ampli fi ers. This output provides a regulated 2.85V with output current capability up to 10mA. The 2.85V output is guaranteed for input supply voltages in excess of 2.95V. When input voltages below 2.95V are used, V REF is equal to V IN - V REF DO . This reference supply is controlled by the same enable pin as the switching regulator. Protection Features The SC251 provides the following protection features: Thermal shutdown Current limit Under voltage lockout Thermal Shutdown The device has a thermal shutdown feature to protect the device if the junction temperature exceeds 160°C. In thermal shutdown the on-chip power devices are disabled, effectively tri-stating the LX output. Switching will resume when the temperature drops by 15°C. Short Circuit Protection The PMOS and NMOS power devices of the buck switcher stage are protected by current limit functions. In the event of a short to ground on the output, the LX pin will switch with minimum duty cycle. The duty cycle is short enough to allow the inductor to discharge during each cycle, thereby preventing the inductor current from “staircasing”. The pass-through PMOS is protected by a current limit function. When the part is enabled in pass-through, the output capacitor charges up with a large surge current. In order to support this surge current and to protect against short circuits, an internal timer is used. A short circuit condition must exist for more than 128 clock cycles before the pass-through device is disabled. After an additional 2048 clock cycles, the pass-through device will turn back on. This cycle will continue until the short circuit is removed. This method allows the part to manage thermal dissipation and recover when the fault condition is removed. Under Voltage Lockout The part will turn itself off if the input supply voltage falls below 2.4V typical. The device is allowed to turn on again when the input supply voltage increases above the lockout voltage. Hysteresis is included to prevent chattering. Applications Information (Cont.)

11© 2006 Semtech Corp. www.semtech.com SC251 POWER MANAGEMENT Table 1: Recommended Inductors Table 2: Recommended Capacitors output voltage ripple component that is dependent upon this ESR, as can be seen in the following equation: )COUT()ripple(L)ESR(OUT ESRIV ×Δ=Δ Capacitors with X7R or X5R ceramic dielectric should be used for their low ESR and superior temperature and voltage characteristics. Y5V capacitors should not be used as their temperature coef fi cients make them impractical for this application. The following tables lists the manufacturers of recommended capacitor and inductor options. Manufacturer/Part # Value μH DCR Ω Saturation Current A Tolerance Dimensions (LxWxH) mm BI Technologies Coilcraft TDK Manufacturer/Part # Value μF Rated Voltage VDC Temperature Characteristic Case Size Murata GRM219R 61A475KE34B 4.7 6.3 X5R 0603 TDK C1608JF0J475Z 4.7 6.3 X5R 0603 Murata GRM219R 60J106K E19B 10 6.3 X5R 0603 TDK C2012JB0J106K 10 6.3 X5R 0805 Applications Information (Cont.)

12© 2006 Semtech Corp. www.semtech.com SC251 POWER MANAGEMENT Applications Information (Cont.) PCB Layout Considerations Poor layout can degrade the performance of the DC- DC converter and can be a contributory factor in EMI problems, ground bounce and resistive voltage losses. Poor regulation and instability can result. A few simple design rules can be implemented to ensure good layout: Place the inductor and fi lter capacitors as close to the device as possible and use short wide traces between the power components. Route the output voltage feedback and V DAC path away from the inductor and LX node to minimize noise and magnetic interference. Maximize ground metal on component side to improve the return connection and thermal dissipation. Separation between the LX node and GND should be maintained to avoid coupling of switching noise to the ground plane. To further reduce noise interference on sensitive circuit nodes, use a ground plane with several vias connecting to the component side ground. PGND VIN LX LOUT COUT PGND CIN SC251 VOUT GD EN VREF VMODE VDAC CREF

13© 2006 Semtech Corp. www.semtech.com SC251 POWER MANAGEMENT Typical Characteristics Effi ciency vs. Load VOUT=1.8V Effi ciency vs. VIN VOUT=1.8V 100 0.001 0.010 0.100 1.000 IOUT(A) Efficiency (%) VIN=4.2VVIN=3.6V Effi ciency vs. Load VOUT=1.2V IOUT(A) 100 0.001 0.010 0.100 1.000 Efficiency (%) VIN=3.6V VIN=4.2V Effi ciency vs. Load VOUT=1.5V 100 0.001 0.010 0.100 1.000 Efficiency (%) IOUT(A) VIN=3.6V VIN=4.2V Effi ciency vs. Load VOUT=2.5V IOUT(A) 100 0.001 0.010 0.100 1.000 Efficiency (%) VIN=3.6V VIN=4.2V Effi ciency vs. Load VOUT=3.4V (Pass-Through) 100 0.001 0.010 0.100 1.000 I OUT(A) Efficiency (%) VOUT=3.4V,VIN=4V 100 Vin(V) Efficiency (%) IOUT=10mA IOUT=100mAIOUT=600mA IOUT=300mA

14© 2006 Semtech Corp. www.semtech.com SC251 POWER MANAGEMENT Effi ciency vs. VOUT VOUT vs. VDAC VOUT vs. IOUT VREF vs. VIN Oscillator Frequency vs. VIN VREF vs. IREF 100 Vout(V) Efficiency (%) IOUT=100mA IOUT=600mA VIN=4V 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 VDAC(V) VMODE=VIN VOUT(V) Pass-Through VMODE=GND 1.550 1.555 1.560 1.565 1.570 1.575 1.580 1.585 1.590 1.595 1.600 I OUT(A) VOUT(V) VIN=4V 2.830 2.831 2.832 2.833 2.834 2.835 2.836 VIN (V) VREF (V) IREF =5mA 850 875 900 925 950 975 1000 2.5 33 . 544 . 5 5VIN (V) Oscillator Frequency (kHz) TJ=-40°C TJ=85°C TJ=0°C TJ=50°C TJ=25°C 2.825 2.830 2.835 2.840 2.845 0.0001 0.0010 0.0100 IREF (A) VREF (V) Typical Characteristics (Cont.)

