Fairchild FAN53541UCX 2.4 mhz, 5 a tinybuck synchronous buck regulator Datasheet

FAN53541
2.4 MHz, 5 A TinyBuck™ Synchronous Buck Regulator
Features
Description
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The FAN53541 is a step-down switching voltage regulator
that delivers an adjustable output from an input voltage
supply of 2.7 V to 5.5 V. Using a proprietary architecture with
synchronous rectification, the FAN53541 is capable of
delivering 5 A at over 90% efficiency, while maintaining a
very high efficiency of over 80% at load currents as low as
2 mA. The regulator operates at a nominal fixed frequency of
2.4 MHz, which reduces the value of the external
components to 470 nH for the output inductor and 20 µF for
the output capacitor. Additional output capacitance can be
added to improve regulation during load transients without
affecting stability and inductance up to 1.2 µH may be used
with additional output capacitance.
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2.4 MHz Fixed-Frequency Operation
Best-in-Class Load Transient Response
5 A Output Current Capability
2.7 V to 5.5 V Input Voltage Range
Adjustable Output Voltage: 0.8 V to 90% of VIN
PFM Mode for High Efficiency in Light Load
(Forced PWM Available on MODE Pin)
50 µA Typical Quiescent Current in PFM Mode
External Frequency Synchronization
Low Ripple Light-Load PFM Mode with Forced
PWM Control
Power Good Output
Internal Soft-Start
Input Under-Voltage Lockout (UVLO)
Thermal Shutdown and Overload Protection
No External Compensation Required
20-Bump WLCSP
Applications
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Set-Top Box
Hard Disk Drive
Communications Cards
DSP Power
At moderate and light loads, pulse frequency modulation
(PFM) is used to operate the device in power-save mode
with a typical quiescent current of 50 µA. Even with such a
low quiescent current, the part exhibits excellent transient
response during large load swings. At higher loads, the
system automatically switches to fixed-frequency control,
operating at 2.4 MHz. In shutdown mode, the supply current
drops below 1 µA, reducing power consumption. PFM mode
can be disabled if constant frequency is desired. The
FAN53541 is available in a 20-bump 1.96 mm x 1.56 mm
Wafer-Level Chip-Scale Package (WLCSP).
PGOOD
VIN
CIN
10µF
L1
SW
CIN1
0.47H
10nF
FAN53541
GND
COUT
COUT
10µF
10µF
VOUT
EN
R1
FB
MODE
R2
Figure 1. Typical Application
Ordering Information
Part Number
Temperature Range
FAN53541UCX
-40 to 85°C
© 2013 Fairchild Semiconductor Corporation
FAN53541 • Rev. 1.0.2
Package
20-Ball Wafer-Level, Chip-Scale Package (WLCSP),
4x5 Array, 0.4 mm Pitch, 250 µm Ball
Packing Method
Tape and Reel
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FAN53541 — 2.4MHz, 5A TinyBuck™ Synchronous Buck Regulator
February 2014
Table 1. Recommended External Components for 5 A Maximum Load Current
Component
Description
Vendor
Parameter
Typical
Unit
L1
470 nH Nominal
See Table 2
L
0.47
H
COUT
10 F, 6.3V, X5R, 0805, 2 Pieces
C
20
F
CIN
10 F, 6.3 V, X5R, 0805
GRM21BR60J106M (Murata)
C2012X5R0J106M (TDK)
C
10
F
CIN1
10 nF, 25 V, X7R, 0402
Any
C
10
nF
Table 2. Recommended Inductors
Component Dimensions
DCR (mΩ) IMAXDC
Manufacturer
Part#
L (nH)
Bourns
SRP5012-R47M
470
19
Bourns
SRP4012-R47M
470
20
(1)
L
W
H
6.0
5.1
4.5
1.2
5.5
4.6
4.0
1.2
Coilcraft
XPL4020-471ML
470
19
7.2
4.2
4.2
2.0
Inter-Technical(2)
SC2511-R47M
470
2.6
16.0
6.5
6.5
3.0
TDK
VLC5020T-R47M
470
15
5.4
5.0
5.0
2.0
Vishay
IHLP1616ABERR47M01
470
20
5.0
4.5
4.1
1.2
Notes:
