TYPICAL APPLICATIO. LT1070/LT1071 5A and 2.5A High Efficiency Switching Regulators DESCRIPTIO FEATURES APPLICATIO S

Transcription

1 FEATRES Wide Input Voltage Range: 3V to 6V Low Quiescent Current: 6mA Internal 5A Switch (.5A for LT7) Very Few External Parts Required Self Protected Against Overloads Operates in Nearly All Switching Topologies Shutdown Mode Draws Only 5µA Supply Current Flyback Regulated Mode Has Fully Floating Outputs Comes in Standard 5-Pin TO- Package Can be Externally Synchronized (Consult Factory) APPLICATIO S Logic Supply at A Logic to ± Op Amp Supply Off-Line Converter p to W Battery pconverter Power Inverter ( to ) or ( to ) Fully Floating Multiple Outputs For Lower Current Applications, See the LT7 SER NOTE: This data sheet is only intended to provide specifications, graphs and a general functional description of the LT7/LT7. Application circuits are included to show the capability of the LT7/LT7. A complete design manual (AN9) should be obtained to assist in developing new designs. This manual contains a comprehensive discussion of both the LT7 and the external components used with it, as well as complete formulas for calculating the values of these components. The manual can also be used for the LT7 by factoring in the lower switch current rating. A second Application Note, AN5, which details off-line applications is available. LT7/LT7 5A and.5a High Efficiency Switching Regulators DESCRIPTIO The LT 7/LT7 are monolithic high power switching regulators. They can be operated in all standard switching configurations including buck, boost, flyback, forward, inverting and Cuk. A high current, high efficiency switch is included on the die along with all oscillator, control and protection circuitry. Integration of all functions allows the LT7/LT7 to be built in a standard 5-pin T- power package. This makes it extremely easy to use and provides bust proof operation similar to that obtained with 3-pin linear regulators. The LT7/LT7 operate with supply voltages from 3V to 6V, and draw only 6mA quiescent current. They can deliver load power up to W with no external power devices. By utilizing current mode switching techniques, they provide excellent AC and DC load and line regulation. The LT7/LT7 have many unique features not found even on the vastly more difficult to use low power control chips presently available. They use adaptive antisat switch drive to allow very wide ranging load currents with no loss in efficiency. An externally activated shutdown mode reduces total supply current to 5µA typical for standby operation. Totally isolated and regulated outputs can be generated by using the optional flyback regulation mode built into the LT7/LT7, without the need for optocouplers or extra transformer windings., LTC and LT are registered trademarks of Linear Technology Corporation. TYPICAL APPLICATIO Boost Converter ( to V) Maximum Output Power* * µf LT7 L** 5µH k µf * REQIRED IF INPT LEADS " ** PLSE ENGINEERING 93 L µh OTPT µf.7k µf % % 7/7 TA V A POWER (W)** 8 6 BOOST ISOLATED BCK/BOOST V O = 3V BCK/BOOST V O = FLYBACK 3 5 INPT VOLTAGE (V) 7/7 TA * ROGH GIDE ONLY. BCK MODE P OT = 5A V OT. SPECIAL TOPOLOGIES DELIVER MORE POWER ** DIVIDE VERTICAL POWER SCALE BY FOR LT7 7fe

