1LT1246 LT1247 1MHz Off Line

Line Converters

Description

Niveau: Supérieur, Doctorat, Bac+8
1LT1246/LT1247 1MHz Off-Line Current Mode PWM and DC/DC Converter + – + – 1 2FEEDBACK COMPENSATION 2.5V 2R R 1V 1.5V – + 3ISENSE BLANKING 1mA 5.6V 4RT/CT OSCILLATOR R S 18V 7 VCC UV LOCKOUT 5 GND 6 OUTPUT 8 VREF 5V REF MAIN BIAS REFERENCE PULLDOWN OUTPUT PULLDOWN REFERENCE ENABLE LT1246 • BD01 D U ESCRIPTIOSFEATURE U SA O PPLICATI n Current Mode Operation to 1MHz n 30ns Current Sense Delay n < 250µA Low Start-Up Current n Current Sense Leading Edge Blanking n Pin Compatible with UC1842 n Undervoltage Lockout with Hysteresis n No Cross-Conduction Current n Trimmed Bandgap Reference n 1A Totem Pole Output n Trimmed Oscillator Frequency and Sink Current n Active Pull-Down on Reference and Output During Undervoltage Lockout n 18V High Level Output Clamp n Off-Line Converters n DC/DC Converters The LT®1246/LT1247 are 8-pin, fixed frequency, current mode, pulse width modulators. These devices are de- signed to be improved plug compatible versions of the industry standard UC1842 PWM circuit. The LT1246/ LT1247 are optimized for off-line and DC/DC converter applications.

• lt1246


• output


• current sense


• start-up current


• undervoltage lockout


• current reference


• start-up threshold


• current

Sujets

• Régulation
• Linear Technology
• Output
• Current

Informations

• Publié par: profil-zyak-2012
• Nombre de lectures: 19
• Langue: English

Extrait

F EA T U RES n Current Mode Operation to 1MHz n 30ns Current Sense Delay n < 250 m A Low Start-Up Current n Current Sense Leading Edge Blanking n Pin Compatible with UC1842 n Undervoltage Lockout with Hysteresis n No Cross-Conduction Current n Trimmed Bandgap Reference n 1A Totem Pole Output n Trimmed Oscillator Frequency and Sink Current n Active Pull-Down on Reference and Output During Undervoltage Lockout n 18V High Level Output Clamp A PP L IC AT I S n Off-Line Converters n DC/DC Converters Minimum DeviceT S h t r a e r s t h -U ol p d O V p o e l r t a a t g i e ng D M ut a y x   i C m y u cl m eReplaces L L T T 1 1 2 2 4 46 78 1 . 6 4 V V7 1 . 0 6 V V 1 1 0 0 0 0 % % U U C C 1 1 8 8 4 4 2 3 BLOCKDIAGRA R T /C T 4 COMPENSATION 1 FEEDBACK 2 – V5.2 + I SENSE 3 OSCILLATOR V6.5 V1 Am1 2R – R + LT1246/LT1247 1MHz Off-Line Current Mode PWM and DC/DC Converter DESCRIPTIO ® T m h o e  d L e, T  p 1 u 2 ls 4 e 6   /L w T id 1 t 2 h 4   7 m  a o r d e u   l 8 a - t p o i r n s ,  .  fi T x h e e d  s f e r   e d q e u v e ic n e c s y   ,  a c r u e r   r d e e n - t i s n ig d n u e st d r   y t   o  st b a e n  i d m ar p d r   o U ve C d 1   8 p 4 lu 2  g  P c W om M p   a c t i i r b c l u e i   t. v   e T rs h i e o   n L s T  o 1 f 2  t 4 h 6 e / LT1247 are optimized for off-line and DC/DC converter applications. They contain a temperature compensated reference, high gain error amplifier, current sensing com- parator, and a high current totem pole output stage ideally suited to driving power MOSFETs. Start-up current has been reduced to less than 250 m A. Cross-conduction cur- rent spikes in the totem pole output stage have been eliminated, making 1MHz operation practical. Several new features have been incorporated. Leading edge blanking has been added to the current sense comparator. This minimizes or eliminates the filter that is normally required. Eliminating this filter allows the current sense loop to operate with minimum delays. Trims have been added to the oscillator circuit for both frequency and sink current, and both of these parameters are tightly specified. The output stage is clamped to a maximum V OUT  of 18V in the on state. The output and the reference output are actively pulled low during under-voltage lockout. , LTC and LT are registered trademarks of Linear Technology Corporation. REFERENCE ENABLE UV  LOCKOUT 5V REF  REFERENCE PULLDOWN 8 V MAIN BIAS OUTPUT  REF PULLDOWN 7V CC S 6OUTPUT R DNG5 BLANKING 18V + V5.1 – LT1246 • BD01 1