1. IMAXDC is the lesser current to produce 40°C temperature rise or 30% inductance roll-off.
2. Inductor used for efficiency and temperature rise measurements.
© 2013 Fairchild Semiconductor Corporation
FAN53541 • Rev. 1.0.2
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2
FAN53541 — 2.4 MHz, 5 A TinyBuck™ Synchronous Buck Regulator
Recommended External Components
PGOOD
EN
FB
VOUT
A1
A2
A3
A4
A4
A3
A2
A1
MODE
GND
B1
B2
B3
B4
B4
B3
B2
B1
C1
C2
C3
C4
C4
C3
C2
C1
D1
D2
D3
D4
D4
D3
D2
D1
E1
E2
E3
E4
E4
E3
E2
E1
VIN
SW
Figure 2. Top View
Figure 3. Top View Bottom View
Pin Definitions
Bump #
Name
Description
A1
PGOOD
A2
EN
Enable. The device is in Shutdown Mode when this pin is LOW. Do not leave this pin floating.
A3
FB
FB. Connect to resistor divider. The IC regulates this pin to 0.8 V.
A4
VOUT
VOUT. Sense pin for VOUT. Connect directly to COUT.
B1
MODE
MODE / SYNC. A logic 0 allows the IC to automatically switch to PFM during light loads. When held
HIGH, the IC to stays in PWM Mode. The regulator also synchronizes its switching frequency to four
times (4X) the frequency provided on this pin (fMODE). Do not leave this pin floating.
B2, B3,
C1 – C4
GND
Ground. Low-side MOSFET is referenced to this pin. CIN and COUT should be returned with a minimal
path to these pins.
B4
AGND
D1, D2,
E1, E2
VIN
Power Input Voltage. Connect to input power source. Connect to CIN with minimal path.
D3, D4,
E3, E4
SW
Switching Node. Connect to inductor.
Power Good. This open-drain pin pulls LOW if the output falls out of regulation or is in soft-start.
Analog Ground. All signals are referenced to this pin. Avoid routing high dV/dt AC currents through
this pin.
© 2013 Fairchild Semiconductor Corporation
FAN53541 • Rev. 1.0.2
www.fairchildsemi.com
3
FAN53541 — 2.4 MHz, 5 A TinyBuck™ Synchronous Buck Regulator
Pin Configuration
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
Parameter
Min.
SW, VIN Pins
VIN
Other Pins
Max.
-0.3
Tied without Series Impedance
Tied through Series Resistance ≥100 
Unit
(3)
7.0
-0.3
4.5
-0.3
VIN⁽4⁾
Human Body Model per JESD22-A114
2250
Charged Device Model per JESD22-C101
1500
V
ESD
Electrostatic Discharge
Protection Level
TJ
Junction Temperature
–40
+150
°C
TSTG
Storage Temperature
–65
+150
°C
+260
°C
TL
Lead Soldering Temperature, 10 Seconds
V
Note:
3. VIN slew rate is limited to 1 V/µs.
4. Lesser of 7 V or VIN+0.3 V.
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
0.8
90% Duty
Cycle
V
IOUT
Output Current
0
5
A
1.20
µH
L
CIN
COUT
Inductor
0.47
Input Capacitor
10
Output Capacitor
µF
20
µF
TA
Operating Ambient Temperature
-40
+85
°C
TJ
Operating Junction Temperature
-40
+125
°C
Typical
Unit
Thermal Properties
Symbol
JA
Parameter
(5)
Junction-to-Ambient Thermal Resistance
38
°C/W
Note:
5. See Thermal Considerations in the Applications section.
© 2013 Fairchild Semiconductor Corporation
FAN53541 • Rev. 1.0.2
www.fairchildsemi.com
4
FAN53541 — 2.4 MHz, 5 A TinyBuck™ Synchronous Buck Regulator
Absolute Maximum Ratings
Minimum and maximum values are at VIN=2.7 V to 5.5 V, and TA=-40°C to +85°C, unless otherwise noted. Typical values are
at TA=25°C, VIN=5 V, and VOUT=1.2 V.
Symbol
Parameter
Condition
Min.
Typ.
