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

2. 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.

3. 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

4. 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

5. FAN5903 Application Diagram

6. 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 nH inductor results in very small footprint with good efficiency optimized for 3G platforms.

7. 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

8. 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 XFL uH DCR=43mW.
Size 3mm x 3mm x 1mm
Efficiency is improved by ~5% for 3MHz switching frequency.
Board Layout w/ µH package: mm 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

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

10. DC Efficiency: VIN = 3.7V

11. DC Efficiency: VIN = 5.0V

12. 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

13. 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%

14. 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
>16dBm (C/W)
16.0 -
Rise in Temperature (C)
9.9
0.9

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

16. Determining PA VCC vs. POUT
Determine PA VCC for a Range of POUT
Determine acceptable Adjacent Channel Power Ratio
3GPP limit: 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.

17. 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)

18. 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)

19. 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

20. 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.

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

22. 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

23. Marketing & Apps Contacts
Marketing Contact
Wayne Seto
Applications Support
Paul Finkel

24. Appendix

25. 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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