UC1573 UC2573 UC3573 Buck Pulse Width Modulator Stepdown Voltage Regulator FEATURES DESCRIPTION • Simple Single Inductor Buck PWM Stepdown Voltage Regulation The UC3573 is a Buck pulse width modulator which steps down and regulates a positive input voltage. The chip is optimized for use in a single inductor buck switching converter employing an external PMOS switch. The block diagram consists of a precision reference, an error amplifier configured for voltage mode operation, an oscillator, a PWM comparator with latching logic, and a 0.5A peak gate driver. The UC3573 includes an undervoltage lockout circuit to insure sufficient input supply voltage is present before any switching activity can occur, and a pulse-by-pulse current limit. Input current can be sensed and limited to a user determined maximum value. In addition, a sleep comparator interfaces to the UVLO circuit which turns the chip off when the input voltage is below the UVLO threshold. This reduces the supply current to only 50µA, making the UC3573 ideal for battery powered applications. • Drives External PMOS Switch • Contains UVLO Circuit • Includes Pulse-by-Pulse Current Limit • Low 50µA Sleep Mode Current BLOCK DIAGRAM UDG-94106-1 SLUS346 - APRIL 1999 Powered by ICminer.com Electronic-Library Service CopyRight 2003 UC1573 UC2573 UC3573 CONNECTION DIAGRAMS ABSOLUTE MAXIMUM RATINGS VCC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35V EAINV . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . –0.6V to VCC IEAOUT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25mA RAMP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . –0.3V to 4V CS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . –0.3V to VCC IOUT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . –0.7A to 0.7A I3VREF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . –15mA Storage Temperature . . . . . . . . . . . . . . . . . . . –65°C to +150°C Junction Temperature . . . . . . . . . . . . . . . . . . . –65°C to +150°C Lead Temperature (Soldering, 10 sec.) . . . . . . . . . . . . . +300°C DIL-8, SOIC-8 (TOP VIEW) J or N, D Packages Currents are positive into, negative out of the specified terminal. Consult Packaging Section of Databook for thermal limitations and considerations of packages. ELECTRICAL CHARACTERISTICS: Unless otherwise specified, these parameters apply for TA = –55°C to +125°C for the UC1573, –40°C to +85°C for the UC2573, and 0°C to +70°C for the UC3573, VCC = 5V, CT = 680pF, TA = TJ. PARAMETER TEST CONDITIONS MIN TYP MAX UNITS 2.94 3 3.06 V Reference Section 3VREF Line Regulation VCC = 4.75 to 30V 1 10 mV Load Regulation I3VREF = 0 to –5mA 1 10 mV 85 100 115 kHz 1.45 1.5 1.55 V –0.2 –1 µA Oscillator Section Frequency VCC = 5V, 30V Error Amp Section EAINV EAOUT = 2V IEAINV EAOUT = 2V AVOL EAOUT = 0.5V to 3V 65 EAOUT High EAINV = 1.4V 3.6 EAOUT Low EAINV = 1.6V IEAOUT EAINV = 1.4V, EAOUT = 2V –350 –500 µA EAINV = 1.6V, EAOUT = 2V 7 20 mA 0.6 1 MHz –0.39 –0.43 –0.47 V 150 800 nA Unity Gain Bandwidth TJ = 25°C, F = 10kHz 90 dB 4 4.4 V 0.1 0.2 V Current Sense Comparator Section Threshold (referred to VCC) Input Bias Current CS = VCC CS Propagation Delay 400 ns Gate Drive Output Section OUT High Saturation IOUT = 0 IOUT = –10mA OUT Low Saturation 0 0.3 V 0.7 1.5 V IOUT = –100mA 1.5 2.5 V IOUT = 10mA 0.1 0.4 V IOUT = 100mA 1.5 2.2 V Rise Time TJ = 25°C, CLOAD = 1nF + 3.3 Ohms 30 80 ns Fall Time TJ = 25°C, CLOAD = 1nF + 3.3 Ohms 30 80 ns Maximum Duty Cycle EAINV = 1.4V 92 96 % Minimum Duty Cycle EAINV = 1.6V Modulator Gain EAOUT = 1.5V to 2.5V Pulse Width Modulator Section 0 % 25 35 45 %/V Start Threshold 3.5 4.2 4.5 V Hysteresis 100 200 300 mV Undervoltage Lockout Section Powered by ICminer.com Electronic-Library Service CopyRight 2003 2 UC1573 UC2573 UC3573 ELECTRICAL CHARACTERISTICS: Unless otherwise specified, these parameters apply for TA = –55°C to +125°C for the UC1573, –40°C to +85°C for the UC2573, and 0°C to +70°C for the UC3573, VCC = 5V, CT = 680pF, TA = TJ. PARAMETER TEST CONDITIONS MIN TYP 1.8 2.2 MAX UNITS