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FAN5358 -- 2MHz, 500mA, SC70 Synchronous Buck Regulator
September 2009
FAN5358 2MHz, 500mA, SC70 Synchronous Buck Regulator
Features
2MHz Nominal-Frequency Operation 25A Typical Quiescent Current 500mA Output Current Capability 2.7V to 5.5V Input Voltage Range 1.0 to 1.8V Fixed Output Voltages Low Ripple, Light-Load PFM Mode Internal Soft-Start Input Under-Voltage Lockout (UVLO) Thermal Shutdown and Overload Protection 6-lead 2 x 2.2mm SC70
Description
The FAN5358 is a step-down switching voltage regulator that delivers a fixed output from an input voltage supply of 2.7V to 5.5V. Using a proprietary architecture with synchronous rectification, the device is capable of delivering 500mA and maintaining a very high efficiency of over 80% at load currents as low as 1mA. The regulator operates at a nominal frequency of 2MHz, which reduces the value of the external components to as low as 2.2H for the output inductor and 4.7F for the output capacitor. At moderate and light loads, pulse frequency modulation is used to operate the device in power-save mode with a typical quiescent current of 25A. Even with such a low quiescent current, the part exhibits excellent transient response during large load swings. In shutdown mode, the supply current drops below 1A, reducing power consumption. FAN5358 is available in a 6-lead SC70 package.
Applications
Cell Phones, Smart Phones 3G, 4G, WiFi , WiMAXTM, and WiBro Data Cards Netbooks , Ultra-Mobile PCs
(R) (R) (R)
Typical Application
L1
Table 1. External Components for Figure 1
SW GND VOUT 1 2 3 6 5 4 VIN GND EN CIN
U1
FAN5358
fSW
2MHz
L1
2.2H
CIN
2.2F
COUT
4.7F
U1
COUT
Figure 1. FAN5358 Typical Application
Wi-Fi(R) is a registered trademark of Wi-Fi Alliance Corporation. WiMaxTM is a trademark of WIMAX Forum Corporation. WiBro(R) is a registered trademark of Telecommunications Technology Association. Netbooks(R) is a registered trademark of Netbooks, Inc.
(c) 2009 Fairchild Semiconductor Corporation FAN5358 * Rev. 1.0.1
www.fairchildsemi.com
FAN5358 -- 2MHz, 500mA, SC70 Synchronous Buck Regulator
Ordering Information
Part Number
FAN5358S710X FAN5358S712X FAN5358S713X FAN5358S718X 2MHz
Switching Frequency
Output Voltage
1.0V 1.2V 1.3V 1.8V
(1)
Temperature Range
Package
Eco Status
Packing Method
-40 to +85C
SC70-6
Green
Tape and Reel
For Fairchild's definition of Eco Status, please visit: http://www.fairchildsemi.com/company/green/rohs_green.html.
Note: 1. Other voltage options are available on request. Contact a Fairchild representative.
Pin Configuration
SW GND VOUT 1 2 3 6 5 4 VIN GND EN
Figure 2. Pin Assignments (Top View)
Pin Definitions
Pin #
1 2, 5 3 4 6
Name
SW GND VOUT EN VIN Switching Node. Connect to output inductor.
Description
Ground. Power and IC ground. All signals are referenced to this pin. VOUT / Feedback. Connect to output voltage. Enable. The device is in shutdown mode when the voltage to this pin is <0.4V and enabled when >1.2V. Do not leave this pin floating. Input Voltage. Connect to input power source and CIN.
(c) 2009 Fairchild Semiconductor Corporation FAN5358 * Rev. 1.0.1
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FAN5358 -- 2MHz, 500mA, SC70 Synchronous Buck Regulator
Absolute Maximum Ratings
Stresses exceeding the absolute maximum ratings may damage the device. The device may not function or be operable above the recommended operating conditions and stressing the parts to these levels is not recommended. In addition, extended exposure to stresses above the recommended operating conditions may affect device reliability. The absolute maximum ratings are stress ratings only.
