September 2008
© 2008 Fairchild Semiconductor Corporation www.fairchildsemi.com
FAN5361 • Rev. 1.0.0
FAN5361 — 6MHz, 600mA TinyBuck™ Synchronous Buck Regulator
FAN5361
6MHz, 600mA TinyBuck™ Synchronous Buck Regulator
Features
6MHz Fixed-Frequency Operation
35µA Typical Quiescent Current
Best-in-Class Load Transient
600mA Output Current Capability
2.3V to 5.5V Input Voltage Range
1.0 to 1.82V Fixed Output Voltage
Low Ripple Light-Load PFM Mode
Forced PWM and External Clock Synchronization
Internal Soft-Start
Input Under-Voltage Lockout (UVLO)
Thermal Shutdown and Overload Protection
6-bump WLCSP, 0.4mm Pitch
6-pin 2 x 2mm UMLP
Applications
Cell Phones
Portable Media Players
WLAN, 3G, and 4G Data Cards
Description
The FAN5361 is a 600mA, step-down, switching voltage
regulator that delivers a fixed output from an input voltage
supply of 2.3V to 5.5V. Using a proprietary architecture with
synchronous rectification, the FAN5361 is capable of
delivering a peak efficiency of 92%, while maintaining
efficiency over 80% at load currents as low as 1mA.
The regulator operates at a nominal fixed frequency of 6MHz,
which reduces the value of the external components to 470nH
for the output inductor and 4.7µF for the output capacitor. The
PWM modulator can be synchronized to an external frequency
source.
At moderate and light loads, pulse frequency modulation is
used to operate the device in power-save mode with a typical
quiescent current of 35µA. 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 6MHz. In
shutdown mode, the supply current drops below 1µA,
reducing power consumption. For applications that require
minimum ripple or fixed frequency, PFM mode can be
disabled using the MODE pin.
The FAN5361 is available in 6-bump, 0.4mm pitch, Wafer-
Level Chip-Scale Package (WLCSP) and a 6-lead 2 x 2mm
ultra-thin MLP package.
Typical Applications
SW
MODE
GND
EN
L1 CIN
2.2 F
470nH
C2
B2
A2
C1
B1
A1
FB
4.7 FCOUT
VIN
Figure 1. Typical Applications
© 2008 Fairchild Semiconductor Corporation www.fairchildsemi.com
FAN5361 • Rev. 1.0.0 2
FAN5361 — 6MHz, 600mA TinyBuck™ Synchronous Buck Regulator
Ordering Information
Part Number Output
Voltage(1) Package Eco Status Temperature Range Packing
FAN5361UC10X(2) 1.0V
FAN5361UC12X 1.2V
FAN5361UC13X(2) 1.3V
FAN5361UC15X(2) 1.5V
FAN5361UC18X(2) 1.8V
FAN5361UC182X 1.82V
WLCSP-6 0.4mm Pitch Green –40 to +85°C Tape and Reel
FAN5361UMP10X(2) 1.0V
FAN5361UMP12X(2) 1.2V
FAN5361UMP13X(2) 1.3V
FAN5361UMP15X(2) 1.5V
FAN5361UMP18X(2) 1.8V
6 Lead UMLP 2 x 2mm RoHS –40 to +85°C Tape and Reel
For Fairchild’s definition of “green” Eco Status, please visit: http://www.fairchildsemi.com/company/green/rohs_green.html.
Notes:
1. Other voltage options available on request. Contact a Fairchild representative.
2. Preliminary release.
Pin Configuration
C2
B2
A2
C1
B1
A1MODE
SW
FB
VIN
EN
GND
Figure 2. WLCSP, Bumps Facing Down
C1
B1
A1
C2
B2
A2 MODE
SW
FB
VIN
EN
GND
Figure 3. WLCSP, Bumps Facing Up
Figure 4. UMLP, Leads Facing Down
Pin Definitions
Pin #
WLCSP MLP Name Description
A1 3 MODE
MODE. Logic 1 on this pin forces the IC to stay in PWM mode. A logic 0 allows the IC to automatically
switch to PFM during light loads. The regulator also synchronizes its switching frequency to four times
the frequency provided on this pin. Do not leave this pin floating.
B1 2 SW
Switching Node. Connect to output inductor.
C1 1 FB
Feedback / VOUT. Connect to output voltage.
