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FAN5331 1.6MHz Boost Converter with 20V Integrated FET Switch
October 2004
FAN5331 1.6MHz Boost Converter with 20V Integrated FET Switch
Features
1.6MHz Switching Frequency Low Noise Low RDS(ON): 0.5 Adjustable Output Voltage 1A Peak Switch Current Low Shutdown Current: <1A Cycle-by-Cycle Current Limit Over-Voltage Protection Fixed -Frequency PWM Operation Internal Compensation 5-lead SOT-23 Package
Description
The FAN5331 is a general purpose, fixed-frequency boost converter designed to operate at high switching frequencies in order to minimize switching noise measured at the battery terminal of hand-held communications equipment. Quiescent current in normal mode of operation as well as in shutdown mode is designed to be minimal in order to extend battery life. Normal mode of operation or shutdown mode can be selected by a logic level shutdown circuitry. The low ON-resistance of the internal N-channel switch ensures high efficiency and low power dissipation. A cycle-by-cycle current limit circuit keeps the peak current of the switch below a maximum value of 1A. The FAN5331 is available in a 5-lead SOT-23 package.
Applications
Cell Phones PDAs Handheld Equipment Display Bias LED Bias
Typical Application
BAT54 COUT 4.7F 5 VIN R1 CF 120pF VOUT
VIN CIN
2.7V to 5.5V
L 10H
4.7F 1
SW
FAN5331
FB
3
R2 ON OFF 4 SHDN GND 2
Figure 1. Typical Application Diagram
(c)2004 Fairchild Semiconductor Corporation
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FAN5331 Rev. 1.0.1
FAN5331 1.6MHz Boost Converter with 20V Integrated FET Switch
Pin Assignment
Top View
SW GND FB
VIN SHDN
5-Lead SOT-23
Figure 2. Pin Assignment
Pin Description
Pin No.
1 2 3 4 5
Pin Name
SW GND FB SHDN VIN Switching node. Analog and power ground.
Pin Description
Feedback node that connects to an external voltage divider. Shutdown control pin. Logic HIGH enables, logic LOW disables the device. Input voltage.
Absolute Maximum Ratings (Note1)
Parameter
VIN to GND FB, SHDN to GND SW to GND Lead Soldering Temperature (10 seconds) Junction Temperature Storage Temperature Thermal Resistance (JA) Electrostatic Discharge Protection (ESD) Level (Note 2) HBM CDM 2.5 1 -55 -0.3 -0.3
Min
Max
6.0 VIN + 0.3 23 300 150 150 265
Unit
V V V C C C C/W kV
Recommended Operating Conditions
Parameter
Input Voltage Output Voltage Operating Ambient Temperature Output Capacitance (Note 3)
Min
2.7 VIN -40 1.6
Typ
Max
5.5 20
Unit
V V C F
25
85
Notes: 1. Stresses above those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. This is a stress rating only and functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. Absolute maximum ratings apply individually only, not in combination. 2. Using EIA/JESD22A114B (Human Body Model) and EIA/JESD22C101-A (Charge Device Model). 3. This load capacitance value is required for the loop stability. Tolerance, temperature variation, and voltage dependency of the capacitance must be considered. Typically a 4.7F ceramic capacitor is required to achieve specified value at VOUT = 15V.
2 FAN5331 Rev. 1.0.1
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FAN5331 1.6MHz Boost Converter with 20V Integrated FET Switch
Electrical Characteristics
Unless otherwise noted, VIN = 3.6V, TA = -40C to +85C, Typical values are at TA = 25C, Test Circuit, Figure 3. Parameter
Switch Current Limit Load Current Switch On-resistance Quiescent Current OFF Mode Current Shutdown Threshold Shutdown Pin Bias Current Feedback Voltage Feedback Pin Bias Current Feedback Voltage Line Regulation Switching Frequency Maximum Duty Cycle Enable Delay Power on Delay Switch Leakage Current VIN = 2.7V, IOUT = 35mA, VOUT = 15V VIN = 2.7V, IOUT = 35mA, VOUT = 15V No Switching, VIN = 5.5V 2.7V < VIN < 5.5V, ILOAD = 0mA 1.15 87 VIN = 3.2V VOUT = 15V, V IN 2.7V VOUT = 15V, V IN 3.2V VIN = 5V VIN = 3.6V VSHDN = 3.6V, No Switching VSHDN = 3.6V, Switching VSHDN = 0V Device ON Device OFF VSHDN = 0V or VSHDN = 5.5V ILoad = 0mA 1.205 10 1.230 10 0.6 1.6 93 0.8 0.8 5 5 1 1.2 1.85 1.255 1.5 0.5
Conditions
Min.
