TinyBuck) Regulator,
Digitally Programmable,
5 A, 2.4 MHz
FAN53200
Descriptions
The FAN53200 is a step−down switching voltage regulator that
delivers a digitally programmable output from an input voltage supply
of 2.5 V to 5.5 V. The output voltage is programmed through an I2C
interface capable of operating up to 3.4 Mbps.
Using a proprietary architecture with synchronous rectification, the
FAN53200 is capable of delivering 5 A continuously at over 80%
efficiency, while maintaining over 80% efficiency at load currents as
low as 10 mA. The regulator operates at a nominal fixed frequency of
2.4 MHz, which reduces the value of the external components.
Additional output capacitance can be added to improve regulation
during load transients without affecting stability. Inductance up to
1.2 mH may be used with additional output capacitance.
At moderate and light loads, Pulse Frequency Modulation (PFM) is
used to operate in Power−Save Mode with a typical quiescent current
of 60 mA. At higher loads, the system automatically switches to
fixed−frequency control, operating at 2.4 MHz. In Shutdown Mode,
the supply current drops to 0.1 mA, reducing power consumption. PFM
Mode can be disabled if constant frequency is desired. The FAN53200
is available in a 20−bump, 1.6 x 2.0 mm, WLCSP.
Features
• Quiescent Current in PFM Mode: 60 mA (Typical)
• Digitally Programmable Output Voltage:
•
•
•
•
•
•
•
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1
WLCSP−20
CASE 567SH
VIN
C IN
EN
VOUT
SDA
SCL
FAN53200
VSEL
SW
GND
L1
C OUT
AGND
VDD
Core
Processor
(System Load)
GND
Figure 1. Typical Application
• Input Under−Voltage Lockout (UVLO)
• Thermal Shutdown and Overload Protection
• 20−Bump Wafer−Level Chip Scale Package (WLCSP)
0.6 −1.3875 V in 12.5 mV Steps
Best−in−Class Load Transient
Continuous Output Current Capability: 5 A
2.5 V to 5.5 V Input Voltage Range
Programmable Slew Rate for Voltage Transitions
Fixed−Frequency Operation: 2.4 MHz
I2C−Compatible Interface Up to 3.4 Mbps
Internal Soft−Start
♦
Applications
• Graphic, and DSP Processors
•
•
•
•
ARMt, Kraitt, OMAPt, NovaThort, ARMADAt
Hard Disk Drives
Tablets, Netbooks, Ultra−Mobile PCs
Smart Phones
Gaming Devices
ORDERING INFORMATION
Power−Up Defaults
Part Number
VSEL0
VSEL1
I2C Slave
Address
Device ID
Device
Marking
Package
FAN53200UC35X
OFF
1.15 V
C0
0000
B9
WLCSP−20
FAN53200UC44X
1.15V
0.85 V
C0
0000
CD
WLCSP−20
© Semiconductor Components Industries, LLC, 2015
May, 2020 − Rev. 3
1
Publication Order Number:
FAN53200/D
FAN53200
Pin Configuration
Figure 2. Pin Assignment (Top View)
Table 1. PIN DESCRIPTIONS
Pin #
Name
Description
A1
VSEL
Voltage Select. When this pin is LOW, VOUT is set by the VSEL0 register. When this pin is HIGH, VOUT is set by
the VSEL1 register.
A2
EN
Enable. The device is in Shutdown Mode when this pin is LOW. All registers go to default values when EN pin is
LOW.
A3
SCL
I2C Serial Clock
A4
VOUT
B1
SDA
I2C Serial Data
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 the input power source. Connect to CIN with minimal path.
D3, D4,
E3, E4
SW
Switching Node. Connect to the inductor.
VOUT. Sense pin for VOUT. Connect to COUT.
Analog Ground. All signals are referenced to this pin. Avoid routing high dV/dt AC currents through this pin.
