FAN5903: 3/6MHz Buck Converter for 3G, 3.5G & 4G PAs September 2011

Introduction Mobile handsets and data cards are becoming an intricate part of everyday life and its use has become ubitiquous. Battery technology has not kept up to pace with the demands to support higher densities to prolong usage time. Since the requirement for longer talk and data transmit times has increased there needs to be a way to reduce power consumption in the 3G and 4G PAs. DC-DC converters that support PAs are an emerging application space to reduce power consumption while enabling longer usage times and lower heat dissipation in portable devices.

RF Power Mgmt for Today, Tomorrow and Yesterday FAN5903 GSM 2G GPRS 2.5G EDGE 2.75G WCDMA 3G HSPA+ 3.5G LTE 4G FAN5904

FAN5903 3/6MHz Buck Converter for 3G/3.5G/4G PAs Features VIN range from 2.7V to 5.5V VOUT range from 0.4V to 3.6V (or VIN) Auto and manual Bypass modes Small 540nH form factor inductor 1.34mm x 1.29mm, 9-Bump, 0.4mm pitch WLCSP High efficiency PFM operation at low power 100% Duty Cycle for low dropout operation 3MHz/6MHz selectable switching frequency to facilitate system optimization <10µs output voltage step response to allow early power loop settling Input Under-Voltage Lockout / Thermal Shutdown Applications Dynamic supply for 3G, 3.5G, 4G PAs Scalable supply for processor core power Status Samples & Eval Boards: Available Now Production: Now

FAN5903 Application Diagram

FAN5903 Optimization (1) FAN5903 offers flexibility to trade efficiency for cost and solution size. Current EVBs offer good efficiency in the smallest form factors. 3MHz/6MHz switching frequencies enable excellent regulation, low ripple, and fast transient response with small inductor size. If efficiency is most important, inductor size may be increased at the cost of increased board space. FAN5903 1.34mm x 1.29mm package coupled with 2012 540nH inductor results in very small footprint with good efficiency optimized for 3G platforms.

FAN5903 Optimization (2) Efficiency Optimization Smallest solution yields lowest cost. Larger inductor may be used with FAN5903 to maximize efficiency. Ripple voltage decreases with increasing inductor value, while larger inductor dimensions yields lower ESR. Low ripple and low ESR increase efficiency. 1µH 3030 inductor (DCR=43mW, Isat > 2.3A) improves efficiency at cost of increased board space. Efficiency improvement typically 3-5%. More at low power

FAN5903 Implementation Options Inductor may be chosen to trade board space and cost for efficiency performance. Inductor may also be chosen to optimize performance for either 3MHz or 6MHz operation. Smallest Board Space – 540nH Inductor Murata LQM21PNR 540nH DCR=75mW. Supports DC currents up to 1.3A. Board Layout w/ 2012 package: 3.55mm x 3.45mm Optimal Efficiency – 1uH Inductor Decreased ripple achieved with larger inductor reduces loss and improves efficiency. Coilcraft XFL3010-102 1uH DCR=43mW. Size 3mm x 3mm x 1mm Efficiency is improved by ~5% for 3MHz switching frequency. Board Layout w/ 3030 1µH package: 4.313mm x 5.052mm Board Layout w/ 2010 package: 3.3mm x 4.0mm FAN5903 Evaluation Board Footprint w/ 540nH 2012 Inductor FAN5903 Evaluation Board Footprint w/ 1µH 3030 Inductor

FAN5903 + 3G PA in WCDMA Mode Battery Current vs. Output Power

DC Efficiency: VIN = 3.7V

DC Efficiency: VIN = 5.0V

FAN5903: Extending Connection Time for Mobile Devices Voice Calls Data Transmit Usage curve from GSMA’s “Battery Life Measurement Technique, v4.7 Assumes System Current Consumption = 100mA

FAN5903: Usage Time Summary WCDMA Mode Type Parameters FAN5903 (minutes) No FAN5903 Improvement Absolute (minutes) Percentage Voice Tx Time using 3 PA Power Modes 641 585 56 9.5% Tx Time with PA in High Power Mode 515 297 218 73.2% Data 436 348 88 25.4% 394 253 141 55.6%

3G/3.5G/4G PA Thermal Issues Common issue facing smartphones today is heat generated by PAs which causes these issues: “Hot” or very warm mobile handset during voice calls and heavy data transmit functions Thermal vias cannot dissipate all of the heat resulting in hotter PAs Parameters 3G PA Only 3G PA + FAN5903 POUT = 17dBm POUT = 0dBm VPA (V) 3.700 0.984 0.718 IBATT (A) 0.167 0.015 0.058 0.004 Power Dissipation (W) 0.618 0.056 0.057 0.003 JC @ >16dBm (C/W) 16.0 - Rise in Temperature (C) 9.9 0.9