0.7 35 50
Typ.
1
Max.
Units
A mA mA
0.5 0.7 0.7 1.6 0.1 3.0 2
mA mA A V V nA V nA % MHz % mS mS A
Test Circuit
VIN
CIN
4.7F
2.7V to 5.5V
L
BAT54
VOUT
COUT
4.7F
10H
5
V
SW
1
R1
150K
CF
120pF
IN
FAN5331
FB
3
ON OFF
4
R2
SHDN
GND
2
13.4K
Figure 3. Test Circuit
3 FAN5331 Rev. 1.0.1
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FAN5331 1.6MHz Boost Converter with 20V Integrated FET Switch
Typical Performance Characteristics
TA = 25C, Test Circuit Figure 3, unless otherwise noted.
Output Voltage vs Input Voltage
Maximum Load Current (mA)
14.98 14.96 14.94 14.92 14.90 14.88 14.86 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0
VIN(V) VIN(V) VIN(V) VIN(V) VIN(V) VIN(V) vs vs vs vs vs vs VOUT(V) at Iload=0mA VOUT(V), at load=10mA VOUT(V), at load=20mA VOUT(V) at Iload=30mA VOUT(V) at Iload=40mA VOUT(V) at Iload=50mA
Maximum Load Current vs Input Voltage
350 300 250 200 150 100 50 0 2.5 3.0 3.5 4.0 4.5 5.0 5.5
Output Voltage (V)
VO
UT
=
V 12
UT VO
=
V 15
1V =2
VOU
T
Input Voltage (V)
Input Voltage (V)
Efficiency vs Input Voltage
0.92 0.90
Feedback Voltage vs Ambient Temperature
1.25
IOUT = 15mA
Feedback Voltage (V)
0.88 0.86 0.84
1.24 1.23 1.22 1.21
Temperature (C) vs Vf (Vin=2.7V, Iload=15m A) Temperature (C) vs Vf (Vin=3.6V, Iload=15m A) Temperature (C) vs Vf (Vin=5.5V, Iload=15m A)
Efficiency
0.82 0.80 0.78 0.76 0.74 0.72 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0
VIN(V) VIN(V) VIN(V) VIN(V) VIN(V) vs vs vs vs vs Efficiency Efficiency Efficiency Efficiency Efficiency at at at at at Iload Iload Iload Iload Iload =10mA =20mA =30mA =40mA =50mA
-50
0
50
100
150
Input Voltage (V)
Ambient Temperature (C)
Supply Current vs Input Voltage
3.0
Switching Frequency vs Ambient Temperature
Switching Frequency (MHz)
1.8
Supply Current (mA)
2.5 2.0 1.5 1.0 0.5 0.0 2.5 3.0 3.5 4.0 4.5
IOUT = 0mA
IOUT = 15mA VOUT = 15V VIN = 3.6V
Switching
1.6
1.4
Non Switching
1.2
1.0 -40 -20 0 20 40 60 80 100 120 140
5.0
5.5
6.0
Input Voltage (V)
Ambient Temperature (C)
4 FAN5331 Rev. 1.0.1
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FAN5331 1.6MHz Boost Converter with 20V Integrated FET Switch
Typical Performance Characteristics (Contd.)
TA = 25C, Test Circuit Figure 3, unless otherwise noted.
