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May 2017
© 2013 Semiconductor Components Industries, LLC. www.fairchildsemi.com
FAN53541 • Rev. 1.1 www.onsemi.com
FAN53541 — 2.4MHz, 5A TinyBuck™ Synchronous Buck Regulator
FAN53541
2.4 MHz, 5 A TinyBuck™ Synchronous Buck Regulator
Features
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
Set-Top Box
Hard Disk Drive
Communications Cards
DSP Power
Description
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.
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).
FAN53541
SW
GND
COUT
L1
FB
VOUT
0.47HCOUT
VIN
CIN1
10nF
EN
MODE
10µF
10µF
R1
R2
PGOOD
CIN
10µF
Figure 1. Typical Application
Ordering Information
Part Number
Temperature Range
Package
FAN53541UCX
-40 to 85°C
20-Ball Wafer-Level, Chip-Scale Package (WLCSP),
4x5 Array, 0.4 mm Pitch, 250 µm Ball
© 2013 Semiconductor Components Industries, LLC. www.fairchildsemi.com
FAN53541 • Rev. 1.1 2 www.onsemi.com
FAN53541 — 2.4 MHz, 5 A TinyBuck™ Synchronous Buck Regulator
Recommended External Components
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
GRM21BR60J106M (Murata)
C2012X5R0J106M (TDK)
C
20
F
CIN
10 F, 6.3 V, X5R, 0805
C
10
F
CIN1
10 nF, 25 V, X7R, 0402
Any
C
10
nF
Table 2. Recommended Inductors
Component Dimensions
Manufacturer
Part#
L (nH)
DCR (mΩ)
IMAXDC(1)
L
W
H
Bourns
SRP5012-R47M
470
19
6.0
5.1
4.5
1.2
Bourns
SRP4012-R47M
470
20
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 Semiconductor Components Industries, LLC. www.fairchildsemi.com
FAN53541 • Rev. 1.1 3 www.onsemi.com
FAN53541 — 2.4 MHz, 5 A TinyBuck™ Synchronous Buck Regulator
Pin Configuration
Figure 2. Top View
Figure 3. Top View Bottom View
Pin Definitions
Bump #
Name
Description
A1
PGOOD
Power Good. This open-drain pin pulls LOW if the output falls out of regulation or is in soft-start.
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
Analog Ground. All signals are referenced to this pin. Avoid routing high dV/dt AC currents through
this pin.
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.
PGOOD
GND
C1
B1
A1 A2
C3
B3
A3
C2
D1 D3D2
B2
C4
B4
A4
D4
E1 E3E2 E4
EN FB VOUT
MODE
VIN SW
C1
B1
A1
C3
B3
A3 A2
C2
D1D3 D2
B2
C4
B4
A4
D4
E1E3 E2E4
© 2013 Semiconductor Components Industries, LLC. www.fairchildsemi.com
FAN53541 • Rev. 1.1 4 www.onsemi.com
FAN53541 — 2.4 MHz, 5 A TinyBuck™ 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
Parameter
Min.
Max.
Unit
VIN
SW, VIN Pins
-0.3
7.0(3)
V
Other Pins
Tied without Series Impedance
-0.3
4.5
Tied through Series Resistance ≥100
-0.3
VIN⁽4⁾
ESD
Electrostatic Discharge
Protection Level
Human Body Model per JESD22-A114
2250
V
Charged Device Model per JESD22-C101
1500
TJ
Junction Temperature
–40
+150
°C
TSTG
Storage Temperature
–65
+150
°C
TL
Lead Soldering Temperature, 10 Seconds
+260
°C
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. ON Semiconductor 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
L
Inductor
0.47
1.20
µH
CIN
Input Capacitor
10
µF
COUT
Output Capacitor
20
µF
TA
Operating Ambient Temperature
-40
+85
°C
TJ
Operating Junction Temperature
-40
+125
°C
Thermal Properties
Symbol
Parameter
Typical
Unit
JA
Junction-to-Ambient Thermal Resistance
38(5)
°C/W
Note:
