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FAN4855 500mA High Efficiency Boost Regulator with Adjustable Output, Shutdown and Low Battery Detect
December 2005
FAN4855 500mA High Efficiency Boost Regulator with Adjustable Output, Shutdown and Low Battery Detect
Features
Low power PFM boost regulator Input voltage range is from 1.6V to 4.5V Output voltage range is from 3V to 5V 500mA maximum load current capability 95% efficient power conversion 2-3 cell and single cell Li-Ion systems Variable on-time Pulse Frequency Modulation (PFM) Internal synchronous rectifier (no need for external
General Description
The FAN4855 is a low power boost regulator designed for low voltage DC to DC conversion in 2-cell battery powered systems such as digital cameras, cell phones and PDAs. The converter starts-up at 1.3V and operates after the start at an input voltage as low as 1V. Output voltage can be adjusted by external resistors from 3.3V to 5V with a maximum load current of 0.5A. Quiescent current in shut-down mode is less than 10A, which maximizes the battery live time. The ON time changes with the input voltage to maintain the ripple current constant and to provide the highest efficiency over a wide load range--while maintaining low peak currents in the boost inductor. The combination of built-in power transistors, synchronous rectification and low supply current, make the FAN4855 ideal for portable applications. The FAN4855 is available in 8-lead TSSOP package.
diode)
Low-battery detection Logic controlled shutdown with true-load disconnect Low (80A) quiescent current TSSOP-8 Package
Applications
DSCs PDAs Cell phones, smart phones Portable instrumentations 2-3 AA / AAA cells operated devices Single cell Li-Ion operated devices
Ordering Information (TA = -40C to +85C)
Part Number
FAN4855MTC FAN4855MTCX
Package
8 Pin TSSOP 8 Pin TSSOP
Packing
Rails Tape and Reel
Typical Application
Input 1.6V to 4.5V FAN4855 On Off Low Battery Detect In Low Battery Detect Out 1 VIN 2 SHDN 3 LBI 4 LB0 GND 8 VL 7 VOUT 6 FB 5 Output 3.3V to 5V up to 0.5A
(c)2005 Fairchild Semiconductor Corporation
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FAN4855 Rev. 1.0.1
FAN4855 500mA High Efficiency Boost Regulator with Adjustable Output, Shutdown and Low Battery Detect
Pin Configuration
8-Pin TSSOP VIN SHDN LBI LB0 1 2 3 4 TOP VIEW 8 7 6 5 GND VL VOUT FB
Pin Description
Pin
1 2 3 4 5 6 7
Name
VIN SHDN LBI LBO FB VOUT VL
Function
Battery Input Voltage. Supplies the IC during start-up. After the output is running, the IC draws power from VOUT. Shut Down. Pulling this pin low shuts down the regulator, isolating the load from the input. Low-Battery Input. Pulling this pin below 0.39V causes the LBO pin to go low. Low-Battery Output. This pin provides an active low signal to alert the user when the LBI voltage falls below its targeted value. The open-drain output can be used to reset a microcontroller. Feedback Input. For setting the output voltage. Connect this pin to the resistor divider. Boost regulator output. Output voltage can be set to be in the 3 to 5V range. Startup at moderate load is achievable at input voltages around 1.35V. Boost inductor connection. Connect an inductor between this pin and VIN. When servicing the output supply, this pin pulls low, charging the inductor, then shuts off dumping the energy through the synchronous rectifier to the output. Ground of the IC.
8
GND
Absolute Maximum Ratings
Absolute Maximum Ratings are those values, beyond which the device could be permanently damaged. Absolute maximum ratings are stress ratings only and functional device operation is not implied.
Parameter
VIN, VOUT Voltages (Relative to GND) Switch Voltage (VL to GND) Voltage on any other Pin Peak Switch Current (Ipeak) Output Current (IOUT) Continuous Power Dissipation Thermal Resistance (JA) Junction Temperature Storage Temperature Range Lead Temperature (soldering, 10s)
Min.
-0.3 -0.3 -0.3
Max.
