ON FAN5903UCX Buck converter with bypass mode Datasheet

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FAN5903
Buck Converter with Bypass Mode for 3G / 3.5G / 4G PAs
Features



Description
2.7 V to 5.5 V Input Voltage Range
VOUT Range from 0.4 V to 3.5 V (or VIN)
Small Form Factor Inductor
o 2012 470 nH or 540 nH for Minimal PCB Area
o 2520 1.0 µH for Higher Efficiency
FAN5903 is a high-efficiency, low-noise, synchronous,
step-down, DC-DC converter designed for powering
3G / 3.5G / 4G RF Power Amplifiers (PAs) in handsets
and other mobile applications.
The output voltage may be dynamically varied from
0.40 V to 3.50 V, proportional to an analog input VCON,
ranging from 0.16 V to 1.40 V provided by an external
DAC. This allows the PA to be supplied with the voltage
that enables maximum power-added efficiency.




Bypass Dropout at 500 mA, 60 mV Typical

3 MHz / 6 MHz Selectable Switching Frequency to
Facilitate System Optimization



High-Efficiency PFM Operation at Low Power
Up to 96% Efficient Synchronous Operation at
High-Power Conditions

The FAN5903 offers fast transition times, enabling
changes to the output voltage in less than 10 µs for
power transitions. Moreover, a Current-Mode control
loop with fast transient response ensures excellent line
and load regulation.
10 µs Output Voltage Step Response for Early
Power Loop Settling
Light-load efficiency is optimized by operating in PFM
Mode for load currents typically less than 100 mA.
100% Duty Cycle for Low Dropout Operation
Input Under-Voltage Lockout / Thermal Shutdown
1.34 mm x 1.29 mm, 9-Bump, 0.4 mm-Pitch,
Wafer-Level Chip-Scale Package (WLCSP)
Sleep Mode for Very Low IQ Operation
Applications