C2 6 GND
Ground. Power and IC ground. All signals are referenced to this pin.
B2 5 EN
Enable. The device is in shutdown mode when voltage to this pin is <0.4V and enabled when >1.2V.
Do not leave this pin floating.
A2 4 VIN
Input Voltage. Connect to input power source.
© 2008 Fairchild Semiconductor Corporation www.fairchildsemi.com
FAN5361 • Rev. 1.0.0 3
FAN5361 — 6MHz, 600mA 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. Units
VIN Input Voltage –0.3 7.0 V
VSW Voltage on SW Pin –0.3 VIN + 0.3(3) V
VCTRL EN and MODE Pin Voltage –0.3 VIN + 0.3(3) V
Other Pins –0.3 VIN + 0.3(3) V
Human Body Model per JESD22-A114 4 kV
ESD Electrostatic Discharge
Protection Level Charged Device Model per JESD22-C101 1.5 kV
TJ Junction Temperature –40 +150 °C
TSTG Storage Temperature –65 +150 °C
TL Lead Soldering Temperature, 10 Seconds +260 °C
Note:
3. Lesser of 7V or VIN+0.3V.
Recommended Operating Conditions
The Recommended Operating Conditions table defines the conditions for actual device operation. Recommended operating
conditions are specified to ensure optimal performance to the datasheet specifications. Fairchild does not recommend exceeding
them or designing to Absolute Maximum Ratings.
Symbol Parameter Min. Typ. Max. Units
VCC Supply Voltage Range 2.3 5.5 V
IOUT Output Current 0 600 mA
L Inductor 0.47 µH
CIN Input Capacitor 2.2 µF
COUT Output Capacitor 4.7 µF
TA Operating Ambient Temperature –40 +85 °C
TJ Operating Junction Temperature –40 +125 °C
Thermal Properties
Junction-to-ambient thermal resistance is a function of application and board layout. This data is measured with four-layer 1s2p
boards in accordance to JEDEC standard JESD51. Special attention must be paid not to exceed junction temperature TJ(max) at a
given ambient temperate TA.
Symbol Parameter Typical Units
WLCSP 150 °C/W
θJA Junction-to-Ambient Thermal Resistance MLP 49 °C/W
© 2008 Fairchild Semiconductor Corporation www.fairchildsemi.com
FAN5361 • Rev. 1.0.0 4
FAN5361 — 6MHz, 600mA TinyBuck™ Synchronous Buck Regulator
Electrical Characteristics
Minimum and maximum values are at VIN = VEN = 2.3V to 5.5V, AUTO Mode, TA = -40°C to +85°C; circuit of Figure 1, unless
otherwise noted. Typical values are at TA = 25°C, VIN = VEN = 3.6V.
Symbol Parameter Conditions Min. Typ. Max. Units
Power Supplies
No load, Not Switching 35 55 µA
IQ Quiescent Current PWM Mode 6 mA
I(SD) Shutdown Supply Current VIN = 3.6V, EN = GND 0.05 1.00 µA
VUVLO Under-Voltage Lockout Threshold Rising VIN 2.15 2.25 V
VUVHYST Under-Voltage Lockout hysteresis 150 mV
V(ENH) Enable HIGH-Level Input Voltage 1.2 V
V(ENL) Enable LOW-Level Input Voltage 0.4 V
I(EN) Enable Input Leakage Current EN to VIN or GND 0.01 1.00 µA
V(MH) MODE HIGH-Level Input Voltage 1.2 V
V(ML) MODE LOW-Level Input Voltage 0.4 V
I(M) MODE Input Leakage Current MODE to VIN or GND 0.01 1.00 µA
Switching and Synchronization
fSW Switching Frequency VIN = 3.6V, TA = 25°C 5.4 6.0 6.6 MHz
fSYNC MODE Synchronization Range(4) Squarewave at MODE Input 1.3 1.5 1.7 MHz
Regulation
ILOAD = 0 to 600mA 1.784 1.820 1.875 V
1.82V PWM Mode 1.784 1.820 1.856 V
ILOAD = 0 to 600mA 1.764 1.800 1.854 V
1.80V PWM Mode 1.764 1.800 1.836 V
ILOAD = 0 to 600mA 1.470 1.500 1.545 V
1.50V PWM Mode 1.470 1.500 1.530 V
ILOAD = 0 to 600mA 1.274 1.300 1.339 V
1.30V PWM Mode 1.274 1.300 1.326 V
ILOAD = 0 to 600mA 1.174 1.200 1.239 V
1.20V PWM Mode 1.174 1.200 1.226 V
ILOAD = 0 to 600mA 0.974 1.000 1.039 V
VO Output Voltage
Accuracy
1.00V PWM Mode 0.974 1.000 1.026 V
tSS Soft-Start From EN Rising Edge 150 300 µs
Output Driver
PMOS On Resistance VIN = VGS = 3.6V 350 mΩ
RDS(on) NMOS On Resistance VIN = VGS = 3.6V 225 mΩ
ILIM PMOS Peak Current Limit Open-Loop 900 1000 1250 mA
TTSD Thermal Shutdown CCM Only 150 °C
THYS Thermal Shutdown Hysteresis 15 °C
Notes:
