LT1508C

LT1508 LINER | Alldatasheet

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Controller (Voltage Mode) , LTC and LT are registered trademarks of Linear Technology Corporation. n PFC and PWM Single Chip Solution n Synchronized Operation up to 300kHz n 99% Power Factor Over 20:1 Load Current Range n Voltage Mode PWM n Instantaneous Overvoltage Protection n Dedicated Overvoltage Protection (OVP Pin) n Minimal Line Current Dead Zone n Typical 250µA Start-Up Supply Current n Line Switching Noise Filter n Low Quiescent Current: 13mA n Fast 1.5A Peak Current Gate Drivers n Separate Soft Start Control FEATURES DESCRIPTIONU APPLICATIONSU n Universal Power Factor Corrected Power Supplies and Preregulators The LT 1508 is a complete solution for universal off-line switching power supplies utilizing active power factor correction. The PFC section is identical to the LT1248 PFC controller except the EN/SYNC pin is removed because PFC and PWM are synchronized internally. The voltage mode PWM section (LT1509 is the current mode counterpart) contains all the primary side functions to convert the PFC preregulated high voltage output to an isolated low voltage output. The PWM duty cycle is internally limited to 47% (maximum 50%) to prevent transformer saturation. PWM soft start begins when the PFC output reaches the preset voltage. In the event of brief line loss, PWM will be shut off when the PFC output voltage drops below 73% of the preset value. IM = IA2IB 200µA2 4 15 19 18 1508 BD VSENSE 7.5V 7.9V VCC 16V TO 10V 14µA 14µA 7µA 7V TO 4.7V EA CA CL 2.2V IA IM IB 25k R VAOUT VREF 7.5V VREF MOUT ISENSE CAOUT CSET RSET ILIM VC 50µA RUN RUN R R Q S S RQ R OSC 55% DELAY 200ns BLANKING PKLIM GND1 VCC GTDR1 16V 16V GND2 GTDR2 IAC OVP SS1 SS2 PWMOK 0.7V NOTE: PWM PULSE IS DELAYED BY 55% DUTY CYCLE AFTER PFC PULSE BLOCK DIAGRAMW

By using fixed high frequency PWM current averaging without the need for slope compensation, the LT1508 achieves far lower line current distortion with a smaller magnetic element than systems that use either peak current detection, or zero current switching approach, in both continuous and discontinuous modes of operation. The LT1508 also provides filtering capability to reject line DESCRIPTIONU switching noise which can cause instability when fed into the multiplier. Line current dead zone is minimized with low bias voltage at the current input to the multiplier. The LT1508 provides many protection features including peak current limiting and overvoltage protection. Implemented with a very high speed process, the LT1508 can be operated at frequencies as high as 300kHz. ABSOLUTE MAXIMUM RATINGSW WW U Operating Junction Temperature Range Thermal Resistance (Junction-to-Ambient) PACKAGE/ORDER INFORMATIONW UU Consult factory for Military grade parts. TOP VIEW SW PACKAGE 20-LEAD PLASTIC SO WIDE N PACKAGE 20-LEAD PDIP GTDR1 GND2 GND1 C SET PKLIM CAOUT ISENSE MOUT IAC VAOUT GTDR2 I LIM VC VCC SS1 R SET VSENSE SS2 V REF OVP TJMAX = 125°C, θJA = 100°C/ W (N) TJMAX = 125°C, θJA = 120°C/ W (SW) ORDER PART NUMBER PARAMETER CONDITIONS MIN TYP MAX UNITS Overall Supply Current (VCC in Undervoltage Lockout) V CC = Lockout Voltage –0.2V l 0.25 0.45 mA Supply Current On 11.5V ≤ VCC ≤ VMAX l 13 19 mA VCC Turn-On Threshold (Undervoltage Lockout) l 15.5 16.5 17.5 V VCC Turn-Off Threshold l 9.5 10.5 11.5 V Voltage Amplifier (PFC Section) Voltage Amp Offset VA OUT = 3.5V l –1 0 1 0 m V Input Bias Current V SENSE = 0V to 7V l –25 –250 nA Voltage Gain 70 100 dB Voltage Amp Unity-Gain Bandwidth 3 MHz Voltage Amp Output High (Internally Clamped) l 11.3 13.3 V Voltage Amp Output Low l 1.1 2 V Voltage Amp Short-Circuit Current VA OUT = 0V l 3 8 17 mA

