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October 2015
© 2010 Fairchild Semiconductor Corporation www.fairchildsemi.com
FAN53601 / FAN53611 • Rev. 1.8
FAN53601 / FAN53611 — 6 MHz 600 mA / 1 A Synchronous Buck Regulator
FAN53601 / FAN53611
6 MHz, 600 mA / 1 A Synchronous Buck Regulator
Features
600 mA or 1 A Output Current Capability
24 µA Typical Quiescent Current
6 MHz Fixed-Frequency Operation
Best-in-Class Load Transient Response
Best-in-Class Efficiency
2.3 V to 5.5 V Input Voltage Range
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
Optional Output Discharge
6-Bump WLCSP, 0.4 mm Pitch
Applications
3G, 4G, WiFi®, WiMAX™, and WiBro® Data Cards
Tablets
DSC, DVC
Netbooks®, Ultra-Mobile PCs
All trademarks are the property of their respective owners.
Description
The FAN53601/11 is a 6 MHz, step-down switching voltage
regulator, available in 600 mA or 1 A options, that delivers a
fixed output from an input voltage supply of 2.3 V to 5.5 V.
Using a proprietary architecture with synchronous
rectification, the FAN53601/11 is capable of delivering a
peak efficiency of 92%, while maintaining efficiency over
80% at load currents as low as 1 mA.
The regulator operates at a nominal fixed frequency of
6 MHz, which reduces the value of the external components
to as low as 470 nH for the output inductor and 4.7 µF for the
output capacitor. In addition, the Pulse Width Modulation
(PWM) modulator can be synchronized to an external
frequency source.
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 24 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 6 MHz. In Shutdown Mode, the supply current
drops below 1 µA, reducing power consumption. For
applications that require minimum ripple or fixed frequency,
PFM Mode can be disabled using the MODE pin.
The FAN53601/11 is available in 6-bump, 0.4 mm pitch,
Wafer-Level Chip-Scale Package (WLCSP).
Figure 1. Typical Application
SW
MODE
GND
EN
L1 CIN
2.2F
470nH
C2
B2
A2
C1
B1
A1
FB
4.7FCOUT
VIN
© 2010 Fairchild Semiconductor Corporation www.fairchildsemi.com
FAN53601 / FAN53611 • Rev. 1.8 2
FAN53601 / FAN53611 — 6 MHz 600 mA / 1 A Synchronous Buck Regulator
Ordering Information
Part Number
Output
Voltage(1)
Max. Output
Current
Active
Discharge(2)
Max.
VIN
Package
Temperature
Range
Packing
FAN53601AUC10X
1.000 V
600 mA
Yes
5.5 V
WLCSP-6,
0.4 mm Pitch
-40 to +85°C
Tape and
Reel
FAN53601AUC105X
1.050 V
600 mA
Yes
FAN53611AUC11X
1.100 V
1 A
Yes
FAN53611AUC115X
1.150 V
1 A
Yes
FAN53611AUC13X
1.300 V
1 A
Yes
FAN53611AUC135X
1.350 V
1 A
Yes
FAN53611UC123X
1.233 V
1 A
No
FAN53601UC182X
1.820 V
600 mA
No
FAN53611AUC205X
2.050 V
1 A
Yes
FAN53611AUC123X
1.233 V
1 A
Yes
FAN53611AUC12X
1.200 V
1 A
Yes
FAN53611AUC18X
1.800 V
1 A
Yes
Notes:
1. Other voltage options available on request. Contact a Fairchild representative.
2. All voltage and output current options are available with or without active discharge. Contact a Fairchild representative.
Pin Configurations
C1
B1
A1
C2
B2
A2
MODE
SW
FB
VIN
EN
GND
C1
B1
A1
C2
B2
A2 MODE
SW
FB
VIN
EN
GND
Figure 2. Bumps Facing Down
Figure 3. Bumps Facing Up
Pin Definitions
Pin #
Name
Description
A1
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
SW
Switching Node. Connect to output inductor.
C1
FB
Feedback / VOUT. Connect to output voltage.
C2
GND
Ground. Power and IC ground. All signals are referenced to this pin.
B2
EN
Enable. The device is in Shutdown Mode when voltage to this pin is < 0.4 V and enabled when
> 1.2 V. Do not leave this pin floating.
