LX2173CP

LIN D O C #: 2172 LX2172/73 1.25A HIGH -E FFICIENCY 100K HZ S WITCHING REGULATOR T H E I P N F I N I T E O W E R O F I P N N O VA T I O N DESCRIPTION The LX2172/73 are fixed-frequency, current-mode switching regulator integrated circuits. These ICs contain all necessary control circuitry plus a 1.25A on-board transistor to design a complete DC:DC switching regulator with minimum external components. All functions are integrated into a single IC, available in 8-pin DIP and SOIC or a 5-pin TO-220 power package, making them extremely easy to design with and use. The LX2172/73 are optimized for ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ PRODUCT HIGHLIGHT SEPIC CONVERTER USING TH E LX2172 Input 6-24V, Output 7V, 300mA 0.1µF R1 13.7k 1 2 3 C4 0.47µF 4 GND VC FB SYNC (See Note 1) R2 3.0k R3 100 E2 VSW E1 VIN D1 Output 7V 300mA H E E T 7V Boost Converter Laptop / Notebook Computers Portable Equipment Small Motor Applications Flyback Converters Part # LX2172 COUT 220µF 8 1.25A, 65V Internal Power Switch 3V - 25V Input Voltage Range Current-Mode Operation Improved Internal Cycle-By-Cycle Current Limiting Thermal Shutdown Less Than 10µA Quiescent Current In Microprocessor Shutdown Mode External Frequency Synchronization Possible 100kHz Operating Frequency A VA I L A B L E O P T I O N S 1N5817 U1 LX2172 22µF C2 330µF 1mH C3 C1 S A P P L I C AT I O N S NOTE: For current data & package dimensions, visit our web site: http://www.linfinity.com. L1 A T A K E Y F E AT U R E S boost and flyback applications, but can also be used in forward and inverting converter configuations. The LX2172 can be connected to an external clock for synchronization, and can enter micropower operation when the VC pin is pulled low. The LX2173 has an enable function, which permits extremely low micropower operation, consuming under 10µA current when the ENABLE pin is brought low. VIN 6-24VDC D R E L I M I N A R Y LX2173 7 PER PAR T # Pin 4 Connections SYNC Input Low µPower Mode (HI ENABLE) = Samples Not Yet Available. 6 5 L2 1mH CDECOUPLE 0.47µF Note 1: SYNC Pin Requirements: A) FMAX = 200kHz B) TTL Compatible Level C) Pulse Width TP Range - 0.1µs < TP < 2.0µs PA C K A G E O R D E R I N F O R M AT I O N TA (°C) 0 to 70 DIP M Plastic 8-pin LX217xCM SOIC DM Plastic 8-pin LX217xCDM TO-220 P Plastic 5-pin LX217xCP Note: All surface-mount packages are available in Tape & Reel. Append the letter "T" to part number. (i.e. LX217xCDMT) Copyright © 1998 Rev. 0.4 12/98 LINFINITY MICROELECTRONICS INC. 11861 W ESTERN A VENUE, G ARDEN G ROVE, CA. 92841, 714-898-8121, F AX: 714-893-2570 1 PRODUCT DATABOOK 1996/1997 LX2172/73 1.25A HIGH -E FFICIENCY 100K HZ SWITCHING REGULATOR P D R E L I M I N A R Y A B S O L U T E M A X I M U M R AT I N G S S A T A H E E T PACKAGE PIN OUTS (Note 1) Supply Voltage (VIN) .................................................................................................... 25V Collector Supply Voltage (VC ) ..................................................................................... 65V Digital Inputs (SYNC) ......................................................................................... -0.3 to 7V Operating Junction Temperature ................................................................. 0°C to 125°C Storage Temperature Range .................................................................... -65°C to +150°C Solder Temperature (Soldering, 10 seconds) .......................................................... 300°C GND VC FB * SYNC / ENABLE GND VC FB * SYNC / ENABLE T H E R MAL DATA M PACKAGE: 95°C/W 7 3 6 4 5 E2 VSW E1 VIN 1 8 2 7 3 6 4 5 E2 VSW E1 VIN DM PACKAGE (Top View) DM PACKAGE: THERMAL RESISTANCE-JUNCTION TO AMBIENT, θ JA 8 2 M PACKAGE (Top View) Note 1. Exceeding these ratings could cause damage to the device. All voltages are with respect to Ground. Currents are positive into, negative out of the specified terminal. THERMAL RESISTANCE-JUNCTION TO AMBIENT, θ JA 1 * Pin 4 = SYNC for LX2172, ENABLE for LX2173/2174 165°C/W P PACKAGE: TAB IS GND THERMAL RESISTANCE-JUNCTION TO TAB, θJT 4.5°C/W THERMAL RESISTANCE-JUNCTION TO AMBIENT, θ JA 60°C/W VIN VSW GND FB VC 5 1 Junction Temperature Calculation: TJ = TA + (PD x θJA). The θ JA numbers are guidelines for the thermal performance of the device/pc-board system. All of the above assume no ambient airflow. P PACKAGE (Top View) BLOCK DIAGRAM V IN V V IN 5 1 .4 V G N D E N A B L E C O M P V 2 .3 V V R EG E N 1 V R E G R E G U V L O C O M P 2 .3 V (N O T E 1 ) E N A B L E V S .D . C O M P S E .A . 