15© 2006 Semtech Corp. www.semtech.com SC251 POWER MANAGEMENT Oscillator Frequency vs. Temperature RDSON vs. VIN RDSON vs. Temperature PMOS FET Leakage vs. Temperature -0.5 0.5 1.5 -40 -15 10 35 60 85 TJ (°C) Leakage (μA) VIN=3.5V VIN=2.7V VIN=4V VIN=5V PASS FET Leakage vs. Input Voltage 2.5 3 3.5 4 4.5 5 5.5 VIN (V) IQ_SW (mA) Dynamic Supply Current vs. VIN 0.1 0.15 0.2 0.25 0.3 0.35 2.5 3 3.5 4 4.5 5 VIN(V) Bypass FET NMOS PMOS RDSON(Ω) 25°C 0.10 0.15 0.20 0.25 0.30 0.35 0.40 -40 -25 -10 5 20 35 50 65 80 95 110 125 T J (° C) Bypass FET NMOS PMOS RDSON(Ω) VIN=4V -0.5 0.5 1.5 -40 -15 10 35 60 85TJ (°C) Leakage (μA) VIN=3.5V VIN=2.7V VIN=4V VIN=5V 850 900 950 1000 1050 1100 1150 -40 -20 0 20 40 60 80 100 120 Switching Frequency (KHz) 140 Temperature( °C) Typical Characteristics (Cont.)

16© 2006 Semtech Corp. www.semtech.com SC251 POWER MANAGEMENT Enable Startup EN 5V/DIV 40μs/DIV LX 5V/DIV VOUT 2V/DIV IIN 500mA/DIV Load Step Response VOUT 100mV/DIV 100μs/DIV ILoad 500mA/DIV VIN = 3.6V VDAC = 0.6V ILOAD = 0 - 800mA VDAC Step Response (Passthrough) VIN = 4.0V LOAD = 5Ω MODE = LP V DAC = 0 to 1.4V VDAC Step Response (100% duty) VDAC 1V/DIV VGD 5V/DIV VOUT 2V/DIV LX 5V/DIV 100μs/DIV VIN = 4.0V LOAD = 5Ω MODE = LP V DAC = 0 to 1.2V VDAC Step Response 100μs/DIV LX 5V/DIV 2V/DIV VOUT 5V/DIV VGD 1V/DIV VDAC VIN = 4.0V LOAD = 5Ω MODE = LP V DAC = 0 to 1.09V VMODE Step Response VDAC 1V/DIV 100μs/DIV VGD 5V/DIV VOUT 2V/DIV LX 5V/DIV VMODE 2V/DIV VGD 5V/DIV VOUT 2V/DIV LX 5V/DIV 100μs/DIV VIN = 4.0V LOAD = 5Ω Mode = LP V DAC = 1.07V Typical Characteristics (Cont.)

17© 2006 Semtech Corp. www.semtech.com SC251 POWER MANAGEMENT Passthrough Current Limit Operation Enable Step Response Output Ripple Waveform LX 5V/DIV VOUT 10mV/DIV IL 100mA/DIV 200ns/DIV 1ms/DIV VIN = 4.0V LOAD = Short MODE = LP V DAC = 1.07V IOUT 1A/DIV IL 500mA/DIV LX 5V/DIV VOUT 200V/DIV VOUT 2V/DIV 100μs/DIV VEN 2V/DIV VIN = 4.0V LOAD = 5Ω Mode = LP V DAC = 0 to 1.07V LX 5V/DIV VGD 5V/DIV Typical Characteristics (Cont.)

18© 2006 Semtech Corp. www.semtech.com SC251 POWER MANAGEMENT MIN aaa bbb b e L N D C E A DIM MILLIMETERS NOM DIMENSIONS MAXNOM INCHES MIN MAX (LASER MARK) INDICATOR PIN 1 N NOTES: CONTROLLING DIMENSIONS ARE IN MILLIMETERS (ANGLES IN DEGREES). COPLANARITY APPLIES TO THE EXPOSED PAD AS WELL AS TERMINALS.2. .003 .007 .042 .009 .048 .000 .031 (.008) 0.08 0.23 .011 .052 0.18 1.06 .039 .002 0.00 0.80 1.31 0.30 1.21 0.05 1.00 (0.20) .004 0.10 0.50 BSC.020 BSC A aaa C SEATING PLANE A bxN bbb C A B B e C C D LxN E E Outline Drawing - MLP-10 3x3

19© 2006 Semtech Corp. www.semtech.com SC251 POWER MANAGEMENT .087 .055 2.20 1.40 .150 .020 .012 .037 3.80 0.30 0.95 0.50 (.112) .075 1.90 (2.85) K H X THIS LAND PATTERN IS FOR REFERENCE PURPOSES ONLY. CONSULT YOUR MANUFACTURING GROUP TO ENSURE YOUR COMPANY'S MANUFACTURING GUIDELINES ARE MET. NOTES: INCHES DIMENSIONS G K H X Y P Z C DIM MILLIMETERS Y ZG(C) P Semtech Corporation Power Management Products Division

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