A2
VIN
Input Voltage. Connect to input power source.
© 2010 Fairchild Semiconductor Corporation www.fairchildsemi.com
FAN53601 / FAN53611 • Rev. 1.8 3
FAN53601 / FAN53611 — 6 MHz 600 mA / 1 A 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
ESD
Electrostatic Discharge
Protection Level
Human Body Model per JESD22-A114
2.0
kV
Charged Device Model per JESD22-C101
1.5
TJ
Junction Temperature
-40
+150
°C
TSTG
Storage Temperature
-65
+150
°C
TL
Lead Soldering Temperature, 10 Seconds
+260
°C
Note:
3. 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.
Units
VCC
Supply Voltage Range
2.3
5.5
V
IOUT
Output Current for FAN53601
0
600
mA
Output Current for FAN53611
0
1
A
L
Inductor
470
nH
CIN
Input Capacitor
2.2
µF
COUT
Output Capacitor
1.6
4.7
12.0
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 2s2p
boards in accordance to JEDEC standard JESD51. Special attention must be paid to not exceed junction temperature TJ(max) at a
given ambient temperature TA.
Symbol
Parameter
Typical
Unit
JA
Junction-to-Ambient Thermal Resistance
125
°C/W
© 2010 Fairchild Semiconductor Corporation www.fairchildsemi.com
FAN53601 / FAN53611 • Rev. 1.8 4
FAN53601 / FAN53611 — 6 MHz 600 mA / 1 A Synchronous Buck Regulator
Electrical Characteristics
Minimum and maximum values are at VIN = VEN = 2.3 V to 5.5 V, VMODE = 0 V (AUTO Mode), TA = -40°C to +85°C; circuit of
Figure 1 , unless otherwise noted. Typical values are at TA = 25°C, VIN = VEN = 3.6 V.
Symbol
Parameter
Conditions
Min.
Typ.
Max.
Units
Power Supplies
IQ
Quiescent Current
No Load, Not Switching
24
50
µA
PWM Mode
8
mA
I(SD)
Shutdown Supply Current
EN = GND, VIN = 3.6 V
0.25
1.00
µA
VUVLO
Under-Voltage Lockout Threshold
Rising VIN
2.15
2.27
V
VUVHYST
Under-Voltage Lockout Hysteresis
200
mV
Logic Inputs: EN and MODE Pins
VIH
Enable HIGH-Level Input Voltage
1.2
V
VIL
Enable LOW-Level Input Voltage
0.4
V
VLHYST
Logic Input Hysteresis Voltage
100
mV
IIN
Enable Input Leakage Current
Pin to VIN or GND
0.01
1.00
µA
Switching and Synchronization
fSW
Switching Frequency(4)
VIN = 3.6 V, TA = 25°C, PWM
Mode, ILOAD = 10 mA
5.4
6.0
6.6
MHz
fSYNC
MODE Synchronization Range(4)
Square Wave at MODE Input
1.3
1.5
1.7
MHz
Regulation
VO
Output Voltage
Accuracy
1.000 V
ILOAD = 0 to 600 mA
0.953
1.000
1.048
V
PWM Mode
0.967
1.000
1.034
1.35 V
ILOAD = 0 to 1 A
1.298
1.350
1.402
PWM mode
1.309
1.350
1.391
1.233 V
ILOAD = 0 to 1 A
1.185
1.233
1.281
PWM Mode
1.192
1.233
1.274
1.820 V
ILOAD = 0 to 600 mA
1.755
1.820
1.885
PWM Mode
1.781
1.820
1.859
1.100 V
ILOAD = 0 to 1 A
1.054
1.100
1.147
PWM Mode
1.061
1.100
1.140
1.300 V
ILOAD = 0 to 1 A
1.250
1.300
1.350
PWM Mode
1.259
1.300
1.341
1.150 V
ILOAD = 0 to 1 A
1.104
1.150
1.196
PWM Mode
1.110
1.150
1.190
1.050 V
ILOAD = 0 to 600 mA
1.003
1.050
1.097
PWM Mode
1.016
1.050
1.084
2.050 V
ILOAD = 0 to 1 A, VIN = 2.7 V to
5.5 V
1.973
2.050
2.127
PWM Mode, VIN = 2.7 V to 5.5 V
2.004
2.050
2.096
1.200 V
ILOAD = 0 to 1 A
1.152
1.200
1.248
PWM Mode
1.160
1.200
1.240
1.800 V
ILOAD = 0 to 1 A
1.732
1.800
1.868
PWM Mode
1.756
1.800
1.844
tSS
Soft-Start
VIN = 4.5 V, From EN Rising Edge
180
300
µs
© 2010 Fairchild Semiconductor Corporation www.fairchildsemi.com
FAN53601 / FAN53611 • Rev. 1.8 5
FAN53601 / FAN53611 — 6 MHz 600 mA / 1 A Synchronous Buck Regulator
Electrical Characteristics (Continued)
Minimum and maximum values are at VIN = VEN = 2.3 V to 5.5 V, VMODE = 0 V (AUTO Mode), TA = -40°C to +85°C; circuit of
Figure 1 , unless otherwise noted. Typical values are at TA = 25°C, VIN = VEN = 3.6 V.