Max. Unit
Power Supplies
IQ
Quiescent Current
I SD
Shutdown Supply Current
VUVLO
Under-Voltage Lockout Threshold
VUVHYST
Under-Voltage Lockout Hysteresis
ILOAD=0, MODE=0 (AUTO PFM/PWM)
50
µA
ILOAD=0, MODE=1 (Forced PWM)
30
mA
EN=GND
0.1
10
µA
VIN Rising
2.67
2.80
V
VIN Falling
2.1
2.3
V
365
mV
Logic Pins
VIH
High-Level Input Voltage
VIL
Low-Level Input Voltage
VLHYST
IIN
1.05
V
0.4
Logic Input Hysteresis Voltage
140
Input Bias Current
Input Tied to GND or 1 kΩ Resistor to VIN
IOUTL
PGOOD Pull-Down Current
VPGOOD=0.4 V
IOUTH
PGOOD HIGH Leakage Current
VPGOOD=VIN
0.01
V
mV
1.00
1
µA
mA
0.01
1.00
µA
VOUT Regulation
VREF
Output Reference DC Accuracy,
Measured at FB Pin
TA=25°C, Forced PWM
0.792
0.800
0.808
V
TA=-40°C to 85°C, Forced PWM
0.787
0.800
0.813
V
AUTO PFM/PWM
0.784
0.800
0.824
V
VOUT
ILOAD
Load Regulation
MODE=VIN (Forced PWM)
–0.02
%/A
VOUT
VIN
Line Regulation
2.7 V ≤ VIN ≤ 5.5 V, IOUT(DC)=1.5 A
-0.16
%/V
FB Pin Leakage Current
FB=0.8 V
Transient Response
ILOAD Step 0.1 A to 1.5 A, tR=100 ns
IREF
1
nA
-30
mV
RDS(ON)P P-Channel MOSFET On Resistance
33
mΩ
RDS(ON)N N-Channel MOSFET On Resistance
28
mΩ
VOUT
Power Switch and Protection
ILIMPK
P-MOS Peak Current Limit
TLIMIT
Thermal Shutdown
THYST
Thermal Shutdown Hysteresis
VSDWN
Input OVP Shutdown
Open Loop
5.8
Closed Loop
8.8
A
8
A
155
°C
20
°C
6.1
V
5.5
5.8
V
2.1
2.4
3.0
MHz
525
600
700
kHz
Rising Threshold
Falling Threshold
7.5
Frequency Control
fSW
fMODE
Oscillator Frequency
MODE Pin Synchronization Range
External Square-Wave, 30% to 70% Duty
Cycle
Soft-Start and Output Discharge
tSS
RDIS
Regulator Enable to Regulated VOUT
(Rising PGOOD)
Output Discharge Resistance
© 2013 Fairchild Semiconductor Corporation
FAN53541 • Rev. 1.0.2
EN=0 V
1.2
ms
175
Ω
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5
FAN53541 — 2.4 MHz, 5 A TinyBuck™ Synchronous Buck Regulator
Electrical Characteristics
95%
95%
90%
90%
Efficiency
Efficiency
Unless otherwise specified; VIN=5 V, VOUT=1.2 V, VMODE=0 V, TA=25°C, circuit in Figure 1, and components per Table 1.
85%
80%
2.7 VIN
75%
85%
80%
-40C
75%
3.3 VIN
+25C
5.0 VIN
+85C
5.5 VIN
70%
70%
0
1000
2000
3000
4000
5000
0
1000
Load Current (mA)
3000
4000
Figure 5. Efficiency vs. ILOAD, 1.2 VOUT
95%
90%
90%
Efficiency
95%
85%
80%
2.7 VIN
75%
85%
80%
-40C
75%
3.3 VIN
+25C
5.0 VIN
+85C
5.5 VIN
70%
70%
0
1000
2000
3000
4000
5000
0
1000
Load Current (mA)
2000
3000
4000
5000
Load Current (mA)
Figure 6. Efficiency vs. ILOAD, 1.8 VOUT
Figure 7. Efficiency vs. ILOAD, 1.8 VOUT
100%
100%
95%
95%
Efficiency
Efficiency
5000
Load Current (mA)
Figure 4. Efficiency vs. ILOAD, 1.2 VOUT
Efficiency
2000
90%
85%
4.2 VIN
80%
90%
85%
-40C
80%
5.0 VIN
+25C
5.5 VIN
+85C
75%
75%
0
1000
2000
3000
4000
5000
0
Load Current (mA)
2000
3000
4000
5000
Load Current (mA)
Figure 8. Efficiency vs. ILOAD, 3.3 VOUT
© 2013 Fairchild Semiconductor Corporation
FAN53541 • Rev. 1.0.2
1000
Figure 9. Efficiency vs. ILOAD, 3.3 VOUT
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6
FAN53541 — 2.4 MHz, 5 A TinyBuck™ Synchronous Buck Regulator
Typical Characteristics
Unless otherwise specified; VIN=5 V, VOUT=1.2 V, VMODE=0 V, TA=25°C, circuit in Figure 1, and components per Table 1.