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2
FAN53200
Table 2. ABSOLUTE MAXIMUM RATINGS
Symbol
VIN
Parameter
Voltage on SW, VIN Pins
Voltage on All Other Pins
VOUT
VINOV_SLEW
ESD
Min
Max
Unit
IC Not Switching
−0.3
7.0
V
IC Switching
−0.3
6.5
IC Not Switching
−0.3
VIN (Note 1)
Voltage on VOUT Pin
−0.3
Maximum Slew Rate of VIN > 6.5 V, PWM Switching
Electrostatic Discharge Protection
Level
Human Body Model per JESD22−A114
2000
Charged Device Model per JESD22−C101
1000
V
3.0
V
100
V/ms
V
TJ
Junction Temperature
−40
+150
°C
TSTG
Storage Temperature
−65
+150
°C
+260
°C
TL
Lead Soldering Temperature, 10 Seconds
Stresses exceeding those listed in the Maximum Ratings table may damage the device. If any of these limits are exceeded, device functionality
should not be assumed, damage may occur and reliability may be affected.
1. Lesser of 7.0 V or VIN + 0.3 V
Table 3. RECOMMENDED OPERATING CONDITIONS
Symbol
Parameter
VIN
Supply Voltage Range
IOUT
Output Current
L
CIN
COUT
Min
Max
Unit
2.5
5.5
V
0
5
A
Inductor
Typ
0.33
mH
Input Capacitor
10
mF
Output Capacitor
44
mF
TA
Operating Ambient Temperature
−40
+85
°C
TJ
Operating Junction Temperature
−40
+125
°C
Product parametric performance is indicated in the Electrical Characteristics for the listed test conditions, unless otherwise noted. Product
performance may not be indicated by the Electrical Characteristics if operated under different conditions.
Table 4. THERMAL PROPERTIES
Symbol
qJA
Parameter
Min
Junction−to−Ambient Thermal Resistance (Note 2)
Typ
38
2. See Thermal Considerations in the Application Information section.
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3
Max
Unit
°C/W
FAN53200
Table 5. ELECTRICAL CHARACTERISTICS Minimum and maximum values are at VIN = 2.5 V to 5.5 V, TA = −40°C to +85°C,
unless otherwise noted. Typical values are at TA = 25°C, VIN = 5 V, and EN = HIGH.
Parameter
Symbol
Condition
Min
Typ
Max
Unit
POWER SUPPLIES
IQ
Quiescent Current
ILOAD = 0
60
ISD
H/W Shutdown Supply Current
EN = GND
0.1
S/W Shutdown Supply Current
EN = VIN, BUCK_ENx = 0
VUVLO
Under−Voltage Lockout Threshold
VIN Rising
VUVHYST
Under−Voltage Lockout Hysteresis
mA
5.0
mA
41
75
mA
2.35
2.45
V
350
mV
EN, VSEL, SDA, SCL
VIH
high−Level Input Voltage
VIL
low−Level Input Voltage
VLHYST
IIN
1.1
V
0.4
Logic Input Hysteresis Voltage
Input Bias Current
160
Input Tied to GND or VIN
0.01
V
mV
1.00
mA
1
mA
1.00
mA
PGOOD
IOUTL
PGOOD Pull−Down Current
IOUTH
PGOOD HIGH Leakage Current
0.01
VOUT REGULATION
VREG
VOUT DC Accuracy
IOUT(DC) = 0, Forced PWM, VOUT = VSEL1
Default Value, 2.5 V ≤ VIN ≤ 5.5 V
−1.5
1.5
%
IOUT(DC) = 0 to 5 A, VOUT = VSEL1, Default
Value, Auto PFM/PWM, 2.5 V ≤ VIN ≤ 4.5 V
−2.0
4.0
%
IOUT(DC) = 0 to 5 A, VOUT = VSEL1, Default
Value, Auto PFM/PWM, 2.5 V ≤ VIN ≤ 5.5 V
−3.0
5.0
%
6.3
8.5
A
POWER SWITCH AND PROTECTION
ILIMPK
P−MOS Peak Current Limit
Open Loop
VSDWN
Input OVP Shutdown
Rising Threshold
Falling Threshold
7.4
6.15
V
5.50
5.85
V
2.05
2.40
FREQUENCY CONTROL
fSW
Oscillator Frequency
ROFF
VOUT Pull−Down Resistance
EN = 0 or VIN < VUVLO
2.75
160
MHz
W
Product parametric performance is indicated in the Electrical Characteristics for the listed test conditions, unless otherwise noted. Product
performance may not be indicated by the Electrical Characteristics if operated under different conditions.