Dynamic Supply Bias for 3G/3.5G and 4G PAs
Power Supply for WCDMA/LTE PAs
Resources
For more information or a full copy of this datasheet,
please contact a Fairchild representative.
An integrated bypass FET automatically switches on
when battery voltage drops close to the desired output
voltage (VOUT = VBAT - 200 mV). The DC-DC switches
back to Synchronous Mode when the voltage dropout
exceeds 375 mV. The integrated bypass FET is also
enabled when VCON is nominally greater than to 1.5 V.
FAN5903 — Buck Converter with Bypass Mode for 3G / 3.5G / 4G PAs
June 2013
The switching frequency may be set to 3 MHz or
6 MHz, enabling further optimization of system
performance. The FAN5903 typically uses a single,
small-form-factor inductor of 470 nH or 540 nH.
Efficiency may be further optimized using a 1.0 µH
inductor when running at 3 MHz.
When output regulation is not required, the FAN5903
may be placed in Sleep Mode by setting VCON nominally
to 50 mV. This ensures a very low IQ (<70 µA) while
enabling a fast return to output regulation. The
FAN5903 enables significant current reduction and
increased talk time and is available in a 1.34 mm x
1.29 mm, 9-bump, 0.40 mm-pitch, WLCSP package.
Ordering Information
Part Number
Operating
Temperature Range
FAN5903UCX
-40 to +85°C
© 2008 Fairchild Semiconductor Corporation
FAN5903 • Rev. 1.0.9
Package
1.34 mm x 1.29 mm, 9-bump, 0.4 mm Pitch,
Wafer-Level Chip-Scale Package (WLCSP)
Packing Method
Tape and Reel
www.fairchildsemi.com
CIN
10 µF
EN
COUT
FB
FAN5903
FSEL
4.7 µF
PGND
3/6 MHz DC-DC
VCON
AGND
BPEN
From
External
DAC
VOUT
SW 470nH
L1
PVIN
Figure 1. Application Circuit
FAN5903
Bypass
Controller
PVIN
VIN
2.7V – 4.5V
CPA
PA
UMTS BAND 1, … ,13
CIN
CPA
FB
0.4Vto 3.4V
Up to
800mArms
Switcher
GPIO
GPIO
Optional
L1
BPEN
Optional
PFM/PWM
Controller
SW
FSEL
GPIO
FAN5903 — Buck Converter with Bypass Mode for 3G / 3.5G / 4G PAs
Application Diagrams
VOUT
PA
UMTS BAND 1, … ,13
COUT
CPA
EN
PGND
DAC/GPIO
VCON
PA
Reference
AGND
UMTS BAND 1, … ,13
CHIPSET
Bandgap
CPA
PA
UMTS BAND 1, … ,13
CPA
PA
UMTS BAND 1, … ,13
Figure 2. Typical Application with a 5-Band WCDMA / HSPA PA System
© 2008 Fairchild Semiconductor Corporation
FAN5903 • Rev. 1.0.9
www.fairchildsemi.com
2
PGND
PGND
AGND
VCON
A1
A2
A3
A3
A2
A1
EN
FSEL
SW
SW
FSEL
EN
B1
B2
B3
B3
B2
B1
BPEN
FB
PVIN
PVIN
FB
BPEN
C1
C2
C3
C3
C2
C1
0.4
1.29 mm
1.29 mm
0.4
AGND
0.4
VCON
1.34 mm
1.34 mm
Figure 3. Top-Through View, Bumps Face Down
0.4
Figure 4. Top-Through View, Bumps Face Up
Pin Definitions
Pin #
Name
Description
A1
VCON
Analog control pin. Shield signal routing against noise.
A2
AGND
Analog ground, reference ground for the IC. Follow PCB routing notes for connecting this pin.
A3
PGND
Power ground of the internal MOSFET switches. Follow routing notes for connections between
PGND and AGND.
B1
EN
Enables switching when HIGH, Shutdown Mode when LOW. This pin should not be left floating.
B2
FSEL
Switching frequency select. When FSEL is LOW, the DC-DC operates at 6 MHz. When FSEL is
HIGH, the DC-DC operates at 3 MHz. This pin should not be left floating.
B3
SW
C1
BPEN
C2
FB
C3
PVIN
FAN5903 — Buck Converter with Bypass Mode for 3G / 3.5G / 4G PAs
Pin Configuration
Switching node of the internal MOSFET switches. Connect to output inductor.
Force bypass transistor when HIGH; auto-bypass when LOW. This pin should not be left floating.
Output voltage-sense pin. Connect to VOUT to establish feedback path for regulation point.
Supply voltage input to the internal MOSFET switches; connect to input power source.
© 2008 Fairchild Semiconductor Corporation
FAN5903 • Rev. 1.0.9
www.fairchildsemi.com
3
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
Min.
Max.
PVIN
-0.3
6.0
Voltage On Any Other Pin
-0.3
PVIN + 0.3
TJ
Junction Temperature
-40
+125
°C
TSTG
Storage Temperature
-65
+150
°C
+260
°C
VIN
TL
ESD
Parameter
Lead Soldering Temperature (10 Seconds)
Electrostatic Discharge
Protection
Human Body Model, JESD22-A114
2.0
Charged Device Model, JESD22-C101
1.5
Unit
V
kV
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
Parameter
Min.
Typ.
Max.
Unit
VIN
Supply Voltage Range
2.7
5.5
V
VOUT
Output Voltage Range
0.35
<VIN
V
2.4
A
1.0
A
IOUT_BYP
Output Current (Bypass Mode)
IOUT_DCDC Output Current (DCDC Mode)
L1
470
fSW = 6 MHz
Inductor
fSW = 3 MHz
CIN
COUT
Input Capacitor
nH
540
(1)
FAN5903 — Buck Converter with Bypass Mode for 3G / 3.5G / 4G PAs
Absolute Maximum Ratings
1.00
µH
10
µF
4.7
µF
Output Capacitor
2.2
TA
Operating Ambient Temperature Range
-40
+85
°C
TJ
Operating Junction Temperature Range
-40
+125
°C
Note:
1. A large enough input capacitor value is required for limiting the input voltage drop during bursts, bypass
transitions, or during large output voltage transitions. Ensure the input capacitor value is greater than the output
capacitor’s. See the inrush current specifications below.
Dissipation Ratings
Symbol
ΘJA
Parameter
Min.
(2)
Junction-to-Ambient Thermal Resistance
Typ.
110
Max.
Unit
°C/W
Note:
2. 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.
© 2008 Fairchild Semiconductor Corporation
FAN5903 • Rev. 1.0.9
www.fairchildsemi.com
4