Sleep Mode Section Threshold 2.6 V Supply Current Section IVCC VCC = 30V 9 12 mA IVCC VCC = 30V, EAINV = 3V 50 150 A PIN DESCRIPTIONS 3VREF: Precision 3V reference. Bypass with 100nF capacitor. EAOUT: Output of error amplifier. Use EAOUT and EAINV for loop compensation components. CS: Peak current limit sense pin. Senses the current across a current sense resistor placed between VCC and source of the PMOS Buck switch. OUT will be held high (PMOS buck switch off) if VCC – CS exceeds 0.4V. GND: Circuit Ground. EAINV: Inverting input to error amplifier. VOUT sense feedback connected to this pin. The non-inverting input of the error amplifier is internally connected to: RAMP: Oscillator and ramp for pulse width modulator. Frequency is set by a capacitor to GND by the equation OUT: Gate drive for external PMOS switch connected between VCC and the flyback inductor. OUT drives the gate of the PMOS switch between VCC and GND. F = 3VREF Volts. 2 1 15k • C RAMP Recommended operating frequency range is 10kHz to 200kHz. Connecting the EAINV pin to an external voltage greater than 2.6V commands the chip to go into a low current sleep mode. VCC: Input voltage supply to chip. Range is 4.75V to 30V. Bypass with a 1µF capacitor. UDG-94107 Typical Waveforms. Powered by ICminer.com Electronic-Library Service CopyRight 2003 3 UC1573 UC2573 UC3573 TYPICAL APPLICATION: 12V TO 5V BUCK CONVERTER VIN +12V IN SLEEP RSLEEP3 1MEG MSLEEP RSLEEP 24k RCS RV SENSE1 91K C V CC 10µF 4 VCC 8 3VREF 7 RAMP 1 EAINV UC1573 CS 3 C3 V REF 100nF CRAMP 680pF RCOMP CBULK 10µF OUT CCOMP 2 5 MSWITCH EAOUT LBUCK RVSENSE2 39k 6 VOUT GND DCATCH 1A GND COUT 100µF GND +5V OUT UDG-99050 UNITRODE CORPORATION 7 CONTINENTAL BLVD. • MERRIMACK, NH 03054 TEL. (603) 424-2410 • FAX (603) 424-3460 Powered by ICminer.com Electronic-Library Service CopyRight 2003 4 IMPORTANT NOTICE Texas Instruments and its subsidiaries (TI) reserve the right to make changes to their products or to discontinue any product or service without notice, and advise customers to obtain the latest version of relevant information to verify, before placing orders, that information being relied on is current and complete. All products are sold subject to the terms and conditions of sale supplied at the time of order acknowledgement, including those pertaining to warranty, patent infringement, and limitation of liability. TI warrants performance of its semiconductor products to the specifications applicable at the time of sale in accordance with TI’s standard warranty. Testing and other quality control techniques are utilized to the extent TI deems necessary to support this warranty. Specific testing of all parameters of each device is not necessarily performed, except those mandated by government requirements. CERTAIN APPLICATIONS USING SEMICONDUCTOR PRODUCTS MAY INVOLVE POTENTIAL RISKS OF DEATH, PERSONAL INJURY, OR SEVERE PROPERTY OR ENVIRONMENTAL DAMAGE (“CRITICAL APPLICATIONS”). TI SEMICONDUCTOR PRODUCTS ARE NOT DESIGNED, AUTHORIZED, OR WARRANTED TO BE SUITABLE FOR USE IN LIFE-SUPPORT DEVICES OR SYSTEMS OR OTHER CRITICAL APPLICATIONS. INCLUSION OF TI PRODUCTS IN SUCH APPLICATIONS IS UNDERSTOOD TO BE FULLY AT THE CUSTOMER’S RISK. In order to minimize risks associated with the customer’s applications, adequate design and operating safeguards must be provided by the customer to minimize inherent or procedural hazards. TI assumes no liability for applications assistance or customer product design. TI does not warrant or represent that any license, either express or implied, is granted under any patent right, copyright, mask work right, or other intellectual property right of TI covering or relating to any combination, machine, or process in which such semiconductor products or services might be or are used. TI’s publication of information regarding any third party’s products or services does not constitute TI’s approval, warranty or endorsement thereof. Copyright 1999, Texas Instruments Incorporated Powered by ICminer.com Electronic-Library Service CopyRight 2003