2 LT7/LT7 ABSOLTE MAXIMM RATINGS W W W (Note ) Supply Voltage LT7/LT7 (Note )... V LT7HV/LT7HV (Note )... 6V Switch Output Voltage LT7/LT LT7HV/LT7HV... 7 Feedback Pin Voltage (Transient, ms)... ± Operating Junction Temperature Range Commercial (Operating)... C to C Commercial (Short Circuit)... C to 5 C Industrial... C to 5 C Military (OBSOLETE) C to 5 C Storage Temperature Range C to 5 C Lead Temperature (Soldering, sec)... 3 C PACKAGE/ORDER INFORMATION BOTTOM VIEW K PACKAGE -LEAD TO-3 METAL CAN T JMAX = C, θ JA = 35 C/ W, Q JC = C (LT7C, I) T JMAX = 5 C, θ JA = 35 C/ W, Q JC = C (LT7M) T JMAX = C, θ JA = 35 C/ W, Q JC = C (LT7C, I) T JMAX = 5 C, θ JA = 35 C/ W, Q JC = C (LT7M) 3 W CASE IS OBSOLETE PACKAGE Consider the T5 Package for Alternate Source ORDER PART NMBER LT7CK LT7HVCK LT7HVMK LT7IK LT7MK LT7CK LT7HVCK LT7HVMK LT7MK Consult LTC Marketing for parts specified with wider operating temperature ranges. FRONT VIEW 5 3 T PACKAGE 5-LEAD PLASTIC TO- T JMAX = C, θ JA = 75 C/ W, Q JC = C (LT7C, I) T JMAX = C, θ JA = 75 C/ W, Q JC = C (LT7C) ORDER PART NMBER LT7CT LT7HVCT LT7HVIT LT7IT LT7CT LT7HVCT LT7HVIT LT7IT ELECTRICAL CHARACTERISTICS The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at T A = 5 C. =, =., V = V REF, output pin open unless otherwise specified. SYMBOL PARAMETER CONDITIONS MIN TYP MAX NITS V REF Reference Voltage Measured at Feedback Pin, =.8V...6 V...7 V I B Feedback Input Current V = V REF na na g m Error Amplifier Transconductance I C = ±5µA 3 6 µmho 7 µmho Error Amplifier Source or Sink Current = µa µa Error Amplifier Clamp Voltage Hi Clamp, V = V.8.3 V Lo Clamp, V = V Reference Voltage Line Regulation 3V V MAX, =.8V.3 %/V A V Error Amplifier Voltage Gain.9V.V 5 8 V/V Minimum Input Voltage.6 3. V I Q Supply Current 3V V MAX, =.6V 6 9 ma Control Pin Threshold Duty Cycle = V.6.5 V Normal/Flyback Threshold on Feedback Pin..5.5 V 7fe

3 ELECTRICAL CHARACTERISTICS LT7/LT7 The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at T A = 5 C. =, =., V = V REF, output pin open unless otherwise specified. SYMBOL PARAMETER CONDITIONS MIN TYP MAX NITS V Flyback Reference Voltage I = 5µA V 8. V Change in Flyback Reference Voltage.5 I ma V Flyback Reference Voltage Line Regulation I = 5µA, 3V V MAX (Note 3)..3 %/V Flyback Amplifier Transconductance (g m ) I C = ±µa µmho Flyback Amplifier Source and Sink Current =.6V, I = 5µA (Source) µa =.6V, I = 5µA (Sink) 5 7 µa B V Output Switch Breakdown Voltage 3V V MAX, I SW =.5mA (LT7/LT7) 65 9 V (LT7HV/LT7HV) 75 9 V V SAT Output Switch On Resistance (Note ) LT7.5. Ω LT7.3.5 Ω Control Voltage to Switch Current LT7 8 A/V Transconductance LT7 A/V I LIM Switch Current Limit (LT7) Duty Cycle 5%, T J 5 C 5 A Duty Cycle 5%, T J < 5 C 5 A Duty Cycle = 8% (Note 5) A Switch Current Limit (LT7) Duty Cycle 5%, T J 5 C.5 5. A Duty Cycle 5%, T J < 5 C A Duty Cycle = 8% (Note 5). 5. A I IN Supply Current Increase During 5 35 ma/a I SW Switch On Time f Switching Frequency 35 5 khz 33 7 khz DC (Max) Maximum Switch Duty Cycle % Flyback Sense Delay Time.5 µs Shutdown Mode Supply Current 3V V MAX, =. 5 µa Shutdown Mode Threshold Voltage 3V V MAX 5 5 mv 5 3 mv Note : Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note : Minimum switch on time for the LT7/LT7 in current limit is µs. This limits the maximum input voltage during short-circuit conditions, in the buck and inverting modes only, to 3. Normal (unshorted) conditions are not affected. Mask changes are being implemented which will reduce minimum on time to µs, increasing maximum short-circuit input voltage above V. If the present LT7/LT7 (contact factory for package date code) is being operated in the buck or inverting mode at high input voltages and short-circuit conditions are expected, a resistor must be placed in series with the inductor, as follows: The value of the resistor is given by: t = Minimum on time of LT7/LT7 in current limit, µs f = Operating frequency (khz) V F = Forward voltage of external catch diode at I LIMIT I LIMIT = Current limit of LT7 ( 8A), LT7 ( A) R L = Internal series resistance of inductor Note 3: V MAX = 5 for LT7HV and LT7HV to avoid switch breakdown. Note : Measured with in hi clamp, V =.8V. I SW = A for LT7 and A for LT7. Note 5: For duty cycles (DC) between 5% and 8%, minimum guaranteed switch current is given by I LIM = 3.33 ( DC) for the LT7 and I LIM =.67 ( DC) for the LT7. R = t f V F I LIMIT R L 7fe 3