Reduced Heat Dissipation POUT = 28dBm @ VPA=2.97V POUT = 28dBm @ VBAT=3.7V POUT = 28dBm @ VBAT=4.2V (Battery Charging) 3G PA w/ FAN5903 Thermal Profile 3G PA without FAN5903 Thermal Profile

Determining PA VCC vs. POUT Determine PA VCC for a Range of POUT Determine acceptable Adjacent Channel Power Ratio 3GPP limit: -33dBc @ 5MHz. Add margin for component and voltage tolerances and manufacturing margins. Limit of -39dBc used here. Measure PA VCC vs. POUT for desired ACPR Use a signal analyzer to measure ACPR Start with PA VCC = 3.4V, then reduce VCC until ACPR = desired value ACPR Measurement -39.0 29.0 dBm -39.2 PA VCC vs. POUT Results Embedded Look Up Table POUT TX_AGC VCON 29 256 1.300 27 244 1.160 25 198 0.944 23 176 0.780 22 150 0.560 POUT (dBm) PIN PA VCC (V) IBATT (mA) VBATT -5 MHz OFFSET (dB) + 5 MHz OFFSET 29.0 3.4 3.25 518.40 3.7 -39.0 -39.2 28.2 2.2 465.12 -38.5 -40.3 27.0 1.2 2.90 369.34 -38.9 -40.7 26.1 0.4 2.61 300.05 -38.8 -40.6 25.0 -0.4 2.36 243.84 -40.4 23.9 -1.2 2.13 198.68 23.0 -1.9 1.95 165.11 -40.5 NEW Fixed values added to calibration table. Not part of factory calibration. Factory calibration values.

Transmit Spurs Far Below Modulation Spurs << Mask for Low & High Power WCDMA PA Output: 26.9dBm (PWM mode) Modulation On Modulation Off High Output Power DCDC in PWM mode Frequency automatically decreases for longer duty cycle (to provide more current) Low Output Power DCDC in PFM mode Frequency automatically decreases to increase efficiency Modulation On Modulation Off WCDMA PA Output: 5dBm (PFM mode) No Spurs for Mid Power Spurs < -87dBc 8dBm < POUT < 25dBm (FSW = 3MHz or 6 MHz)

Transmit EVM: Almost No Change EVM increased by 0.6% with FAN5903, but still far below limit. RF POUT MEASURED EVMRMS EVM LIMIT Lab Supply FAN5903 WCDMA Specification 29dBm 1.4% (VCC = 3.4V) 1.9% (VCC = 3.25V) 17.5% 16dBm 1.2% 1.8% (VCC = 2.275V) 5dBm 1.3% (VCC = 1.764V)

Rx Band Output Noise: No change FAN5903 adds no noise in the receive bands. POUT [dBm] VCC [V] PA MODE Rx Noise [dBm/Hz] FAN5903 Lab Supply 29.0 3.25 High Power -135.1 -135.2 16.0 2.275 Med. Power -148.5 5.0 1.764 Low Power Analyzer picture with limits -6dB N9010A Signal Analyzer E4438C Signal Generator VBIAS VCC Rx 881 MHz Tx 836 MHz PA

Bill of Materials & Evaluation Board Part Type Case Size Value Vendor Part Number FAN5903 Inductor 2012 540nH Murata LQM21PNR54MG0 Input Capacitor 0603 10µF Panasonic ECJ-1VB1A106M Output Capacitor 0402 4.7µF GRM155R60J475ME87D FAN5903 Evaluation Board Connect to PA evaluation boards. *C6 is for evaluation only and not needed for the actual application.

Pricing & Availability Fairchild Part Number Package Unit Price @ 1ku Availability FAN5903UCX WLCSP-9 $0.760 Now

Summary Best in-class power management solutions to support all cellular standards Meets specifications outlined in cellular standards FAN5903 is a compact, high efficiency buck converter that provides these benefits: More than 55 minutes of increased talk/usage time in 3G mode Lowers heat dissipation by 40% Smallest solution footprint Smaller passive components due to 6MHz switching frequency Lowers total cost of ownership Reduce battery size, weight and cost

Marketing & Apps Contacts Marketing Contact Wayne Seto wayne.seto@fairchildsemi.com +1-408-822-2197 Applications Support Paul Finkel paul.finkel@fairchildsemi.com +1-408-822-2543

Appendix

Test Configuration VCC VBATT IBATT FAN5903 -10dB PA VBIAS Power Mode Control VBIAS E4438C Signal Generator VCC VCC N9010A Signal Analyzer VCON FAN5903 VBATT IBATT Power Supply

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