VIN = VOUT + 0.6 V, IOUT = 200 mA, EN = VIN, TA = -40°C to +85°C, unless otherwise noted. Typical values are at
TA = +25°C, VIN = 3.7 V.
Symbol
Parameter
Condition
Min.
Typ.
Max.
Unit
5.5
V
3
µA
Power Supplies
VIN
Input Voltage Range
IOUT ≤ 800 mA
ISD
Shutdown Supply Current
EN = 0 V
1
IQ
Quiescent Current
Sleep Enabled
70
VUVLO
VIH
Under Voltage Lockout Threshold
VIN Rising
2.7
2.30
Hysteresis
VIL
Logic Threshold Voltage: EN,
FSEL and BPEN
Input HIGH Threshold
IEN
EN Input Bias Current
EN = VIN or GND
fSW
Average Oscillator Frequency
FSEL = 0
fSW
Average Oscillator Frequency
FSEL = 1
2.45
µA
2.60
175
V
mV
1.2
V
Input LOW Threshold
0.5
V
0.01
1.00
µA
5.4
6.0
6.6
MHz
2.7
3.0
3.3
MHz
Oscillator
DC-DC Mode
RDSON
PMOS On Resistance(3)
VIN = VGS = 3.7 V
230
mΩ
NMOS On Resistance(3)
VIN = VGS = 3.7 V
150
mΩ
ILIMp
P-Channel Current Limit
1.2
1.5
1.8
A
ILIMn
N-Channel Current Limit
0.8
1.1
1.4
A
VOUT_MIN
Minimum Output Voltage
VCON = 0.16 V
0.35
0.40
0.45
V
VOUT_MAX
Maximum Output Voltage
VCON = 1.40 V
3.45
3.50
3.55
V
+50
mV
Gain
VOUT_ACC
Gain in Control Range 0.16V to
1.40V
VOUT Accuracy
2.5
Ideal = 2.5 x VCON
-50
FAN5903 — Buck Converter with Bypass Mode for 3G / 3.5G / 4G PAs
Electrical Characteristics
Bypass Mode
RFET
VOUT_BP
Bypass FET Resistance(4)
VIN = VGS = 3.7 V
Bypass Mode Output Voltage Drop IOUT = 500 mA
210
mΩ
60
mV
+5
mV
+25
mV
Output Regulation
VOUT_RLine
VOUT Line Regulation
VOUT_RL
VOUT Load Regulation
IOUT ≤ 800 mA
VCON_SL_EN VCON Sleep Mode Enter
VCON Voltage that Forces Very
Low IQ Sleep Mode
VCON_SL_EX VCON Sleep Mode Exit
VCON Voltage that Exits Sleep
Mode
VCON_BP_EN VCON Forced Bypass Mode Enter
VCON Voltage that Forces
Bypass, VIN = 2.70 V – 4.75 V
VCON_BP_EX VCON Forced Bypass Mode Exit
VCON Voltage that Exits
Forced; Bypass,
VIN = 2.70 V – 4.75 V
50
mV
135
1.6
mV
V
1.4
V
VBP_ThH
Voltage Threshold to Enter Bypass
VIN – VOUT
Mode
160
200
240
mV
VBP_ThL
Voltage Threshold to Exit Bypass
Mode
320
375
440
mV
TOTP
Over-Temperature Protection
© 2008 Fairchild Semiconductor Corporation
FAN5903 • Rev. 1.0.9
VIN – VOUT
Rising Temperature
+150
Hysteresis
+20
°C
www.fairchildsemi.com
5
VIN = VOUT + 0.6 V, IOUT = 200 mA, EN = VIN, TA = -40°C to +85°C, unless otherwise noted. Typical values are at
TA = +25°C, VIN = 3.7 V.
Symbol
Parameter
Condition
Min.
Typ.
Max.
Unit
40
µs
Timings
Startup Time
VIN = 3.7 V, VOUT from 0 V to
3.1 V, COUT = 4.7 µF, 10 V,
X5R
30
tSP_en
Sleep Mode Enter Time
VCON < 50 mV
40
µs
tSP_ex
Sleep Mode Exit Time
VCON ≥ 135 mV
11
µs
tDC-DC_TR
VOUT Step Response Rise Time(3)
VOUT from 5% to 95%,
VOUT < 2 V (1.4 V – 3.4 V) ,
RLOAD ≤ 7 
10
µs
tDC-DC_TF
VOUT Step Response Fall Time(3)
VOUT from 95% to 5%,
VOUT < 2 V (3.4 V – 1.4 V),
RLOAD ≤ 7 
12
µs
tDC-DC_CL
Maximum Allowed Time for
(5)
Consecutive Current Limits
40
µs
tDCDC_CLR
Consecutive Current Limit
Recovery Time(3)
180
µs
tSS
Notes:
3. Guaranteed by design; not tested in production.
4. Bypass FET resistance does not include the PFET RDSON and inductor DCR in parallel with the bypass FET in
Bypass Mode.
5. Protects part under short circuit conditions. After 40 µs, operation halts and restarts after 180 µs. Under heavy
capacitive loads, VCON slew rate may be reduced to avoid consecutive current limits. Under typical conditions for
a 3 V change at the output, a capacitive only load of up to 40 µF is supported, assuming a step at the VCON input.
© 2008 Fairchild Semiconductor Corporation
FAN5903 • Rev. 1.0.9
FAN5903 — Buck Converter with Bypass Mode for 3G / 3.5G / 4G PAs
Electrical Characteristics
www.fairchildsemi.com
6
Unless otherwise noted, VIN = EN = 3.7 V, L1 = 1.0 µH, CLOAD = 4.7 µF, and TA = +25°C.
90%
90%
80%
80%
Efficiency (%)
100%
Efficiency (%)
100%
70%
VIN = 2.7V
VIN = 3.7V
VIN = 4.2V
VIN = 5.5V
60%
50%
40%
70%
60%
VIN = 2.7V
50%
VIN = 4.2V
VIN = 3.7V
VIN = 5.5V
40%
0
100
200
300
400
500
0
Output Current (mA)
90%
80%
80%
Efficiency (%)
90%
Efficiency (%)
100%
70%
VIN = 2.7V
VIN = 3.7V
VIN = 4.2V
VIN = 5.5V
1
2
3
70%
VIN = 2.7V
60%
VIN = 3.7V
VIN = 4.2V
50%
VIN = 5.5V
0
4
Figure 7. Efficiency vs. Output Voltage vs. Input
Voltage, fSW = 6 MHz, RPA = 7 
90%
80%
80%
Efficiency (%)
90%
Efficiency (%)
100%
70%
VIN = 2.7V
VIN = 3.7V
VIN = 4.2V
VIN = 5.5V
100
200
300
4
400
70%
VIN = 2.7V
60%
VIN = 3.7V
VIN = 4.2V
50%
VIN = 5.5V
0
500
100
200
300
400
Output Current (mA)
Output Current (mA)
Figure 9. Efficiency vs. Output Current vs. Input
Voltage, fSW = 3 MHz, RPA = 7 
© 2008 Fairchild Semiconductor Corporation
FAN5903 • Rev. 1.0.9
3
40%
40%
0
2
Figure 8. Efficiency vs. Output Voltage vs. Input
Voltage, fSW = 6 MHz, RPA = 10 
100%
50%
1
Output Voltage (V)
Output Voltage (V)
60%
400
40%
40%
0
300
Figure 6. Efficiency vs. Output Current vs. Input
Voltage, fSW = 6 MHz, RPA = 10 
100%
50%
200
Output Current (mA)
Figure 5. Efficiency vs. Output Current vs. Input
Voltage, fSW = 6 MHz, RPA = 7 
60%
100
FAN5903 — Buck Converter with Bypass Mode for 3G / 3.5G / 4G PAs
Typical Characteristics
Figure 10. Efficiency vs. Output Current vs. Input
Voltage, fSW = 3 MHz, RPA = 10 
www.fairchildsemi.com
7
Unless otherwise noted, VIN = EN = 3.7 V, L1 = 1.0 µH, CLOAD = 4.7 µF, and TA = +25°C.
90%
90%
80%
80%
Efficiency (%)
100%
Efficiency (%)
100%