4. Limited by the effect of tOFF minimum (see Figure 13 in Typical Performance Characteristics).
© 2008 Fairchild Semiconductor Corporation www.fairchildsemi.com
FAN5361 • Rev. 1.0.0 5
FAN5361 — 6MHz, 600mA TinyBuck™ Synchronous Buck Regulator
Typical Performance Characteristics
Unless otherwise noted, VIN = VEN = 3.6V, VMODE = 0V, VOUT = 1.82V, TA = 25°C.
50%
55%
60%
65%
70%
75%
80%
85%
90%
95%
100%
1 10 100 1000
I
LOAD
Output Current (mA)
Efficiency
Auto 2.3VIN
Auto 2.7VIN
Auto 3.6VIN
Auto 4.2VIN
50%
55%
60%
65%
70%
75%
80%
85%
90%
95%
100%
1 10 100 1000
I
LOAD
Output Current (mA)
Efficiency
25C
85C
-30C
Figure 5. Efficiency vs. Load Current vs. Input Supply
Figure 6. Efficiency vs. Load Current vs. Temperature
50%
55%
60%
65%
70%
75%
80%
85%
90%
95%
100%
1 10 100 1000
I
LOAD
Output Current (mA)
Efficiency
VIN=2.3V
VIN=2.7V
VIN=3.6V
VIN=4.2V
V
OUT
= 1.2 V
50%
55%
60%
65%
70%
75%
80%
85%
90%
95%
100%
1 10 100 1000
I
LOAD
Output Current (mA)
Efficiency
Auto PFM/PWM
Forced PWM
Figure 7. Efficiency vs. Load Current vs. Input Supply
Figure 8. Efficiency, Auto PWM/PFM vs. Forced PWM
1.78
1.79
1.80
1.81
1.82
0 100 200 300 400 500 600
Load Current (mA)
Output Voltage (V)
VIN=2.3V
VIN=2.7V
VIN=3.6V
VIN=4.2V
1.190
1.195
1.200
1.205
1.210
1.215
0.0 0.1 0.2 0.3 0.4 0.5 0.6
I
LOAD
Output Current (A)
V
OUT
(V)
VIN=2.3V
VIN=2.7V
VIN=3.6V
VIN=4.2V
Figure 9. Load Regulation vs. Input Supply
Figure 10. 1.2V
OUT
Load Regulation vs. Input Supply
© 2008 Fairchild Semiconductor Corporation www.fairchildsemi.com
FAN5361 • Rev. 1.0.0 6
FAN5361 — 6MHz, 600mA TinyBuck™ Synchronous Buck Regulator
Typical Performance Characteristics (Continued)
Unless otherwise noted, VIN = VEN = 3.6V, VMODE = 0V, VOUT = 1.82V, TA = 25°C.
5
10
15
20
25
30
35
40
45
50
0 0.1 0.2 0.3 0.4 0.5 0.6
V
OUT
Ripple (mVpp)
VIN=2.5V
VIN=3.6V
VIN=5.5V
I
LOAD
Output Current (A)
C
OUT
=4.7μF nom.
0
5
10
15
20
25
30
35
40
45
0 0.1 0.2 0.3 0.4 0.5 0.6
I
LOAD
Output Current (A)
V
OUT
Ripple (mVpp)
2.5VIN
3.6VIN
5.5VIN
V
OUT
=1.2V
C
OUT
=4.7µF nom.