Symbol
Parameter
Conditions
Min.
Typ.
Max.
Units
Output Driver
RDS(on)
PMOS On Resistance
VIN = VGS = 3.6 V
175
m
NMOS On Resistance
VIN = VGS = 3.6 V
165
m
ILIM(OL)
PMOS Peak Current Limit
Open-Loop for FAN53601,
VIN = 3.6 V, TA = 25°C
900
1100
1250
mA
Open-Loop for FAN53611,
VIN = 3.6 V, TA = 25°C
1500
1750
2000
mA
RDIS
Output Discharge Resistance
EN = GND
230
TTSD
Thermal Shutdown
150
°C
THYS
Thermal Shutdown Hysteresis
15
°C
Notes:
4. Limited by the effect of tOFF minimum (see Operation Description section).
5. The Electrical Characteristics table reflects open-loop data. Refer to the Operation Description and Typical Characteristics Sections for
closed-loop data.
© 2010 Fairchild Semiconductor Corporation www.fairchildsemi.com
FAN53601 / FAN53611 • Rev. 1.8 6
FAN53601 / FAN53611 — 6 MHz 600 mA / 1 A Synchronous Buck Regulator
Typical Performance Characteristics
Unless otherwise noted, V IN = VEN = 3.6 V, VMODE = 0 V (AUTO Mode), VOUT = 1.82 V, and TA = 25°C.
70%
75%
80%
85%
90%
95%
0200 400 600 800 1000
Efficiency
Load Current (mA)
2.7 VIN
3.6 VIN
4.2 VIN
5.0 VIN
60%
62%
64%
66%
68%
70%
72%
74%
76%
78%
80%
82%
84%
86%
88%
90%
92%
0200 400 600 800 1000
Efficiency
Load Current (mA)
- 40C, AUTO
+25C, AUTO
+85C, AUTO
- 40C, PWM
+25C, PWM
+85C, PWM
Figure 4. Efficiency vs. Load Current and
Input Voltage, Auto Mode, Dotted for Decreasing Load
Figure 5. Efficiency vs. Load Current
and Temperature, Auto Mode, Dotted for FPWM
64%
66%
68%
70%
72%
74%
76%
78%
80%
82%
84%
86%
88%
90%
0200 400 600 800 1000
Efficiency
Load Current (mA)
2.7 VIN
3.6 VIN
4.2 VIN
5.0 VIN
60%
62%
64%
66%
68%
70%
72%
74%
76%
78%
80%
82%
84%
86%
88%
90%
0200 400 600 800 1000
Efficiency
Load Current (mA)
- 40C, AUTO
+25C, AUTO
+85C, AUTO
- 40C, PWM
+25C, PWM
+85C, PWM
Figure 6. Efficiency vs. Load Current and
Input Voltage, V
OUT
= 1.23 V, Auto Mode, Dotted
for Decreasing Load
Figure 7. Efficiency vs. Load Current
and Temperature, V
OUT
= 1.23 V, Auto Mode,
Dotted for FPWM
-2
-1
0
1
2
3
0100 200 300 400 500 600
Output Regulation (%)
Load Current (mA)
2.7VIN, AUTO
3.6VIN, AUTO
4.2VIN, AUTO
5.0VIN, AUTO
2.7VIN, PWM
3.6VIN, PWM
4.2VIN, PWM
5.0VIN, PWM
64%
66%
68%
70%
72%
74%
76%
78%
80%
82%
84%
86%
88%
90%
0100 200 300 400 500 600
Efficiency
Load Current (mA)
2.7 VIN
3.6 VIN
4.2 VIN
5.0 VIN
Figure 8. Output Regulation vs. Load Current,
V
OUT
= 1.00 V, Dotted for Auto Mode
Figure 9. Efficiency vs. Load Current, V
OUT
= 1.00 V,
Dotted for Decreasing Load
© 2010 Fairchild Semiconductor Corporation www.fairchildsemi.com
FAN53601 / FAN53611 • Rev. 1.8 7
FAN53601 / FAN53611 — 6 MHz 600 mA / 1 A Synchronous Buck Regulator
Typical Performance Characteristics (Continued)
Unless otherwise noted, VIN = VEN = 3.6 V, VMODE = 0 V (AUTO Mode), VOUT = 1.82 V, and TA = 25°C.