70%
VIN = 2.7V
VIN = 3.7V
VIN = 4.2V
VIN = 5.5V
60%
50%
70%
VIN = 2.7V
60%
VIN = 3.7V
VIN = 4.2V
50%
VIN = 5.5V
40%
40%
0
1
2
3
4
0
Output Voltage (V)
2
3
4
Output Voltage (V)
Figure 11. Efficiency vs. Output Voltage vs. Input
Voltage, fSW = 3 MHz, RPA = 7 
Figure 12. Efficiency vs. Output Voltage vs. Input
Voltage, fSW = 3 MHz, RPA = 10 
100
3.30
Sleep Current (mA)
Shutdown Current (mA)
1
2.80
2.30
1.80
1.30
-40°C
+25°C
0.80
90
80
70
-40°C
60
+25°C
+85°C
+85°C
50
0.30
2.5
3.5
4.5
2.5
5.5
3.5
4.5
5.5
Input Voltage (V)
Input Voltage (V)
Figure 13. Shutdown Current vs. Input Voltage
vs. Temperature
Figure 14. Sleep Mode Current vs. Input Voltage
vs. Temperature
Figure 15. Rise Times for 300 mV, 500 mV, and
2 V VOUT (VIN = 3.7 V)
Figure 16. Rise Times for 300 mV, 500 mV, and
2 V VOUT (VIN = 3.7 V)
© 2008 Fairchild Semiconductor Corporation
FAN5903 • Rev. 1.0.9
FAN5903 — Buck Converter with Bypass Mode for 3G / 3.5G / 4G PAs
Typical Characteristics
www.fairchildsemi.com
8
Unless otherwise noted, VIN = EN = 3.7 V, L1 = 1.0 µH, CLOAD = 4.7 µF, and TA = +25°C.
Figure 17. Line Transient VIN = 3.7 V to 4.2 V,
VOUT = 2.5 V, 10  Load, 50 µs/div.
Figure 18. Line Transient VIN = 3.7 V to 4.2 V,
VOUT = 1.0 V, 10  Load, 50 µs/div.
Figure 19. Load Transient, 0 mA to 400 mA,
VOUT = 1.0 V
Figure 20. Load Transient, 200 mA to 800 mA,
VOUT = 1.0 V
Figure 21. Load Transient, 0 mA to 400 mA,
VOUT = 2.5 V
Figure 22. Load Transient, 200 mA to 800 mA,
VOUT = 2.5 V
© 2008 Fairchild Semiconductor Corporation
FAN5903 • Rev. 1.0.9
FAN5903 — Buck Converter with Bypass Mode for 3G / 3.5G / 4G PAs
Typical Characteristics
www.fairchildsemi.com
9
Unless otherwise noted, VIN = EN = 3.7 V, L1 = 1.0 µH, CLOAD = 4.7 µF, and TA = +25°C.
Figure 23. Switching Waveforms, PFM Mode,
ILOAD = 10 mA (Light Load)
Figure 24. Switching Waveforms, PWM Mode,
fSW = 6 MHz, ILOAD = 300 mA (Heavy Load)
Figure 25. VOUT Rising Transition 0.5 V to 2.5 V,
VIN = 3.7 V
Figure 26. VOUT Falling Transition 2.5 V to 0.5 V,
VIN = 3.7 V
Figure 27. VOUT Transient Response VOUT = 3 V
Figure 28. VOUT Transient and Bypass Response VOUT
> 3 V, VCON Stepped Above 1.5 V
© 2008 Fairchild Semiconductor Corporation
FAN5903 • Rev. 1.0.9
FAN5903 — Buck Converter with Bypass Mode for 3G / 3.5G / 4G PAs
Typical Characteristics
www.fairchildsemi.com
10
Unless otherwise noted, VIN = EN = 3.7 V, L1 = 1.0 µH, CLOAD = 4.7 µF, and TA = +25°C.
ILIM
Figure 29. Soft-Start Transient Response from
0 mA to 100 mA
Figure 30. Cold-Start Transient Response from
0 mA to 100 mA
Figure 31. Soft-Start Transient Response from
0 mA to 800 mA
Figure 32. Cold-Start Transient Response from
0 mA to 800 mA
FAN5903 — Buck Converter with Bypass Mode for 3G / 3.5G / 4G PAs
Typical Characteristics
Figure 33. Shutdown Transient Response
© 2008 Fairchild Semiconductor Corporation
FAN5903 • Rev. 1.0.9
www.fairchildsemi.com
11
FB
Bypass
Controller
PVIN
Positive
Current Limit
CIN
PWM
VCON
Controller
SW
3 MHz OSC
L1
0 : Div 1
1 : Div 2
COUT
FSEL
To PWM CTL
EN
BPEN
Negative
Current Limit
PGND
AGND
Figure 34. Block Diagram
Operating Mode Description
The FAN5903 is a high-efficiency synchronous stepdown DC-DC converter operating with a Current-Mode
control. It adjusts the output voltage, VOUT, depending
on the set voltage VCON provided by an external DAC.
Regulated VOUT is set to 2.5 times input voltage VCON.
monitored. A current sense flags when the P-channel
transistor current exceeds the current limit and the
switcher is turned off to decrease the inductor current and
prevent magnetic saturation. Similarly, the current sense
flags when the N-channel transistor current exceeds the
current limit and re-directs discharging current through
the inductor back to the battery.
The DC-DC operates in PWM Mode or PFM Mode,
depending on the output voltage and load current.
Bypass Mode is supported where the output voltage is
shorted to the input voltage via a low on-state resistance
bypass FET.
In Pulse Frequency Modulation (PFM) Mode, at low
output voltages and load currents, typically less than
100 mA; the DC-DC operates in a constant On-Time
Mode. In the on-state, the P-channel is turned on during a
well-defined on-time before switching to the off state,
whereby the N-channel switch is turned on and the
inductor current is decreased to 0 A. The switcher output
is put into high-resistance state until the new regulation
cycle starts.
The FAN5903 supports a wide range of load currents.
High-current applications, up to a DC output of 800 mA,
mandated by 3G / 3.5G and 4G applications, for
example, are supported. System performance may be
optimized by enabling the DC-DC to run at either a
3 MHz or 6 MHz switching rate.
PFM Mode realizes high efficiency while maintaining RF
system performance down to low load currents.
Auto Mode
In Pulse Width Modulation (PWM) Mode, regulation
starts with an on-state where a P-channel transistor is
turned on and the inductor current is ramped up until the
off state begins. In the off state, the P-channel is switched
off and an N-channel transistor is turned on. The inductor
current decreases to maintain an average value equal to