Symbol
VIN TJ TSTG TL ESD
Parameter
Input Voltage with Respect to GND Voltage on Any Other Pin with Respect to GND Junction Temperature Storage Temperature Lead Temperature (Soldering 10 Seconds) Human Body Model, JESD22-A114 Charged Device Model, JESD22-C101
Min.
-0.3 -0.3 -40 -65
Max.
6.0 VIN +0.3V +150 +150 +260
(2)
Units
V V C C C
2 kV 1
Electrostatic Discharge Protection Level
Note: 2. Lesser of 6.0V or VIN + 0.3V
Recommended Operating Conditions
The Recommended Operating Conditions table defines the conditions for actual device operation. Recommended operating conditions are specified to ensure optimal performance to the datasheet specifications. Fairchild does not recommend exceeding them or designing to Absolute Maximum Ratings.
Symbol
VCC IOUT L CIN COUT TA TJ Supply Voltage Range Output Current Inductor Input Capacitor Output Capacitor
(3)
Parameter
Min.
2.7 0
Typ.
Max.
5.5 500
Units
V mA H F F
2.2 2.2 4.7 -40 -40 +85 +125
Operating Ambient Temperature Operating Junction Temperature
C C
Thermal Properties
Symbol
JA
Parameter
Junction-to-Ambient Thermal Resistance
(4)
Min.
Typ.
285
Max.
Units
C/W
Note: 3. Refer to Operation Description section for guidance on maximum COUT capabilities. 4. Junction-to-ambient thermal resistance is a function of application and board layout. This data is measured with four-layer 2s2p boards in accordance to JESD51- JEDEC standard. Special attention must be paid not to exceed junction temperature TJ(max) at a given ambient temperate TA.
(c) 2009 Fairchild Semiconductor Corporation FAN5358 * Rev. 1.0.1
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FAN5358 -- 2MHz, 500mA, SC70 Synchronous Buck Regulator
Electrical Characteristics
Minimum and maximum values are at VIN = 2.7V to 5.5V, TA = -40C to +85C, circuit of Figure 1 unless otherwise noted. Typical values are at TA = 25C, VIN =3.6V.
Symbol
Power Supplies IQ I(SD) VUVLO VUVHYST V(ENH) V(ENL) I(EN) Oscillator fOSC Regulation
Parameter
Conditions
Min.
Typ.
Max.
Units
Quiescent Current Shutdown Supply Current Under-Voltage Lockout Threshold Under-Voltage Lockout Hysteresis Enable HIGH-Level Input Voltage Enable LOW-Level Input Voltage Enable Input Leakage Current Switching Frequency 1.0V
No Load, EN=VIN EN = GND Rising VIN 1.2
25 0.05 2.4 225
48 1.00 2.6
A A V mV V
0.4 EN = VIN or GND In PWM Mode ILOAD = 0 to 500mA ILOAD = 0 to 500mA ILOAD = 0 to 500mA ILOAD = 0 to 500mA From EN Rising Edge VIN = VGS = 3.6V VIN = VGS = 3.6V Open-Loop
(1)
V A MHz
0.01 2 -4.5 -4.5 -4.5 -4.0 70 750 650 750 850 150 20
1.00
+4.5 +4.5 +4.5 +4.0 s m m 1150 mA C C %
VO
Output Voltage Accuracy Soft-Start
1.2V 1.3V 1.8V
tSS
Output Driver RDS(on) ILIM TTSD THYS PMOS On Resistance NMOS On Resistance PMOS Peak Current Limit Thermal Shutdown Thermal Shutdown Hysteresis
Note: 5. The Electrical Characteristics table reflects open-loop data. Refer to Operation Description and Typical Characteristic for closed-loop data.