Table 6. SYSTEM CHARACTERISTICS
Symbol
Parameter
DVOUT_LOAD
Load Regulation
IOUT = 1 A to 5 A
0.2
mV/A
DVOUT_LINE
Line Regulation
3.6 V ≤ VIN ≤ 4.0 V, IOUT = 3 A
−0.5
mV/V
VOUT_RIPPLE
Ripple Voltage
IOUT = 100 mA, PFM Mode
16
mV
IOUT = 2000 mA, PWM Mode
3
VOUT = 1.15 V, IOUT = 100 mA
87
VOUT = 1.15 V, IOUT = 500 mA
88
VOUT = 1.15 V, IOUT = 2 A
88
η
Efficiency
Min
Typ
Max
Unit
%
TSS
Soft−Start
EN High to 95% of VOUT Target (1.15 V) RLOAD = 50 W
340
ms
DVOUT_LOAD_TRAN
Load Transient
IOUT = 0.1 A ⇔ 1.2 A, TR = TF = 100 ns
±20
mV
DVOUT_LINE_TRAN
Line Transient
VIN = 3.0 V ⇔ 3.6 V, TR = TF = 10 ms, IOUT = 500 mA
±20
mV
NOTE:
The table above is verified by design and bench test while using the following external components: L = 0.33 mH,
DFE252012F−R33M (TOKO), CIN = 10 mF, C2012X5R1A106M (TDK), COUT = 2 x 22 mF, C2012X5R0J226M (TDK).
These parameters are not tested in production. Minimum and maximum values are at VIN = 2.5 V to 5.5 V, VEN = 1.8 V, TA =
−40°C to +85°C; circuit of Figure 1, unless otherwise noted. Typical values are at TA = 25°C, VIN = 3.6 V, VOUT = 1.15 V, VEN =
1.8 V, Auto PFM Mode.
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FAN53200
Typical Characteristics
Unless otherwise specified, VIN = 3.6 V, VOUT = 1.15 V, VEN = 1.8 V, Auto PFM Mode, TA = 25°C; circuit and components according to Figure 1.
25
94%
2.7 VIN
2.7 VIN
92%
3.6 VIN
3.6 VIN
90%
20
5.0 VIN
VOUT Shift (mV)
Efficiency
88%
86%
84%
82%
5.0 VIN
15
10
80%
5
78%
76%
74%
0
0
1000
2000
3000
4000
0
5000
1000
3000
4000
5000
Load Current (mA)
Load Current (mA)
Figure 3. Efficiency vs. Load Current and Input
Voltage
Figure 4. Output Regulation vs. Load Current
and Input Voltage
40
1,200
−40C
+25C
35
+85C
1,000
Load Current (mA)
30
VOUT Shift (mV)
2000
25
20
15
10
800
600
400
PFM Exit
5
PFM Enter
200
2.5
0
0
1000
2000
3000
4000
5000
3.0
3.5
4.0
4.5
5.0
5.5
Input Voltage (V)
Load Current (mA)
Figure 5. Output Regulation vs. Load Current,
Over−Temperature
Figure 6. PFM Entry / Exit Level vs. Input
Voltage
25
3,000
3.6VIN,Auto
3.6VIN,PWM
2,500
5.0VIN,Auto
Switching Frequency (KHz)
Output Ripple (mVpp)
20
5.0VIN,PWM
15
10
5
2,000
1,500
1,000
3.6VIN,Auto
500
5.0VIN,Auto
0
0
1000
2000
3000
4000
0
5000
0
Load Current (mA)
1000
2000
3000
4000
Load Current (mA)
Figure 7. Output Ripple vs. Load Current
Figure 8. Frequency vs. Load Current
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5
5000
FAN53200
Typical Characteristics
80
60
70
50
60
40
Input Current (mA)
Input Supply Current (mA)
Unless otherwise specified, VIN = 3.6 V, VOUT = 1.15 V, VEN = 1.8 V, Auto PFM Mode, TA = 25°C; circuit and components according to Figure 1.