6.5 VOUT + 0.3 VOUT + 0.3 -- Internally Limited -- 500 525 124 150
Units
V V V mA mW C/W C C C
-65
150 300
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FAN4855 Rev. 1.0.1
FAN4855 500mA High Efficiency Boost Regulator with Adjustable Output, Shutdown and Low Battery Detect
Recommended Operating Conditions
Parameter
Ambient Temperature Range VIN Operating Range VOUT Operating Range
Min.
-40 1.6 3.0
Max.
+85 0.9 VOUT 5.0
Units
C V V
Electrical Characteristics
Unless otherwise specified, VIN = 1.6V to 3V, ILOAD = 1mA, TA = -40C to +85C. Test Circuit Fig.1. Typical values are at TA = +25C
Parameter
Start Up Voltage Operating Voltage Output Voltage Output Voltage Adjust Range Steady State Output Current Pulse Width ILOAD < 1mA
Conditions
After start ILOAD =10mA, VOUT = 3.3V or 5V VOUT(nom.) = 3.3V (Note 1) VOUT(nom.) = 5V VOUT = 3.3V, VIN = 2.5V VOUT = 5V, VIN = 2.5V VIN = 3V VIN = 2.4V VIN = 1.8V VIN = 1.6V
Min.
Typ.
1.35 1.0
Max.
1.6 3.45 5.225 5
Units
V V V V V mA mA
3.15 4.775 3 300 200 0.8 1.2 1.6 1.7
3.3 5 500 330 1.4 1.7 2.2 2.5 1 0.5 0.5 0.5 1 1.243 0.390 25
2 2.5 3.3 4.0 2 2
s s s s s % % % % V V mV %
Minimum Off-Time Line Regulation Load Regulation Feedback Voltage (VFB) LBI Threshold Voltage LBI Hysteresys Internal NFET, PFET ON Resist. Power Efficiency Input Current in Shut Down Mode Quiescent Current LBO Output Voltage Low SHDN Input Threshold Voltage SHDN Input Threshold Voltage ILOAD = 100mA ILOAD = 200mA, VIN = 3V, VOUT = 3.3V SHDN = 0V, VIN = 3V (Note 2) SHDN = 3V, VIN = 3V, VOUT = 3.3V (Note 2) VLBI = 0, ISINK = 1mA VIN = 3V, VOUT = 3.3V/5V VIN = 1.6V, VOUT = 3.3V/5V IOUT = 2mA, VOUT = 3.3V VOUT = 5V 0 to 250mA, VIN = 2.4V, VOUT = 3.3V 0 to 150mA, VIN = 2.4V, VOUT = 5V
0.35 95 8 80 0.2 1.5 0.8 50 160
A A V V V
Notes: 1. R4, R5, R6 tolerance 0.1%. 2. Current through R1, R2 is not taken into account.
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FAN4855 Rev. 1.0.1
FAN4855 500mA High Efficiency Boost Regulator with Adjustable Output, Shutdown and Low Battery Detect
VIN 2 1 1.6V to 3.0V
10uH R1 750K JP2 U1 FAN4855 1 Vin 8 Gnd 2 SHDN JP3 3 LBI 4 + LBO VL Vout FB 7 6 5 C3 18pF R4 402K VOUT JP1 1 2 3.3V or 5V + C2 47F Tantalum J1 SCOPE JACK
SHDN 2 1 Reset 2 1 C1 47F
R2 240K
R3 100K
Ext Pull Up 2 1 R6 287K R5 240K
C5 0.1F
GND 2 1
GND1 1 2
Figure 1. Test Circuit
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FAN4855 Rev. 1.0.1
FAN4855 500mA High Efficiency Boost Regulator with Adjustable Output, Shutdown and Low Battery Detect
Typical Operating Characteristics (L = 10H, CIN = 47F, COUT = 47F/1.0F, T = 25C)
Load Current vs. Start-Up Voltage (Resistive Load) 600 500 Load Current, mA 400 300 200 100 0 1.5 VOUT = 5V Efficiency, % VOUT = 3.3V Efficiency vs. Load Current Vout = 3.3V Vin=3V Vin=2.0V
100.0 90.0 80.0 70.0 60.0 50.0 40.0 30.0 20.0 10.0 0.0 0.1
Vin=1.5V
2
2.5
3
3.5
4
1
Input Voltage, V
10 100 Output Current, mA
1000
Efficiency vs. Load Current Vout = 5V 100.0 90.0 80.0 Efficiency, % 70.0 60.0 50.0 40.0 30.0 20.0 10.0 0.0 0.1 1 10 Output Current, mA 100 1000 Vin=2.0V Vin=1.5V SHDN Voltage, V Vin=3V 2.3 2.1 1.9 1.7 1.5 1.3 1.1 0.9 0.7 0.5 1.5 2
SHDN Threshold Voltage
2.5
3
3.5
4
4.5
Input Voltage, V
4 3.5 Output Voltage, V
Starting Up and Turning Off VOUT = 3.3V, Iloads = 10mA to 50mA 5
Starting Up and Turning Off VOUT = 5V, Iloads = 10mA to 50mA
Output Voltage, V
3 2.5 2 1.5 1 0.5 0 0.6 0.8
START UP TURN OFF: Iload=50mA Iload=10mA START UP
4 3 2
TURN OFF: Iload=50mA Iload=10mA Iload=10mA to 50mA
1 0 0.6
1.0 1.2 1.4 Input Voltage, V
1.6
1.8
0.8
1.0 1.2 1.4 Input Voltage, V
1.6
1.8
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FAN4855 Rev. 1.0.1