Figure 11. Peak-to-Peak Output Voltage Ripple
Figure 12. 1.2V
OUT
Peak-to-Peak Output Voltage Ripple
0
1
2
3
4
5
6
7
0 0.10.20.30.40.50.6
Load Current (A)
Switching Frequency (MHz)
VIN>2.4V
VIN=2.3V
V
OUT
=1.2V
Figure 13. Effect of t
OFF(MIN)
on Switching Frequency Figure 14. 1.2V
OUT
Effect of t
OFF(MIN)
on
Switching Frequency
0
50
100
150
200
250
300
350
2.53.03.54.04.55.05.5
Input Voltage (V)
Load Current (mA)
PFM Border
PWM Borde
The switching mode changes
at these borders
Always PFM
Always PWM
0
50
100
150
200
250
300
350
2.5 3.0 3.5 4.0 4.5 5.0 5.5
Input Voltage (V)
Load Current (mA)
PFM border
PWM border
The switching mode changes
at these borders
Always PWM
Always PFM
Figure 15. PFM / PWM Boundaries
Figure 16. 1.2V
OUT
PFM / PWM Boundaries
© 2008 Fairchild Semiconductor Corporation www.fairchildsemi.com
FAN5361 • Rev. 1.0.0 7
FAN5361 — 6MHz, 600mA TinyBuck™ Synchronous Buck Regulator
Typical Performance Characteristics (Continued)
Unless otherwise noted, VIN = VEN = 3.6V, VMODE = 0V, VOUT = 1.82V, TA = 25°C.
30
32
34
36
38
40
42
2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5
V
IN
Input Voltage (V)
Quiescent Current (μA)
VEN=VIN
VEN=1.8V
1.785
1.790
1.795
1.800
1.805
1.810
1 10 100 1,000
I
LOAD
Output Current (mA)
V
OUT
(V)
Auto PWM/PFM
Forced PWM
Figure 17. Quiescent Curent vs. Input Voltage
Figure 18. Load Regulation, Auto PFM / PWM and
Forced PWM
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
0.18
0.20
-40-20 0 20406080
Ambient Temperature (°C)
Supply Current (µA)
V
IN
=5.5V
V
EN
=0V
Figure 19. Shutdown Current vs. Temperature
© 2008 Fairchild Semiconductor Corporation www.fairchildsemi.com
FAN5361 • Rev. 1.0.0 8
FAN5361 — 6MHz, 600mA TinyBuck™ Synchronous Buck Regulator
Typical Performance Characteristics (Continued)
Unless otherwise noted, VIN = VEN = 3.6V, VMODE = 0V, VOUT = 1.82V, TA = 25°C, 5µs/div. horizontal sweep.
Figure 20. Line Transient 3.3V
IN
to 3.9V
IN
,
50mA Load, 10µs/div.
Figure 21. Line Transient 3.3V
IN
to 3.9V
IN
,
250mA Load, 10µs/div.
Figure 22. Combined Line/Load Transient 3.3 to
3.9V
IN
Combined with 400mA to 40mA Load Transient
Figure 23. Combined Line/Load Transient 3.9 to 3.3V
IN
Combined with 400mA to 40mA Load Transient
Figure 24. Load Transient 0 to 150mA, 2.5V
IN
Figure 25. Load Transient 50 to 250mA, 2.5V
IN
© 2008 Fairchild Semiconductor Corporation www.fairchildsemi.com
FAN5361 • Rev. 1.0.0 9
FAN5361 — 6MHz, 600mA TinyBuck™ Synchronous Buck Regulator
Typical Performance Characteristics (Continued)
Unless otherwise noted, VIN = VEN = 3.6V, VMODE = 0V, VOUT = 1.82V, TA = 25°C, 5µs/div. horizontal sweep.
Figure 26. Load Transient 150 to 400mA, 2.5V
IN
Figure 27. Load Transient 0 to 150mA, 3.6V
IN
Figure 28. Load Transient 50 to 250mA, 3.6V
IN
Figure 29. Load Transient 150 to 400mA, 3.6V
IN
Figure 30. Load Transient 0 to 150mA, 4.5V
IN
Figure 31. Load Transient 50 to 250mA, 4.5V
IN
Figure 32. Load Transient 150 to 400mA, 4.5VIN
© 2008 Fairchild Semiconductor Corporation www.fairchildsemi.com
FAN5361 • Rev. 1.0.0 10
FAN5361 — 6MHz, 600mA TinyBuck™ Synchronous Buck Regulator
Typical Performance Characteristics (Continued)
Unless otherwise noted, VIN = VEN = 3.6V, VMODE = 0V, VOUT = 1.82V, TA = 25°C, 5µs/div. horizontal sweep.