5. See Thermal Considerations in the Applications section.
© 2013 Semiconductor Components Industries, LLC. www.fairchildsemi.com
FAN53541 • Rev. 1.1 5 www.onsemi.com
FAN53541 — 2.4 MHz, 5 A TinyBuck™ Synchronous Buck Regulator
Electrical Characteristics
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
ILOAD=0, MODE=0 (AUTO PFM/PWM)
15
50
200
µA
ILOAD=0, MODE=1 (Forced PWM)
8
30
100
mA
I SD
Shutdown Supply Current
EN=GND
0.1
10
µA
VUVLO
Under-Voltage Lockout Threshold
VIN Rising
2.67
2.80
V
VIN Falling
2.1
2.3
V
VUVHYST
Under-Voltage Lockout Hysteresis
365
mV
Logic Pins
VIH
High-Level Input Voltage
1.05
V
VIL
Low-Level Input Voltage
0.4
V
VLHYST
Logic Input Hysteresis Voltage
140
mV
IIN
Input Bias Current
Input Tied to GND or 1 kΩ Resistor to VIN
0.01
1.00
µA
IOUTL
PGOOD Pull-Down Current
VPGOOD=0.4 V
1
mA
IOUTH
PGOOD HIGH Leakage Current
VPGOOD=VIN
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
Load Regulation
MODE=VIN (Forced PWM)
–0.02
%/A
Line Regulation
2.7 V ≤ VIN ≤ 5.5 V, IOUT(DC)=1.5 A
-0.16
%/V
IREF
FB Pin Leakage Current
FB=0.8 V
1
nA
VOUT
Transient Response
ILOAD Step 0.1 A to 1.5 A, tR=100 ns
-30
mV
Power Switch and Protection
RDS(ON)P
P-Channel MOSFET On Resistance
33
mΩ
RDS(ON)N
N-Channel MOSFET On Resistance
28
mΩ
ILIMPK
P-MOS Peak Current Limit
Open Loop
5.8
7.5
8.8
A
Closed Loop
8
A
TLIMIT
Thermal Shutdown
155
°C
THYST
Thermal Shutdown Hysteresis
20
°C
VSDWN
Input OVP Shutdown
Rising Threshold
6.1
V
Falling Threshold
5.5
5.8
V
Frequency Control
fSW
Oscillator Frequency
2.1
2.4
3.0
MHz
fMODE
MODE Pin Synchronization Range
External Square-Wave, 30% to 70% Duty
Cycle
525
600
700
kHz
Soft-Start and Output Discharge
tSS
Regulator Enable to Regulated VOUT
(Rising PGOOD)
1.2
ms
RDIS
Output Discharge Resistance
EN=0 V
175
Ω
LOAD
OUT
I
V
IN
OUT
V
V
© 2013 Semiconductor Components Industries, LLC. www.fairchildsemi.com
FAN53541 • Rev. 1.1 6 www.onsemi.com
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 4. Efficiency vs. ILOAD, 1.2 VOUT
Figure 5. Efficiency vs. ILOAD, 1.2 VOUT
Figure 6. Efficiency vs. ILOAD, 1.8 VOUT
Figure 7. Efficiency vs. ILOAD, 1.8 VOUT
Figure 8. Efficiency vs. ILOAD, 3.3 VOUT
Figure 9. Efficiency vs. ILOAD, 3.3 VOUT
70%
75%
80%
85%
90%
95%
01000 2000 3000 4000 5000
Efficiency
Load Current (mA)
2.7 VIN
3.3 VIN
5.0 VIN
5.5 VIN
70%
75%
80%
85%
90%
95%
01000 2000 3000 4000 5000
Efficiency
Load Current (mA)
-40C
+25C
+85C
70%
75%
80%
85%
90%
95%
01000 2000 3000 4000 5000
Efficiency
Load Current (mA)
2.7 VIN
3.3 VIN
5.0 VIN
5.5 VIN
70%
75%
80%
85%
90%
95%
01000 2000 3000 4000 5000
Efficiency
Load Current (mA)
-40C
+25C
+85C
75%
80%
85%
90%
95%
100%
01000 2000 3000 4000 5000
Efficiency
Load Current (mA)
4.2 VIN
5.0 VIN
5.5 VIN
75%
80%
85%
90%
95%
100%
01000 2000 3000 4000 5000
Efficiency
Load Current (mA)
-40C
+25C
+85C
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FAN53541 • Rev. 1.1 7 www.onsemi.com
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 10. Regulation, 1.2 VOUT
Figure 11. Regulation, 3.3 VOUT
Figure 12. PFM / PWM Boundaries, 1.2 VOUT
Figure 13. PFM / PWM Boundaries, 3.3 VOUT
Figure 14. Output Voltage Ripple
Figure 15. Switching Frequency
-5
0
5
10
15
20
25
30
35
01000 2000 3000 4000 5000
VOUT Shift (mV)
Load Current (mA)
2.7 VIN
3.3 VIN
5.0 VIN
5.5 VIN
-5
0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
01000 2000 3000 4000 5000
VOUT Shift (mV)
Load Current (mA)
4.2 VIN
5.0 VIN
5.5 VIN
0
200
400
600
800
1,000
1,200
1,400
2.5 3.0 3.5 4.0 4.5 5.0 5.5
Load Current (mA)
Input Voltage (V)
PFM Exit
PFM Enter
0
200
400
600
800
1,000
1,200
1,400
3.5 4.0 4.5 5.0 5.5
Load Current (mA)
Input Voltage (V)
PFM Exit
PFM Enter
0
5
10
15
20
25
30
01000 2000 3000 4000 5000
Output Ripple (mVpp)
Load Current (mA)
3.6VIN, Auto
3.6VIN, PWM
5.0VIN, Auto
5.0VIN, PWM
0
500
1,000
1,500
2,000
2,500
3,000
01000 2000 3000 4000 5000