the DC load current. The inductor current is continuously
© 2008 Fairchild Semiconductor Corporation
FAN5903 • Rev. 1.0.9
FAN5903 — Buck Converter with Bypass Mode for 3G / 3.5G / 4G PAs
Block Diagram
Bypass Mode
In Bypass Mode, the FAN5903 operates at 100% duty
cycle with the bypass FET turned on. This enables a very
low voltage dropout with up to 2.4 A DC load current. In
applications with 3G / 3.5G and 4G PAs, the Bypass
Mode typically handles 800 mA.
www.fairchildsemi.com
12
#
Mode
Conditions
Mode Description
FSEL BPEN EN VCON
1 Shutdown Mode
The whole IC is disabled.
X
X
0
0
2 Sleep Mode
The DC-DC is in Sleep Mode and consumes less than
70 µA of current.
X
X
1
0
3 6 MHz Auto Mode
The DC-DC is in Auto Mode and switches at 6 MHz.(6,7)
0
0
1
1
4 3 MHz Auto Mode
The DC-DC is in Auto Mode and switches at 3 MHz.
1
0
1
1
5 Bypass Mode
The bypass FET is forced ON. The DC-DC is set to 100%
duty cycle.
X
1
1
1
Notes:
6. When VOUT exceeds VIN – 200 mV, the bypass FET is enabled and the DC-DC goes to 100% duty cycle. When
VOUT ≤ VIN – 375 mV, the bypass FET is disabled and the DC-DC goes to Auto Mode.
7. When the load current is smaller than PFM current threshold, the DC-DC changes to PFM Mode.
DC Output Voltage
Bypass Mode
The output voltage of the DC-DC is determined by VCON,
provided by an external DAC or voltage reference:
The trigger to enter Bypass Mode is based on the
voltage difference between the battery voltage (sensed
through the PVIN pin) and the internally generated
reference voltage, VREF, as depicted in Figure 36. The
DC-DC enters Bypass Mode when VIN = VOUT + 200 mV.
It then turns into 100% duty cycle and the low-RDSON
bypass FET is turned on. As VOUT approaches VIN; the
DC-DC operates in a constant off-time mode, the
frequency is decreased to achieve a high duty cycle,
and the system continues to run in a regulated mode
until the bypass condition is satisfied.
VOUT  2.5  VCON
(1)
5.0
4.5
4.0
3.5
VOUT (V)
3.0
FAN5903 — Buck Converter with Bypass Mode for 3G / 3.5G / 4G PAs
Table 1. Mode Descriptions
As noted above, Bypass Mode is also entered when
VCON exceeds 1.5 V.
2.5
2.0
1.5
Sleep Mode
1.0
0.0
0.00
FB
PVIN
DCDC Mode
0.5
Bypass Mode
-
0.25
0.50
0.75
1.00
1.25
1.50
1.75
250mV
2.00
VCON (V)
VCON
+
Bypass Slew
Controller
+
VREF
-
Figure 35. Output Voltage vs. Control Voltage
VREF
The DC-DC is able to provide a regulated VOUT only if
VCON is between 0.16 V to 1.40 V. This allows VOUT to
be adjusted between 0.40 V and 3.50 V. If VCON is below
this range, VOUT is clamped to 0.40 V as minimum and
enters bypass for VCON > 1.50 V. If VCON is less than
50 mV, FAN5903 enters a non-regulated Sleep Mode.
This reduces current consumption to less than 70 µA
while allowing for a rapid return to regulation.
DC-DC
Switcher
SW
L1
Figure 36. Enabling Bypass Transistor Circuit
The bypass FET is turned on progressively using a slew
rate controller to limit the inrush current. The inrush
current is expressed as a function of the specified slew
rate as follows:
FAN5903 automatically switches between PFM, PWM,
and Bypass Modes.
I INRUSH  COUT
The DC-DC is able to provide a regulated VOUT only if
the battery voltage is 200 mV greater than VOUT.
© 2008 Fairchild Semiconductor Corporation
FAN5903 • Rev. 1.0.9
PWM
Controller
V REF ranges from 0.4 V to 3.4V
when VIN is higher than 3.4V
VOUT
 COUT  VBP_SLEW
t
(2)
The slew rate controller is not used when releasing the
Bypass Mode.
www.fairchildsemi.com
13
In some cases, it may be desirable to change the DCDC’s switching frequency from 6 MHz (FSEL = 0) to
3 MHz (FSEL = 1). At 3 MHz operation the DC-DC’s
efficiency is generally higher than that at 6 MHz. The
primary tradeoff with this is increased voltage ripple at
the lower frequency. A 1.0 µH inductor may be used in
3 MHz operation to optimize efficiency and ripple.
VOUT Transition to or from Bypass Mode
The transition to or from Bypass Mode requires the
bypass conditions be met. The FAN5903 performs
detection of the bypass conditions 2 µs after VCON
transition and enables the required charging /
discharging circuit to realize a transition time of 10 µs.
The FAN5903 is designed to have minimal impact on
the RF output spectrum at either switching frequency.
VOUT Transition at Startup
At startup, after EN rising edge is detected, the system
requires 40 µs to enable all internal voltage references
and amplifiers before enabling the DC-DC function.
Dynamic Output Voltage Transitions
The FAN5903 has a complex voltage transition
controller that realizes less than 10 µs transition times
with a large output capacitor and output voltage ranges.
VOUT negative step
VOUT Transition After BPEN
When BPEN goes HIGH, the controller dismisses the
internal bypass flags and sensors and enables
Bypass Mode. However, the transition is managed
with the same current limit and slew rate used during
regular transitions.
VOUT transition to or from Bypass Mode
Thermal Protection
VOUT transition at startup
If the junction temperature exceeds the maximum
specified junction temperature, the FAN5903 enters
Power-Down Mode (except the thermal detection circuit).
The transition controller manages five transitions:
 VOUT positive step




