SC250WLTRT | DigiCamel IC Datasheet

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1 www.semtech.com SC250 Step-Down DC-DC Converter with Bias LDO for RF Power Ampliﬁ ers POWER MANAGEMENT August 28, 2006 Typical Application Circuit

Applications

The SC250 is a synchronous step-down converter designed speci ﬁ cally for use as an adaptive voltage supply for CDMA and WCDMA RF Power Ampli ﬁ ers (PAs). The output voltage can be adjusted dynamically between 0.3V and (Vin - 0.4)V through a linear analog control input. For high power operation, a maximum control input signal level forces the device into bypass mode where the input is connected directly to the output via an internal P- Channel pass transistor. Bypass mode also occurs when the output load demands duty cycles in excess of the maximum rated duty cycle. The SC250 also provides an LDO regulator which can be used to supply a 2.85V bias to the PA. The internal clock runs at 1MHz to maximize ef ﬁ ciency while still allowing the use of small surface mount inductors and capacitors can be used. The peak current rating of the internal PMOS switch allows a DC output current of 600mA. The bypass PMOS current rating allows a minimum of 1A DC output current in the bypass mode. Shutdown turns off all the control circuitry to achieve a typical shutdown current of 0.1μA. CDMA and WCDMA Phones Handheld Radios RF PC Cards Battery Powered RF Devices Adjustable output voltage range — 0.3 to 3.6V Linearly proportional V DAC to VOUT relationship for increased PA efﬁ ciency Pass-through mode automatic and on demand Input voltage range — 2.7V to 5V Typical settling time — 40μs Output current capability — 600mA Maximum output current in bypass mode — 1A Up to 96% efﬁ ciency Constant frequency operation — 1MHz Less than 1μA shutdown current Internal 75mΩ PMOS bypass transistor PA bias voltage supply — 2.85V, 20mA, 1.5% MLPD-W8, 2.3 x 2.3mm package 4.7μH CIN 10μF VIN VOUT VREF GND LX VDAC PGND CREF 1μF EN COUT 4.7μF VIN PA RF OutputRF Input Vcc GNDBIAS ENABLE VDAC SC250 Description Features

Electrical Characteristics

Unless otherwise noted: VIN = VEN =3.6V, 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 5.0 V VOUT Accuracy V OUT VOUT Line Regulation V OUT LINE VIN = 2.7V to 5.0V, VDAC = 0.7V 0.4 %/V VOUT Load Regulation V OUT LOAD IOUT = 0A to 600 mA, VDAC = 0.7V -0.7 % VREF Accuracy V REF IREF = 10 mA 2.8 2.85 2.9 V VREF Line Regulation V REF LINE IREF = 1 mA, IOUT = 0A 0.3 %/V VREF Load Regulation V REF LOAD IREF = 0.1 to 20 mA -0.5 % VREF Load Current I REF 20 mA Peak Inductor Current I LX PK 0.8 1.5 A Bypass FET Current Limit I PASS 1 2.5 A Exceeding the speciﬁ cations below may result in permanent damage to the device or device malfunction. Operation outside of the parameters speci ﬁ ed in the Electrical Characteristics section is not recommended. Parameter Symbol Maximum Units Input Supply Voltage V IN -0.3 to 7 V EN and VDAC Inputs V EN, VDAC -0.3 to 7 V LX Pin Voltage (Power switch OFF) V LX -1 to VIN + 1, 7V MAX V VOUT Voltage V OUT -0.3 to 7 V VOUT Short Circuit to GND duration t SC Continuous s Thermal Impedance Junction to Ambient (1) θJA 110 °C/W Operating Ambient Temperature Range T A -40 to +85 °C Junction Temperature T JC +150 °C Storage Temperature T S -60 to +160 °C Peak IR Reﬂ ow Temperature T P 260 °C ESD Protection Level (2) VESD 2k V Absolute Maximum Ratings Note: 1) Calculated from package in still air, mounted to 3” x 4.5”, 4 layer FR4 PCB with thermal vias under the exposed pad per JESD51 standards. 2) Tested according to JEDEC standard JESD22-A114-B.