ELECTRICAL CHARACTERISTICS

Maximum operating voltage (VMAX) = 25V, VCC = 18V, RSET = 15k to GND, CSET = 1nF to GND, IAC = 100µA, ISENSE = 0V, CAOUT = 3.5V, VAOUT = 5V, OVP = VREF. No load on any outputs unless otherwise noted. LT1508CN LT1508CSW LT1508IN LT1508ISW

ELECTRICAL C CHARA TERISTICS PARAMETER CONDITIONS MIN TYP MAX UNITS Current Amplifier (PFC Section) Current Amp Offset Voltage l ±1 ±4m V ISENSE Bias Current l –25 –250 nA Current Amp Voltage Gain 80 110 dB Current Amp Unity-Gain Bandwidth 3 MHz Current Amp Output High l 7.2 8.5 V Current Amp Output Low l 1.1 2 V Current Amp Short-Circuit Current CA OUT = 0V l 3 8 17 mA Input Range, ISENSE, MOUT (Linear Operation) l – 0.3 1 V Reference Reference Output Voltage I REF = 0mA, TA = 25°C 7.39 7.50 7.60 V VREF Load Regulation –5mA < I REF < 0mA 5 mV VREF Line Regulation 11.5V < V CC < VMAX l –20 5 20 mV VREF Short-Circuit Current V REF = 0V l 12 28 50 mA VREF Worst Case Load, Line, Temperature l 7.32 7.5 7.68 V Current Limit PKLIM Offset Voltage l –2 5 2 5 m V PKLIM Input Current PK LIM = –0.1V l – 50 – 100 µA PKLIM to GTDR Propagation Delay PK LIM Falling from 50mV to –50mV 400 ns Multiplier Multiplier Output Current I AC = 100µA, RSET = 15k 35 µA Multiplier Output Current Offset R AC = 1M from IAC to GND l – 0.05 –0.5 µA Multiplier Maximum Output Current I AC = 450µA, RSET = 15k, VAOUT = 7V, MOUT = 0V l – 286 – 260 – 235 µA Multiplier Gain Constant (Note 1) 0.035 V –2 IAC Input Resistance I AC from 50µA to 1mA 15 25 35 k Ω Oscillator Oscillator Frequency R SET = 15k, CSET = 1000pF l 85 100 115 kHz RSET = 15k, CSET = 1500pF l 58 68 78 kHz CSET Ramp Peak-to-Peak Amplitude 4.35 4.7 5.0 V CSET Ramp Valley Voltage 1.15 1.3 1.55 V Overvoltage Comparator (PFC Section) Comparator Trip Voltage Ratio (VTRIP/VREF) l 1.04 1.05 1.06 Hysteresis 0.35 V OVP Bias Current OVP = 7.5V l 0.2 1 µA OVP Propagation Delay 100 ns Gate Drivers (GTDR1 and GTDR2) Max Output Voltage 0mA Load, 18V < V CC l 12 15 17.5 V Output High –200mA Load, 11.5V ≤ VCC ≤ 15V l VCC – 3.0 V Output Low (Device Unpowered) V CC = 0V, 50mA Load (Sinking) l 0.9 1.5 V Output Low (Device Active) 200mA Load (Sinking) l 0.5 1 V 10mA Load l 0.2 0.4 V Peak Output Current 10nF from GTDR to GND 2 A Rise and Fall Time 1nF from GTDR to GND 25 ns Max Duty Cycle (PFC) 90 96 % Max Duty Cycle (PWM) (Note 2) 44 50 % Maximum operating voltage (VMAX) = 25V, VCC = 18V, RSET = 15k to GND, CSET = 1nF to GND, IAC = 100µA, ISENSE = 0V, CAOUT = 3.5V, VAOUT = 5V, OVP = VREF. No load on any outputs unless otherwise noted.