FAN4855 500mA High Efficiency Boost Regulator with Adjustable Output, Shutdown and Low Battery Detect
Typical Operating Characteristics (L = 10H, CIN = 47F, COUT = 47F/1.0F, T = 25C)
No Load Supply Current vs. Input Voltage 1000 "ON" Input Current (A) 100
VOUT = 3.3V VOUT = 5V
Output Voltage vs. Temperature 0.2 VOUT Relative Change (%)
0
10 "OFF" 1
-0.2
-0.4
0.1
0
1
2 3 Input Voltage (V)
4
5
-0.6 -50
-25
0
25
50
75
100
Temperature (C)
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FAN4855 Rev. 1.0.1
FAN4855 500mA High Efficiency Boost Regulator with Adjustable Output, Shutdown and Low Battery Detect
Typical Operating Characteristics (Continued)
Line Transient Response @100mA Load Exiting Shutdown
VOUT
VSHDN
Load Transient Response
Load Transient Response
Heavy-Load Switching Waveforms
Inductor Current and Switching Node Voltage
VL
Inductor Current
IL
VOUT
VL
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FAN4855 Rev. 1.0.1
FAN4855 500mA High Efficiency Boost Regulator with Adjustable Output, Shutdown and Low Battery Detect
Block Diagram
LBO 4 7 SHDN Control Logic LBI 3 0.39V - A3 + ILIMIT VIN 1 VOUT Start-Up Synchronous Rectifier Control A2 - SHDN 2 VL
Q2 VOUT + 6
Minimum Off-Time Logic Variable On-Time One Shot ILIMIT SHDN
Current Limit Control N 1 - A1 +
ILIMIT 5
VFB
Q1
VREF 8 GND
Functional Description
Boost Regulator
FAN4855 is an adjustable boost regulator that combines variable ON and minimum OFF architecture with synchronous rectification. Unique control circuitry provides high-efficiency power conversion for both light and heavy loads by transitioning between discontinuous and continuous conduction mode based on load conditions. There is no oscillator; a constant-peak-current limit of 0.8A in the inductor allows the inductor current to vary between this peak limit and some lesser value. The switching frequency depends upon the load, the input and output voltage ranging up to 430kHz. The input voltage VIN comes to VIN pin and through the external inductor to the VL pin of the device. The loop from VOUT closes through the external resistive voltage divider to the feedback pin VFB. The transfer ratio of this divider determines the output voltage. When VFB voltage drops below the VREF = 1.24V the error amplifier A1 signals to regulator to deliver charge to the output by triggering the Variable On-Time One Shot. One Shot generates a pulse at the gate of the Power NMOS transistor Q1. This transistor will charge the Inductor L1 for the time interval TON resulting in a peak current given by: T ON x V IN I L ( PEAK ) = -------------------------L1
When the one-shot times out, the Q1 transistor releases the VL pin, allowing the inductor to fly-back and momentarly charge the output through the body diode of the transistor Q2. But, as the voltage across the Q2 changes polarity, its gate will be driven low by the Synchronous Rectifier Control Circuit (SRC), causing Q2 to short out its body diode. The inductor then delivers the charge to the load by discharging into it through Q2. Under light load conditions, the amount of energy delivered in this single pulse satisfies the voltage-control loop, and the converter does not command any more energy pulses until the output drops again below the lower-voltage threshold. Under medium and heavy loads, a single energy pulse is not sufficient to force the output voltage above its upper threshold before the minimum off time has expired and a second charge cycle is commanded. Since the inductor current has not reached zero in this case, the peak current is greater than the previous value at the end of the second cycle. The result is a ratcheting of inductor current until either the output voltage is satisfied, or the converter reaches its set current limit. After a period of time TOFF > 1S, determined by Minimum Off-Time Logic and if VOUT is low (VFB < VREF), the Variable On-Time One Shot will be turned ON again and the process repeats. The output capacitor of the converter filters the variable component, limiting the output voltage ripple to a value determined by its capacitance and its ESR.