Switching Frequency (KHz)
Load Current (mA)
3.6VIN, Auto
5.0VIN, Auto
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FAN53541 • Rev. 1.1 8 www.onsemi.com
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 16. Quiescent Current, Auto Mode, EN=VIN
Figure 17. Quiescent Current, PMW Mode, EN=VIN
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
10
20
30
40
50
60
2.5 3.0 3.5 4.0 4.5 5.0 5.5
Input Current (A)
Input Voltage (V)
-40C
+25C
+85C
0
10
20
30
40
50
2.5 3.0 3.5 4.0 4.5 5.0 5.5
Input Current (mA)
Input Voltage (V)
-40C
+25C
+85C
10
20
30
40
50
60
70
10 100 1,000 10,000 100,000
PSRR (dB)
Frequency (Hz)
1.2VOUT,
25mA Load
1.2VOUT,
1.0A Load
3.3VOUT,
1.0A Load
70%
75%
80%
85%
90%
95%
100%
01000 2000 3000 4000 5000
Efficiency
Load Current (mA)
1.2 VOUT, L=SC2511
1.2 VOUT, L=IHLP16
1.8 VOUT, L=SC2511
1.8 VOUT, L=IHLP16
3.3 VOUT, L=SC2511
3.3 VOUT, L=IHLP16
© 2013 Semiconductor Components Industries, LLC. www.fairchildsemi.com
FAN53541 • Rev. 1.1 9 www.onsemi.com
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 Semiconductor Components Industries, LLC. www.fairchildsemi.com
FAN53541 • Rev. 1.1 10 www.onsemi.com
FAN53541 — 2.4 MHz, 5 A TinyBuck™ Synchronous Buck Regulator
Operation Description
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.
Control Scheme
The FAN53541 uses a proprietary non-linear, fixed-
frequency PWM modulator to deliver very fast load transient
response, while maintaining a constant switching frequency
over a wide range of operating conditions.
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.
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.
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.
Setting Output Voltage
The output voltage is set by the R1, R2, and VREF (0.8 V):
(1)
R1 must be set at or below 100 KΩ; therefore:
(2)
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.
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
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:
(3)
where COUTMAX is expressed in F and ILOAD is
the load current during soft-start, expressed in A.
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.
When EN is LOW, a 150 resistor discharges VOUT.
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)
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
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.
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.
External Frequency Synchronization
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).
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.
REF
REFOUT
VVV
2R1R
8.0V 8.01R
2R OUT
OUT
LOAD
OUT
V
800
I
8
.
5
C
MAX
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FAN53541 • Rev. 1.1 11 www.onsemi.com
FAN53541 — 2.4 MHz, 5 A TinyBuck™ Synchronous Buck Regulator
PGOOD Pin
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
The IC is performing a soft-start.
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.
Minimum Off-Time Effect on Switching
Frequency
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.
Switching frequency is the lower of 2.4 MHz or:
(4)
where:
IOUT = load current, in A;
RON = RDS(ON)_P + DCRL, in Ohms; and
ROFF = RDS(ON)_N + DCRL, in Ohms.
A result of <0 MHz indicates 100% duty cycle operation.
Application 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, output
voltage ripple, transient response, and efficiency.
The ripple current (∆I) of the regulator is:
(5)
The maximum average load current, IMAX(LOAD), is related to
the peak current limit, ILIM(PK), by the ripple current as:
(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.
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.
(7)
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 on regulator performance of higher
inductance than the recommended 470 nH.
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.