IAC (VAOUT – 2)2 The l denotes specifications which apply over the full operating temperature range. Note 1: Multiplier Gain Constant: K = Note 2: GTDR2 (PWM) pulse is delayed by 53% duty cycle after GTDR1 (PFC) is set. See PFC/PWM Synchronization graph in the Typical Performance Characteristics section. TYPICAL PERFORMANCE CHARACTERISTICS UW PFC Voltage Amplifier Open-Loop Gain and Phase FREQUENCY (Hz) GAIN (dB) 100 –20 100 1k 10k 100k

1508 G01

–20 –40 –60 –80 –100 –120 PHASE (DEG) PHASE GAIN FREQUENCY (Hz) GAIN (dB) 100 –20 100 1k 10k 100k

1508 G02

–20 –40 –60 –80 –100 –120 PHASE (DEG) PHASE GAIN PFC Current Amplifier Open-Loop Gain and Phase TIME

1508 G03

PFC (GTDR1) 53% PWM (GTDR2) PFC/PWM Synchronization ELECTRICAL C CHARA TERISTICS VCC = 18V, RSET = 15k to GND, CSET = 1nF to GND, IAC = 100µA, ISENSE = 0V, CAOUT = 3.5V, VAOUT = 5V, OVP = VREF. No load on any outputs, unless otherwise noted. PARAMETER CONDITIONS MIN TYP MAX UNITS Soft Start Current SS1 Current (PFC) SS1 = 2.5V l 51 2 3 0 µA SS2 Current (PWM) SS2 = 1V l 51 2 3 0 µA Comparators in PWM Section ILIM Input Current I LIM = 0V, VC = 1.6V l – 0.3 – 2 µA Current Limit Comparator (CL) Threshold V C > 2.6V l 0.95 1.1 1.20 V GTDR2 Switching Off Threshold at VC or at SS2 I LIM = 0V l 1V VC Input Current V C = 0V l –20 –80 µA PWMOK Comparator Low Threshold (in Terms of VREF) l 0.57 0.63 0.70 VC Pin High Voltage 1mA into V C Pin l 6.2 6.9 7.5 V GTDR2 Turn-On Blanking Time 180 ns

TYPICAL PERFORMANCE CHARACTERISTICS UW Reference Voltage vs Temperature Supply Current vs Supply Voltage GTDR Rise and Fall Time Start-Up Supply Current vs Supply Voltage MOUT Pin CharacteristicsFrequency vs RSET and CSET GTDR1 Maximum Duty Cycle vs RSET and CSET Multiplier Current JUNCTION TEMPERATURE (°C) –75 REFERENCE VOLTAGE (V) 7.536 7.524 7.512 7.500 7.488 7.476 7.464 7.452 7.440 7.428

1508 G04

–50 150–25 0 25 50 100 125 IAC (µA) IM (µA) 300 150

1508 G05

VAOUT = 7V VAOUT = 6.5V VAOUT = 6V VAOUT = 5.5V VAOUT = 5V VAOUT = 4.5V VAOUT = 4V VAOUT = 3.5V VAOUT = 3V VAOUT = 2.5V SUPPLY VOLTAGE (V) SUPPLY CURRENT (mA)

1508 G06

TJ = 25°CTJ = 125°C TJ = –55°C LOAD CAPACITANCE (nF) TIME (ns) 400 300 200 100 10 20 30 40

1508 G07

NOTE: GTDR SLEWS BETWEEN 1V AND 16V FALL TIME SUPPLY VOLTAGE (V) SUPPLY CURRENT (µA) 550 500 450 400 350 300 250 200 150 100

