SP4446 EXAR | Alldatasheet
Document overview
- Manufacturer or author: Provided By ALLDATASHEET.COM(FREE DATASHEET DOWNLOAD SITE)
- PDF pages: 10
Technical content
Mar28-08 SP4446 High Output Voltage Boost Regulator, LCD Bias Regulator © 2008 Exar Corporation SP4446
FEATURES
■ High Output Voltage: Up to 30V ■ High Efficiency ■ Low Quiescent Current: ~20uA ■ Single Battery Cell Operation ■ Programmable Output Voltage ■ 1Ω Switch (150mV at 150mA) ■ Lead Free, RoHS Compliant Package: 5 Pin SOT-23 High Output Voltage Boost Regulator LCD Bias Regulator The SP4446 is a micro power Boost Regulator in a 5-lead SOT-23 package. It is a current limited, fixed off-time regulator configured for use in boost mode applications. The operating voltage can be less than 3Volts and is capable of generating voltages as high as 30Volts. The SP4446 is available in a Lead Free, RoHS compliant package and permits the construction of complete regulators that occupy < 0.2 square inches of board space. TYPICAL APPLICATION SCHEMATIC 5 4 1 2 3 SP4446 VIN SHDN SW GND FB
5 Pin SOT-23
10µH D1 L1 2.2 µF High Voltage Output VIN 4.7µF 2 to 7V SP4446
APPLICATIONS
■ LCD Bias ■ Tuner Pin Voltage ■ White LED Driver ■ High Voltage Bias ■ Digital Cameras ■ Cell Phone ■ Battery Backup ■ Handheld Computers
DESCRIPTION
Mar28-08 SP4446 High Output Voltage Boost Regulator, LCD Bias Regulator © 2008 Exar Corporation PIN DESCRIPTION PARAMETER SYMBOL MIN TYP MAX UNITS CONDITIONS Input voltage VIN 1.0 8.0 V Switch Current Limit = 150mA Supply Current IQ 20 30 µA ♦ No Switching 0.01 1 µA SHDN = 0.0V Reference Voltage VFB 1.17 1.22 1.27 V ♦ FB Hysteresis HYST 8 mV VFB Input Bias Current IFB 15 80 nA ♦ VFB = 1.22V Line Regulation ∆Vo/∆VI 0.04 %/V 1.2 ≤ VIN ≤ 8V Switch Off Time TOFF 300 nS VFB > 1V 1200 nS VFB < 0.3V Switch Saturation Voltage VC ESAT 50 mV ♦ ISW = 50mA 150 mV ISW = 150mA Switch Current Limit ILIM 100 150 200 mA ♦ SHDN Bias Current ISHDN 5 12 µA ♦ VSH D N = 5V SHDN High Threshold (on) VIH 0.9 V SHDN Low Threshold (off) VIL 0.25 V Switch Leakage Current ISWLK 2 5 µA ♦ Switch Off, VSW = 5V
ELECTRICAL CHARACTERISTICS
Specifications are at VIN = 3.3V, VSHDN = VIN, TA = 25°C, ♦ denotes the specifications which apply over the full operating temperature range, unless otherwise specified. ABSOLUTE MAXIMUM RATINGS These are stress ratings only and functional operation of the device at these ratings or any other above those indicated in the operation sections of the specifications below is not implied. Exposure to absolute maximum rating conditions for extended periods of time may affect reliability. PIN NUMBER PIN NAME DESCRIPTION 1 SW Switch input to the internal power switch.
2 GND Ground
3 FB Feedback
4 SHDN Shutdown. Pull high (on) to enable. Pull low (off) for shutdown. 5 VIN Input Voltage. Bypass this pin with a capacitor as close to the device as possible.