3© 2006 Semtech Corp. www.semtech.com SC250 PRELIMINARYPOWER MANAGEMENT Electrical Characteristics (Cont.) Parameter Symbol Conditions Min Typ Max Units Quiescent Current I Q Normal Mode (VDAC < 1V) 1.5 mA Bypass Mode (VDAC > 1.4V) 1 Shutdown Current ISD LX = open, EN = GND, VOUT = open, TA= 25°C 0.1 1 μA VDAC Regulated Output Mode VDAC VIN = 4.2V 0.10 1.20 V VDAC Pass-Through Mode Threshold VDAC PT VDAC Rising 1.28 1.37 V VDAC Falling 1.20 1.3 VDAC to VOUT Transfer Ratio GV 3 V/V RDS ON of Bypass P-Channel FET RPASS IOUT = 100mA, VIN = 3V, VDAC= 1.4V 75 m Ω RDS ON of P-Channel Switching FET RDSP IOUT = 100mA, VIN = 3V 400 m Ω RDS ON of N-Channel Switching FET RDSN IOUT = 100mA, VIN = 3V 250 m Ω LX Leakage Current PMOS I LXP VIN = 3.6V, LX = 0V, EN = GND 2 μA LX Leakage Current NMOS I LXN VIN = 3.6V, LX = 3.6V, EN = GND 2 μA VOUT Pin Bypass PMOS Leakage ILVOUT VIN = 3.6V, VOUT = 0V, EN = GND 2 μA Oscillator Frequency (Fixed Frequency) fOSC VDAC > 0.2V 0.85 1 1.15 MHz Oscillator Frequency (Variable Frequency) fOSCV VDAC = 0.1V 0.65 MHz Logic Input High V IH 1.6 V Logic Input Low V IL 0.6 V Control Input Current - High I IH VDAC/EN =3.6V ±2 μA Control Input Current - Low I IL VDAC/EN = GND ±2 μA Enable Transient Over/Undershoot OSEN 20 % Enable Transient Settling Time tEN-ST 40 μs VDAC Transient Over/Undershoot OSVDAC 20 % VDAC Transient Settling Time tVDAC-ST 40 μs

4© 2006 Semtech Corp. www.semtech.com SC250 PRELIMINARYPOWER MANAGEMENT Electrical Characteristics (Cont.) Parameter Symbol Conditions Min Typ Max Units Pass-Through Transition Over/Undershoot OSPASS 20 % Pass-Through Transition Settling Time tPASS-ST 40 μs Thermal Shutdown T SD 160 °C Thermal Shutdown Hysteresis TSDH 15 °C Auto Pass-Through Threshold (VIN-VOUT) PTTH 400 430 460 mV Auto Pass-Through Threshold Hysteresis PTTH_HYST 135 160 190 mV

5© 2006 Semtech Corp. www.semtech.com SC250 PRELIMINARYPOWER MANAGEMENT Pin Conﬁ guration Ordering InformationNote: 1) Available on tape and reel only. A reel contains 3000 devices. 2) Device is WEEE and RoHS compliant. DEVICE PACKAGE SC250WLTRT(1)(2) MLPD-W8 2.3x2.3 SC250EVB Evaluation Board

Ordering Information

MLPD-W8 2.3 x 2.3 4 5

8 PGND

Marking for the 2.3 x 2.3mm MLPD 8 Lead Package: ww = Datecode (Reference Package Marking Design Guidelines, Appendix A) 250 yw

6© 2006 Semtech Corp. www.semtech.com SC250 PRELIMINARYPOWER MANAGEMENT Block Diagram Control Logic References VIN VREF EN GND VDAC PGND LX VOUT SENSE SENSE Error Amp. PWM Comparator Oscillator Slope Generator Current Sense

2 VIN Input voltage connection

3 VREF 2.85V, 20mA reference supply — can be used as a supply for power ampliﬁ er bias inputs or to supply a resistive divider on VDAC to set a ﬁ xed level of VOUT.

4 GND Ground connection

5 VDAC

Analog control voltage input ranges between 0.1 and 1.2V for control of VOUT in accordance with the VOUT= 3 x VDAC transfer function. VDAC > 1.4V enables pass-through mode using the internal pass MOSFET.

6 VOUT Regulated output voltage and feedback

7E N Enable digital input: a high input enables the SC250, a low disables the output and reduces quiescent current to less than 1μA and LX becomes high impedance.