4 LT7/LT7 TYPICAL PERFORMANCE CHARACTERISTICS W Switch Current Limit vs Duty Cycle Maximum Duty Cycle Flyback Blanking Time SWITCH CRRENT (A) FOR LT7, DIVIDE VERTICAL SCALE BY 55 C 5 C 5 C DTY CYCLE (%) TIME (µs) DTY CYCLE (%) JNCTION TEMPERATRE ( C) JNCTION TEMPERATRE ( C) 7/7 G 7/7 G 7/7 G3 Minimum Input Voltage Switch Saturation Voltage MINIMM INPT VOLTAGE (V) SWITCH CRRENT = 5A SWITCH CRRENT = A SWITCH SATRATION VOLTAGE (V) FOR LT7, DIVIDE CRRENT BY C 5 C 55 C 5 C FLYBACK VOLTAGE (V) R FEEDBACK = 5Ω R FEEDBACK = k R FEEDBACK = k TEMPERATRE ( C) SWITCH CRRENT (A) TEMPERATRE ( C) 7/7 G 7/7 G5 7/7 G6 Line Regulation Reference Voltage vs Temperature Feedback Bias Current vs Temperature REFERENCE VOLTAGE CHANGE (mv) T J = 5 C T J = 5 C T J = 55 C 3 5 INPT VOLTAGE (V) 6 REFERENCE VOLTAGE (V) SWITCHING FREQENCY REFERENCE VLTAGE TEMPERATRE ( C) SWITCHING FREQENCY (khz) FEEDBACK BIAS CRRENT (na) TEMPERATRE ( C) 7/7 G7 7/7 G8 7/7 G9 7fe

5 LT7/LT7 TYPICAL PERFORMANCE CHARACTERISTICS W Driver Current* vs Switch Current Supply Current vs Input Voltage* Supply Current vs Supply Voltage (Shutdown Mode) DRIVER CRRENT (ma) T J = 55 C T J 5 C INPT CRRENT (ma) T J = 5 C 9% DTY CYCLE 5% DTY CYCLE % DTY CYCLE % DTY CYCLE I SWITCH ma SPPLY CRRENT (µa) T J = 5 C = 5mV = V 3 5 SWITCH CRRENT (A) 7/7 G * AVERAGE LT7 POWER SPPLY CRRENT IS FOND BY MLTIPLYING DRIVER CRRENT BY DTY CYCLE, THEN ADDING QIESCENT CRRENT INPT VOLTAGE (V) * NDER VERY LOW OTPT CRRENT CONDITIONS, DTY CYCLE FOR MOST CIRCITS WILL APPROACH % OR LESS 7/7 G SPPLY VOLTAGE (V) 6 7/7 G FEEDBACK PIN VOLTAGE (mv) Normal/Flyback Mode Threshold on Feedback Pin FEEDBACK PIN VOLTAGE (AT THRESHOLD) FEEDBACK PIN CRRENT (AT THRESHOLD) TEMPERATRE ( C) FEEDBACK PIN CRRENT (µa) SPPLY CRRENT (µa) Shutdown Mode Supply Current T J = 5 C 55 C T J 5 C PIN VOLTAGE (mv) TRANSCONDCTANCE (µmho) Error Amplifier Transconductance g m = I V ( PIN) ( PIN) TEMPERATRE ( C) PIN VOLTAGE (mv) Shutdown Thresholds CRRENT (OT OF PIN) VOLTAGE VOLTAGE IS REDCED NTIL 5 REGLATOR CRRENT DROPS 5 BELOW 3µA TEMPERATRE ( C) 7/7 G PIN CRRENT (µa) IDLE SPPLY CRRENT (ma) Idle Supply Current vs Temperature =.6V V SPPLY = 6V V SPPLY = 3V 7/7 G TEMPERATRE ( C) FEEDBACK VOLTAGE (mv) Feedback Pin Clamp Voltage 55 C 5 C 5 C 7/7 G FEEDBACK CRRENT (ma) 7/7 G6 7/7 G 7/7 G8 7fe 5