1508 G08

125°C –55°C 25°C 4 81 2 1 626 1 0 14 18 CSET CAPACITANCE (pF) 200 FREQUENCY (kHz) 500 450 400 350 300 250 200 150 100

1508 G09

RSET = 10k RSET = 15k RSET = 20k RSET = 30k CSET CAPACITANCE (pF) 200 MAXIMUM DUTY CYCLE 1.00 0.99 0.98 0.97 0.96 0.95 0.94 0.93 0.92 0.91 0.90

1508 G10

RSET = 10k RSET = 15k RSET = 20k RSET = 30k MOUT VOLTAGE (V) MOUT CURRENT (mA) 1.5 1.0 0.5 –0.5 –1.0 –1.5 –2.0 –2.5 –3.0 –3.5 –4.0

1508 G11

2.41.20–1.2–2.4 TJ = 125°C TJ = 25°C TJ = –55 °C

TYPICAL PERFORMANCE CHARACTERISTICS UW RSET Voltage vs Current PK LIM Pin Characteristics PFC SECTION GTDR1 (Pin 1): The PFC MOSFET gate driver is a fast totem pole output which is clamped at 15V. Capacitive loads like the MOSFET gates may cause overshoot. A gate series resistor of at least 5Ω will prevent the overshoot. GND2 (Pin 2): Power Ground. High current spikes occur in this line when either GTDR1 or GTDR2 switches low. GND1 (Pin 3): Analog Ground. C SET (Pin 4): The capacitor from this pin to GND and RSET determines oscillator frequency. The oscillator ramp is 5V and the frequency = 1.5/(RSET CSET). PKLIM (Pin 5): The threshold of the peak current limit comparator is GND. To set current limit, a resistor divider can be connected from VREF to the current sense resistor. CAOUT (Pin 6): This is the output of the current amplifier that senses and forces the line current to follow the reference signal that comes from the multiplier by com- manding the pulse width modulator. When CAOUT is low, the modulator has zero duty cycle. ISENSE (Pin 7): This is the inverting input of the current amplifier. This pin is clamped at –0.6V by an ESD protec- tion diode. M OUT (Pin 8): This is the multiplier high impedance current output and the noninverting input of the current amplifier. This pin is clamped at – 0.6V and 3V. I AC (Pin 9): This is the AC line voltage sensing input to the multiplier. It is a current input that is biased at 2V to minimize the crossover dead zone caused by low line voltage. At the pin, a 25k resistor is in series with the current input, so that a lowpass RC can be used to filter out the switching noise coming down from the line with a high line impedance environment. VA OUT (Pin 10): This is the output of the voltage error amplifier. The output is clamped at 13.5V. When the output goes below 2.5V, the multiplier output current is zero. OVP (Pin 11): This is the input to the overvoltage com- parator. The threshold is 1.05 times the reference voltage. When the comparator trips, the multiplier, which is quickly inhibited, blanks PFC switching to prevent further over- shoot. This pin is also the input to the PWMOK comparator that releases the PWM soft start (SS2) after the PFC output gets close to the final voltage and has a hysteresis of approximately 150V for 382V PFC output. V REF (Pin 12): This is the 7.5V reference. When VCC goes low, VREF will stay at 0V. VREF biases most of the internal circuitry and can source up to 5mA externally. VSENSE (Pin 14): This is the inverting input to the voltage amplifier. (For application help with the PFC portion of this chip, see the LT1248 data sheet)PIN FUNCTIONSUU U RSET CURRENT (mA) VRSET – VREF (mV) 120 100 –20 –40 –60 –80 –100