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FAN4855 Rev. 1.0.1
FAN4855 500mA High Efficiency Boost Regulator with Adjustable Output, Shutdown and Low Battery Detect
The synchronous rectifier significantly improves efficiency without the addition of an external component, so that conversion efficiency can be as high as 94% over a large load range, as shown in the Typical Operating Characteristics. Even at light loads, the efficiency stays high because the switching losses of the converter are minimized by reducing the switching frequency.
Error Detection Comparator (LBI - LBO)
An additional comparator A3 is provided to detect low VIN or any other error conditions that is important to the user. The non-inverting input of the comparator is internally connected to a reference threshold voltage Vth while the inverting input is connected to the LBI pin. The output of the low battery comparator is a simple open-drain output that goes active low if the battery voltage drops below the programmed threshold voltage on LBI. The output requires a pull-up resistor having a recommended value of 100 k, should be connected only to VOUT. The low-battery detector circuit is typically used to supervise the battery voltage and to generate an error flag or a RESET command when the battery voltage drops below a user-set threshold voltage. The function is active only when the device is enabled. When the device is disabled, the LBO-pin is high impedance.
The battery voltage, at which the detection circuit switches, can be programmed with a resistive divider connected to the LBI-pin. The resistive divider scales down the battery voltage to a voltage level of tenths of volt, which is then compared to the LBI threshold voltage. The LBI-pin has a built-in hysteresis of 25 mV. The resistor values R1 and R2 can be calculated using the following equation: VIN_MIN = 0.39 x (R1+R2)/R2 The value of R2 should be 270k or less to minimize bias current errors. R1 is then found by rearranging the equation: R1 = R2 x (VIN_MIN/0.39 - 1) If the low-battery detection circuit is not used, the LBI-pin should be connected to GND (or to VIN) and the LBO-pin can be left unconnected or tied to GND. Do not let the LBI-pin float.
Component Selection Input and Output Capacitors Selection
For common general purpose applications, 47F tantalum capacitors are recommended. Ceramic capacitors are recommended at input only; if connected at the output they cannot improve significantly the voltage ripple. More effective in reducing the output ripple at light load is to connect a small capacitor of 18 to 100pF between VOUT and FB pin. Table 1. Recommended capacitors
Shutdown
The device enters shutdown when VSHDN is approximately less than 0.5VIN. During shutdown the regulator stops switching, all internal control circuitry including the low-battery comparator is switched off and the load is disconnected from the input. The output voltage may drop below the input voltage during shutdown. The typical dependence shutdown voltage versus input voltage and the timing process of the exiting shutdown are shown on the Diagrams. For normal operation VSHDN should be driven up 0.8VIN or connected to the VIN.