VOUT transition after BPEN
In most cases, sharp VCON transitions and letting the
transition controller optimize the output voltage slew rate
are recommended.
Sleep Mode
The FAN5903 offers a Sleep mode to minimize current,
while also enabling a rapid return to regulation. Sleep
Mode is entered when VCON is held below 50 mV for at
least 40 µs. In this mode, current consumption is
reduced to under 70 µA. Sleep Mode is exited after
approximately 12 µs when VCON is set above 135 mV.
VOUT Positive Step
After a VCON positive step, the DC-DC enters a CurrentLimit Mode, where VOUT ramps with a constant slew rate
dictated by the output capacitor and the current limit.
FAN5903 — Buck Converter with Bypass Mode for 3G / 3.5G / 4G PAs
VOUT Negative Step
After a VCON negative step, the DC-DC enters CurrentLimit Mode, where VOUT is reduced with a constant slew
rate dictated by the output capacitor and the current limit.
Switching Frequency Selection (FSEL)
Typical Voltage Transitions
Figure 37. Rise and Fall Times for 300 mV, 500 mV,
and 2 V VOUT (VIN = 3.7 V)
© 2008 Fairchild Semiconductor Corporation
FAN5903 • Rev. 1.0.9
Figure 38. Rise Times for 300 mV, 500 mV, and 2 V
VOUT (VIN = 3.7 V)
www.fairchildsemi.com
14
Figure 39 illustrates an application of the FAN5903 in a 3G / 4G transmitter. The FAN5903 is designed for driving
multiple PAs. Figure 40 presents a timing diagram designed to meet WCDMA specifications. The FAN5903 supports
voltage transients less than 10 µs.
FB
PVIN
CIN
10µF
540nH
FAN5903
SW
L1
0.4V to VBAT
Up to 800mA DC
FSEL
COUT
BPEN
VIN
EN
From
DAC
4.7µF
PGND
VCON
Power
Ground
Plane
AGND
Analog
Ground
Plane
VOUT
1000pF
100pF
1000pF
1000pF
100pF
100pF
PA
PA
RF
Ground
Plane
PA
RF
Ground
Plane
RF
Ground
Plane
Figure 39. Typical Application Diagram of FAN5903 Supplying Power to Three 3G or 4G PAs
30µs
DC-DC_EN
VCON
8µs
8µs
DC - DC VOUT
PA Supply
10ms
10ms
2.5 x VCON
RF Power
Figure 40. Timing Diagram for 3G/4G Transmitters
© 2008 Fairchild Semiconductor Corporation
FAN5903 • Rev. 1.0.9
www.fairchildsemi.com
15
FAN5903 — Buck Converter with Bypass Mode for 3G / 3.5G / 4G PAs
Application Information
Table 2. Recommended Inductors
Follow these guidelines:

