Electronic Components Datasheet Search |
|
LM5115 Datasheet(PDF) 10 Page - Texas Instruments |
|
|
LM5115 Datasheet(HTML) 10 Page - Texas Instruments |
10 / 24 page Phase signal RAMP pin HS pin 12V 12V 6V 6V Main Output = 3.3V Secondary Output = 2.5V PWM Threshold SYNC CLK RAMP BUFFER 2.5K 15 PA CLK Isync Isync x 3 2.5k Phase Signal R SYNC C RAMP LM5115 SNVS343D – MARCH 2005 – REVISED JULY 2006 www.ti.com Synchronization (SYNC) and Feed-Forward (RAMP) The pulsing “phase signal” from the main converter synchronizes the PWM ramp and gate drive outputs of the LM5115. The phase signal is the square wave output from the transformer secondary winding before rectification (Figure 1). A resistor connected from the phase signal to the low impedance SYNC pin produces a square wave current (ISYNC) as shown in Figure 4. A current comparator at the SYNC input monitors ISYNC relative to an internal 15µA reference. When ISYNC exceeds 15µA, the internal clock signal (CLK) is reset and the capacitor connected to the RAMP begins to charge. The current source that charges the RAMP capacitor is equal to 3 times the ISYNC current. The falling edge of the phase signal sets the CLK signal and discharges the RAMP capacitor until the next rising edge of the phase signal. The RAMP capacitor is discharged to ground by a low impedance (100 Ω) n-channel MOSFET. The input impedance at SYNC pin is 2.5kΩ which is normally much less than the external SYNC pin resistance. Figure 4. Line Feed-Forward Diagram The RAMP and SYNC functions illustrated in Figure 4 provide line voltage feed-forward to improve the regulation of the auxiliary output when the input voltage of the main converter changes. Varying the input voltage to the main converter produces proportional variations in amplitude of the phase signal. The main channel PWM controller adjusts the pulse width of the phase signal to maintain constant volt*seconds and a regulated main output as shown in Figure 5. The variation of the phase signal amplitude and duration are reflected in the slope and duty cycle of the RAMP signal of the LM5115 (ISYNC α phase signal amplitude). As a result, the duty cycle of the LM5115 is automatically adjusted to regulate the auxiliary output voltage with virtually no change in the PWM threshold voltage. Transient line regulation is improved because the PWM duty cycle of the auxiliary converter is immediately corrected, independent of the delays of the voltage regulation loop. Figure 5. Line Feed-forward Waveforms The recommended SYNC input current range is 50µA to 150µA. The SYNC pin resistor (RSYNC) should be selected to set the SYNC current (ISYNC) to 150µA with the maximum phase signal amplitude, VPHASE(max). This will guarantee that ISYNC stays within the recommended range over a 3:1 change in phase signal amplitude. The SYNC pin resistor is therefore: 10 Submit Documentation Feedback Copyright © 2005–2006, Texas Instruments Incorporated Product Folder Links: LM5115 |
Similar Part No. - LM5115 |
|
Similar Description - LM5115 |
|
|
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 |