70
35
30
25
2.7 VIN
65
4.2 VIN
3.3 VIN
60
5.0 VIN
5.0 VIN
55
5.5 VIN
5.5 VIN
50
VOUT Shift (mV)
VOUT Shift (mV)
45
20
15
10
40
35
30
25
20
15
5
10
0
5
-5
-5
0
0
1000
2000
3000
4000
0
5000
1000
Load Current (mA)
Figure 10. Regulation, 1.2 VOUT
3000
4000
5000
Figure 11. Regulation, 3.3 VOUT
1,400
1,400
1,200
1,200
1,000
1,000
Load Current (mA)
Load Current (mA)
2000
Load Current (mA)
800
600
400
PFM Exit
200
800
600
400
PFM Exit
200
PFM Enter
PFM Enter
0
0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
3.5
4.0
Input Voltage (V)
4.5
5.0
5.5
Input Voltage (V)
Figure 12. PFM / PWM Boundaries, 1.2 VOUT
Figure 13. PFM / PWM Boundaries, 3.3 VOUT
30
3,000
3.6VIN, Auto
3.6VIN, PWM
2,500
5.0VIN, Auto
Switching Frequency (KHz)
Output Ripple (mVpp)
25
5.0VIN, PWM
20
15
10
5
2,000
1,500
1,000
3.6VIN, Auto
5.0VIN, Auto
500
0
0
0
1000
2000
3000
4000
0
5000
Figure 14. Output Voltage Ripple
© 2013 Fairchild Semiconductor Corporation
FAN53541 • Rev. 1.0.2
1000
2000
3000
4000
5000
Load Current (mA)
Load Current (mA)
Figure 15. Switching Frequency
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7
FAN53541 — 2.4 MHz, 5 A TinyBuck™ Synchronous Buck Regulator
Typical Characteristics
60
50
50
40
Input Current (mA)
Input Current (A)
Unless otherwise specified; VIN=5 V, VOUT=1.2 V, VMODE=0 V, TA=25°C, circuit in Figure 1, and components per Table 1.
40
30
20
30
20
10
-40C
-40C
+25C
+25C
+85C
10
+85C
0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
2.5
3.0
Input Voltage (V)
4.0
4.5
5.0
5.5
Input Voltage (V)
Figure 16. Quiescent Current, Auto Mode, EN=VIN
Figure 17. Quiescent Current, PMW Mode, EN=VIN
70
100%
1.2VOUT,
25mA Load
1.2VOUT,
1.0A Load
3.3VOUT,
1.0A Load
60
95%
50
90%
Efficiency
PSRR (dB)
3.5
40
30
85%
1.2 VOUT, L=SC2511
80%
1.2 VOUT, L=IHLP16
1.8 VOUT, L=SC2511
20
75%
10
70%
1.8 VOUT, L=IHLP16
3.3 VOUT, L=SC2511
10
100
1,000
10,000
100,000
3.3 VOUT, L=IHLP16
0
Frequency (Hz)
1000
2000
3000
4000
5000
Load Current (mA)
Figure 18. Power Supply Rejection (PSRR)
Figure 19. Inductor Efficiency Comparison, 5.0 VIN
Figure 20. Line Transient, 50  Load, tR=tF=10 s
Figure 21. Line Transient, ILOAD=1.0 A, tR=tF=10 s
© 2013 Fairchild Semiconductor Corporation
FAN53541 • Rev. 1.0.2
www.fairchildsemi.com
8
FAN53541 — 2.4 MHz, 5 A TinyBuck™ Synchronous Buck Regulator
Typical Characteristics
Unless otherwise specified; VIN=5 V, VOUT=1.2 V, VMODE=0 V, TA=25°C, circuit in Figure 1, and components per Table 1.
