 |
Electronic Components Datasheet Search |
|
|
Electronic Components Datasheet Search |
|
FSDM0565RB Datasheet(PDF) 11 Page - Fairchild Semiconductor |
|
||||||||||||||||||||||||||||||
FSDM0565RB Datasheet(HTML) 11 Page - Fairchild Semiconductor |
|
|
11 / 20 page  FSDM0565RB 11 Functional Description 1. Startup : In previous generations of Fairchild Power Switches (FPSTM) the Vcc pin had an external start-up resistor to the DC input voltage line. In this generation the startup resistor is replaced by an internal high voltage current source. At startup, an internal high voltage current source supplies the internal bias and charges the external capacitor (Cvcc) that is connected to the Vcc pin as illustrated in Figure 4. When Vcc reaches 12V, the FSDM0565RB begins switching and the internal high voltage current source is disabled. Then, the FSDM0565RB continues its normal switching operation and the power is supplied from the auxiliary transformer winding unless Vcc goes below the stop voltage of 8V. Figure 4. Internal startup circuit 2. Feedback Control : FSDM0565RB employs current mode control, as shown in Figure 5. An opto-coupler (such as the H11A817A) and shunt regulator (such as the KA431) are typically used to implement the feedback network. Comparing the feedback voltage with the voltage across the Rsense resistor plus an offset voltage makes it possible to control the switching duty cycle. When the reference pin voltage of the KA431 exceeds the internal reference voltage of 2.5V, the H11A817A LED current increases, thus pulling down the feedback voltage and reducing the duty cycle. This event typically happens when the input voltage is increased or the output load is decreased. 2.1 Pulse-by-pulse current limit: Because current mode control is employed, the peak current through the Sense FET is limited by the inverting input of PWM comparator (Vfb*) as shown in Figure 5. Assuming that the 0.9mA current source flows only through the internal resistor (2.5R +R= 2.8 k Ω), the cathode voltage of diode D2 is about 2.5V. Since D1 is blocked when the feedback voltage (Vfb) exceeds 2.5V, the maximum voltage of the cathode of D2 is clamped at this voltage, thus clamping Vfb*. Therefore, the peak value of the current through the Sense FET is limited. 2.2 Leading edge blanking (LEB) : At the instant the internal Sense FET is turned on, there usually exists a high current spike through the Sense FET, caused by primary-side capacitance and secondary-side rectifier reverse recovery. Excessive voltage across the Rsense resistor would lead to incorrect feedback operation in the current mode PWM control. To counter this effect, the FSDM0565RB employs a leading edge blanking (LEB) circuit. This circuit inhibits the PWM comparator for a short time (TLEB) after the Sense FET is turned on. Figure 5. Pulse width modulation (PWM) circuit 3. Protection Circuit : The FSDM0565RB has several self protective functions such as over load protection (OLP), over voltage protection (OVP) and thermal shutdown (TSD). Because these protection circuits are fully integrated into the IC without external components, the reliability can be improved without increasing cost. Once the fault condition occurs, switching is terminated and the Sense FET remains off. This causes Vcc to fall. When Vcc reaches the UVLO stop voltage, 8V, the protection is reset and the internal high voltage current source charges the Vcc capacitor via the Vstr pin. When Vcc reaches the UVLO start voltage,12V, the FSDM0565RB resumes its normal operation. In this manner, the auto-restart can alternately enable and disable the switching of the power Sense FET until the fault condition is eliminated (see Figure 6). 8V/12V 3 Vref Internal Bias Vcc 6 Vstr I start Vcc good V DC C Vcc 4 OSC Vcc Vref I delay I FB V SD R 2.5R Gate driver OLP D1 D2 + V fb* - Vfb KA431 C B Vo H11A817A R sense SenseFET |
Similar Part No. - FSDM0565RB_06 |
|
Similar Description - FSDM0565RB_06 |
|
|
|
Link URL |
| Privacy Policy |
| ALLDATASHEET.COM |
| Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | Datasheet Upload | 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