Use a low noise source or a driver with good
PSRR to generate VCON.

The VCON driver must be referenced to AGND.

VCON routing must be protected against PVIN,
SW, PGND signals, and other noisy signals. Use
AGND shielding for better isolation.

Be sure the DAC output can drive the 470 pF
capacitor on VCON. It may be necessary to insert
a low value resistor to ensure DAC stability
without slowing VCON fast transition times.
Inductor
No Floating Inputs
Inductor Selection
The FAN5903 is able to operate at 3 MHz or 6 MHz
switching frequency, so 470 nH (or 540 nH) or 1.0 µH
inductors can be used, respectively. To achieve
optimum efficiency, it is recommended that the
FAN5903 switch at 3 MHz (FSEL = HIGH), using a
1.0 µH inductor. For applications that require the
smallest possible PCB area, the FAN5903 should be
configured for 6 MHz operation (FSEL = LOW) to allow
use of a 470 nH or 540 nH 2012 inductor.
fSW
Description
The FAN5903 does not have internal pull-down resistors
on its inputs. Therefore, unused inputs should not be left
floating and should be pulled HIGH or LOW.
470 nH, ±20%, 1100 mA, 2012
(metric)
Murata: LQM21PNR47MC0
L1
470 nH, ±30%, 1200 mA, 2012
6 MHz (metric)
Panasonic: ELGTEAR47NA
PCB Layout & Component Placement
540 nH, ±20%, 1300 mA, 2012
(metric)
Murata: LQM21PNR54MG0
1.0 µH, ±20%, 2500 mA, 3030
3 MHz (metric)
Coilcraft: XFL3010-102ME
Capacitor Selection
The minimum required output capacitor COUT is 4.7 µF,
6.3 V, X5R with an ESR of 10 m or lower and an ESL
of 0.3 nH or lower. Larger case sizes result in increased
loop parasitic inductance and higher noise.

Make sure the FAN5903, CIN, and COUT are all tied
to the same power ground (PGND). This minimizes
the parasitic inductance of the switching loop paths.

Place PGND on the top layer and connect it to the
AGND ground plane next to COUT using several vias.

Ensure that the routing loop, PVIN – PGND –
VOUT is the shortest possible.