50
40
30
EN_BUCK=0, −40C
EN_BUCK=0, +25C
20
EN_BUCK=0, +85C
EN=0, +25C
30
−40C
10
+25C
+85C
20
2.5
3.0
3.5
4.0
4.5
5.0
0
5.5
2.5
3.0
Input Supply Voltage (V)
3.5
4.0
4.5
5.0
5.5
Input Voltage (V)
Figure 9. Quiescent Current vs. Input Voltage,
Over−Temperature
Figure 10. Shutdown Current vs. Input
Voltage, Over−Temperature
Figure 11. Load Transient, IOUT = 0.1 A @
1.2 A, Auto PFM Mode, TR = TF = 100 ns
Figure 12. Line Transient, VIN = 3.0 V @ 3.6 V,
TR = TF = 10 ms, IOUT = 500 mA
Figure 13. Startup, Rload = 50 W
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FAN53200
Operation Description
If large output capacitance values are used, the regulator
may fail to start. Maximum COUT capacitance for
successfully starting with a heavy constant−current load is
approximately:
The FAN53200 is a step−down switching voltage
regulator that delivers a programmable output voltage from
an input voltage supply of 2.5 V to 5.5 V. Using a proprietary
architecture with synchronous rectification, the FAN53200
is capable of delivering 5 A at over 80% efficiency. The
regulator operates at a nominal frequency of 2.4 MHz at full
load, which reduces the value of the external components to
330 nH for the output inductor and 44 mF for the output
capacitor. High efficiency is maintained at light load with
single−pulse PFM.
The FAN53200 integrates an I2C−compatible interface,
allowing transfers up to 3.4 Mbps. This communication
interface can be used to:
• Dynamically re−program the output voltage in 12.5 mV
steps;
• Reprogram the mode to enable or disable PFM;
• Control voltage transition slew rate; or
• Enable / disable the regulator.
C OUTMAX [ ǒI LIMPK * I LOADǓ @
320 m
V OUT
(eq. 1)
where COUTMAX is expressed in mF and ILOAD is the load
current during soft−start, expressed in A.
If the regulator is at its current limit for 16 consecutive
current limit cycles, the regulator shuts down and enters
tri−state before reattempting soft−start 1700 ms later. This
limits the duty cycle of full output current during soft−start
to prevent excessive heating.
The IC allows for software enable of the regulator, when
EN is HIGH, through the BUCK_EN bits. Only
BUCK_EN1 is initialized HIGH.
Table 7. HARDWARE AND SOFTWARE ENABLE
Pins
Control Scheme
The FAN53200 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 FAN53200 operates in
Discontinuous Conduction Mode (DCM) single−pulse
PFM, which produces low output ripple compared with
other PFM architectures. Transition between PWM and
PFM is relatively seamless, providing a smooth transition
between DCM and Continuous Conduction Mode (CCM).
PFM can be disabled by programming the MODE bit
HIGH in the VSEL registers.
Bits
Output Voltage
EN
VSEL
BUCK_EN0
BUCK_EN1
35X
44X
0
X
X
X
OFF
OFF
1
0
0
X
0V
0V
1
0
1
X
1.1 V
1.15 V
1
1
X
0
0V
0V
1
1
X
1
1.15 V
0.85 V
VSEL Pin and I2C Programming Output Voltage
The output voltage is set by the NSELx control bits in
VSEL0 and VSEL1 registers. The output voltage is given as:
V OUT + 0.60 V ) NSELx @ 12.5 mV
(eq. 2)
Output voltage can also be controlled by toggling the
VSEL pin LOW or HIGH. VSEL LOW corresponds to
VSEL0 and VSEL HIGH corresponds to VSEL1. Upon
POR, VSEL0 and VSEL1 are reset to their default voltages,
shown in Table 11.
Transition Slew Rate Limiting
When transitioning from a low to high voltage, the IC can
be programmed for one of eight possible slew rates using the
SLEW bits in the CONTROL register (Table 12).