Block Diagram
VIN
Q1
EN REF
U1
CIN
VOUT
RAMP GEN
LOGIC & GATE DRIVE
SW
Q2
L1
VOUT COUT
GND
GND
Figure 3. IC Block Diagram
(c) 2009 Fairchild Semiconductor Corporation FAN5358 * Rev. 1.0.1 www.fairchildsemi.com 4
FAN5358 -- 2MHz, 500mA, SC70 Synchronous Buck Regulator
Typical Characteristics
Unless otherwise noted, VIN = VEN = 3.6V, VOUT = 1.8V, and TA = 25C.
95 90
100 V IN=3.6V 90
Efficiency (%)
80 75 70 65 60 0.001 2.7V IN 3.6V IN 4.2V IN 0.01 0.1 1
Efficiency (%)
85
80
70
-40C 25C 85C 0.01 0.1 1
60 0.001
Load Current (A)
Figure 4. Efficiency vs. Load Current and Input Supply
1.815
Load Current (A)
Figure 5. Efficiency vs. Load Current and Temperature
20
Output Voltage (V)
1.810
15
1.800 1.795 1.790 1.785 1.780 0 2.7V IN 3.6V IN 4.2V IN 5.5V IN 0.1 0.2 0.3 0.4 0.5 0.6
VOUT (mVpp)
1.805
10
5
2.7VIN 3.6VIN 5.5VIN 1 10 100 1000
0
Load Current (A)
Figure 6. Voltage Regulation
3.0 2.5 2.0 1.5 1.0 0.5 0 2.7V IN 3.6V IN 5.5V IN 0 0.1 0.2 0.3 0.4 0.5 0.6
Load Current (mA)
Figure 7. Peak-to-Peak Output Voltage Ripple
180
Load Current (mA)
Frequency (MHz)
160 140 120 100 80 2.7 3.2
Always PWM
PFM Border PWM Border
The switching mode changes at these borders Always PFM
3.7
4.2
4.7
5.2
Load Current (A)
Figure 8. Switching Frequency vs. Load Current
(c) 2009 Fairchild Semiconductor Corporation FAN5358 * Rev. 1.0.1
Input Voltage (V)
Figure 9. PFM / PWM Boundaries
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FAN5358 -- 2MHz, 500mA, SC70 Synchronous Buck Regulator
Typical Characteristics
Unless otherwise noted, VIN = VEN = 3.6V, VOUT = 1.8V, and TA = 25C.
32 Supply Current (uA) 30 28 26 24 22
-40
2.7VIN 3.6VIN 5.5VIN
-20
0
20
40
60
80
Ambient Temperature (deg.C)
Figure 10. Quiescent Current vs. Input Voltage and Temperature
Figure 11. Line Transient 3.3VIN to 3.9VIN, 50mA Load, 10s/div.
Figure 12. Line Transient 3.3VIN to 3.9VIN, 250mA Load, 10s/div.
(c) 2009 Fairchild Semiconductor Corporation FAN5358 * Rev. 1.0.1
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FAN5358 -- 2MHz, 500mA, SC70 Synchronous Buck Regulator
Typical Characteristics
Unless otherwise noted, VIN = VEN = 3.6V, VOUT = 1.8V, and TA = 25C.
Figure 13. Load Transient 0 to 150mA, 3.6VIN, 5s/div.
Figure 14. Load Transient 50 to 250mA, 3.6VIN, 5s/div.
Figure 15. Load Transient 200 to 500mA, 3.6VIN, 5s/div.
Figure 16. Metallic Short Applied at VOUT, 50s/div.
(c) 2009 Fairchild Semiconductor Corporation FAN5358 * Rev. 1.0.1
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FAN5358 -- 2MHz, 500mA, SC70 Synchronous Buck Regulator
Typical Characteristics
Unless otherwise noted, VIN = VEN = 3.6V, VOUT = 1.8V, and TA = 25C.
Figure 17. Overload Recovery to Light Load, 100s/div.
Figure 18. Soft-Start, RLOAD = 6, 20s/div.