)RR(IV RIV
1 2.22)MHz(f ONOFFOUTIN
OFFOUTOUT
SW
SW
OUTIN
IN
OUT fL VV
V
V
I
2I
II )PK(LIM)LOAD(MAX
12
I
I I 2
2
)DC(OUTRMS
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FAN53541 • Rev. 1.1 12 www.onsemi.com
FAN53541 — 2.4 MHz, 5 A TinyBuck™ Synchronous Buck Regulator
Output Capacitor and VOUT Ripple
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.
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:
(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 square-
wave component of output ripple that results from the division
ratio COUT ESL and the output inductor (LOUT). The square-
wave component due to the ESL can be estimated as:
(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.
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.
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.
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.
Layout Recommendations
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.
Switching current paths through CIN 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.
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.
If the MODE function is not required, extend the ground
plane through the MODE pin to reduce the loop inductance
for the VIN bypass.
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.
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 ON Semiconductor evaluation board in still air (38°C/W).
ESR
fC8 1
IV SWOUT
OUT
1L
ESL
VV COUT
IN)SQ(OUT
© 2013 Semiconductor Components Industries, LLC. www.fairchildsemi.com
FAN53541 • Rev. 1.1 13 www.onsemi.com
FAN53541 — 2.4 MHz, 5 A TinyBuck™ Synchronous Buck Regulator
Figure 29. Power Derating
To calculate maximum operating temperature (<125°C) for a
specific application:
1. Use efficiency graphs to determine efficiency for the
desired VIN, VOUT, and load condition
2. Calculate IC power dissipation using:
(10)
where η is efficiency from Figure 4 through Figure 9.
3. Compute inductor copper losses using:
(11)
4. Combine IC (step 2) and inductor losses (step 3) to
determine total dissipation:
(12)
5. Determine device operating temperature:
and
(13)
Device temperature (TIC) should not exceed 125°C.
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.
E. 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.
To meet the design requirements, an inductor with a room
temperature DCR of <13.6 mΩ is necessary.
Figure 30 shows the maximum ambient temperature where
FAN53541 can be used for a continuous load, at 5.0 VIN:
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.
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
025 50 75 100 125
Maximum Power Dissipation (W)
Ambient Temperature (C)
2.88W, max.
1
1
IVP LOADOUTIC
L
2
LOADL DCRIP
LICDPPP
JADRPT
TTT AMBIC
0
1
2
3
4
5
6
25 50 75 100 125
Maximum RMS Load Current (A)
Ambient Temperature (C)
1.2 VOUT
1.8 VOUT
3.3 VOUT
© 2013 Semiconductor Components Industries, LLC. www.fairchildsemi.com
FAN53541 • Rev. 1.1 14 www.onsemi.com
FAN53541 — 2.4 MHz, 5 A TinyBuck™ Synchronous Buck Regulator
Physical Dimensions
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 ON Semiconductor components. Drawings may change in any manner
without notice. Please note the revision and/or date on the drawing and contact a ON Semiconductor representative to verify or obtain the
most recent revision. Package specifications do not expand the terms of ON Semiconductor’s worldwide terms and conditions, specifically the
warranty therein, which covers ON Semiconductor products.
BOTTOM VIEW
SIDE VIEWS
TOP VIEW
BALL A1
INDEX AREA
1234
A
B
C
D
E
SEATING PLANE
20X
A1
C
0.005 C A B
F
Ø0.260±0.02
E
D
B
A
0.625
0.547
0.06 C
0.05 CE
D
F
0.378±0.018
0.208±0.021
NOTES:
A. NO JEDEC REGISTRATION APPLIES.
B. DIMENSIONS ARE IN MILLIMETERS.
C. DIMENSIONS AND TOLERANCE
PER ASMEY14.5M, 1994.
D. DATUM C IS DEFINED BY THE SPHERICAL
CROWNS OF THE BALLS.
E. PACKAGE NOMINAL HEIGHT IS 586 MICRONS
±39 MICRONS (547-625 MICRONS).
F. FOR DIMENSIONS D, E, X, AND Y SEE
PRODUCT DATASHEET.