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. In this
state, I2C cannot be written to or read from. All registers are
reset to default values when EN pin is LOW.
When the OUTPUT_DISCHARGE bit in the CONTROL
register is enabled (logic HIGH) and the EN pin is LOW or
the BUCK_ENx bit is LOW, a load is connected from
VOUT to GND to discharge the output capacitors.
Raising EN while the BUCK_ENx bit is HIGH activates
the part and begins the soft−start cycle. During soft−start, the
modulator’s internal reference is ramped slowly to minimize
surge currents on the input and prevent overshoot of the
output voltage. Synchronous rectification is inhibited
during soft−start, allowing the IC to start into a pre−charged
capacitive load.
Table 8. TRANSITION SLEW RATE
Decimal
Bin
0
000
80
mV / ms
1
001
40
mV / ms
2
010
20
mV / ms
3
011
10
mV / ms
4
100
5
mV / ms
5
101
2.5
mV / ms
6
110
1.25
mV / ms
7
111
0.625
mV / ms
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7
Slew Rate
FAN53200
of SCL to allow ample time for the data to set up before the
next SCL rising edge.
Transitions from high to low voltage rely on the output
load to discharge VOUT to the new set point. Once the
high−to−low transition begins, the IC stops switching until
VOUT has reached the new set point.
Data change allowed
SDA
Under−Voltage Lockout (UVLO)
When EN is HIGH, the under−voltage lockout keeps the
part from operating until the input supply voltage raises high
enough to properly operate. This ensures proper operation of
the regulator during startup or shutdown.
tH
Figure 14. Data Transfer Timing
Input Over−Voltage Protection (OVP)
When VIN exceeds VSDWN (about 6.2 V) the IC stops
switching to protect the circuitry from internal spikes above
6.5 V. An internal filter prevents the circuit from shutting
down due to noise spikes.
Each bus transaction begins and ends with SDA and SCL
HIGH. A transaction begins with a START condition, which
is defined as SDA transitioning from 1 to 0 with SCL high,
as shown in Figure 15.
Current Limiting
SDA
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. Sixteen consecutive current
limit cycles in current limit cause the regulator to shut down
and stay off for about 1700 ms before attempting a restart.
Slave Address
MS Bit
Figure 15. START Bit
A transaction ends with a STOP condition, which is
defined as SDA transitioning from 0 to 1 with SCL high, as
shown in Figure 16.
When the die temperature increases, due to a high load
condition and/or 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 17°C
hysteresis.
Slave Releases
SDA
Master Drives
tHD;STO
ACK(0) or
NACK(1)
SCL
I2C Interface
Figure 16. STOP Bit
The FAN53200’s serial interface is compatible with
Standard, Fast, Fast Plus, and HS Mode I2C−Bus®
specifications. The FAN53200’s SCL line is an input and its
SDA line is a bi−directional open−drain output; it can only
pull down the bus when active. The SDA line only pulls
LOW during data reads and when signaling ACK. All data
is shifted in MSB (bit 7) first.
During a read from the FAN53200, the master issues a
REPEATED START after sending the register address, and
before resending the slave address. The REPEATED
START is a 1 to 0 transition on SDA while SCL is HIGH, as
shown in Figure 17.
Slave Releases
I2C Slave Address
SDA
In hex notation, the slave address assumes a 0 LS Bit. The
hex slave address is C0.
ACK(0) or
NACK(1)
tSU;STA
tHD;STA
SLADDR
MS Bit
SCL
Table 9. I2C SLAVE ADDRESS
C0
tHD;STA
SCL
Thermal Shutdown
Hex
tSU
SCL
Bits
Figure 17. REPEATED START Timing
7
6
5
4
3
2
1
0
1
1
0
0
0
0
0
R/W
High−Speed (HS) Mode
The protocols for High−Speed (HS), Low−Speed (LS),
and Fast−Speed (FS) Modes are identical, except the bus
speed for HS mode is 3.4 MHz. HS Mode is entered when
the bus master sends the HS master code 00001XXX after
a START condition. The master code is sent in Fast or
Fast−Plus Mode (less than 1 MHz clock); slaves do not ACK
this transmission.