8 PGND Ground reference for internal N-channel MOSFET

8© 2006 Semtech Corp. www.semtech.com SC250 PRELIMINARYPOWER MANAGEMENT Applications Information SC250 Detailed Description The SC250 adaptive power controller is a step-down, ﬁ xed frequency pulse-width modulated DC-DC converter designed for use with RF Power Ampli ﬁ ers (PAs) in CDMA and WCDMA handsets and modules. The SC250 output is used to supply DC power to the PA rather than connecting the DC input pin directly to the battery supply. A substantial system power ef ﬁ ciency improvement can be achieved by allowing the system controller to adaptively adjust the DC power to the PA, reducing the total power consumption of the device when in low-power mode. To improve efﬁ ciency at all RF output gain settings, the PA supply voltage is adjusted in a linear fashion, minimizing PA supply headroom and losses. A consequence of using the SC250 to power the PA, rather than using a linear regulator or direct connection to the battery, is that less current is needed. Reduced current consumption results in more talk-time for the handset. Operation Modes The SC250 output voltage is dependent on the V DAC analog control voltage, deﬁ ned by the following relationship: V OUT = 3 × VDAC In a typical PA system application, the system controller determines what output power level is needed from the PA and adjusts the VDAC voltage to match the required PA headroom for optimized efﬁ ciency. Pass-Through Mode When the VDAC voltage reaches 1.36V, the SC250 enters pass-through mode. If the demanded output voltage is within 430mV of the input voltage, the SC250 automatically enters pass-through as this exceeds the maximum controlled duty cycle of the power converter. In pass-through mode, the device enables an internal P- Channel MOSFET that bypasses the converter, connecting the output directly to the input. The R DSON of this FET is extremely low, so there is little voltage drop across the part. Pass-through allows the lowest insertion loss possible between V IN and VOUT under high-power conditions, thereby maintaining maximum efﬁ ciency under these conditions. Bias Supply Output In addition to the main output, the SC250 also provides a low current LDO output that can be used as a bias supply for power ampli ﬁ ers. This output provides a regulated 2.85V with output current capability up to 20mA. The 2.85V output is guaranteed for input supply voltages in excess of 2.95V. Protection Features The SC250 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 150°C. In thermal shutdown, the PWM drive is disabled, effectively tri-stating the LX output. The device will not be enabled again until the temperature reduces by 10°C. Short-Circuit Protection The PMOS and NMOS power devices of the buck switcher stage are protected by current limit functions. In the case 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 also protected by a current limit function. When the part is ﬁ rst enabled in pass- through, the output capacitor charges up with a large surge current. This surge current is internally limited for protection purposes, but the limit is set high enough to meet fast start-up times. In order to protect against a short-circuit condition and to allow the transient response time, an internal timer allows the part to operate under current limit conditions for a maximum of 64 cycles of the internal clock (1MHz typical). If the short-circuit conditions persists, the pass-through PMOS will turn off for 1ms, after which the ﬁ rst timer is restarted. This allows the part to manage thermal dissipation while giving it the ability to recover when the fault condition is removed.

9© 2006 Semtech Corp. www.semtech.com SC250 PRELIMINARYPOWER MANAGEMENT Under-Voltage Lockout Under-voltage lockout protection is used to prevent erroneous operation. As the input decreases, the device shuts down when the voltage drops below 2.35V and will not restart until the input voltage exceeds approximately 2.5V. Inductor Selection The SC250 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 u

¨© This equation demonstrates the relationship between input voltage, output voltage, and inductor ripple current. The inductor should have a low DC resistance 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 Final inductor selection depends on various design considerations such as ef ﬁ ciency, EMI, size, and cost. Table 1 lists the manufacturers of practical inductor options. Table 1 — Recommended Inductors Manufacturer/Part # Value (μH) DCR (Ω) Saturation Current (A) Tolerance (%) Dimensions LxWxH (mm) BI Technologies Coilcraft TDK CIN Selection The source input current to a buck converter is non- continuous. To prevent large input voltage ripple, a low Applications Information (Cont.) 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 uS 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 will reduce the output voltage ripple component that is dependent upon this ESR, as can be seen in the following equation: )COUT()ripple(L)ESR(OUT ESRIV u' ' Capacitors with X7R or X5R ceramic dielectric are strongly recommended for their low ESR and superior temperature and voltage characteristics. Y5V capacitors should not be used as their temperature coef ﬁ cients make them unsuitable for this application. Table 2 lists the manufacturers of recommended capacitor options. Table 2 — Recommended Capacitors Manufacturer/Part Number Value (μF) Rated Voltage (VDC) Type Case Size Murata GRM21BR60J226ME39L 22 6.3 X5R 0805 Murata GRM188R60J106MKE19 10 6.3 X5R 0603 TDK C2012X5R0J106K 10 6.3 X5R 0603 Murata GRM188R60J475KE19D 4.7 6.3 X5R 0603