Startup After Enable
RL = 300
Line Transient Response
IOUT = 30mA VIN = 4.2V Tr = Tf = 10S VOUT = 15V
Input Voltage
VIN = 3V VOUT = 15V
(5V/div)
VIN = 3.2V
Output Voltage
+0.6V
(200mA/div)
-0.6V
Inductor Current= 0mA
Time (200s/div)
Time (100s/div)
Load Transient Response
(100mV/Div)
Output Power Spectral Density
VIN = 3.6V IOUT = 35mA
(10mA/Div)
Tr = Tr = <1S VOUT = 15V IOUT = 0 to 35mA
Time (20s/div)
5 FAN5331 Rev. 1.0.1
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FAN5331 1.6MHz Boost Converter with 20V Integrated FET Switch
Block Diagram
SHDN 4 VIN 5 SW 1
Shutdown Circuitry
FB
+ Comp -
1.15 x VREF
Thermal Shutdown
R FB 3 +
Error Amp
S
Ramp Generator Oscillator
+ Comp Current Limit Comparator -
R R S
Q
Driver
n
+
+ Amp Reference Soft-Start
0.05
2 GND
Figure 4. Block Diagram
Circuit Description
The FAN5331 is a pulse-width modulated (PWM) current-mode boost converter. The FAN5331 improves the performance of battery powered equipment by significantly minimizing the spectral distribution of noise at the input caused by the switching action of the regulator. In order to facilitate effective noise filtering, the switching frequency was chosen to be high, 1.6MHz. An internal soft start circuitry minimizes in-rush currents. The timing of the soft start circuit was chosen to reach 95% of the nominal output voltage within maximum 5mS following an enable command when VIN = 2.7V, VOUT = 15V, ILOAD = 35mA and COUT (EFFECTIVE) = 3.2F. The device architecture is that of a current mode controller with an internal sense resistor connected in series with the N-channel switch. The voltage at the feedback pin tracks the output voltage at the cathode of the external Schottky diode (shown in the test circuit). The error amplifier amplifies the difference between the feedback voltage and the internal bandgap reference. The amplified error voltage serves as a reference voltage to the PWM comparator. The inverting input of the PWM comparator consists of the sum of two components: the amplified control signal received from the 50m current sense resistor and the ramp generator voltage derived from the oscillator. The oscillator sets the latch, and the latch turns on the FET switch. Under normal operating conditions, the PWM comparator resets the latch and turns off the FET, thus terminating the pulse. Since the comparator input contains information about the output voltage and the control loop is arranged to form a negative feedback loop, the value of the peak inductor current will be adjusted to maintain regulation. Every time the latch is reset, the FET is turned off and the current flow through the switch is terminated. The latch can be
reset by other events as well. Over-current condition is monitored by the current limit comparator which resets the latch and turns off the switch instantaneously within each clock cycle. Over-voltage condition is detected by a fast comparator limiting the duty cycle in a similar manner to over-current monitoring described above.
Applications Information
Setting the Output Voltage
The internal reference is 1.23V (Typical). The output voltage is divided by a resistor divider, R1 and R2 to the FB pin. The output voltage is given by R1 V OUT = V REF 1 + ------ R
2
According to this equation, and assuming desired output voltage of 15V, good choices for the feedback resistors are, R1=150k and R2=13.4k.
Inductor Selection
The inductor parameters directly related to device performances are saturation current and dc resistance. The FAN5331 operates with a typical inductor value of 10H. The lower the dc resistance, the higher the efficiency. Usually a trade-off between inductor size, cost and overall efficiency is needed to make the optimum choice. The inductor saturation current should be rated around 1A, which is the threshold of the internal current limit circuit. This limit is reached only during the start-up and with heavy load condition; when this event occurs the converter can shift over in
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FAN5331 1.6MHz Boost Converter with 20V Integrated FET Switch
discontinuous conduction mode due to the automatic turn-off of the switching transistor, resulting in higher ripple and reduced efficiency. Some recommended inductors are suggested in the table below:
ground plane connected to the pin 2 of the IC is recommended. This ground plane acts as an electromagnetic shield to reduce EMI and parasitic coupling between components.
Inductor Value
10H 10H 10H
Vendor
Panasonic Murata Coilcraft
Part Number
ELL6GM100M LQS66SN100M03L DO1605T-103Mx
Comment
Lower Profile (1.6mm) Highest Efficiency Small Size
Table 1: Recommended Inductors
Capacitors Selection
For best performance, low ESR input and output capacitors are required. Ceramic capacitors in the range 4.7F to 10F, placed as close to the IC pins, are recommended for the lower input and output ripple. The output capacitor voltage rating should be according to the VOUT setting. A feed forward capacitor CF, is required for stability. The recommended value (R1 x CF) is around 18S. Some capacitors are suggested in the table below.