Figure 19. Power Supply Rejection Ratio at 200mA Load
(c) 2009 Fairchild Semiconductor Corporation FAN5358 * Rev. 1.0.1
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FAN5358 -- 2MHz, 500mA, SC70 Synchronous Buck Regulator
Operation Description
The FAN5358 is a step-down switching voltage regulator that delivers a fixed output from an input voltage supply of 2.7V to 5.5V. Using a proprietary architecture with synchronous rectification, the device is capable of delivering 500mA and maintaining a very high efficiency of over 80% at load currents as low as 1mA. The regulator operates at a nominal frequency of 2MHz, which reduces the value of the external components to as low as 2.2H for the output inductor and 4.7F for the output capacitor.
Under-Voltage Lockout (UVLO)
When EN is HIGH, the under-voltage lockout keeps the part from operating until the input supply voltage rises high enough to properly operate. This ensures no misbehavior of the regulator during startup or shutdown.
Current Limiting
A heavy load or short circuit on the output causes the current in the inductor to increase until a maximum current threshold is reached in the high-side switch. Upon reaching this point, the high-side switch turns off, preventing current from increasing further. After 12 consecutive PWM cycles that terminate in current limit, the IC shuts down. About 275s after shutting down, the IC attempts to restart. If the fault has not cleared, the IC continues to shut down, then attempts to restart as shown in Figure 16.
Control Scheme
The FAN5358 uses a proprietary, non-linear, quasi fixedfrequency PWM modulator to deliver a fast load transient response, while maintaining a nominal switching frequency over a wide range of load conditions. The regulator performance is independent of the output capacitor ESR, allowing the use of ceramic output capacitors. For very light loads, the device operates in discontinuous current (DCM) single-pulse PFM mode, which produces low output ripple compared with other PFM architectures. Transition between PWM and PFM is near seamless, exhibiting very little VOUT glitch. Combined with exceptional transient response characteristics, the very low quiescent current of the controller (25A) maintains high efficiency, even at very light loads, while preserving fast transient response for applications requiring very tight output regulation.
Thermal Shutdown
When the die temperature increases, due to a heavy load condition and/or high ambient temperature, output switching is disabled until the die temperature falls sufficiently. The junction temperature at which the thermal shutdown activates is nominally 150C with a 20C hysteresis. Upon cooling, the output is enabled and goes through the regular soft start.
Enable and Soft Start
Maintaining the EN pin LOW keeps the FAN5358 in nonswitching mode in which all circuits are off and the part draws ~50nA of current. Increasing EN above its threshold voltage activates the part and starts the soft-start cycle. During soft start, the output is ramped using a slow RC time constant. This minimizes any large surge currents on the input and prevents any overshoot of the output voltage. Current limit is enforced in case the output cannot keep pace with the reference or in case of a shorted output. The current-limit fault response protects the IC in the event of an over-current condition present during soft-start. This protection can cause the IC to fail to start if heavy load is applied during startup or if excessive COUT is used. Table 2 shows combinations of COUT that allow the IC to start successfully with the minimum RLOAD that can be supported. Table 2. Minimum RLOAD Values for Soft-Start with Various COUT Values COUT 4.7F 10F Minimum RLOAD No restriction VOUT / 0.40
(c) 2009 Fairchild Semiconductor Corporation FAN5358 * Rev. 1.0.1
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FAN5358 -- 2MHz, 500mA, SC70 Synchronous Buck Regulator
Applications Information
Selecting the Inductor
The output inductor must meet both the required inductance and the energy handling capability of the application. The inductor value affects the average current limit, the PWM-to-PFM transition point, the output voltage ripple, and the efficiency. The ripple current (I) of the regulator is: I VOUT VIN - VOUT * L*f VIN SW
(1)
Thermal Considerations