Figure 22. Load Transient, 0.1-1.5 A Load,
tR=tF=100 ns
Figure 23. Load Transient, 0.1-3.0 A Load,
tR=tF=100 ns, COUT=2x22 F
Figure 24. Startup / Shutdown, No Load
Figure 25. Startup / Shutdown, 240 m Load,
COUT=2x22 F
Figure 26. Overload Protection and Recovery
Figure 27. Startup into Overload
© 2013 Fairchild Semiconductor Corporation
FAN53541 • Rev. 1.0.2
www.fairchildsemi.com
9
FAN53541 — 2.4 MHz, 5 A TinyBuck™ Synchronous Buck Regulator
Typical Characteristics
The FAN53541 is a step-down switching voltage regulator
that delivers an adjustable output from an input voltage
supply of 2.7 V to 5.5 V. Using a proprietary architecture with
synchronous rectification, the FAN53541 is capable of
delivering up to 5 A at over 90% efficiency. The regulator
operates at a nominal frequency of 2.4 MHz at full load,
which reduces the value of the external components to
470 nH for the output inductor and 20 µF for the output
capacitor. High efficiency is maintained at light load with
single-pulse PFM Mode.
limits the COUT capacitance when a heavy load ( ILOAD(SS) ) is
applied during the startup.
The maximum COUT capacitance for successful starting with
a heavy constant-current load is approximately:
COUT
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 operate properly. This ensures no misbehavior of
the regulator during startup or shutdown.
Input Over-Voltage Protection (OVP)
For very light loads, the FAN53541 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
seamless, with a glitch of less than 3% of VOUT during the
transition between DCM and CCM Modes.
When VIN exceeds VSDWN (about 6.1 V), the IC stops
switching to protect the circuitry from excessive internal
voltage spikes. An internal filter prevents the circuit from
shutting down due to VIN noise spikes.
Current Limiting
PFM Mode is disabled by holding the MODE pin HIGH. The
IC synchronizes to the MODE pin frequency. When
synchronizing to the MODE pin, PFM Mode is disabled.
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 high currents from
causing damage. 16 consecutive PWM cycles in current limit
cause the regulator to shut down and stay off for about
1.6 ms before attempting a restart.
Setting Output Voltage
The output voltage is set by the R1, R2, and VREF (0.8 V):
(1)
In the event of a short circuit, the soft-start circuit attempts to
restart and produces an over-current fault after 16
consecutive cycles in current limit, which results in a duty
cycle of less than 5%, providing current into a short circuit.
(2)
External Frequency Synchronization
R1 must be set at or below 100 KΩ; therefore:
R1 0.8
Logic 1 on the MODE pin forces the IC to stay in PWM
Mode. Logic 0 allows the IC to automatically switch to PFM
during light loads. If the MODE pin is toggled, the converter
synchronizes its switching frequency to four times the
frequency on the mode pin (fMODE).
For example, for VOUT=1.2 V, R1=100 kΩ, R2=200 kΩ.
Enable and Soft-Start
When the EN pin is LOW, the IC is shut down, all internal
circuits are off, and the part draws very little current. Raising
EN above its threshold voltage activates the part and starts
the soft-start cycle. During soft-start, the modulator’s internal
reference is ramped slowly to minimize surge currents on the
input and prevents overshoot of the output voltage.
The MODE pin is internally buffered with a Schmitt trigger,
which allows the MODE pin to be driven with slow rise and
fall times. An asymmetric duty cycle for frequency
synchronization is permitted, provided it is consistent with
parametric table limits.
If large values of output capacitance are used, the regulator
may fail to start. If VOUT fails to achieve regulation within
1.2 ms from the beginning of soft-start, the regulator shuts
down and waits 1.6 ms before attempting a restart. If the
regulator is in current limit for 16 consecutive PWM cycles,
the regulator shuts down before restarting 1.6 ms later. This
© 2013 Fairchild Semiconductor Corporation
FAN53541 • Rev. 1.0.2
(3)
When EN is LOW, a 150  resistor discharges VOUT.
Regulator performance is independent of the output
capacitor ESR, allowing for the use of ceramic output
capacitors. Although this type of operation normally results in
a switching frequency that varies with input voltage and load
current, an internal frequency loop holds the switching
frequency constant over a large range of input voltages and
load currents.