Other slave addresses can be assigned. Contact an
ON Semiconductor representative.
Bus Timing
As shown in Figure 14, data is normally transferred when
SCL is LOW. Data is clocked in on the rising edge of SCL.
Typically, data transitions shortly at or after the falling edge
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FAN53200
The master generates a REPEATED START condition
that causes all slaves on the bus to switch to HS Mode. The
master then sends I2C packets, as described above, using the
HS Mode clock rate and timing.
The bus remains in HS Mode until a STOP bit (Figure 16)
is sent by the master. While in HS Mode, packets are
separated by REPEATED START conditions (Figure 17).
Table 10. I2C BIT DEFINITIONS
for Figure 18 & Figure 19
Symbol
Read and Write Transactions
The following figures outline the sequences for data read
and write. Bus control is signified by the shading of the
packet, defined as
ŸŸŸŸŸŸŸ
ŸŸŸŸŸŸŸ
Definition
S
START, see Figure 15
A
ACK. The slave drives SDA to 0 to acknowledge
the preceding packet.
A
NACK. The slave sends a 1 to NACK the preceding packet.
R
Repeated START, see Figure 17
P
STOP, see Figure 16
Master Drives Bus
and
Slave Drives Bus
All addresses and data are MSB first.
7 bits
S
Slave Address
0
0
8 bits
0
8 bits
0
A
Reg Addr
A
Data
A
P
Figure 18. Write Transaction
7 bits
S
Slave Address
0
0
8 bits
0
A
Reg Addr
A
7 bits
R
Slave Address
1
0
8 bits
1
A
Data
A
P
Figure 19. Read Transaction
Register Description
Table 11. REGISTER MAP
Hex
Address
Name
00
VSEL0
Controls VOUT settings when VSEL pin = 0
01
VSEL1
Controls VOUT settings when VSEL pin = 1
02
CONTROL
03
ID1
Read−only register identifies vendor and chip type
04
ID2
Read−only register identifies die revision
05
MONITOR
Function
Determines whether VOUT output discharge is enabled and also the slew rate of positive transitions
Indicates device status
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FAN53200
The following table defines the operation of each register bit.
Table 12. BIT DEFINITIONS
Bit
Name
VSEL0
35X
44X
R/W
Description
Register Address: 00
7
BUCK_EN0
0
1
Software buck enable. When EN pin is LOW, the regulator is off. When EN pin is
HIGH, BUCK_EN bit takes precedent.
6
MODE0
0
0
0: Allow Auto PFM Mode during light load.
1: Forced PWM Mode.
5:0
NSEL0
101000
101100
VSEL1
R/W
Sets VOUT value from 0.6V to 1.3875 V in 12.5 mV steps (see Equation 2).
Register Address: 01
7
BUCK_EN1
1
1
Software buck enable. When EN pin is LOW, the regulator is off. When EN pin is
HIGH, BUCK_EN bit takes precedent.
6
MODE1
0
0
0: Allow Auto PFM Mode during light load.
1: Forced PWM Mode.
5:0
NSEL1
101100
010100
CONTROL
R/W
Sets VOUT value from 0.6V to 1.3875 V in 12.5 mV steps (see Equation 2).
Register Address: 02
7
OUTPUT_DISCHARGE
1
0
6:4
SLEW
000
000
3
Reserved
0
0
Always reads back 0
2
RESET
Reserved
0
0
1: Reset all registers to default values.
0: Always reads back 0
1:0
Reserved
00
00
Always reads back 00
ID1
R
VENDOR
100
4
Reserved
0
3:0
DIE_ID
0000
Signifies ON Semiconductor as the IC vendor
Always reads back 0
Refer to ordering information
R
7:4
Reserved
3:0
DIE_REV
MONITOR
Sets the slew rate for positive voltage transitions (see Table 8).
Register Address: 03
7:5
ID2
0: When the regulator is turned off, VOUT is not discharged.
1: When the regulator is turned off, VOUT discharges through an internal pull−
down.