Place the inductor away from the FB connection to
prevent unpredictable loop behavior.

Use the application circuit layout in Figure 41
whenever possible. The performance of this layout
has been verified.

Review the layout guidelines for the IC package.
This is especially important for the WLCSP
package. Refer to “Surface Mount Assembly of
Amkor’s Eutectic and Lead-Free CSPnl™ WaferLevel Chip-Scale Package” available from the
Amkor website.

PVIN and PGND must be routed with the widest
and shortest traces possible. It is acceptable for the
traces connecting the inductor to be long rather
than having long PVIN or PGND traces. The SW
node is a source of electrical switching noise. Do
not route it near sensitive analog signals.

Two small vias are used to connect the SW node to
the inductor L1. Use solder-filled vias if available.

The connection from COUT to FB should be wide to
minimize the Bypass mode voltage drop and the
series inductance. Even if the current in Bypass
Mode is small, keep this trace short and at least
5mm wide.

The ground plane should be not be broken into
pieces. Ground currents must have a direct, wide
path from input to output.
A 0.1 µF capacitor may be added in parallel with COUT to
reduce the effect of the capacitor’s parasitic inductance.
Table 3. Recommended Capacitor Values
Capacitor
Description
CIN
10 µF, ±20%, X5R, 10 V
COUT
4.7 µF, ±20%, X5R, 6.3 V
C on VCON
470 pF, ±20%, X5R
Filter VCON
VCON is the analog control pin of the DC-DC and
should be connected to an external Digital-to-Analog
Converter (DAC). It is recommended to place up to
470 pF decoupling capacitance between VCON and
AGND to filter the DAC noise. This capacitor also helps
protect the DAC from the DC-DC high-frequency
switching noise coupled through the VCON pin.
Any noise on the VCON input is transferred to VOUT with a
gain of two and a half (2.5). If the DAC output is noisy, a
series resistor may be inserted between the DAC output
and the capacitor to form an RC filter.
© 2008 Fairchild Semiconductor Corporation
FAN5903 • Rev. 1.0.9
www.fairchildsemi.com
16
FAN5903 — Buck Converter with Bypass Mode for 3G / 3.5G / 4G PAs
Application Information
Assembly
Each capacitor should have at least two dedicated
ground vias. Place vias within 0.1 mm of the
capacitors.

Ensure the traces are wide enough to handle the
maximum current value, especially in Bypass Mode.

Ensure the vias are able to handle the current
density. Use metal-filled vias if available.


Use metal-filled or solder-filled vias if available.
Poor soldering can cause low DC-DC conversion
efficiency. If the efficiency is low, X-ray the solder
connections to verify their integrity.
L1
COUT
CIN
Figure 41. Recommended PCB Layout
© 2008 Fairchild Semiconductor Corporation
FAN5903 • Rev. 1.0.9
www.fairchildsemi.com
17
FAN5903 — Buck Converter with Bypass Mode for 3G / 3.5G / 4G PAs

F
0.03 C
A
E
2X
0.40
B
Ø0.20
Cu Pad
A1
PIN A1
INDEX AREA
0.40
D
Ø0.30
Solder Mask
0.03 C
2X
LAND PATTERN RECOMMENDATION
(NSMD PAD TYPE)
TOP VIEW
0.06 C
0.05 C
0.539
0.461
C
SEATING PLANE
D
0.292±0.018
E
0.208±0.021
SIDE VIEWS
NOTES:
A. NO JEDEC REGISTRATION APPLIES.
Ø0.260±0.020
9X
0.40
C. DIMENSIONS AND TOLERANCE
PER ASMEY14.5M, 1994.
C
B
A
0.40
B. DIMENSIONS ARE IN MILLIMETERS.
D. DATUM C IS DEFINED BY THE SPHERICAL
CROWNS OF THE BALLS.
(Y)±0.018
E. PACKAGE NOMINAL HEIGHT IS 500 MICRONS
±39 MICRONS (461-539 MICRONS).
F
1 2 3
(X)±0.018
F. FOR DIMENSIONS D, E, X, AND Y SEE
PRODUCT DATASHEET.
BOTTOM VIEW
G. DRAWING FILNAME: MKT-UC009AErev1
Product
D
E
X
Y
Unit
FAN5903UCX
1.292 ± 0.030
1.342 ± 0.030
0.271
0.246
mm
Figure 42. 1.34 x 1.29 mm, 9-Bump, 0.4 mm-Pitch WLCSP
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/.
© 2008 Fairchild Semiconductor Corporation
FAN5903 • Rev. 1.0.9
www.fairchildsemi.com
18
FAN5903 — Buck Converter with Bypass Mode for 3G / 3.5G / 4G PAs
Physical Dimensions
FAN5903 — Buck Converter with Bypass Mode for 3G / 3.5G / 4G PAs
© 2008 Fairchild Semiconductor Corporation
FAN5903 • Rev. 1.0.9
www.fairchildsemi.com
19
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