-2
-1
0
1
2
3
0200 400 600 800 1000
Output Regulation (%)
Load Current (mA)
2.7VIN, AUTO
3.6VIN, AUTO
4.2VIN, AUTO
5.0VIN, AUTO
2.7VIN, PWM
3.6VIN, PWM
4.2VIN, PWM
5.0VIN, PWM
-2
-1
0
1
2
3
0200 400 600 800 1000
Output Regulation (%)
Load Current (mA)
2.7VIN, AUTO
3.6VIN, AUTO
4.2VIN, AUTO
5.0VIN, AUTO
2.7VIN, PWM
3.6VIN, PWM
4.2VIN, PWM
5.0VIN, PWM
Figure 10. ∆V
OUT
(%) vs. Load Current and Input
Voltage, Normalized to 3.6 V
IN
, 500 mA Load, FPWM,
Dotted for Auto Mode
Figure 11. ∆V
OUT
(%) vs. Load Current and Input
Voltage, V
OUT
= 1.23 V, Normalized to 3.6 V
IN
, 500 mA
Load, FPWM, Dotted for Auto Mode
50
100
150
200
250
300
350
2.5 3.0 3.5 4.0 4.5 5.0 5.5
Load Current (mA)
Input Voltage (V)
PWM
PFM
50
100
150
200
250
300
350
2.5 3.0 3.5 4.0 4.5 5.0 5.5
Load Current (mA)
Input Voltage (V)
PWM
PFM
Figure 12. PFM / PWM Boundary vs. Input Voltage
Figure 13. PFM / PWM Boundary vs. Input Voltage,
V
OUT
= 1.23 V
15
20
25
30
35
2.5 3.0 3.5 4.0 4.5 5.0 5.5
Input Current (A)
Input Voltage (V)
- 40C, EN=VIN
+25C, EN=VIN
+85C, EN=VIN
- 40C, EN=1.8V
+25C, EN=1.8V
+85C, EN=1.8V
0
3
6
9
12
15
2.5 3.0 3.5 4.0 4.5 5.0 5.5
Input Current (mA)
Input Voltage (V)
-40C
+25C
+85C
Figure 14. Quiescent Current vs. Input Voltage and
Temperature, Auto Mode; EN = V
IN
Solid, Dotted for
EN=1.8 V (-40
o
C, +25
o
C, +85
o
C)
Figure 15. Quiescent Current vs. Input Voltage and
Temperature, Mode = EN = V
IN
(FPWM)
© 2010 Fairchild Semiconductor Corporation www.fairchildsemi.com
FAN53601 / FAN53611 • Rev. 1.8 8
FAN53601 / FAN53611 — 6 MHz 600 mA / 1 A Synchronous Buck Regulator
Typical Performance Characteristics (Continued)
Unless otherwise noted, V IN = VEN = 3.6 V, VMODE = 0 V (AUTO Mode), VOUT = 1.82 V, and TA = 25°C.