10© 2006 Semtech Corp. www.semtech.com SC250 PRELIMINARYPOWER 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 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. LX LOUT COUT SC250 VOUT VREF GND CREF VIN CIN VDAC EN PGND

11© 2006 Semtech Corp. www.semtech.com SC250 PRELIMINARYPOWER MANAGEMENT Typical Characteristics 100 0.001 0.01 0.1 1 I OUT (V) Efficiency (%) VIN=3.6V VIN=3.9V VIN=4.2V Efﬁ ciency vs. Load Current VOUT = 3.2V 100 0.001 0.01 0.1 1 Efficiency (%) IOUT (V) VIN=3.9V VIN=4.2V VIN=3.3V Efﬁ ciency vs. Load Current VOUT = 2.5V 100 0.001 0.01 0.1 1 Efficiency (%) IOUT (V) VIN=4.2V VIN=2.7V VIN=3.6V Efﬁ ciency vs. Load Current VOUT = 1.5V 100 0.001 0.01 0.1 1 Efficiency (%) IOUT (V) VIN=4.2V VIN=2.7V VIN=3.6V Efﬁ ciency vs. Load Current VOUT = 1.2V 100 Efficiency (%) VIN (V) IOUT=10mA IOUT=600mAIOUT=300mA IOUT=100mA Efﬁ ciency vs. VIN 100 00 . 5 11 . 522 . 533 . 5 Efficiency(%) VIN (V) IOUT=100mA IOUT=600mA Efﬁ ciency vs. VOUT, VIN = 3.6V

12© 2006 Semtech Corp. www.semtech.com SC250 PRELIMINARYPOWER MANAGEMENT Typical Characteristics (Cont.) 0.0 1.0 2.0 3.0 4.0 5.0 6.0 VDAC (V) VIN=5.5V VOUT (V) VIN=4.2V VIN=3.6V VIN=3.0V VIN=2.7V Control Transfer Function IOUT = 0.3A 2.5 2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 V IN(V) VOUT (V) VIN Up VIN Down Auto Bypass Function, VOUT = 3.25V 0.001 0.002 0.003 0.004 0.005 0.006 2.5 3 3.5 4 4.5 5 5.5 6 VOUT=2.1V VIN (V) IIN (A) VOUT=1.5V VOUT=0.3V Dynamic Supply Current vs. VIN TJ (°C) IQ Shutdown (μA) -40 -20 0 20 40 60 80 100 120 Shutdown Current vs. Temperature, VIN = 3.6V 2.05 2.1 2.15 2.2 IOUT (A) VOUT (V) Load Regulation, VOUT = 2.1V 1.49 1.495 1.5 1.505 1.51 1.515 1.52 2 . 533 . 544 . 555 . 56 VOUT (V) 50mA 150mA 300mA 600mA TA (°C) Line Regulation, VOUT = 1.5V

13© 2006 Semtech Corp. www.semtech.com SC250 PRELIMINARYPOWER MANAGEMENT Typical Characteristics (Cont.) 1.46 1.48 1.5 1.52 1.54 1.56 -60 -40 -20 0 20 40 60 80 100 VOUT (V) TA (°C) IOUT=10mA IOUT=600mAIOUT=300mA IOUT=100mA VOUT vs. Temperature (VOUT = 1.5V) 3.16 3.18 3.2 3.22 3.24 3.26 -60 -40 -20 0 20 40 60 80 100 VOUT (V) TA (°C) IOUT=10mA IOUT=600mAIOUT=300mAIOUT=100mA VOUT vs. Temperature (VOUT = 3.2V) 2.6 2.65 2.7 2.75 2.8 2.85 2.9 VIN (V) VREF (V) VREF vs. VIN 2.835 2.84 2.845 2.85 2.855 2.86 2.865 IREF (A) VREF (V) VREF vs. IREF 0.5 1.5 2.5 IOUT (A) VIN=5.0V VOUT (V) VIN=4.5V VIN=3.5V VIN=4.0V Maximum Output Current, VOUT = 2.5V 0.2 0.4 0.6 0.8 1.2 1.4 1.6 1.8 IOUT (A) VIN=5.0V VOUT (V) VIN=4.5V VIN=3.5V VIN=4.0V Maximum Output Current, VOUT = 1.8V