1508 G12

TJ = 125°C TJ = 25°C TJ = –55 °C PKLIM VOLTAGE (V) PKLIM CURRENT (µA) –360 –300 –240 –180 –120 –60 120 180 240 300

1508 G13

0.80.40–0.4–0.8 TJ = 125°C TJ = 25°C TJ = –55 °C

APPLICATIONS INFORMATIONWU UU input up to VC and then the SS2 voltage continues beyond VC. The PWMOK comparator contains hysteresis and will pull SS2 low disabling the PWM section if the PFC output voltage falls below approximately 62% of its preset value (240V with nominal 382V output). Start-Up and Supply Voltage The LT1508 draws only 250 µA before the chip starts at 16V on V CC. To trickle start, a 91k resistor from the power line to VCC supplies trickle current, and C4 holds VCC up while switching starts (see Figure 8); then the auxiliary winding takes over and supplies the operating current. Note that D3 and the larger values of C3 are only necessary for systems that have sudden large load variations down to minimum load and/or very light load conditions. Under these conditions the loop may exhibit a start/restart mode because switching remains off long enough for C4 to discharge below 10V. Large values for C3 will hold V CC up until switching resumes. For less severe load variations D3 is replaced with a short and C3 is omitted. The turns ratio between the primary winding determines V CC according to : NP NS VOUT VCC – 2V = for 382V VOUT and 18V VCC, Np/Ns ≈ 19. Figure 8 VCC NP NS 91k 2µF 1508 • F08 + C2 2µF 390µF + C4 100µF LINE MAIN INDUCTOR D3D1 Output Capacitor (PFC Section) GTDR2 (PWM) pulse is synchronized to GTDR1 (PFC) pulse with 53% duty cycle delay to reduce RMS ripple current in the output capacitor. See PFC/PWM Synchronization graph in the Typical Performance Characteristics section. The peak-to-peak 120Hz PFC output ripple is determined by: VP-P = 2ILOAD(DC)(Z) where ILOAD(DC) is the DC load current of the PWM stage and Z is the capacitor impedance at 120Hz. For 470µF, impedance is 2.8 Ω at 120Hz. At 335W load, ILOAD(DC) = 335V/382V = 0.88A, VP-P = (2)(0.88)(2.8Ω ) = 5V. If less ripple is desired higher capacitance should be used. The selection of the output capacitor is based on voltage ripple, hold-up time and ripple current. Assuming the DC converter (PWM section) is designed to operate with 240V to 382V IN , the minimum hold-up time is a function of the energy storage capacity of the capacitor: (0.5)COUT POUT tHOLD = (382V – 0.5V P–P)2 – 240V2 with C OUT = 470 µF, V P-P = 11.5V, and P OUT = 335W, tHOLD = 60ms which is 3.6 line cycles at 60Hz. The ripple current can be divided into two major components. The first is the 120Hz component which is related to the DC load current as follows: I120HZ ≈ ILOAD(DC) 2√ The second component is made up of switching frequency components due to the PFC stage charging the capacitor and the PWM stage discharging the capacitor. For a 300W output PFC forward converter running from an input voltage of 100V RMS, the total high frequency ripple current was measured to be 1.79ARMS. For the United Chemicon KMH 450V capacitor series, ripple current at 100kHz is specified 1.43 times higher than the 120Hz limit.

IHF = 100kHz Ripple Current. rent, R is capacitor ESR and KA is a volume constant. Table 1. PFC Capacitor RMS Ripple Current or parallel capacitors should be used.