VOUT  0.8
800
VOUT
Diode Emulation Mode is employed during soft-start,
allowing the IC to start into a pre-charged output. Diode
emulation prohibits reverse inductor current from flowing
through the synchronous rectifier.
The FAN53541 uses a proprietary non-linear, fixedfrequency PWM modulator to deliver very fast load transient
response, while maintaining a constant switching frequency
over a wide range of operating conditions.
R2 
 5.8  ILOAD 
where COUTMAX is expressed in F and ILOAD is
the load current during soft-start, expressed in A.
Control Scheme
R1 VOUT  VREF

R2
VREF
MAX
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FAN53541 — 2.4 MHz, 5 A TinyBuck™ Synchronous Buck Regulator
Operation Description
Application Information
The PGOOD pin is an open-drain that indicates that the IC is
in regulation when its state is open. PGOOD pulls LOW
under the following conditions:

The IC has operated in cycle-by-cycle current limit for
eight consecutive PWM cycles;

The circuit is disabled, either after a fault occurs or when
EN is LOW; or

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, output
voltage ripple, transient response, and efficiency.
The ripple current (∆I) of the regulator is:
The IC is performing a soft-start.
I 
Thermal Shutdown
When the die temperature increases, due to a high load
condition and/or a high ambient temperature, the output
switching is disabled until the temperature on the die has
fallen sufficiently. The junction temperature at which the
thermal shutdown activates is nominally 155°C with a
20°C hysteresis.
IMAX (LOAD)  ILIM(PK) 
(5)
I
2
(6)
The FAN53541 is optimized for operation with L=470 nH, but
is stable with inductances up to 1.2 H (nominal). The
inductor should be rated to maintain at least 80% of its value
at ILIM(PK). Failure to do so lowers the amount of DC current
the IC can deliver.
tOFF(MIN) is 45 ns, which constrains the maximum VOUT/VIN
that the FAN53541 can provide, while still maintaining a fixed
switching frequency in PWM Mode. Regulation is maintained
even though the regulator is unable to provide sufficient
duty-cycle and operate at 2.4 MHz.
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.
Switching frequency is the lower of 2.4 MHz or:








The maximum average load current, IMAX(LOAD), is related to
the peak current limit, ILIM(PK), by the ripple current as:
Minimum Off-Time Effect on Switching
Frequency

VOUT  IOUT  R OFF
fSW (MHz)  22.2  1 
V
IN  IOUT  (R OFF  R ON )

VOUT  VIN  VOUT

VIN  L  fSW
IRMS 
(4)
IOUT(DC ) 2 
I2
12
(7)
The increased RMS current produces higher losses through
the RDS(ON) of the IC MOSFETs as well as the inductor ESR.
where:
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.
IOUT = load current, in A;
RON = RDS(ON)_P + DCRL, in Ohms; and
ROFF = RDS(ON)_N + DCRL, in Ohms.
Table 3 shows the effects on regulator performance of higher
inductance than the recommended 470 nH.
A result of <0 MHz indicates 100% duty cycle operation.
Table 3. Inductor Value and Regulator
Performance
IMAX(LOAD)
∆VOUT (Eq.(8))
Transient Response
Increase
Decrease
Degraded
Inductor Current Rating
The FAN53541’s current-limit circuit can allow a peak current
of about 8.8 A to flow through L1 under worst-case
conditions. If it is possible for the load to draw that much
continuous current, the inductor should be capable of
sustaining that current or failing in a safe manner.
For space-constrained applications, a lower current rating for
L1 can be used. The FAN53541 may still protect these
inductors in the event of a short circuit, but may not be able
to protect the inductor from failure if the load is able to draw
higher currents than the DC rating of the inductor.
© 2013 Fairchild Semiconductor Corporation
FAN53541 • Rev. 1.0.2
www.fairchildsemi.com
11
FAN53541 — 2.4 MHz, 5 A TinyBuck™ Synchronous Buck Regulator
PGOOD Pin
Layout Recommendations
Table 1 suggests 0805 capacitors, but 0603 capacitors may
be used if space is at a premium. Due to voltage effects, the
0603 capacitors have a lower in-circuit capacitance, which
can degrade transient response and output ripple.
The layout example below illustrates the recommended
component placement and top copper (green) routing. The
inductor in this example is the TDK VLC5020T-R47N.