1 .2 7 V g B P W M C O M P M P W M L A T C H C Q 1 R 3 2 O W Q 2 Q S V V 7 0 .1 5 V O F IN Q V O FS (0 .9 V ) 1 0 0 k H z 2 5 0 m V E N 1 0 0 k H z O S C 0 .1 6 W 0 .1 6 W 1 .4 V C .S . A M P S L O P E C O M P IN (N O T E 1 ) S Y N C 6 E 1 8 E 2 Note 1: LX2172 Only: SYNC brought out to pin 4. ENABLE is tied to V IN. LX2173 Only: ENABLE brought out to pin 4. SYNC is open. 2 Copyright © 1998 Rev. 0.4 12/98 PRODUCT DATABOOK 1996/1997 LX2172/73 1.25A HIGH -E FFICIENCY 100K HZ S WITCHING REGULATOR P R E L I M I N A R Y D A T A S H E E T ELECTRICAL CHARACTERISTICS (Unless otherwise specified, these specifications apply over the ranges TA = 0 to 70ºC for the LX217xC. VIN = VC = 5V. All devices must be functional over junction temperature of -65°C to 150°C. Typ. number represents TA = 25ºC value.) Parameter Symbol Test Conditions LX2172 / 2173 Min. Typ. Max. Units Reference Section Initial Accuracy VREF Line Regulation TJ = 25ºC, Measured at FB pin Over Temperature, Measured at FB pin 3V < VCC < 25V 1.224 1.214 1.244 1.244 0.03 1.264 1.274 V V %/V 90 85 100 100 110 115 ±5 kHz kHz % 350 750 1100 1000 6000 7000 nA nA V/V µMHO µMHO µA µA V V V/µsec Oscillator Section Switching Frequency f Line Voltage Stability TA = 25ºC Over Temperature VIN = 3V to 25V Error Amplifier Section Input Bias Current Open Loop Gain Transconductance Output Sink Current Output Source Current Output HI Voltage Output LO Voltage Slew Rate IB AVOL gm TJ = 25ºC; VFB = VREF Over Temperature TJ = 25ºC; VFB = V REF; ∆I = ±25µA Over Temperature IEA (SINK) I EA (SOURCE) VCOMP-HI VFB = 1V VCOMP-LO VFB = 1.5V S 3000 2400 120 120 1.8 0.2 500 4400 200 2.1 0.3 2 2.3 0.52 C.S. Comparator Section C.S. Delay to Driver Output VC to Output Transconductance 10% Over drive GBNT 100 2 ns A/V PWM Section E.A. Output to PWM Drive Offset (VPWM) Minimum Duty Cycle Maximum Duty Cycle VOFS Duty Cycle = 0 0.6 80 1.2 36 90 1.25 40 98 V % % 0.4 1.7 1.5 100 0.6 2.8 2.0 V Ω A A mW 2.7 5 150 2.9 8 260 300 Output Drive Section Output Switch Breakdown Voltage Output Switch On Resistance Switch Current Limit RON ILIM Total Switching Loss (On Time + Off Time) ISW = 1.5mA IO = 2A D.C = 50% 50% < D.C < 80% VIN = 25V, D.C = 50%, IO = 1A, VSW = 60V 65 1.25 1.0 Input Supply Section Start-Up Threshold Normal Mode Quiescent Current VC Shutdown Threshold Sleep Mode Current Copyright © 1998 Rev. 0.4 12/98 2.2 IQ ENABLE = HI, VC = 0.6V, IO = 0A 3V < VIN < VMAX , TJ = 25°C 3V < VIN < VMAX , Over Temperature ENABLE = HI, VC = 50mV ENABLE = LO (LX2173 only) 100 50 100 5 V mA mV mV µA µA 3 PRODUCT DATABOOK 1996/1997 LX2172/73 1.25A HIGH -E FFICIENCY 100K HZ SWITCHING REGULATOR P R E L I M I N A R Y D A T A S H E E T ELECTRICAL CHARACTERISTICS Parameter Symbol Test Conditions LX2172 / 2173 Min. Typ. Max. Units SYNC Input Section (LX2172 only) SYNC Pulse Width SYNC Input HI SYNC Input LO SYNC Input Current HI SYNC Input Current LO 0.2 2 Input = 2V Input = 0.4V 100 1 2 6 0.7 400 5 µsec V V µA µA 2.4 200 100 V µA µA ENABLE Section (LX2173 only) Enable Input Threshold HI Input Current LO Input Current 0.4 1.2 Input = 2.4V Input = 0.4V FUNCTIONAL PIN DESCRIPTION Pin Name 4 Pin # Pin # (8-pin Pkgs.) (5-pin TO-220) Description GND 1 3 Signal ground. Keep separate from power grounds (E1 and E2). VC 2 1 Output of transconductance error amplifier. An R-C compensation network is connected from this pin to the ground to stabilize the feedback loop. If this pin is pulled lower than 0.15V, the IC goes into micropower mode. FB 3 2 Error amplifier inverting input. A resistor divider from the output of the converter to this pin sets its nominal voltage. SYNC 4 LX2172 only. This pin is used to synchronize the device directly with a logic level input pulse. External synchronization frequency must always be at a higher frequency than the minimum internal clock. When not used, should be left open. ENABLE 4 LX2173 only. This pin is the input to the enable comparator. A voltage under 1.4V will put the device in micropower mode. Pin must be connected to VIN when not in use. VIN 5 E1 6 VSW 7 E2 8 5 Input supply voltage (3.0V to 25V). Power return of first transistor (Q1). This pin must be connected to ground. 