14© 2006 Semtech Corp. www.semtech.com SC250 PRELIMINARYPOWER MANAGEMENT Typical Characteristics (Cont.) 0.2 0.4 0.6 0.8 1.2 1.4 1.6 IOUT (A) VIN=5.0V VOUT (V) VIN=3.5V VIN=3.0V VIN=2.7V VIN=4.0V VIN=4.5V Maximum Output Current, VOUT = 1.5V Dropout Voltage (mV) IOUT (A) Dropout Voltage vs. Bypass Load Current 1120 1140 1160 1180 1200 1220 1240 1260 1280 -40 -20 0 20 40 60 80 100 120 PMOS Current Limit (mA) TJ (°C) PMOS Current Limit vs. Temperature 1400 1450 1500 1550 1600 1650 1700 -40 -20 0 20 40 60 80 100 120 Passthrough Current Limit (mA) TJ (°C) Passthrough Current Limit vs. Temperature 500 550 600 650 700 750 800 850 900 950 1000 1050 1100 Switching Frequency (kHz) VDAC(V) Oscillator Frequency vs. VDAC, VIN = 3.6V 940 960 980 1000 1020 1040 1060 1080 -40 -20 0 20 40 60 80 100 120 140 Oscillator Frequency (kHz) TJ (°C) Oscillator Frequency vs. Temperature, VIN = 3.6V

15© 2006 Semtech Corp. www.semtech.com SC250 PRELIMINARYPOWER MANAGEMENT VDAC Step Response (100% duty) VDAC Step Response VDAC Step Response (Pass-through) Typical Characteristics (Cont.) Time (40μs/div) Condition VIN=3.6V, Load=15Ω, VDAC=0.7 to 1.7V VOUT (1V/div) VDAC (1V/div) VLX (2V/div) VOUT (1V/div) VDAC (500mV/div) VLX (2V/div) Time (40μs/div) Condition VIN=4.2V, Load=15Ω, VDAC=0.5 to 1.1V Time (40μs/div) Condition VIN=3V, Load=15Ω, VDAC=0.7 to 1V VOUT (1V/div) VDAC (500mV/div) VLX (2V/div) Enable Transient VOUT (1V/div) VLX (2V/div) VEN (2V/div) Time (40μs/div) Condition VIN=3.6V, Load=15Ω, VDAC=0.7V 100 150 200 250 300 350 400 450 -45 5 55 105 155 TJ (°C) PASS PMOS NMOS RDSON (mΩ) RDSON vs. Temperature, VIN = 3.6V 100 150 200 250 300 350 400 VIN(V) PMOS NMOS PASS RDSON (mΩ) RDSON vs. VIN

16© 2006 Semtech Corp. www.semtech.com SC250 PRELIMINARYPOWER MANAGEMENT Typical Characteristics (Cont.) Enable Start-Up VEN (2V/div) VOUT (1V/div) VLX (5V/div) IIN (500mA/div) Time (20μs/div) Condition VIN=4.2V, Load=15Ω, VOUT=3.4V Output Ripple Waveform (VOUT=3.25V) VOUT (50mV/div) VLX(5V/div) Time (1μs/div) Condition VIN=4.2V, Load=300mA, VOUT=3.25V Pass-Through Current Limit VOUT (1V/div) VLX(2V/div) Time (1ms/div) Condition VIN=3.6V, Load=1Ω, VDAC=1.4V Output Ripple Waveform (VOUT=1.5V) VOUT (50mV/div) VLX(5V/div) Time (1μs/div) Condition VIN=3.6V, Load=300mA, VOUT=1.5V Load Step response (VOUT=3.25V) VOUT (100mV/div) IOUT(500mA/div) Time (40μs/div) Condition VIN=4.2V, Load=600mA-60mA, VOUT=3.25V Load Step response (VOUT=1.5V) VOUT (100mV/div) IOUT(500mA/div) Time (40μs/div) Condition VIN=3.6V, Load=600mA-60mA, VOUT=1.5V

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Product Information

SC250WLTRT specifications and overview.

Summary

Step-Down DC-DC Converter with Bias LDO for RF Power Amplifi ers

Description

The SC250 is a synchronous step-down converter designed specifically for use as an adaptive voltage supply for CDMA and WCDMA RF Power Amplifiers (PAs). The output voltage can be adjusted dynamically between 0.3V and (Vin - 0.4)V through a linear analog control input. For high power operation, a maximum control input signal level forces the device into bypass mode where the input is connected directly to the output via an internal PChannel pass transistor. Bypass mode also occurs when the output load demands duty cycles in excess of the maximum rated duty cycle.

Source title SC250WLTRT Datasheet(PDF) - Semtech Corporation

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