0
5
10
15
20
25
0200 400 600 800 1000
Output Ripple (mVpp)
Load Current (mA)
2.7VIN, AUTO
3.6VIN, AUTO
5.0VIN, AUTO
2.7VIN, PWM
3.6VIN, PWM
5.0VIN, PWM
0
1,500
3,000
4,500
6,000
7,500
0200 400 600 800 1000
Switching Frequency (KHz)
Load Current (mA)
2.7VIN, AUTO
3.6VIN, AUTO
5.0VIN, AUTO
2.7VIN, PWM
3.6VIN, PWM
5.0VIN, PWM
Figure 16. Output Ripple vs. Load Current and
Input Voltage, FPWM, Dotted for Auto Mode
Figure 17. Frequency vs. Load Current and
Input Voltage, Auto Mode, Dotted for FPWM
Figure 18. Load Transient, 10-200-10 mA, 100 ns Edge
Figure 19. Load Transient, 200-800-200 mA,
100 ns Edge
Figure 20. Line Transient, 3.3-3.9-3.3 V
IN
, 10 µs Edge,
36 mA Load
Figure 21. Line Transient, 3.3-3.9-3.3 V
IN
, 10 µs Edge,
600 mA Load
© 2010 Fairchild Semiconductor Corporation www.fairchildsemi.com
FAN53601 / FAN53611 • Rev. 1.8 9
FAN53601 / FAN53611 — 6 MHz 600 mA / 1 A Synchronous Buck Regulator
Typical Performance Characteristics (Continued)
Unless otherwise noted, V IN = VEN = 3.6 V, VMODE = 0 V (AUTO Mode), VOUT = 1.82 V, and TA = 25°C.
Figure 22. Combined Line / Load Transient, 3.9-3.3 V
IN
,
10 µs Edge, 36-400 mA Load, 100 ns Edge
Figure 23. Combined Line / Load Transient, 3.3-3.9 V
IN
,
10 µs Edge, 400-36 mA Load, 100 ns Edge
Figure 24. Startup, 50 Ω Load
Figure 25. Startup, 3 Ω Load
Figure 26. Shutdown, 10k Ω Load, No Output Discharge
Figure 27. Shutdown, No Load, Output Discharge
Enabled
© 2010 Fairchild Semiconductor Corporation www.fairchildsemi.com
FAN53601 / FAN53611 • Rev. 1.8 10
FAN53601 / FAN53611 — 6 MHz 600 mA / 1 A Synchronous Buck Regulator
Typical Performance Characteristics (Continued)
Unless otherwise noted, V IN = VEN = 3.6 V, VMODE = 0 V (AUTO Mode), VOUT = 1.82 V, and TA = 25°C.
Figure 28. Over-Current, Load Increasing Past
Current Limit, FAN53601
Figure 29. 250 mΩ Fault, Rapid Fault,
Hiccup, FAN53601
Figure 30. Over-Current, Load Increasing Past
Current Limit, FAN53611
Figure 31. 250 mΩ Fault, Rapid Fault,
Hiccup, FAN53611
20
30
40
50
60
70
0.1 1 10 100 1000
PSRR (dB)
Frequency (KHz)
36mA Load
600mA Load
20
30
40
50
60
70
0.1 1 10 100 1000
PSRR (dB)
Frequency (KHz)
24mA Load
500mA Load
Figure 32. PSRR, 50 Ω and 3 Ω Load
Figure 33. PSRR, 50 Ω and 3 Ω Load, V
OUT
= 1.23 V
© 2010 Fairchild Semiconductor Corporation www.fairchildsemi.com
FAN53601 / FAN53611 • Rev. 1.8 11
FAN53601 / FAN53611 — 6 MHz 600 mA / 1 A Synchronous Buck Regulator
Operation Description
The FAN53601/11 is a 6 MHz, step-down switching voltage
regulator available in 600 mA or 1 A options that delivers a
fixed output from an input voltage supply of 2.3 V to 5.5 V.
Using a proprietary architecture with synchronous
rectification, the FAN53601/11 is capable of delivering a
peak efficiency of 92%, while maintaining efficiency over
80% at load currents as low as 1 mA.
The regulator operates at a nominal fixed frequency of
6 MHz, which reduces the value of the external components
to as low as 470 nH for the output inductor and 4.7 µF for the
output capacitor. In addition, the PWM modulator can be
synchronized to an external frequency source.