Figure 9. 24V, 300W Off-Line PFC Supply

1. ALL CAPACITANCE VALUES IN MICROFARADS

1508 F09

APPLICATIONS INFORMATIONWU UU An LT1431 reference/amplifier coupled to a low cost optoisolator closes the loop from secondary side to pri- mary side. Efficiency versus power and line voltage is shown in Figure 10. The PFC preregulator alone has efficiency numbers between 90% and 97% over line and load. A 3-turn secondary added to the 70-turn primary of T1 bootstraps V CC to about 15V supplying the chip’s 13mA requirement as well as about 39mA to cover the gate current of the three FETs and high side transformer. A 0.15Ω sense resistor is used to sense input current and servo to the command created by the outer voltage and multiplier. Thus the input current follows the input line voltage, and changes as necessary, in order to maintain constant bank voltage. The forward converter sees a voltage input of 382VDC unless the line voltage drops out, in which case the 330 µF main capacitor discharges to 240VDC before the PWM stage is shut down. Compared to a typical off-line converter, the effective input voltage range of the forward converter is much smaller, simplify- ing the design. Additionally, the higher bus voltage pro- vides greater hold-up times for given capacitor size. VRMS EFFICIENCY (%) 250 1508 • F1O 132 180 200W/300W 100W 30W Figure 10

Dimensions in inches (millimeters) unless otherwise noted.PACKAGE DESCRIPTIONU Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen- tation that the interconnection of its circuits as described herein will not infringe on existing patent rights. N Package 20-Lead PDIP (Narrow 0.300) (LTC DWG # 05-08-1510) N20 0695 0.015 (0.381) MIN 0.125 (3.175) MIN 0.130 – 0.005 (3.302 – 0.127) 0.065 (1.651) TYP 0.045 – 0.065 (1.143 – 1.651) 0.018 – 0.003 (0.457 – 0.076) 0.005 (0.127) MIN 0.100 – 0.010 (2.540 – 0.254) 0.255 – 0.015* (6.477 – 0.381) 1.040* (26.416) MAX 12 3 4 5 6 7 8 91 0 19 11 12131416 15171820 0.009 – 0.015 (0.229 – 0.381) 0.300 – 0.325 (7.620 – 8.255) 0.325 +0.025 –0.015 +0.635 –0.3818.255() *THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.010 INCH (0.254mm)

 LINEAR TECHNOLOGY CORPORA TION 1995 1508f LT/TP 0697 7K • PRINTED IN USA Dimensions in inches (millimeters) unless otherwise noted.PACKAGE DESCRIPTIONU 20-Lead Plastic Small Outline (Wide 0.300) (LTC DWG # 05-08-1620) S20 (WIDE) 0396 NOTE 1 0.496 – 0.512* (12.598 – 13.005) 20 19 18 17 16 15 14 13 1 23 4 5 6 78 0.394 – 0.419 (10.007 – 10.643) 91 0 1112 0.037 – 0.045 (0.940 – 1.143) 0.004 – 0.012 (0.102 – 0.305) 0.093 – 0.104 (2.362 – 2.642) 0.050 (1.270) TYP 0.014 – 0.019 (0.356 – 0.482) TYP 0° – 8° TYP NOTE 1 0.009 – 0.013 (0.229 – 0.330) 0.016 – 0.050 (0.406 – 1.270) 0.291 – 0.299** (7.391 – 7.595) × 45°0.010 – 0.029 (0.254 – 0.737) NOTE: 1. PIN 1 IDENT, NOTCH ON TOP AND CAVITIES ON THE BOTTOM OF PACKAGES ARE THE MANUFACTURING OPTIONS. THE PART MAY BE SUPPLIED WITH OR WITHOUT ANY OF THE OPTIONS DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE PART NUMBER DESCRIPTION COMMENTS LT1084 5A Low Dropout Linear Regulator Good for Post Regulation of Switching Power Supplies LT1105 Simplified Off-Line Controller Solution for Universal Off-Line Inputs with Output to 100W LT1241-5 High Frequency Current Mode PWM Controller Operates at Oscillator Frequencies up to 500kHz LT1247 High Frequency Current Mode PWM Controller Operates at Oscillator Frequencies up to 1MHz LT1248 Full-Feature Average Current Mode Power Factor Controller Provides All Features in 16-Lead Package LT1249 Minimal Parts Count Power Factor Controller Simplified PFC Design LT1509 Power Factor and PWM Controller Current Mode PWM RELATED PARTS Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 l (408) 432-1900 FAX: (408) 434-0507 l TELEX: 499-3977 l www.linear-tech.com