LSP5504. PWM Control 2A Step-Down Converter. Applications. General Description. Features LSP5504. Typical Application Circuit

Transcription

1 Applications Cellular Phones PC Motherboard LCD Monitor Graphic Card DVD-Video Player Telecom Equipment ADSL Modem Networking power supply Networking power supply Microprocessor core supply Printer and other Peripheral Equipment Features Input voltage: 3.6V to 18V. Output voltage: 0.8V to VCC. Duty ratio: 0% to 100% PWM control Oscillation frequency: 300KHz typ. Soft-start, Current limit, Enable function Thermal Shutdown function SOP-8L Package. General Description The LSP5504 is high efficiency, simple to use, 2A step-down regulator flexible enough to be optimized for a variety of applications. LSP5504 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 from 300KHz to 50KHz. Also, an internal compensation block is built in to minimum external component count. With the addition of an internal buffer driver, a coil, capacitors, and resistors 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 18V, it is also suitable for the operation via an AC adapter. Typical Application Circuit Vout=5V/2A LSP5504 1/11 Ver.1.0

2 Ordering Information LSP5504 X X X X Package: S: SOP-8L Output Voltage: Balnk: adj Packing: A: Tape & Real Temperature Grade: G: -20 ~ 125 C Pin Assignment Top View FB 1 8 VSS EN OCSET 2 3 SOP-8L 7 6 VSS OUTPUT VCC 4 5 OUTPUT Pin Description Pin NO. Pin Name Pin Function 1 FB Feedback Pin 2 EN Enable Input Pin 3 OCSET Add an external resistor to set max output current 4 VCC IC power supply pin 5,6 OUTPUT Switch pin. Connect external inductor here. Minimize trace area at this pin to reduce EMI. 7,8 VSS GND pin 2/11 Ver.1.0

3 Functional Block Diagram Output Buffer Absolute Maximum Ratings Parameter Value Unit VCC Pin Voltage, V CC V SS -0.3 to V SS +20 V Feedback Pin Voltage, V FB V SS -0.3 to V CC V EN Pin Voltage, V EN V SS -0.3 to V IN V Switch Pin Voltage, V OUTPUT V SS -0.3 to V IN V Power Dissipation, P D Internally limited mw Operating Temperature Range, T OPR -20 to +125 C Storage Temperature Range, T STG -40 to +150 C Note: Do not exceed these limits to prevent damage to the device. Exposure to absolute maximum rating conditions for long periods may affect device reliability. 3/11 Ver.1.0

4 Electrical Characteristics (V IN = 12V, T A = 25 C, unless otherwise specified.) Parameter Symbol Test Conditions Min. Typ. Max. Unit Input Voltage V IN V Feedback Voltage V FB I IOUT = 0.1A V Feedback Bias Current I FB I IOUT = 0.1A µa Switch Current I SW 3.5 A Current Consumption During Power Off I SSS V EN = 0 10 µa Line Regulation V OUT / V OUT V IN =5V~18V, I IOUT = 0.3A 1 2 % Load Regulation V OUT / V OUT I IOUT = 0.1A~0.3A % Oscillation Frequency fosc Measure waveform at SW pin KHz Frequency of Current Limit or Short Circuit Protect fosc1 Measure waveform at SW pin KHz V SH Evaluate oscillation at SW pin 2.0 Enable Pin Input Voltage V SL Evaluate oscillation stop at SW pin 0.8 V Enable Pin Input Leakage Current I SH 20 I SL -10 µa OCSET Pin Bias Current I OCSET µa Soft-Start Time T SS ms Internal MOSFET Rdson R dson V IN =5V, V FB = V IN =12V, V FB = mω Efficiency EFFI V IN =12V, V OUT =5V, I IOUT = 2A 91 % Thermal Resistance Junction to Ambient Thermal Resistance Junction to Case θ JA 65 C/W θ JC 20 C/W Over temperature shutdown TSD 140 C Over temperature shutdown Hysteresis THYS 50 C 4/11 Ver.1.0

5 Functional Description Vout=5V/2A LSP PWM Control The LSP5504 is a DC/DC converter that employs a pulse-width modulation (PWM) system. 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. Thus, the converter provides a low-ripple power over broad ranges of input voltage and load current. 2. Under Voltage Lockout The under voltage lockout circuit of the LSP5504 will turn off PWM-Switched control circuit when the supply voltage drops below 3.3V. Normal operation resumes once VCC rises above 3.5V. 3. Output Voltage Programming Output voltage can be set by a resistor divider network. In this application circuit, a designer can calculate the Vout as below equation: R V OUT = A R B The resistor should be large enough to avoid power loss in feedback voltage divider that combination of R A and R B. And the lower resistor values minimize noise pickup in the sensitive feedback pin. Designer can reference the values of Table 1, to initial your design. 5/11 Ver.1.0

6 Vout (V) R A ( ) R B ( ) open R DS(ON) Current Limiting The current limit threshold is set by the external resistor, which connects from VCC 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 protection is triggered. The current limit value can be set through the formula below, I PEAK R DS(ON) =I OCSET R OCSET Some useful values of inductor and R OCSET are list as below: V IN =12V, I MAX =2A Vout (V) 2.5V 3.3V 5V L1 Value 15uH 18uH 22uH Vout (V) V IN 5V 12V 18V K 3.0K 3.3K K 3.0K 3.9K K 3.0K 3.9K K 3.0K 3.9K K 3.0K 3.9K K 3.0K 3.9K 5.0 N/A 3.0K 4.7K 6/11 Ver.1.0

7 Typical Characteristics 0.83 V IN vs. V FB (V OUT =3.3V, IOUT = 0.2A) 350 V IN vs. Frequency (V OUT =3.3V, I OUT = 0.2A) VFB (V) FOSC (khz) V IN (V) V IN (V) 3.50 Line Regulation (V OUT =3.3V, IOUT = 0.2A) 3.35 Load Regulation (VIN =12V) V OUT (V) V OUT (V ) V IN (V) I OUT (A) 100% Efficiency (V IN =12V, V OUT =3.3V) 90% Efficiency (%) 80% 70% 60% 50% I OUT (A) 7/11 Ver.1.0

8 Typical Characteristics (Continued) Vout Ripple Vout Ripple ( Vin =12V; Vout = 3.3V; Iout = 0.1A ) ( Vin = 12V; Vout = 3.3V; Iout = 2A ) 8/11 Ver.1.0

9 Test Circuit 1) Enable Function Test 2) Feedback Function Test 3) Operation Function Test 9/11 Ver.1.0

10 Marking Information LSC LSP5504 YYWW ZZ Logo Part ID Internal Code Date Code YY: Year(09=2009) WW: Week(01-52) Package Information SOP-8L: E H L 7 ο (4 ) D ο 7 ο (4 ) A2 A e B A1 C VIEW A 10/11 Ver.1.0

11 Symbol Dimensions In Millimeters Dimensions In Inches Min. Nom. Max. Min. Nom. Max. A A A B C D E e 1.27TYP TYP. H L θ 0 ο 8 ο 0 ο 8 ο 11/11 Ver.1.0