To minimize VIN and SW spikes and thereby reduce voltage
stress on the IC’s power switches, it is critical to minimize the
loop length for the VIN bypass capacitors.
Increasing COUT has a negligible effect on loop stability and
can be increased to reduce output voltage ripple or to
improve transient response. Output voltage ripple, ∆VOUT, is:
VOUT


1
 I  
 ESR 
8

C

f
OUT
SW


Switching current paths through C IN and COUT should be
returned directly to the GND bumps of the IC on the top
layer of the printed circuit board (PCB). VOUT and GND
connections to the system power and ground planes can
be made through multiple vias placed as close as possible
to the COUT capacitors. The regulator should be placed as
close to its load as possible to minimize trace inductance
and capacitance.
(8)
where COUT is the effective output capacitance. The
capacitance of COUT decreases at higher output voltages,
which results in higher ∆VOUT. If large values are used for
COUT, the regulator may fail to start under load. If an inductor
value greater than 1.0 H is used, at least 30 F of COUT
should be used to ensure transient response performance.
The lowest ∆VOUT is obtained when the IC is in PWM Mode
and, therefore, operating at 2.4 MHz. In PFM Mode, fSW is
reduced, causing ∆VOUT to increase.
ESL Effects
The Equivalent Series Inductance (ESL) of the output
capacitor network should be kept low to minimize the squarewave component of output ripple that results from the division
ratio COUT ESL and the output inductor (LOUT). The squarewave component due to the ESL can be estimated as:
VOUT(SQ )  VIN 
ESLCOUT
L1
(9)
A good practice to minimize this ripple is to use multiple
output capacitors to achieve the desired COUT value. For
example, to obtain COUT=20 F, a single 22 F 0805 would
produce twice the square wave ripple of two 10 F 0805.
Figure 28. Recommended Layout
Connect the VOUT pin and R1 directly to COUT using a low
impedance path (shown in red in Figure 28. Recommended
Layout). A >0.4 mm wide trace is recommended. Avoid
routing this trace directly beneath SW unless separated by
an internal GND plane.
To minimize ESL, try to use capacitors with the lowest ratio
of length to width. 0805 s have lower ESL than 1206 s. If
very low output ripple is necessary, research vendors that
produce 0508 or 0612 capacitors with ultra-low ESL. Placing
additional small value capacitors near the load also reduces
the high-frequency ripple components.
If the MODE function is not required, extend the ground
plane through the MODE pin to reduce the loop inductance
for the VIN bypass.
Input Capacitor
The 10 F ceramic input capacitor should be placed as close
as possible between the VIN pin and PGND 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 under-damped ringing that can occur between the
inductance of the power source leads and CIN.
Thermal Considerations
Heat is removed from the IC through the solder bumps to the
PCB copper. The junction-to-ambient thermal resistance
(JA) is largely a function of the PCB layout (size, copper
weight, and trace width) and the temperature rise from
junction to ambient (T).
The JA is 38°C/W when mounted on its four-layer evaluation
board in still air, with 2 oz. outer layer copper weight and
1 oz. inner layers. Halving the copper thickness results in an
increased JA of 48°C/W.
The effective CIN capacitance value decreases as VIN
increases due to DC bias effects. This has no significant
impact on regulator performance.
To reduce ringing and overshoot on VIN and SW, an
additional bypass capacitor CIN1 is recommended. Because
this lower value capacitor has a higher resonant frequency
than CIN; CIN1 should be placed closer to the VIN and GND
pins of the IC than CIN.
© 2013 Fairchild Semiconductor Corporation
FAN53541 • Rev. 1.0.2
For long term reliable operation, the IC’s junction
temperature (TJ) should be maintained below 125°C.
Maximum IC power loss is 2.88 W. Figure 29 shows required
power dissipation and derating for a FAN53541 mounted on
the Fairchild evaluation board in still air (38°C/W).
www.fairchildsemi.com
12
FAN53541 — 2.4 MHz, 5 A TinyBuck™ Synchronous Buck Regulator
Output Capacitor and VOUT Ripple
Maximum Power Dissipation (W)
3.0
2.88W, max.
2.5
2.0
1.5
1.0
0.5
E.
0
25
50
75
100
From Eq. (11), DCR<16.4 m
Due to the +0.4%/°C temperature coefficient of copper,
inductor DCR must be further reduced to accommodate the
~50°C temperature rise.