Figure 33. Metallic Short Applied at V
OUT
, 20μs/div.
Figure 34. Metallic Short Applied at V
OUT
Figure 35. Over-Current Fault Response,
R
LOAD
= 1Ω, 20μs/div.
Figure 36. Over-Current Fault Response, R
LOAD
= 1Ω
Figure 37. 1.2V
OUT
Overload Recovery to Light Load
© 2008 Fairchild Semiconductor Corporation www.fairchildsemi.com
FAN5361 • Rev. 1.0.0 11
FAN5361 — 6MHz, 600mA TinyBuck™ Synchronous Buck Regulator
Typical Performance Characteristics (Continued)
Unless otherwise noted, VIN = VEN = 3.6V, VMODE = 0V, VOUT = 1.82V, TA = 25°C.
Figure 38. Soft-Start, R
LOAD
= 50Ω, 20μs/div.
Figure 39. SW-Node Jitter (Infinite Persistence),
I
LOAD
= 200mA, 50ns/div.
Figure 40. Power Supply Rejection Ratio at 300mA Load
© 2008 Fairchild Semiconductor Corporation www.fairchildsemi.com
FAN5361 • Rev. 1.0.0 12
FAN5361 — 6MHz, 600mA TinyBuck™ Synchronous Buck Regulator
Operation Description
The FAN5361 is a 600mA, step-down, switching voltage
regulator that delivers a fixed output from an input voltage
supply of 2.3V to 5.5V. Using a proprietary architecture with
synchronous rectification, the FAN5361 is capable of
delivering a peak efficiency of 92%, while maintaining
efficiency over 80% at load currents as low as 1mA. The
regulator operates at a nominal frequency of 6MHz at full load,
which reduces the value of the external components to 470nH
for the inductor and 4.7µF for the output capacitor.
Control Scheme
The FAN5361 uses a proprietary, non-linear, fixed-frequency
PWM modulator to deliver a fast load transient response,
while maintaining a constant switching frequency over a wide
range of operating conditions. The 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 FAN5361 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 18mV at VOUT during the transition between DCM
and CCM modes.
Combined with exceptional transient response characteristics,
the very low quiescent current of the controller (35µA)
maintains high efficiency; even at very light loads, while
preserving fast transient response for applications requiring
tight output regulation.
Enable and Soft-Start
Maintaining the EN pin LOW keeps the FAN5361 in non-
switching mode, in which all circuits are off and the part draws
~50nA of current. Increasing EN above its threshold voltage
activates the part and starts the soft-start cycle. The output
ramp during soft-start is a fixed slew rate of 50mV/μs from 0 to
1VOUT, then 25mV/μs for 1.82VOUT or 12mV/µs for 1.2VOUT
until the output reaches its setpoint.
MODE pin
Logic 1 on this pin forces the IC to stay in PWM mode. A 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 must be held LOW for at least
10μs or HIGH for 10μs to ensure that the converter does not
attempt to synchronize to this pin.
Current Limit, Fault Shutdown, and Restart
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. The regulator continues to limit the current
cycle-by-cycle. After 21µs of current limit, the regulator
triggers an over-current fault, causing the regulator to shut
down for about 86μs before attempting a restart.
If the fault was caused by short circuit, the soft-start circuit
attempts to restart at 33% of normal current limit and produces
an over-current fault after about 21μs, which results in a duty
cycle of less than 25% providing current into a short.
Under-Voltage Lockout (UVLO)
When EN is high, the under-voltage lock-out keeps the part
from operating until the input supply voltage rises high enough
to properly operate. This ensures no misbehavior of the
regulator during start-up or shutdown.
Thermal Shutdown (TSD)
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 150°C with a 15°C
hysteresis.
Minimum Off-Time Effect on Switching
Frequency
tOFF(MIN) is 50ns. This imposes constraints on the maximum
IN
OUT
V
V that the FAN5361 can provide, while maintaining a
fixed switching frequency in PWM mode.
7.01 )( ≈•−≤ SWMINOFF
IN
OUT ft
V
V
IN
OUTIN
SW VnsVV
f•
−
≈50
The switching frequency drops when the regulator cannot
provide sufficient duty cycle at 6Mhz to maintain regulation.