Control Scheme
The FAN53601/11 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 FAN53601/11 operates in
Discontinuous Current Mode (DCM) single-pulse PFM Mode,
which produces low output ripple compared with other PFM
architectures. Transition between PWM and PFM is
seamless, allowing for a smooth transition between DCM
and CCM.
Combined with exceptional transient response
characteristics, the very low quiescent current of the
controller maintains high efficiency; even at very light loads;
while preserving fast transient response for applications
requiring tight output regulation.
Enable and Soft-Start
When EN is LOW, all circuits are off and the IC draws
~250 nA of current. When EN is HIGH and VIN is above its
UVLO threshold, the regulator begins a soft-start cycle. The
output ramp during soft-start is a fixed slew rate of 50 mV/s
from Vout = 0 to 1 V, then 12.5 mV/µs until the output reaches
its setpoint. Regardless of the state of the MODE pin, PFM
Mode is enabled to prevent current from being discharged
from COUT if soft-start begins when COUT is charged.
In addition, all voltage options can be ordered with a feature
that actively discharges FB to ground through a 230 path
when EN is LOW. Raising EN above its threshold voltage
activates the part and starts the soft-start cycle. During soft-
start, the internal reference is ramped using an exponential
RC shape to prevent overshoot of the output voltage. Current
limiting minimizes inrush during soft-start.
The current-limit fault response protects the IC in the event
of an over-current condition present during soft-start. As a
result, the IC may fail to start if heavy load is applied during
startup and/or if excessive COUT is used.
The current required to charge COUT during soft-start
commonly referred to as “displacement current” is given as:
dt
dV
CI OUTDISP
(1)
where
dt
dV
refers to the soft-start slew rate.
To prevent shut down during soft-start, the following condition
must be met:
)DC(MAXLOADDISP I I I
(2)
where IMAX(DC) is the maximum load current the IC is
guaranteed to support.
Startup into Large COUT
Multiple soft-start cycles are required for no-load startup if
COUT is greater than 15 µF. Large COUT requires light initial
load to ensure the FAN53601/11 starts appropriately. The IC
shuts down for 1.3 ms when IDISP exceeds ILIMIT for more
than 200 µs of current limit. The IC then begins a new soft-
start cycle. Since COUT retains its charge when the IC is off,
the IC reaches regulation after multiple soft-start attempts.
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 with a frequency
between 1.3 MHz and 1.7 MHz, the converter synchronizes
its switching frequency to four times the frequency on the
MODE pin.
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 also permitted as long as the minimum
time below VIL(MAX) or above VIH(MAX) is 100 ns.
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 16 cycles of current limit, the regulator
triggers an over-current fault, causing the regulator to shut
down for about 1.3 ms before attempting a restart.
If the fault is caused by short circuit, the soft-start circuit
attempts to restart and produces an over-current fault after
about 200 µs, which results in a duty cycle of less than 15%,
limiting power dissipation.
The closed-loop peak-current limit is not the same as the
open-loop tested current limit, ILIM(OL), in the Electrical
Characteristics table. This is primarily due to the effect of
propagation delays of the IC current limit comparator.
Under-Voltage Lockout (UVLO)
When EN is HIGH, the under-voltage lockout keeps the part
from operating until the input supply voltage rises high
enough to properly operate. This ensures no misbehavior of
the regulator during startup or shutdown.
© 2010 Fairchild Semiconductor Corporation www.fairchildsemi.com
FAN53601 / FAN53611 • Rev. 1.8 12
FAN53601 / FAN53611 — 6 MHz 600 mA / 1 A Synchronous Buck Regulator
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 die temperature falls 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 40 ns. This imposes constraints on the maximum
IN
OUT
V
V
that the FAN53601/11 can provide or the maximum
output voltage it can provide at low VIN while maintaining a
fixed switching frequency in PWM Mode.
When VIN is LOW, fixed switching is maintained as long as:
7.01 )( SWMINOFF
IN
OUT ft
V
V
.
The switching frequency drops when the regulator cannot
provide sufficient duty cycle at 6 MHz to maintain regulation.
This occurs when VOUT is 1.82 V and VIN is below 2.7 V at
high load currents (see Figure 34).