0.0
125
Ambient Temperature (C)
Figure 29. Power Derating
To meet the design requirements, an inductor with a room
temperature DCR of <13.6 mΩ is necessary.
To calculate maximum operating temperature (<125°C) for a
specific application:
Figure 30 shows the maximum ambient temperature where
FAN53541 can be used for a continuous load, at 5.0 VIN:
2.
Use efficiency graphs to determine efficiency for the
desired VIN, VOUT, and load condition
6
1.2 VOUT
Maximum RMS Load Current (A)
1.
Calculate IC power dissipation using:
1 
PIC  VOUT  ILOAD    1
 
(10)
where η is efficiency from Figure 4 through Figure 9.
3.
Compute inductor copper losses using:
2
PL  ILOAD  DCRL
4.
3
2
1
50
75
100
125
Ambient Temperature (C)
(12)
Figure 30. Load Current Derating(6)
Note:
6. The graph was empirically determined using an ultra-low
DCR (2.6 m) inductor. For physically smaller devices
with higher DCR, further derating may be necessary.
(13)
Device temperature (TIC) should not exceed 125°C.
© 2013 Fairchild Semiconductor Corporation
FAN53541 • Rev. 1.0.2
4
25
Determine device operating temperature:
T  PD  RJA and TIC  TAMB  T
3.3 VOUT
0
Combine IC (step 2) and inductor losses (step 3) to
determine total dissipation:
PD  PIC  PL
5.
(11)
1.8 VOUT
5
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13
FAN53541 — 2.4 MHz, 5 A TinyBuck™ Synchronous Buck Regulator
A different approach, shown here as an example, uses the
same equations to determine maximum inductor DCR for a
specific application:
Suppose a design requires a 5.0 VIN, 1.2 VOUT, 4 ARMS, at
75°C:
A. From Figure 4, η is ~82%.
B. From Eq. (10), PIC=1,054 mW.
C. From Eq. (13), maximum PD=1,316 mW for 50°C
rise.
D. From Eq. (12), PL=262 mW.
3.5
BALL A1
INDEX AREA
F
A
E
1.20
B
1.20
Ø0.20
A1
Cu Pad
0.03 C
2X
1.60
D
Ø0.215
Cu Pad
A1
0.40
Ø0.30 Solder
Mask Opening
Ø0.315 Solder
Mask Opening
0.40
0.03 C
0.40
option 1
2X
TOP VIEW
option 2
RECOMMENDED LAND PATTERN
(NSMD TYPE)
0.06 C
0.625
0.547
0.05 C
0.378±0.018
0.208±0.021
E
C
SEATING PLANE
SIDE VIEWS
D
NOTES:
0.005
1.20
A. NO JEDEC REGISTRATION APPLIES.
C A B
B. DIMENSIONS ARE IN MILLIMETERS.
Ø0.260±0.02
20X
0.40
E
D
C
B
A
1.60
0.40
C. DIMENSIONS AND TOLERANCE
PER ASMEY14.5M, 1994.
D. DATUM C IS DEFINED BY THE SPHERICAL
CROWNS OF THE BALLS.
(Y) ±0.018
E. PACKAGE NOMINAL HEIGHT IS 586 MICRONS
±39 MICRONS (547-625 MICRONS).
F
1 2 3 4
(X) ±0.018
F. FOR DIMENSIONS D, E, X, AND Y SEE
PRODUCT DATASHEET.
BOTTOM VIEW
G. DRAWING FILNAME: MKT-UC020AArev3.
Figure 31 20-Ball WLCSP, 4x5 Array, 0.4mm Pitch, 250 µm Ball
Product-Specific Dimensions
Product
D
E
X
Y
FAN53541UCX
1.96 +0.030
1.56 +0.030
0.180
0.180
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/dwg/UC/UC020AA.pdf.
© 2013 Fairchild Semiconductor Corporation
FAN53541 • Rev. 1.0.2
www.fairchildsemi.com
14
FAN53541 — 2.4 MHz, 5 A TinyBuck™ Synchronous Buck Regulator
Physical Dimensions
FAN53541 — 2.4 MHz, 5 A TinyBuck™ Synchronous Buck Regulator
© 2013 Fairchild Semiconductor Corporation
FAN53541 • Rev. 1.0.2
www.fairchildsemi.com
15