6 LT7/LT7 TYPICAL PERFORMANCE CHARACTERISTICS SWITCH CRRENT (µa) Switch Off Characteristics V SPPLY = 3V V 5 SWITCH VOLTAGE (V) W /7 G9 VC PIN CRRENT (µa) 3 3 Pin Characteristics T J = 5 C V =. (CRRENT INTO PIN) V =.8V (CRRENT OT OF PIN) PIN VOLTAGE (V) 7/7 G TRANSCONDCTANCE (µmho) Transconductance of Error Amplifier k k k M M FREQENCY (Hz) θ g m 7/7 G PHASE ( ) BLOCK DIAGRAM.3V REG W FLYBACK ERROR AMP 6V SWITCH OT khz OSC LOGIC DRIVER 5A, 7 SWITCH MODE SELECT COMP ANTISAT ERROR AMP.V REF SHTDOWN CIRCIT. GAIN 6 CRRENT AMP.Ω (.Ω LT7) 7/7 BD OPERATION The LT7/LT7 is a current mode switcher. This means that switch duty cycle is directly controlled by switch current rather than by output voltage. Referring to the Block Diagram, the switch is turned on at the start of each oscillator cycle. It is turned off when switch current reaches a predetermined level. Control of output 6 voltage is obtained by using the output of a voltage sensing error amplifier to set current trip level. This technique has several advantages. First, it has immediate response to input voltage variations, unlike ordinary switchers which have notoriously poor line transient response. Second, it reduces the 9 phase shift at 7fe

7 7/7 TA3 LT7/LT7 OPERATION midfrequencies in the energy storage inductor. This greatly simplifies closed-loop frequency compensation under widely varying input voltage or output load conditions. Finally, it allows simple pulse-by-pulse current limiting to provide maximum switch protection under output overload or short-circuit conditions. A low dropout internal regulator provides a.3v supply for all internal circuitry of the LT7/LT7. This low dropout design allows input voltage to vary from 3V to 6V with virtually no change in device performance. A khz oscillator is the basic clock for all internal timing. It turns on the output switch via the logic and driver circuitry. Special adaptive antisat circuitry detects onset of saturation in the power switch and adjusts driver current instantaneously to limit switch saturation. This minimizes driver dissipation and provides very rapid turn-off of the switch. A.V bandgap reference biases the positive input of the error amplifier. The negative input is brought out for output voltage sensing. This feedback pin has a second function; when pulled low with an external resistor, it programs the LT7/LT7 to disconnect the main error amplifier output and connects the output of the flyback amplifier to the comparator input. The LT7/ LT7 will then regulate the value of the flyback pulse with respect to the supply voltage. This flyback pulse is directly proportional to output voltage in the traditional transformer coupled flyback topology regulator. By regulating the amplitude of the flyback pulse, the output voltage can be regulated with no direct connection between input and output. The output is fully floating up to the breakdown voltage of the transformer windings. Multiple floating outputs are easily obtained with additional windings. A special delay network inside the LT7/ LT7 ignores the leakage inductance spike at the leading edge of the flyback pulse to improve output regulation. The error signal developed at the comparator input is brought out externally. This pin ( ) has four different functions. It is used for frequency compensation, current limit adjustment, soft starting and total regulator shutdown. During normal regulator operation this pin sits at a voltage between.9v (low output current) and.v (high output current). The error amplifiers are current output (g m ) types, so this voltage can be externally clamped for adjusting current limit. Likewise, a capacitor coupled external clamp will provide soft start. Switch duty cycle goes to zero if the pin is pulled to ground through a diode, placing the LT7/LT7 in an idle mode. Pulling the pin below. causes total regulator shutdown, with only 5µA supply current for shutdown circuitry biasing. See AN9 for full application details. TYPICAL APPLICATIONS (Note that maximum output currents are divided by for the LT7) Driving High Voltage NPN Driving High Voltage FET (for Off-Line Applications, See AN5) G D S Q ** * Q V TO V LT7/LT7 LT7/LT7 * SETS I B(ON) ** SETS I B(OFF) 7/7 TA3 7/7 TA6 7fe 7