Figure 5. Recommended Layout
Application Examples
1. LED Driver
One or more serial LED strings can be driven with a constant current, set by the series resistor, given by 1.23V I LED = --------------R1
Capacitor Value
4.7F 4.7F
Vendor
Panasonic Murata
Part Number
ECJ3YB1C475K GRM31CR61C475
VIN CIN
2.7V to 5.5V
L 10H
BAT54 COUT 4.7F
VOUT
4.7F 5 V
IN
SW
1
FAN5331
Table 2: Recommended Capacitors
FB
3
Diode Selection
The external diode used for rectification is usually a Schottky diode. Its average forward current and reverse voltage maximum ratings should exceed the load current and the voltage at the output of the converter respectively. A barrier Schottky diode such as BAT54 is preferred, due to its lower reverse current over the temperature range. Care should be taken to avoid any short circuit of VOUT to GND, even with the IC disabled, since the diode can be instantly damaged by the excessive current.
ON OFF
4
SHDN
GND
2
R1
R2
Figure 6. Low Noise Boost LED Driver
Thermal Shutdown
When the die temperature exceeds 150C, a reset occurs and will remain in effect until the die cools to 130C, at that time the circuit will be allowed to restart.
LED Current (mA)
20.2 20.1 20.0 19.9 19.8 19.7 2.5
LED Current vs Input Voltage (String Connected to FB Pin)
PCB Layout Recommendations
The inherently high peak currents and switching frequency of power supplies require careful PCB layout design. Therefore, use wide traces for high current paths and place the input capacitor, the inductor, and the output capacitor as close as possible to the integrated circuit terminals. The resistor divider that sets the output voltage should be routed away from the inductor to avoid RF coupling. A four layer PCB with at least one
3.0
3.5
4.0
4.5
5.0
5.5
6.0
Input Voltage (V)
7 FAN5331 Rev. 1.0.1
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FAN5331 1.6MHz Boost Converter with 20V Integrated FET Switch
The feedback loop tightly regulates the current in the branch connected to FB pin, while the current in the other branch depends on the sum of the LED's forward voltages, VOUT and the ballast resistor. The input and the output ripple is less than 3mVRMS, for load currents up to 40mA. A Zener diode (VZ = 22V) connected between VOUT and GND can prevent the FAN5331 from being damaged by over-voltage, if the load is accidently disconnected during operation.
While the feedback loop tightly regulates VOUT, the negative output voltage (-VOUT) can supply a light load with a negative voltage. Nevertheless, the negative voltage depends on the changes of the load current in both -VOUT and +VOUT, as shown in the graph below.
Negative Output Voltage vs Load Current
-18
Negative Output Voltage (V)
2. Dual Boost Converter
A negative voltage can be provided by adding an external charge pump (C1, C2, D2, and D3).
C1 0.1F BAT54S D2 C2 D3 4.7F -VOUT IOUT = 10mA
-15V/Unloaded
-16
-15V/10mA Load
-14
VIN CIN
2.7V to 5.5V
L 10H
BAT54
VOUT COUT I OUT = 50mA 4.7F R1 CF 120pF
-12
D1
4.7F 5 V
IN
SW
1
-10 0 10 20 30 40 50
FAN5331
FB
3
Load Current On Positive Output Side (mA)
ON OFF
4
R2 SHDN GND 2
Figure 7. Dual () Boost Converter
8 FAN5331 Rev. 1.0.1
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FAN5331 1.6MHz Boost Converter with 20V Integrated FET Switch
Mechanical Dimensions
5-Lead SOT-23Package
B e c E H e1 D A A1 L
Symbol Min
A A1 B c D E e e1 H L .087 .004 0 .035 .000 .008 .003 .106 .059
Inches Max
.057 .006 .020 .010 .122 .071 .037 BSC .075 BSC .126 .024 10
Millimeters Min
.90 .00 .20 .08 2.70 1.50 .95 BSC 1.90 BSC 2.20 .10 0 3.20 .60 10
Notes
Max
1.45 .15 .50 .25 3.10 1.80
Ordering Information
Product Number
FAN5331
Package Type
5-Lead SOT23
Order Code
FAN5331SX
9 FAN5331 Rev. 1.0.1
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FAN5331 1.6MHz Boost Converter with 20V Integrated FET Switch
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Preliminary
First Production
No Identification Needed
Full Production
Obsolete
Not In Production
This datasheet contains specifications on a product that has been discontinued by Fairchild semiconductor. The datasheet is printed for reference information only.
Rev. I7
10 FAN5331 Rev. 1.0.1
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