2A / 350KHz PWM Controller Buck Converter JAN. 2010

Transcription

1 2A / 350KHz PWM Controller Buck Converter JAN Product Description consists of step-down switching regulator with PWM control. These devices include a reference voltage source, oscillation circuit, error amplifier, internal P-channel Power MOSFET and etc. provides low-ripple power, high efficiency, and excellent transient characteristics. The PWM control circuit is able to vary the duty ratio linearly from 0 up to 100%. This converter also contains an error amplifier circuit as well as a soft-start circuit that prevents overshoot at startup. An enable function, an over current protect function and a short circuit protect function are built inside, and when OCP or SCP happens, the operation frequency will be reduced 350KHz to 30KHz. Also an internal compensation block is built in to minimum external component count. With the addition of an internal P-channel Power MOS, a coil, capacitors, and a diode connected externally, these ICs can function as step-down switching regulators. They serve as ideal power supply units for portable devices when coupled with the SOP-8L mini-package, providing such outstanding features as low current consumption. Since this converter can accommodate an input voltage up to 20V, it is also suitable for the operation via an AC adapter. Features Input voltage: 3.6V to 20V voltage: 0.8V to V CC. Duty ratio: 0% to 100% PWM control Oscillation frequency: 350KHz typ. Soft-start, Current limit, Enable function Thermal Shutdown Function Built-In internal SW P-CH Power MOS-FET SOP-8/PSOP-8 Pb-Free Package Applications Battery Charger Adapter PC Motherboard LCD Monitor Graphic Card DVD-Video Player Telecom Equipment ADSL Modem Printer and other Peripheral Equipment Microprocessor core supply Networking power supply Block Diagram VCC Oscillation Circuit Reference Voltage Source With Soft Start PWM-Switched Control Circuit + - FB Thermal Shutdown VEN 100uF VSS EN OCSET 1

2 Pin Assignments S (SOP- 8) PS (PSOP- 8) Exposed Thermal Pad PSOP-8 9 Name Pin Description FB 1 Feedback pin. EN 2 Power-off pin H: Normal operation (Step-down operation) L: Step-down operation stopped (All circuits deactivated) OCSET 3 Add an external resistor to set max output current V CC 4 IC power supply pin 5,6 V SS 7,8 GND Pin Switch Pin. Connect external inductor/diode here. Minimize trace area at this pin to reduce EMI Ordering Information SOP-8 SF PSOP-8 PSF Marking Information 2

3 Absolute Maximum Rating Symbol Parameter Rating Units V CC V CC Pin Voltage V SS to V SS + 22 V V FB Feedback Pin Voltage V SS to V CC V V EN EN Pin Voltage V SS to V IN V P D Power Dissipation Internally Limited W θ JA θ JC Thermal Resistance Junction to Ambient PSOP-8 45 ºC/W SOP Thermal Resistance Junction to Case PSOP-8 7 ºC/W SOP-8 20 T J Operating Junction Temperature Range -20 to +125 ºC T STG Storage Temperature Range -40 to +150 ºC Electrical Characteristics (T A = 25ºC unless otherwise noted, V DD = 15V) Symbol Parameter Test Conditions Min Typ Max Units V IN Supply Voltage Range V V FB Feedback Voltage I OUT = 0.1A V I FB Feedback Bias Current I OUT = 0.1A ua I SW Switch Current A I SSS Current Consumption During Power Off V EN = 0V 10 ua REG (LINE) Line Regulation V IN = 5V to 18V 1 2 % REG (LOAD) Load Regulation I OUT = 0.1A to 2A % F OSC Oscillation Frequency Measure Waveform at SW Frequency of Current pin F OSC1 Limit or Short Circuit 10 Protect V SH Evaluate OSC. at SW pin 2.0 V SL EN Pin Input Voltage Evaluate OSC. Stop at SW pin I SH 20 EN Pin Input Current I SL 0.8 KHz V ua I OCSET OCSET Pin Bias Current ua T SS Soft-Start Time ms R DS(ON) EFFI Internal MOSFET R DS(ON) Efficiency V IN = 5V, V FB = 0V V IN =12V, V FB = 0V V IN = 12V, V OUT = 5V, I OUT = 2A mω 92 % 3

4 Typical Applications Vin Vcc L1 33uH Vout =5V Cin 470uF CVcc 0.1uF Rocset 3K REN 100K CEN 0.1uF Cocset 0.1uF OCSET FB EN Vss D1 Cc Optional R1 6.8K R2 1.3K C 0.1uF Cout 470uF V OUT = V FB x (1 + R1/R2) ; R2 = 0.7K to 5K ohm V OUT R1 R2 L1 1.8V 2.5K 2.2K 18uH 2.5V 4.7K 2.2K 22uH 3.3V 4.7K 1.5K 27uH 5.0V 6.8K 1.3K 33uH Table 1. Test Circuit Vin Vcc Open Vin A Vcc 1K 1K OCSET EN FB Vss Open OCSET EN FB Vss A Enable Function Test Feedback Function Test Vin Vcc L Vout ROCSET R1 Cin OCSET FB Cout REN EN Vss R2 Operating Function Test 4

5 Typical Performance Characteristics Vout (V) Line Regulation Vout = 3.3V, Iout = 0.2A Vout (V) Load Regulation Vin = 12V Vin (V) Vfb (V) Vin V.S. Vfb Vout = 3.3V, Iout = 0.2A Iout (A) Vin (V) Operating Description PWM Control The consists of DC/DC converters that employ a pulse-width modulation (PWM) system. In converters of the, the pulse width varies in a range from 0 to 100%, according to the load current. The ripple voltage produced by the switching can easily be removed through a filter because the switching frequency remains constant. Therefore, these converters provide a low-ripple power over broad ranges of input voltage and load current. Under Voltage Lockout The under voltage lockout circuit of the assures that the high-side MOSFET driver outputs remain in the off state whenever the supply voltage drops below 3.3V. Normal operation resumes once V CC rises above 3.5V. R DS(ON) Current Limiting The current limit threshold is setting by the external resistor connecting from V CC supply to OCSET. The internal 100uA sink current crossing the resistor sets the voltage at the pin of OCSET. When the PWM voltage is less than the voltage at OCSET, an over-current condition is triggered. I LOAD R DS(ON) =I OCSET R OCSET See above formula for setting the current limit value. 5

6 Package Dimension SOP-8 PLASTIC PACKAGE D θ1 E1 E1/2 PIN 1 MARKING e E/2 b E θ1 h θ2 L L1 R1 R θ GAUGE PLANE L2 A A2 A1 Dimensions Millimeters Inches SYMBOL MIN MAX MIN MAX A A A b c D 4.90 (TYP).193 (TYP) E 6.00 (TYP).236 (TYP) E (TYP).154 (TYP) e 1.27 (TYP).050 (TYP) L L (TYP).041 (TYP) L (TYP).010 (TYP) R R h θ θ θ

7 PSOP-8 PLASTIC PACKAGE Dimensions Millimeters Inches SYMBOL MIN MAX MIN MAX A A A b b c c D D (TYP).130 (TYP) E E E (TYP).094 (TYP) e 1.27 (TYP).050 (TYP) L L (TYP).041 (TYP) R R h θ θ θ

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