The FAN5358 is designed to supply a maximum of 500mA, at the specified output voltage, with an operating junction temperature of up to 125C. Once the power dissipation and thermal resistance is known, the maximum junction temperature of the device can be calculated. The power dissipation by the IC can be calculated from the power efficiency diagram Figure 5 and subtracting the power dissipated by the inductor due to its serial resistance (ESR). The inductor ESR is dependent, not only upon the size and type of inductor, but also upon the switching frequency, which depends on the load and VIN. Some inductor manufacturers provide full information regarding the variation of the inductor ESR with the switching frequency. This information can be used to show that, at high switching frequency (~2 MHz) and maximum load, the power dissipated by the inductor can exceed the power dissipated by the IC package itself. The actual thermal resistance depends upon the thermal characteristics of the SC-70 surface-mount package and the surrounding printed circuit board (PCB) copper to which it is mounted. This can be improved by providing a heat sink of surrounding copper ground on the PCB. Depending on the size of the copper area, the resulting JA can be reduced below 280C/W. The addition of backside copper with through holes, stiffeners, and other enhancements can also help reduce thermal resistance. The heat contributed by the dissipation of other devices, particularly the inductor, located nearby, must be included in the design considerations. Once the limiting parameters are determined, the design can be modified to ensure that the device remains within specified operating conditions even if the maximum load is applied permanently. In short circuit VOUT-to-GND condition, the FAN5358 is fully protected and the power dissipated is internally reduced below 100mW. Overload conditions at minimum VIN should be considered as worst case, when it is possible for the device to enter a thermal cycling loop in which the circuit enters a shutdown condition, cools, re-enables, and again overheats and shuts down repeatedly due to an unmanaged fault condition. The diagram in Figure 20 was determined experimentally, using the recommended two-layer PCB in still air, to be used as a thermal guide.
Ambient Temperature (C)
90 85 80 75 70 65 60 55 2.7 2.9 3.1 Input Voltage (V) 3.3 3.5
Safe Operating Area for 500mA Load Area Where Thermal Protection May Trigger
The maximum average load current, IMAX(LOAD), is related to the peak current limit, ILIM(PK) by the ripple current: I (2) 2 The transition between PFM and PWM operation is determined by the point at which the inductor valley current crosses zero. The regulator DC current when the inductor current crosses zero, IDCM, is: IMAX(LOAD ) = ILIM(PK ) -
IDCM = I 2
(3)
The FAN5358 is optimized for operation with L=2.2H. The inductor should be rated to maintain at least 70% of its value at ILIM(PK). Efficiency is affected by the inductor DCR and inductance value. Decreasing the inductor value for a given physical size typically decreases the DCR; but since I increases, the RMS current increases, as do core and skin effect losses.
IRMS = IOUT(DC) 2 + I 12
2
(4)
The increased RMS current produces higher losses through the RDS(ON) of the IC MOSFETs as well as the inductor ESR. Increasing the inductor value produces lower RMS currents, but degrades transient response. For a given physical inductor size, increased inductance usually results in an inductor with lower saturation current. Table 3 shows the effects of inductance higher or lower than the recommended inductor on regulator performance.
Figure 20. Maximum Ambient Temperature vs. Input Voltage at 500mA
(c) 2009 Fairchild Semiconductor Corporation FAN5358 * Rev. 1.0.1
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FAN5358 -- 2MHz, 500mA, SC70 Synchronous Buck Regulator
PCB Layout Considerations
There are only three external components: the inductor and the input and output capacitors. For any buck regulator IC, including the FAN5358, it is important to place a low-ESR input capacitor very close to the IC, as shown in Figure 21. The input capacitor ensures good input decoupling, which helps reduce noise appearing at the output terminals and ensures that the control sections of the IC do not behave erratically due to excessive noise. This reduces switching cycle jitter and ensures good overall performance. It is important to place the common GND of CIN and COUT as close as possible to any of the FAN5358 GND terminals. There is some flexibility in moving the inductor further away from the IC; in that case, VOUT should be considered at the COUT terminal.
