UNISONIC TECHNOLOGIES CO., LTD P1785 Preliminary LINEAR INTEGRATED CIRCUIT PWM CONTROL 2A STEP-DOWN CONVERTER DESCRIPTION UTC P1785 consists of 2A step-down switching regulator control which includes a reference voltage source, oscillation circuit, error amplifier, internal PMOS and etc with PWM. UTC P1785 can provide low-ripple power, high efficiency, and excellent transient characteristics and an enable function, an over current protect function and a short circuit protect function are built inside, so the operation frequency will be reduced from 300KHz to 30KHz when OCP or SCP happens. And the PWM control circuit can vary the duty ratio linearly from 100 down to 0%. This converter also includes an error amplifier circuit as well as a soft-start circuit that prevents overshoot at startup. Also, to minimum external component count an internal compensation block is built in. These ICs can work as step-down switching regulators with the addition of an internal P-channel Power MOS, a coil, capacitors, and a diode connected externally. They provide such outstanding features: low current consumption. It is also suitable for the operation via an AC adapter because this converter can accommodate an input voltage up to 23V. SOP-8 FEATURES * Soft-start, Current Limit, Enable function * Thermal Shutdown function * Built-in internal SW P-channel MOS * Input voltage: 3.6V to 23V. * Output voltage: 0.8V to VCC. * Duty ratio: 0% to 100% PWM control * Oscillation frequency: 300KHz typ. ORDERING INFORMATION Ordering Number Lead Free Halogen Free P1785L-S08-R P1785G-S08-R P1785L-S08-T P1785G-S08-T www.unisonic.com.tw Copyright © 2011 Unisonic Technologies Co., Ltd Package Packing SOP-8 SOP-8 Tape Reel Tube 1 of 7 QW-R103-043.b P1785 Preliminary PIN CONFIGVRATIONS PIN DESCRIPTIONS PIN NO. 1 PIN NAME FB I/O I I 2 EN 3 4 OCSET VCC I 5, 6 Output O 7, 8 VSS DESCRIPTION Feedback pin. Chip enable, H: enable step-down function L: chip disable Add an external resistor to set max output current. IC power supply pin Switch Pin. Connect external inductor/diode here. Minimize trace area at this pin to reduce EMI. GND Pin UNISONIC TECHNOLOGIES CO., LTD www.unisonic.com.tw LINEAR INTEGRATED CIRCUIT 2 of 7 QW-R103-043.b P1785 Preliminary LINEAR INTEGRATED CIRCUIT BLOCK DIAGRAM Output 5,6 Oscillation Circuit Reference Voltage Source with Soft Start + PWM-Switched Control Circuit FB - Thermal Shutdown 4 VCC 100μA Vss VEN 7,8 OCSET UNISONIC TECHNOLOGIES CO., LTD www.unisonic.com.tw 1 3 2 EN 3 of 7 QW-R103-043.b P1785 Preliminary LINEAR INTEGRATED CIRCUIT ABSOLUTE MAXIMUM RATINGS PARAMETER SYMBOL RATING UNIT VCC Pin Voltage VCC VSS-0.3 ~ VSS+25 V Feedback Pin Voltage VFB VSS-0.3 ~ VCC V EN Pin Voltage VEN VSS-0.3 ~ VIN+0.3 V Switch Pin Voltage VOUT VSS-0.3 ~ VIN+0.3 V Power Dissipation PD Internally limited mW ℃ Operating Temperature TOPR -20 ~ +125 ℃ Storage Temperature TSTG -40 ~ +150 Note: 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. THERMAL DATA PARAMETER Junction to Ambient SYMBOL θJA RATING 65 UNIT °C/W ELECTRICAL CHARACTERISTICS (VIN = 12V, Ta=25°C, unless otherwise specified) PARAMETER SYMBOL CONDITIONS Input Voltage VIN Feedback Voltage VFB IOUT=0.1A Feedback Bias Current IFB(BIAS) IOUT=0.1A Switch Current ISW Standby Current ISTN-BY VEN=0V Line Regulation ΔVOUT/VOUT VIN=6V~23V, IOUT=0.2A Load Regulation ΔVOUT/VOUT IOUT=0.1~2A Oscillation Frequency fOSC Measure waveform at SW pin Frequency of Current Limit or Short Measure waveform at SW pin fOSC1 Circuit Protect VSH Evaluate oscillation at SW pin EN Pin Input Voltage Evaluate oscillation stop at SW pin VSL ISH EN Pin Input Leakage Current ISL OCSET Pin Bias Current IOCSET Soft-Start Time TSS VIN=5V, VFB=0V Internal MOSFET RDS(ON) RDS(ON) VIN=12V, VFB=0V Efficiency η VIN=12V, VOUT=5V, IOUT=2A UNISONIC TECHNOLOGIES CO., LTD www.unisonic.com.tw MIN. TYP. MAX. UNIT 3.6 23 V 0.784 0.8 0.816 V 0.1 0.5 μA 2.15 A 10 μA 1 2.1 % 0.2 0.5 % 240 300 360 KHz 10 75 0.3 KHz 0.79 0.72 20 -10 90 2 180 130 91 V 105 5 230 200 μA μA μA ms mΩ % 4 of 7 QW-R103-043.b P1785 Preliminary LINEAR INTEGRATED CIRCUIT FUNCTION DESCRIPTION PWM Control The UTC P1785 consists of DC/DC converters which employ a PWM system. In this DC/DC converter, the pulse width varies in a range from 0 to 100% which is according to the load current. Cause the switching frequency remains constant the ripple voltage which produced by the switching can be removed easily through a filter. 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 makes sure that the outputs of high-side MOSFET driver remain in the off state after the supply voltage drops below 3.3V. When VCC rises above 3.5V normal operation resumes. RDS(ON) Current Limiting The current limit threshold is fixed by the external resistor which is connected from VCC supply to OCSET. An over-current condition is triggered when the PWM voltage is less than the voltage at OCSET. ILOAD × RDS(ON) = IOCSET × ROCSET above formula is setting the current limit value. UNISONIC TECHNOLOGIES CO., LTD www.unisonic.com.tw 5 of 7 QW-R103-043.b P1785 Preliminary LINEAR INTEGRATED CIRCUIT TEST CIRCUIT + - UNISONIC TECHNOLOGIES CO., LTD www.unisonic.com.tw 6 of 7 QW-R103-043.b P1785 Preliminary LINEAR INTEGRATED CIRCUIT TYPICAL APPLICATION CIRCUIT VOUT L1 Value VIN=12V, IMAX=2A 2.5V 3.3V 15uH 18uH 5V 22uH UTC assumes no responsibility for equipment failures that result from using products at values that exceed, even momentarily, rated values (such as maximum ratings, operating condition ranges, or other parameters) listed in products specifications of any and all UTC products described or contained herein. UTC products are not designed for use in life support appliances, devices or systems where malfunction of these products can be reasonably expected to result in personal injury. Reproduction in whole or in part is prohibited without the prior written consent of the copyright owner. The information presented in this document does not form part of any quotation or contract, is believed to be accurate and reliable and may be changed without notice. UNISONIC TECHNOLOGIES CO., LTD www.unisonic.com.tw 7 of 7 QW-R103-043.b