8 LT7/LT7 TYPICAL APPLICATIONS (Note that maximum output currents are divided by for the LT7) Negative Buck Converter OPTIONAL INPT L3 V µf LT7 L** µh µf Q N396 * REQIRED IF INPT LEADS " ** PLSE ENGINEERING 93.6k LOAD OPTIONAL OTPT L µh 7/7 TA 5.V.5A C µf Positive Buck Converter D3 L µh C5* µf.µf LT7 7Ω µf r 3.7k N9 OPTIONAL OTPT µf L** Ω µh C µf C5 µf.5a ma MINIMM * REQIRED IF INPT LEADS " ** PLSE ENGINEERING 9 7/7 TA Negative Current Boosted Buck Converter R5 T :N Q N396 k = MINIMM LOAD = ma V OT.6V ma V OT A LT7 8 7/7 TA3 7fe

9 LT7/LT7 TYPICAL APPLICATIONS (Note that maximum output currents are divided by for the LT7) Positive Current Boosted Buck Converter 8V 7Ω W.7µF R6 7Ω C6.µF :N C5* µf LT7 68Ω.33µF k R7 7 6 V V LM38 COMP 3 8 pf N.5 R5 5k *REQIRED IF INPT LEADS " 5k 5µF V OT A 7/7 TA9 Negative to Positive Buck/Boost Converter Positive to Negative Buck/Boost Converter L3 OPTIONAL INPT C* µf V * REQIRED IF INPT LEADS " ** PLSE ENGINEERING 93 LT7 L** 5µH.k.µF µf 7/7 TA5 L OPTIONAL OTPT Q V OT V A.3k D3 N C 5µF LT7 R5 7Ω W 5k.µF.7k L** µh C5* µf V TO 3V N9 7Ω µf µf TO AVOID START-P PROBLEMS FOR INPT VOLTAGES BELOW V, CONNECT ANODE OF D3 TO AND REMOVE R5. MAY BE REDCED FOR LOWER OTPT CRRENTS. (5µF)(I OT ) FOR OTPTS, REDCE TO.5k, INCREASE TO.3µF AND REDCE R6 TO Ω. R6 7Ω V OT V 7/7 TA9 A * REQIRED IF INPT LEADS " ** PLSE ENGINEERING 93 7fe 9

10 LT7/LT7 TYPICAL APPLICATIONS (Note that maximum output currents are divided by for the LT7) Voltage Boosted Boost Converter Current Boosted Boost Converter LT7 68Ω W k.7µf.68µf 98k L N = 5 µf TOTAL INDCTANCE = mh INTERLEAVE PRIMARY AND SECONDARY FOR LOW LEAKAGE INDCTANCE V OT V 3mA 6V TO V LT7 I N 7k V OT 8V A 7/7 TA 7/7 TA Negative Boost Regulator Negative Input/Negative Output Flyback Converter C* 7µF LT7 3.3k L µh.µf *REQIRED IF INPT LEADS " 7k µf µf V OT 8V A R O (MINIMM LOAD) 7/7 TA5 LT7/LT7 R5 R6 T :N Q N396 k V OT * = V OT.6V µa 7/7 TA7 5k * External Current Limit External Current Limit Q k pf R S LT7/LT7 NOTE THAT THE LT7/LT7 PIN IS NO LONGER COMMON TO V IN 7/7 TA6 5Ω V X = V LT7/LT7 7/7 TA 7fe