Output Capacitor
Table 4 suggests 0402 capacitors. 0603 capacitors may further improve performance in that the effective capacitance is higher. This improves the transient response and output ripple as shown in Table 3. Increasing COUT has no effect on loop stability and can therefore be increased to reduce output voltage ripple or to improve transient response. Output voltage ripple, VOUT, is: 1 VOUT = I * + ESR 8*C OUT * fSW
(5)
Input Capacitor
The 2.2F ceramic input capacitor should be placed as close as possible between the VIN pin and GND to minimize the parasitic inductance. If a long wire is used to bring power to the IC, additional "bulk" capacitance (electrolytic or tantalum) should be placed between CIN and the power source lead to reduce ringing that can occur between the inductance of the power source leads and CIN. The effective capacitance value decreases as VIN increases due to DC Bias effects. This has no significant impact on regulator performance. Figure 21. PCB Layout Guidance
0402 CAP
Table 3. Effects of Changes in Inductor Value (from Recommended Value) on Regulator Performance
Inductor Value
Increase Decrease
Table 4. Recommended Passive Components and Their Variation Due to DC Bias
d
IMAX(LOAD)
Increase Decrease
ILIM(PK)
Decrease Increase
VOUT
(5)
Transient Response
Degraded Improved
Decrease Increase
Component
Description
2.2H, 2520, 100m,1.3A
Vendor
FDK MIPF2520D Hitachi Metal:KSLI 252010AG-2R2 Murata: LQM31PN2RM00L TOKO: MDT2520CN2R2M Murata or Equivalent GRM155R60G475M GRM155R60E475ME760 Murata or Equivalent GRM155R60J225ME15 GRM188R60J225KE19D
Min.
Typ.
Max.
Comment
L1 2.2H, 2520, 80m,1.3A
1.5H
2.2H
Minimum value occurs at maximum current
COUT
4.7F, X5R, 0402
1.6F
4.7F
5.2F
Decrease primarily due to DC bias (VOUT) Decrease primarily due to DC bias (VIN) and elevated temperature
CIN
2.2F, X5R, 0402
1.0F
2.2F
2.4F
(c) 2009 Fairchild Semiconductor Corporation FAN5358 * Rev. 1.0.1
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FAN5358 -- 2MHz, 500mA, SC70 Synchronous Buck Regulator
Physical Dimensions
SYMM C L 2.000.20 A 0.65 0.50 MIN 6 4 B
PIN ONE
1.250.10
1.90
1 (0.25) 0.65 1.30 1.00 0.80
3 0.30 0.15 0.10
M
0.40 MIN AB 1.30
LAND PATTERN RECOMMENDATION
SEE DETAIL A
1.10 0.80 0.10 0.00 SEATING PLANE
NOTES: UNLESS OTHERWISE SPECIFIED A) THIS PACKAGE CONFORMS TO EIAJ SC-88A B) ALL DIMENSIONS ARE IN MILLIMETERS. C) DIMENSIONS DO NOT INCLUDE BURRS OR MOLD FLASH. D) DRAWING FILENAME AND REVISION; MAA06AREV6
C
0.10 C 2.100.30
GAGE PLANE (R0.10) 0.25 0.10
0.20 0.46 0.26
30 0
SCALE: 2X
DETAIL A
Figure 22. 6-Lead SC70
Package drawings are provided as a service to customers considering Fairchild components. Drawings may change in any manner without notice. Please note the revision and/or date on the drawing and contact a Fairchild Semiconductor representative to verify or obtain the most recent revision. Package specifications do not expand the terms of Fairchild's worldwide terms and conditions, specifically the warranty therein, which covers Fairchild products. Always visit Fairchild Semiconductor's online packaging area for the most recent package drawings: http://www.fairchildsemi.com/packaging/.
(c) 2009 Fairchild Semiconductor Corporation FAN5358 * Rev. 1.0.1
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FAN5358 -- 2MHz, 500mA, SC70 Synchronous Buck Regulator
(c) 2009 Fairchild Semiconductor Corporation FAN5358 * Rev. 1.0.1
www.fairchildsemi.com 13

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