This occurs when VOUT is 1.8V or 1.82V and VIN is below 3V at
high load currents (see Figure 13).
The calculation for switching frequency is given by:
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
=nst
fMAXSW
SW 6.166
1
,
1
min
)(
where:
(1)
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
−•−
•+
+•= OUTONOUTIN
OFFOUTOUT
MAXSW VRIV RIV
nst 150
)( (2)
where:
OFF
R=LNDSON DCRR +
_
ON
R=LPDSON DCRR +
_
© 2008 Fairchild Semiconductor Corporation www.fairchildsemi.com
FAN5361 • Rev. 1.0.0 13
FAN5361 — 6MHz, 600mA TinyBuck™ Synchronous Buck Regulator
Applications Information
Selecting the Inductor
The output inductor must meet both the required inductance
and the energy handling capability of the application. The
inductor value affects average current limit, the PWM-to-PFM
transition point, output voltage ripple, and efficiency.
The ripple current (∆I) of the regulator is:
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
•
−
•≈Δ SW
OUTIN
IN
OUT fL VV
V
V
I (3)
The maximum average load current, IMAX(LOAD), is related to the
peak current limit, ILIM(PK) by the ripple current, given by:
2
I
II )PK(LIM)LOAD(MAX
Δ
−= (4)
The transition between PFM and PWM operation is
determined by the point at which the inductor valley current
crosses zero. The regulator DC current when the inductor
current crosses zero, IDCM, is:
2
I
IDCM
Δ
= (5)
The FAN5361 is optimized for operation with L = 470nH, but is
stable with inductances up to 1.2μH (nominal). The inductor
should be rated to maintain at least 80% of its value at ILIM(PK).
Efficiency is affected by the inductor DCR and inductance
value. Decreasing the inductor value for a given physical size
typically decreases the DCR; but since ∆I increases, the RMS
current increases, as do the core and skin effect losses.
12
I
I I
2
2
)DC(OUTRMS
Δ
+= (6)
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 1 shows the effects of inductance higher or lower than
the recommended 470nH on regulator performance.
Output Capacitor
Table 2 suggests 0402 capacitors. 0603 capacitors may
further improve performance in that the effective capacitance
is higher. This improves transient response and output ripple.
Increasing COUT has no effect on loop stability and can
therefore be increased to reduce output voltage ripple or to
improve transient response. Output voltage ripple, ∆VOUT, is:
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛+
••
•Δ=Δ ESR
fC
IV SWOUT
OUT 8
1 (7)
Input Capacitor
The 2.2μF ceramic input capacitor should be placed as close
as possible between the VIN pin and GND to minimize the
parasitic inductance. If a long wire is used to bring power to
the IC, additional “bulk” capacitance (electrolytic or tantalum)
should be placed between CIN and the power source lead to
reduce ringing that can occur between the inductance of the
power source leads and CIN.
The effective capacitance value decreases as VIN increases
due to DC Bias effects. This has no significant impact on
regulator performance.
Table 1. Effects of Changes in Inductor Value (from 470nH Recommended Value) on Regulator Performance
Inductor Value IMAX(LOAD) ∆VOUT EQ. 7 Transient Response
Increase Increase Decrease Degraded
Decrease Decrease Increase Improved
Table 2. Recommended Passive Components and their Variation Due to DC Bias
Component Description Vendor Min. Typ. Max. Comment
L1 470nH, 2012,
90mΩ,1.1A
Murata LQM21PNR47MG0
Hitachi Metals JLSI-2012AG-R47(D2A) 300nH 470nH 520nH Minimum value occurs
at maximum current
CIN 2.2μF, X5R,
0402
Murata or Equivalent
GRM155R60J225ME15 1.0μF2.2μF 2.4μF
Decrease primarily due
to DC bias (VIN) and
elevated temperature
COUT 4.7μF, X5R,
0402 Murata or Equivalent GRM155R60G475M 1.6μF4.7μF 5.2μF Decrease primarily due
to DC bias (VOUT)
© 2008 Fairchild Semiconductor Corporation www.fairchildsemi.com
FAN5361 • Rev. 1.0.0 14
FAN5361 — 6MHz, 600mA TinyBuck™ Synchronous Buck Regulator
PCB Layout Guidelines
There are only three external components: the inductor and
the input and output capacitors. For any buck switcher IC,
including the FAN5361, it is important to place a low-ESR
input capacitor very close to the IC, as shown in Figure 41.