Register Address: 04
0000
0001
Always reads back 0000
0000
R
IC mask revision
Register Address: 05
7
PGOOD
1
6:0
Not used
0000000
1: buck is enabled and soft−start is completed
Always reads back 000 0000
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10
FAN53200
Application Information
Selecting the Inductor
Output Capacitor and VOUT Ripple
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, the output voltage ripple, and the efficiency.
The ripple current (DI) of the regulator is:
DI [
ǒ
Ǔ
V OUT
V IN * V OUT
@
V IN
L @ f SW
Table 14 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 than
the 0805 package, which can degrade transient response and
output ripple.
Increasing COUT has negligible effect on loop stability
and can be increased to reduce output voltage ripple or to
improve transient response. Output voltage ripple, DVOUT,
is calculated by:
(eq. 3)
The maximum average load current, IMAX(LOAD), is
related to the peak current limit, ILIM(PK)by the ripple
current such that:
I MAX(LOAD) + I LIM(PK) * DI
2
ƪ
DV OUT + DI L
(eq. 4)
The FAN53200 is optimized for operation with L =
330 nH, but is stable with inductances up to 1.0 mH
(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 DI increases, the
RMS current increases, as do core and skin−effect losses.
I RMS +
ǸI
OUT(DC)
2
) DI
12
2
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.
Transient Response
Increase
Decrease
Degraded
)
ƫ
1
8 @ f SW @ C OUT
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:
Table 13. EFFECTS OF INDUCTOR VALUE (from
330 nH Recommended) on Regulator Performance
DVOUT (Equation 7)
f SW @ C OUT @
2 @ D @ (1 * D )
where COUT is the effective output capacitance.
The capacitance of COUT decreases at higher output
voltages, which results in higher DVOUT. Equation 6 is only
valid for Continuous Current Mode (CCM) operation,
which occurs when the regulator is in PWM Mode.
For large COUT values, the regulator may fail to start under
a load. If an inductor value greater than 1.0 mH is used, at
least 30 mF of COUT should be used to ensure stability.
The lowest DVOUT is obtained when the IC is in PWM
Mode and, therefore, operating at 2.4 MHz. In PFM Mode,
fSW is reduced, causing DVOUT to increase.
(eq. 5)
IMAX(LOAD)
(eq. 6)
ESR 2
DV OUT(SQ) [ V IN @
ESL COUT
L1
(eq. 7)
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 mF, a single 22 mF 0805 would
produce twice the square wave ripple as two x 10 mF 0805.
To minimize ESL, try to use capacitors with the lowest
ratio of length to width. 0805s have lower ESL than 1206s.
If low output ripple is a chief concern, some vendors
produce 0508 or 0612 capacitors with ultra−low ESL.
Placing additional small−value capacitors near the load also
reduces the high−frequency ripple components.
Inductor Current Rating
The current limit circuit can allow substantial peak
currents to flow through L1 under worst−case conditions. If
it is possible for the load to draw such currents, the inductor
should be capable of sustaining the current or failing in a safe
manner.
For space−constrained applications, a lower current rating
for L1 can be used. The FAN53200 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.
Input Capacitor
The ceramic input capacitors 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.
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11
FAN53200
2. Calculate total power dissipation using:
The effective CIN capacitance value decreases as VIN
increases due to DC bias effects. This has no significant
impact on regulator performance.
P T + V OUT
ǒ1h * 1Ǔ
I LOAD
(eq. 8)
where h is efficiency.
Estimate inductor copper losses using:
Thermal Considerations
Heat is removed from the IC through the solder bumps to
the PCB copper. The junction−to−ambient thermal
resistance (θJA) is largely a function of the PCB layout (size,
copper weight, and trace width) and the temperature rise
from junction to ambient (ΔT).
For the FAN53200UC, qJA is 38°C/W when mounted on
its four−layer evaluation board in still air with two−ounce
outer layer copper weight and one−ounce inner layers.
Halving the copper thickness results in an increased θJA of
48°C/W.
For long−term reliable operation, the IC’s junction
temperature (TJ) should be maintained below 125°C.
To calculate maximum operating temperature (
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