11 LT7/LT7 TYPICAL APPLICATIONS (Note that maximum output currents are divided by for the LT7) Flyback Converter V SNB CLAMP TRN-ON SPIKE V TO 3V C* µf LT7.7µF N L µh OPTIONAL N = /3 µf C µf V OT 6A 3.7k V V a c I b d V OT V F I PRI I PRI (N)( ) I PRI N V PRIMARY FLYBACK VOLTAGE = OT V F N LT7/LT7 SWITCH VOLTAGE AREA a = AREA b TO MAINTAIN ZERO DC VOLTS ACROSS PRIMARY SECONDARY VOLTAGE AREA c = AREA d TO MAINTAIN ZERO DC VOLTS ACROSS SECONDARY PRIMARY CRRENT SECONDARY CRRENT.5k.5µF I PRI LT7 SWITCH CRRENT SNBBER DIODE CRRENT *REQIRED IF INPT LEADS " t = (I PRI)(L L ) V SNB 7/7 TA8 PACKAGE DESCRIPTION K Package -Lead TO-3 Metal Can (Reference LTC DWG # 5-8-3) T Package 5-Lead Plastic TO- (Standard) (Reference LTC DWG # 5-8-).3.35 ( ) ( ).6.35 (.5 3.9).39.5 (9.96.5).7.55 ( ) DIA.65.8 (.9.57).5.55 (.3.397)..8 (.67.9).3.7 ( ) (9.9 3.).38.3 (.965.9).6.5 (.68.7) ( ).57.6 ( ).7.78 ( ).6 (5.75) TYP.7 TP P.C.D ( ).5.6 (3.8.9) DIA PLC SEATING PLANE ( ) ( ).95.5 (.3.9).55.95* ( ) (..9) R.9.5 (.5.95) R K(TO-3) 98 BSC.67 (.7).8.38 (.7.965) (3.9.9).3.3 (.33.58) T5 (TO-) 399 * MEASRED AT THE SEATING PLANE OBSOLETE PACKAGE 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 representation that the interconnection of its circuits as described herein will not infringe on existing patent rights. 7fe

12 LT7/LT7 TYPICAL APPLICATIONS C5* µf *REQIRED IF INPT LEADS " LT7/LT7 (Note that maximum output currents are divided by for the LT7).5k.µF 5k Totally Isolated Converter N =.875 = 7:8 FOR V OT = 5Ω :N.7µF N N V V t OFF 5µF C 5µF 6V t ON V OT COM OPTIONAL OTPT L µf L µf (N)( ) C5 µf C6 µf SWITCH VOLTAGE V F (DIODE FORWARD VOLTAGE) SECONDARY VOLTAGE 7/7 TA7 Forward Converter D3 T I M N L 7µH µf V OT 6A V TO 3V LT7 D 3.7k Q C R6 33Ω R5 Ω 7/7 TA8 RELATED PARTS PART NMBER DESCRIPTION COMMENTS LT7/LT76 High Voltage Switching Regulators V Input (6V for HV Versions), khz, 5A and A LT7/LT7/ khz High Efficiency Switching Regulators V Input (6 for HV Versions), 5A/.5A/.5A Internal Switch LT7 LT37/LT37 5kHz High Efficiency Switching Regulators 3, 6A/3A Internal Switch LT37/LT376 khz High Efficiency Switching Regulators Input,.5A/.5A Internal Switch LT765.5MHz, 3A, Step-Down Regulator Input, TSSOP-6E, SO8 Package Linear Technology Corporation 63 McCarthy Blvd., Milpitas, CA (8) 3-9 FAX: (8) fe LT/CPI.5K REV E PRINTED IN SA LINEAR TECHNOLOGY CORPORATION 989