 |
Electronic Components Datasheet Search |
|
|
Electronic Components Datasheet Search |
|
LT1952EGN Datasheet(PDF) 10 Page - Linear Technology |
|
||||||||||||||||||||||||||||||
LT1952EGN Datasheet(HTML) 10 Page - Linear Technology |
|
|
10 / 24 page  LT1952/LT1952-1 10 19521fd OPERATION Introduction The LT1952/LT1952-1 are current mode synchronous PWM controllers optimized for control of the simplest forward converter topology—using only one primary MOSFET. The LT1952/LT1952-1 are ideal for 25W to 500W power systems where very high efficiency and reliability, low complexity and cost are required in a small space. Key features of the LT1952/LT1952-1 include an adaptive maximum duty cycle clamp for the single primary MOSFET. An additional output signal is included for synchronous rectifier control. A precision 107mV threshold senses overcurrent conditions and triggers Soft-Start for low stress short-circuit protection and control. The key functions of the LT1952/LT1952-1 are shown in the Block Diagram in Figure 2. Part Start-up In normal operation the SD_VSEC pin must exceed 1.32V and the VIN pin must exceed 14.25V (7.75V LT1952-1) to allow the part to turn on. This combination of pin voltages allows the 2.5V VREF pin to become active, supplying the LT1952/LT1952-1 control circuitry and providing up to 2.5mA external drive. SD_VSEC threshold can be used for externally programming an undervoltage lockout (UVLO) threshold on the system input voltage. Hysteresis on the UVLO threshold can also be programmed since the SD_VSEC pin draws 11μA just before part turn on and 0μA after part turn on. With the LT1952/LT1952-1 turned on, the VIN pin can drop as low as 8.75V (6.5V LT1952-1) before part shutdown occurs. This VIN pin hysteresis (5.5V LT1952; 1.25V LT1952-1) combined with low 460μA (400μA LT1952-1) start-up input current allows low power start-up using a resistor/capacitor network from system VIN to supply the VIN pin (Figure 3). The VIN capacitor value is chosen to prevent VIN falling below its turn off threshold before an auxiliary winding in the converter takes over supply to the VIN pin. Output Drivers The LT1952/LT1952-1 have two outputs, SOUT and OUT. The OUT pin provides a ±1A peak MOSFET gate drive clamped to 13V. The SOUT pin has a ±50mA peak drive clamped to 12V and provides sync signal timing for synchronous rectification control. For SOUT and OUT turn on, a PWM latch is set at the start of each main oscillator cycle. OUT turn on is delayed from SOUT turn on by a time tDELAY (Figure 2). tDELAY is pro- grammed using a resistor from the DELAY pin to ground and is used to set the timing control of the secondary synchronous rectifiers for optimum efficiency. SOUT and OUT turn off at the same time each cycle by one of three methods: (1) MOSFET peak current sense at ISENSE pin (2) Adaptive maximum duty cycle clamp reached during load/line transients (3) Maximum duty cycle reset of the PWM latch During any of the following conditions—low VIN, low SD_VSEC or overcurrent detection at the OC pin—a soft- start event is latched and both SOUT and OUT turn off immediately (Figure 1). Leading Edge Blanking To prevent MOSFET switching noise causing premature turn off of SOUT or OUT, programmable leading edge blanking exists. This means both the current sense comparator and overcurrent comparator outputs are ignored during MOSFET turn on and for an extended period after the OUT leading edge (Figure 6). The extended blanking period is programmable by adjusting a resistor from the BLANK pin to ground. Adaptive Maximum Duty Cycle Clamp (Volt-Second Clamp) For forward converter applications using the simplest topology of a single MOSFET on the primary, a maximum switch duty cycle clamp which adapts to transformer input voltage is necessary for reliable control of the MOSFET. This volt-second clamp provides a safeguard for transformer reset that prevents transformer saturation. Instantaneous load changes can cause the converter loop to demand maximum duty cycle. If the maximum duty cycle of the switch is too great, the transformer reset voltage can exceed the voltage rating of the primary-side MOSFET with |
Similar Part No. - LT1952EGN |
|
Similar Description - LT1952EGN |
|
|
|
Link URL |
| Privacy Policy |
| ALLDATASHEET.NET |
| Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | Contact us | Privacy Policy | Link Exchange | Manufacturer List All Rights Reserved©Alldatasheet.com |
| Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
|
Family Site : ic2ic.com |
icmetro.com |
English ▼
English
Chinese
German
Japanese
Russian
Korean
Spanish
French
Italian
Portuguese
Polish
Vietnamese
Indian
Mexican
British
New Zealand