0
1,500
3,000
4,500
6,000
7,500
0200 400 600 800 1000
Switching Frequency (KHz)
Load Current (mA)
2.7VIN, AUTO
2.3VIN, AUTO
2.7VIN, PWM
2.3VIN, PWM
Figure 34. Frequency vs. Load Current to
Demonstrate t
OFFMIN
Effect, V
IN
= 2.3 V and 2.7 V,
V
OUT
= 1.82 V, Auto Mode, FPWM Dotted
The calculation for switching frequency is given by:
MHz
t
fMAXSW
SW 6 ,
1
min )(
(3)
where:
OUTONOUTIN
OFFOUTOUT
MAXSW VRIV RIV
nst140
)(
(4)
where:
OFF
R
=
LNDSON DCRR
_
ON
R
=
LPDSON DCRR
_
© 2010 Fairchild Semiconductor Corporation www.fairchildsemi.com
FAN53601 / FAN53611 • Rev. 1.8 13
FAN53601 / FAN53611 — 6 MHz 600 mA / 1 A 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:
SW
OUTIN
IN
OUT fL VV
V
V
I
(5)
The maximum average load current, IMAX(LOAD), is related to
the peak current limit, ILIM(PK), by the ripple current, given by:
2I
II )PK(LIM)LOAD(MAX
(6)
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:
2I
IDCM
(7)
The FAN53601/11 is optimized for operation with L = 470 nH,
but is stable with inductances up to 1 µH (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 because ∆I increases, the
RMS current increases, as do the core and skin effect losses.
12
I
I I 2
2
)DC(OUTRMS
(8)
The increased RMS current produces higher losses through
the RDS(ON) of the IC MOSFETs, as well as the inductor DCR.
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 and higher DCR.
Table 1 shows the effects of inductance higher or lower than
the recommended 1 µH 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:
OUTSW
2
OUTSW
LOUT Cf8 1
D1D2 ESRCf
IV
(9)
Input Capacitor
The 2.2 µF 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 the 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.
Table 1. Effects of Changes in Inductor Value (from 470 nH Recommended Value) on Regulator Performance
Inductor Value
IMAX(LOAD)
∆VOUT
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.
L1
470 nH,
2012,90 mΩ,
1.1 A
Murata LQM21PNR47MC0
Murata LQM21PNR54MG0
Hitachi Metals HLSI 201210R47
300 nH
470 nH
520 nH
CIN
2.2 µF, 6.3 V,
X5R, 0402
Murata or Equivalent GRM155R60J225ME15
GRM188R60J225KE19D
1.0 µF
2.2 µF
COUT
4.7 µF, X5R,
0402
Murata or Equivalent GRM155R60G475M
GRM155R60E475ME760
1.6 µF
4.7 µF
© 2010 Fairchild Semiconductor Corporation www.fairchildsemi.com
FAN53601 / FAN53611 • Rev. 1.8 14
FAN53601 / FAN53611 — 6 MHz 600 mA / 1 A 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 FAN53601/11, it is important to place a low-ESR
input capacitor very close to the IC, as shown in Figure 35.
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 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.
Figure 35. PCB Layout Guidance
The following information applies to the WLCSP package dimensions on the next page:
Product-Specific Dimensions
D
E
X
Y
1.160 ±0.030
0.860 ±0.030
0.230
0.180
SEATING PLANE
0.06 C
0.05 C
C
SIDE VIEWS NOTES:
A. NO JEDEC REGISTRATION APPLIES.
B. DIMENSIONS ARE IN MILLIMETERS.
C. DIMENSIONS AND TOLERANCES PER
ASMEY14.5M, 2009.
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. DRAWING FILENAME: MKT-UC006ACrev6.
BOTTOM VIEW
TOP VIEW RECOMMENDED LAND PATTERN
(NSMD PAD TYPE)
E
D
B
A
BALL A1
INDEX AREA
A1
0.03 C
2X
0.03 C
2X
0.208±0.021
0.378±0.018
12
A
B
C
0.40
0.40
0.005 C A B
(X) +/-0.015
(Y) +/-0.015
Ø0.260±0.010
0.40
6X
E
D
F
F0.40
(Ø0.20)
Bottom of Cu Pad
(Ø0.30)
Solder Mask
Opening
F
0.586±0.039
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