4 Collector of output transistors. Connect to external inductor or input voltage, depending on circuit topology. Grounding this pin sets the current limit point to the maximum value. If pin is left open, the current limit is set to half its maximum value. Copyright © 1998 Rev. 0.4 12/98 PRODUCT DATABOOK 1996/1997 LX2172/73 1.25A HIGH -E FFICIENCY 100K HZ S WITCHING REGULATOR P R E L I M I N A R Y D A T A S H E E T T H E O R Y O F O P E R AT I O N IC OPERATION OSCILLATOR Referring to the block diagram, when VIN is above the UVLO start threshold the 2.3V UVLO comparator output switches to low state, allowing Q1 to turn on upon receiving a clock pulse from the internal 100kHz oscillator. Once Q1 is on, current in the inductor ramps up. Inductor current is then sensed, and amplified by a current sense amplifier and compared to a threshold set by the output of the error amplifier minus the offset voltage (VOFS typically 0.9V). This allows the PWM comparator to reset the flip flop, causing Q1 to turn off. The oscillator then sets the flip flop, and the operation repeats itself. The oscillator is designed to operate at 100kHz frequency. Its function is to turn the switch Q1 on at a fixed 10µs interval and to provide a slope compensation for the feedback loop. Slope compensation is required for fixed frequency continuous Current Mode regulators operating above 50% duty cycle in order to prevent loop instability. The SYNC input is a logic input that allows easy synchronization to an external clock. Synchronization is done such that the external clock terminates the cycle before the internal oscillator sets the PWM latch again. UNDER-VOLTAGE LOCKOUT CURRENT LIMIT Current limiting is performed by sensing the peak switch current and turning Q1 off until the next clock cycle. When the converter goes into current limit the error amplifier output goes to the rail and sets a maximum limit on the current. ERROR AMPLIFIER The function of the error amplifier is to set a threshold voltage for inductor peak current and control the switch duty cycle so that the power supply output voltage is closely regulated. Regulation is accomplished by sensing the output voltage and comparing it to the internal 1.27V bandgap reference. A compensation network is placed from the output of the amplifier to ground for closed loop stability purposes, as well as a high d.c. gain for tight regulation. The function of V OFS is to keep Q1 off without requiring an error amplifier output to swing to ground level. It is required the VOL of the error amplifier is always less than the offset at all times. The transfer function between the error amplifier output (VC ) and peak inductor current is therefore given by: The 2.3V internal regulator is monitored as the input supply ramps up, ensuring glitch-free operation. EXTRA PINS ON 8-PIN DEVICE The 8-pin versions of the LX217x have the emitters of the power transistors brought out separately. Connecting these pins to ground reduces errors due to ground pin voltage drops. The E2 pin also allows the user to half the switch current limit if the pin is left open. Note that the switch resistance will increase when E2 is open, so efficiency will decrease and heat dissipation will increase, especially for currents over 300mA. MICROPOWER SHUTDOWN The LX2172/73 enter micropower shutdown mode when the VC pin is pulled below 0.15V. Supply current required for biassing shutdown circuitry is less than 250µA. The LX2173 has an ENABLE pin which allows ultra-low micropower shutdown operation, consuming less than 10µA. VC - V OFS = I P * G * R S Where: IP = Inductor peak current G = Current sense gain (typically 6) R S = Internal sense resistor Copyright © 1998 Rev. 0.4 12/98 5 PRODUCT DATABOOK 1996/1997 LX2172/73 1.25A HIGH -E FFICIENCY 100K HZ SWITCHING REGULATOR P R E L I M I N A R Y D S A T A H E E T T H E O R Y O F O P E R AT I O N VIN +3V to +12V 22µF 180µH 1 VOUT 2 14.7kΩ 3 1.27Ω 0.03µF 100Ω 4 E2 GND VC LX2172 FB VSW E1 SYNC VIN 8 7 1N5817 VOUT +16V 6 5 VIN VIN FIGURE 1 — Boost Coverter Circuit Using The LX2172 / 2173 PRELIMINARY DATA - Information contained in this document is pre-production data, and is proprietary to Linfinity. It may not modified in any way without the express written consent of Linfinity. Product referred to herein is offered in sample form only, and Linfinity reserves the right to change or discontinue this proposed product at any time. 6 Copyright © 1998 Rev. 0.4 12/98