Vendor
MuRata AVX Sprague Kemet
Description
X5R Ceramic TAJ,TPS series tantalum 595D series tantalum T494 series tantalum
Application Information
Selecting the Output Voltage
The output voltage VOUT can be adjusted from 3V to 5V, choosing resistors R4 and R5 of the divider in the feedback circuit (see Test Circuit). The value of the R5 is recommended to be less than 270k. R4 can be calculated using the following equation: R4 = R5[(VOUT/VREF) - 1] where VREF = 1.24V
Inductor Selection
The inductor parameters directly influencing the device performance are the saturation current and the DC resistance. The FAN4855 operates with a typical inductance of 10H. The lower the resistance, the higher the efficiency. The saturation current should be rated higher than 0.8A, which is the typical threshold to switch off the N-channel power FET. Table 2. Recommended Inductors
Setting the LBI Threshold of Low-Battery Detector Circuit
The LBO-pin goes active low when the voltage on the LBI-pin decreases below the set threshold typical voltage of 390 mV, which is set by to the internal reference voltage.
Supplier
MuRata Coilcraft Coiltronics Sumida
Manufacturer Part Number
LQ66C100M4 DT1608C-103 UP1B100 CDR63B-100
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FAN4855 Rev. 1.0.1
FAN4855 500mA High Efficiency Boost Regulator with Adjustable Output, Shutdown and Low Battery Detect
Layout and Grounding Considerations
Careful design of printed circuit board is recommended since high frequency switching and high peak currents are present in DC/DC converters applications. A general rule is to place the converter circuitry well away from any sensitive analog components. The printed circuit board layout should be based on some simple rules to minimize EMI and to ensure good regulation performances: 1. 2. Place the IC, inductor, input and output capacitor as close together as possible. Keep the output capacitor as close to the FAN4855 as possible with very short traces to VOUT and GND pins. Typically it should be within 0.25 inches or 6 mm. Keep the traces for the power components wide, typically > 50 mils or 1.25 mm. Place the external networks for LBI and FB close to FAN4855, but away from the power components as far as possible to prevent voltage transient from coupling into sensitive nodes. On multilayer boards use component side copper for grounding around the IC and connect back to a quiet ground plane using vias. The ground planes act as electromagnetic shields for some of the RF energy radiated. The connection of the GND pin of the IC (pin 8) to the overall grounding system should be directly to the bottom of the output filter capacitor. A star grounding system radiating from where the power enters the PCB, is a recommended practice.
Application Example
The FAN4855 can be used as a constant current source to drive white LEDs like QTLP670C-IW. As shown in the diagram below, the current is maintained constant over a wide range of input voltages.
L = 10H FAN4855
1 2 3 4 8 7 6 5
D1
62
D2
62
+
+ Cin 10F
+
D3 Cout 10F D4
62
3. 4.
62
5.
6.
20 19.8 19.6 19.4 19.2 19 18.8 18.6 18.4 18.2 18 0 1 2 3 4 5 Input Voltage (V)
10
LED Current (mA)
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FAN4855 Rev. 1.0.1
FAN4855 500mA High Efficiency Boost Regulator with Adjustable Output, Shutdown and Low Battery Detect
Mechanical Dimensions
Package: T08, 8-Pin TSSOP
0.113 - 0.123 (2.87 - 3.12) 8
0.169 - 0.177 0.246 - 0.258 (4.29 - 4.50) (6.25 - 6.55) PIN 1 ID
1 0.026 BSC (0.65 BSC) 0.043 MAX (1.10 MAX) 0-8
0.033 - 0.037 (0.84 - 0.94)
0.008 - 0.012 (0.20 - 0.30)
0.002 - 0.006 (0.05 - 0.71)
0.020 - 0.028 (0.51 - 0.71)
0.004 - 0.008 (0.10 - 0.20)
SEATING PLANE
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FAN4855 Rev. 1.0.1
FAN4855 500mA High Efficiency Boost Regulator with Adjustable Output, Shutdown and Low Battery Detect
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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. I16
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FAN4855 Rev. 1.0.1

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