G. DRAWING FILNAME: MKT-UC020AArev3.
0.03 C
2X
0.03 C
2X
0.40 1.20
0.40
1.60 (Y) ±0.018
(X) ±0.018
RECOMMENDED LAND PATTERN
(NSMD TYPE)
Ø0.215
Cu Pad
Ø0.315 Solder
Mask Opening
0.40
1.20
0.40
1.60
A1
Ø0.20
Cu Pad
Ø0.30 Solder
Mask Opening
0.40
1.20
option 1 option 2
© 2013 Semiconductor Components Industries, LLC. www.fairchildsemi.com
FAN53541 • Rev. 1.1 15 www.onsemi.com
FAN53541 — 2.4 MHz, 5 A TinyBuck™ Synchronous Buck Regulator
ON Semiconductor and the ON Semiconductor logo are trademarks of Semiconductor Components Industries, LLC dba ON Semiconductor or its subsidiaries in the United States
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Semiconductor’s product/patent coverage may be accessed at www.onsemi.com/site/pdf/Patent-Marking.pdf. ON Semiconductor reserves the right to make changes without further
notice to any products herein. ON Semiconductor makes no warranty, representation or guarantee regarding the suitability of its products for any particular purpose, nor does ON
Semiconductor assume any liability arising out of the application or use of any product or circuit, and specifically disclaims any and all liability, including without limitation special,
consequential or incidental damages. Buyer is responsible for its products and applications using ON Semiconductor products, including compliance with all laws, regulations and
safety requirements or standards, regardless of any support or applications information provided by
ON Semiconductor. “Typical” parameters which may be provided in ON Semiconductor data sheets and/or specifications can and do vary in different applications and actual
performance may vary over time. All operating parameters, including “Typicals” must be validated for each customer application by customer’s technical experts. ON Semiconductor
does not convey any license under its patent rights nor the rights of others. ON Semiconductor products are not designed, intended, or authorized for use as a critical component in life
support systems or any FDA Class 3 medical devices or medical devices with a same or similar classification in a foreign jurisdiction or any devices intended for implantation in the
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indirectly, any claim of personal injury or death associated with such unintended or unauthorized use, even if such claim alleges that ON Semiconductor was negligent regarding the
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1
ON Semiconductor and are trademarks of Semiconductor Components Industries, LLC dba ON Semiconductor or its subsidiaries in the United States and/or other countries.
ON Semiconductor owns the rights to a number of patents, trademarks, copyrights, trade secrets, and other intellectual property. A listing of ON Semiconductor’s product/patent
coverage may be accessed at www.onsemi.com/site/pdf/Patent−Marking.pdf. ON Semiconductor reserves the right to make changes without further notice to any products herein.
ON Semiconductor makes no warranty, representation or guarantee regarding the suitability of its products for any particular purpose, nor does ON Semiconductor assume any liability
arising out of the application or use of any product or circuit, and specifically disclaims any and all liability, including without limitation special, consequential or incidental damages.
Buyer is responsible for its products and applications using ON Semiconductor products, including compliance with all laws, regulations and safety requirements or standards,
regardless of any support or applications information provided by ON Semiconductor. “Typical” parameters which may be provided in ON Semiconductor data sheets and/or
specifications can and do vary in different applications and actual performance may vary over time. All operating parameters, including “Typicals” must be validated for each customer
application by customer’s technical experts. ON Semiconductor does not convey any license under its patent rights nor the rights of others. ON Semiconductor products are not
designed, intended, or authorized for use as a critical component in life support systems or any FDA Class 3 medical devices or medical devices with a same or similar classification
in a foreign jurisdiction or any devices intended for implantation in the human body. Should Buyer purchase or use ON Semiconductor products for any such unintended or unauthorized
application, Buyer shall indemnify and hold ON Semiconductor and its officers, employees, subsidiaries, affiliates, and distributors harmless against all claims, costs, damages, and
expenses, and reasonable attorney fees arising out of, directly or indirectly, any claim of personal injury or death associated with such unintended or unauthorized use, even if such
claim alleges that ON Semiconductor was negligent regarding the design or manufacture of the part. ON Semiconductor is an Equal Opportunity/Affirmative Action Employer. This
literature is subject to all applicable copyright laws and is not for resale in any manner.
PUBLICATION ORDERING INFORMATION
N. American Technical Support: 800−282−9855 Toll Free
USA/Canada
Europe, Middle East and Africa Technical Support:
Phone: 421 33 790 2910
Japan Customer Focus Center
Phone: 81−3−5817−1050
www.onsemi.com
LITERATURE FULFILLMENT:
Literature Distribution Center for ON Semiconductor
19521 E. 32nd Pkwy, Aurora, Colorado 80011 USA
Phone: 303−675−2175 or 800−344−3860 Toll Free USA/Canada
Fax: 303−675−2176 or 800−344−3867 Toll Free USA/Canada
Email: orderlit@onsemi.com
ON Semiconductor Website: www.onsemi.com
Order Literature: http://www.onsemi.com/orderlit
For additional information, please contact your local
Sales Representative
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