Mar28-08 SP4446 High Output Voltage Boost Regulator, LCD Bias Regulator © 2008 Exar Corporation FUNCTIONAL DIAGRAM VI (EXTERNAL) (EXTERNAL) SHDN 4 Q1 Q2 R6 R5 Shutdown Logic 300ns ONE-SHOT CLEAR X2 + SET DRIVER 52.5mV 0.35 GND SW C2 D1 VO U T POWER TRANSISTOR DISABLE VIN FB General Overview: Operation can be best understood by referring to the above block diagram. Q1 and Q2 along with R3 and R4 form a band gap reference. The input to this circuit completes a feedback path from the high voltage output through a voltage di- vider, and is used as the regulation control input. When the voltage at the FB pin is slightly above 1.22V, comparator X1 disables most of the internal circuitry. Current is then provided by capacitor C2, which slowly discharges until the voltage at the FB pin drops below the lower hysteresis point of X1, about 6mV. X1 then enables the internal circuitry, turns on chip power, and the current in the inductor begins to ramp up. When the current through the driver transistor reaches about 150mA, comparator X2 clears the latch, which turns off the driver tran- sistor for a preset 0.3µs. At the instant of shutoff, inductor current is diverted to the output through diode D1. During this 0.3µs time limit, inductor current decreases while its energy charges C2. THEORY OF OPERATION At the end of the 0.3µs time period, the driver transistor is again allowed to turn on which ramps the current back up to the 150mA level. Comparator X2 clears the latch, its output turns off the driver transistor, and this allows delivery of inductor L1’s stored kinetic energy to C2. This switching action continues until the output capacitor voltage is charged to the point where FB is at band gap (1.22V). When this condition is reached, X1 turns off the internal circuitry and the cycle repeats. The SP4446 contains circuitry to provide protection during startup and while in short-circuit conditions. When FB pin voltage is less than approximately 300mV, the switch off time is increased to about 1.2µs and the current limit is reduced to about 70% of its normal value. While in this mode, the average inductor current is reduced and helps minimize power dissipation in the SP4446, the external inductor and diode.
Mar28-08 SP4446 High Output Voltage Boost Regulator, LCD Bias Regulator © 2008 Exar Corporation inherently low ESR, which will help produce low peak to peak output ripple, and reduce high fre- quency spikes. For the typical application, a 4.7µF input capacitor and a 2.2µF output capacitor are sufficient. The input and output ripple could be further reduced by increasing the value of the input and output capaci- tors. Place all the capacitors as close to the SP4446 as possible for layout. For use as a voltage source, to reduce the output ripple, a small feedforward capacitor (47pF) across the top feedback resistor can be used to provide sufficient overdrive for the error comparator, thus reduce the output ripple. Refer to Table 2 for some suggested low ESR capacitors. MANUF. PART CAP/ SIZE/ NUMBER VOLTAGE TYPE MURATA GRM32RR71E 2.2 µF/25V 1210/X5R 770-436-1300 225KC01B MURATA GRM31CR61A 4.7 µF/10V 1206/X5R 770-436-1300 475KA01B TDK C3225X7R1E 2.2 µF/25V 1206/X7R 847-803-6100 225M TDK C3216X5R1A 4.7µF/10V 1206/X5R 847-803-6100 475K
APPLICATION INFORMATION
For SP4446, the internal switch will be turned off only after the inductor current reaches the typical DC current limit (ILIM =150mA). However, there is typically a propagation delay of 200nS between the time when the current limit is reached and when the switch is actually turned off. During this 200nS delay, the peak inductor current will in- crease, exceeding the current limit by a small amount. The peak inductor current can be estimated by: IPK = ILIM + VIN (M A X ) • 200nS L The larger the input voltage and the lower the inductor value, the greater the peak current. In selecting an inductor, the saturation current specified for the inductor needs to be greater than the SP4446 peak current to avoid saturating the inductor, which would result in a loss of efficiency and could damage the inductor. Choosing an in- ductor with low DCR decreases power losses and increase efficiency. Refer to Table 1 for some suggested low ESR inductors. MANUF. PART NUMBER DCR Current (Ω) Rating (mA) MURATA LQH32CN100K21 0.44 300 770-436-1300 (10 µH) MURATA LQH32CN220K21 0.71 250 770-436-1300 (22 µH) TDK NLFC453232T-100K 847-803-6100 (10µH) 0.273 250 TDK NLC453232T-100K 0.9 370 847-803-6100 (22µH) Table 1. Suggested Low ESR inductors diode should be larger than the output voltage. Table 2. Suggested Low ESR Capacitor Figure 1. Using SP4446 as Voltage Source
Table 3. Divider Resistor Selection ground plane that is tied directly to the GND pin. especially the feedback network. impedance isolation between the input and load. maximum current of 3mA and 5mA to the load. can be added as shown in Figure 3.
Mar28-08 SP4446 High Output Voltage Boost Regulator, LCD Bias Regulator © 2008 Exar Corporation PACKAGE: 5 PIN SOT-23
Mar28-08 SP4446 High Output Voltage Boost Regulator, LCD Bias Regulator © 2008 Exar Corporation Exar Corporation reserves the right to make changes to any products described herein. Sipex does not assume any liability arising out of the application or use of any product or circuit described herein; neither does it convey any license under its patent rights nor the rights of others. Exar Corporation Headquarters and Sales Office
248720 Kato Rd,33 South Hillview Drive
M Fremont, CA 94538 TEL: (510) 668-7000 FAX: (510) 668-7001
ORDERING INFORMATION
Part Number Operating Temperature Range Package Type -G: “Green”/Halogen free package. Substitute “-L” by “-G” in the ordering part number. /TR = Tape and Reel Pack quantity is 2,500 for SOT-23.