The input capacitor ensures good input decoupling, which
helps reduce noise appearing at the output terminals and
ensures that the control sections of the IC do not behave
erratically due to excessive noise. This reduces switching
cycle jitter and ensures good overall performance. It is
important to place the common GND of CIN and COUT as close
as possible to the FAN5361 C2 terminal. There is some
flexibility in moving the inductor further away from the IC; in
that case, VOUT should be considered at the COUT terminal.
C
OUT
V
IN
GND
A1 A2
B2B1
C1 C2
C
IN
470nH
V
OUT
Figure 41. PCB Layout Guidance
© 2008 Fairchild Semiconductor Corporation www.fairchildsemi.com
FAN5361 • Rev. 1.0.0 15
FAN5361 — 6MHz, 600mA TinyBuck™ Synchronous Buck Regulator
Physical Dimensions
0.625
0.547
SEATING PLANE
0.06 C
0.05 C
D
C
SIDE VIEWS
NOTES:
A. NO JEDEC REGISTRATION APPLIES.
B. DIMENSIONS ARE IN MILLIMETERS.
C. DIMENSIONS AND TOLERANCES PER
ASMEY14.5M, 1994.
D. DATUM C, THE SEATING PLANE IS DEFINED
BY THE SPHERICAL CROWNS OF THE BALLS.
E. PACKAGE TYPICAL HEIGHT IS 586 MICRONS
±39 MICRONS (547-625 MICRONS).
F. FOR DIMENSIONS D, E, X, AND Y SEE
PRODUCT DATASHEET.
G. BALL COMPOSITION: Sn95.5-Ag3.9-Cu0.6.
H. DRAWING FILENAME: UC006ACrev1.
BOTTOM VIEW
TOP VIEW RECOMMENDED LAND PATTERN (NSMD)
E
E
D
B
A
BALL A1
INDEX AREA
0.40
0.80
A1
F
F
(Ø0.180)
CU PAD
SOLDER MASK
OPENING
(1.080)
(0.680)
(R0.140)
0.03 C
2X
0.03 C
2X
0.208±0.021
0.378±0.018
12
A
B
C
0.80
0.40
0.40
6X
0.005 CAB
(X) +/-0.018
(Y) +/-0.018
Ø0.260±0.010
F
Figure 42. 6-Bump WLCSP, 0.4mm Pitch
Product Specific Dimensions
Product D E X Y
FAN5361UCX 1.390 +/-0.030 0.990 +/-0.030 0.295 0.295
Package drawings are provided as a service to customers consideri ng Fairchild components. Drawings may change in any manner without
notice. Pleas e note the revision and/or date on the drawing and contact a Fairchild Semiconduct or represent ative 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 www.fairchildsemi.com
FAN5361 • Rev. 1.0.0 16
FAN5361 — 6MHz, 600mA TinyBuck™ Synchronous Buck Regulator
Physical Dimensions
SIDE VIEW
NOTES:
A. OUTLINE BASED ON JEDEC REGISTRATION
MO-229, VARIATION VCCC.
B. DIMENSIONS ARE IN MILLIMETERS.
C. DIMENSIONS AND TOLERANCES PER
ASME Y14.5M, 1994.
D. DRAWING FILENAME: MKT-UMLP06Crev1
BOTTOM VIEW
TOP VIEW
RECOMMENDED LAND PATTERN
2.401.401.10
13
64
13
64
0.30
0.65
0.50
B
A
2X
2X
0.05
0.00
0.55 MAX
0.10 C
0.08 C
(0.15)
C
SEATING
PLANE
2.0
2.0
0.65
1.30
1.10
MAX
1.50
MAX
0.35
0.25
0.35
0.25
PIN1
IDENT
0.10 C A B
0.05 C
6x
6x
1.50
1.60
PIN1
IDENT
0.10 C
0.10 C
Figure 43. 6-Pin UMLP
Package drawings are provided as a service to customers consideri ng Fairchild components. Drawings may change in any manner without
notice. Pleas e note the revision and/or date on the drawing and contact a Fairchild Semiconduct or represent ative 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 www.fairchildsemi.com
FAN5361 • Rev. 1.0.0 17
FAN5361 — 6MHz, 600mA TinyBuck™ Synchronous Buck Regulator
