Electronic Components Datasheet Search |
|
ISL6742AAZA Datasheet(PDF) 10 Page - Intersil Corporation |
|
ISL6742AAZA Datasheet(HTML) 10 Page - Intersil Corporation |
10 / 18 page 10 FN9183.1 July 25, 2005 The maximum duty cycle, D, and percent deadtime, DT, can be calculated from: Soft-Start Operation The ISL6742 features a soft-start using an external capacitor in conjunction with an internal current source. Soft-start reduces component stresses and surge currents during start-up. Upon start-up, the soft-start circuitry limits the error voltage input (VERR) to a value equal to the soft-start voltage. The output pulse width increases as the soft-start capacitor voltage increases. This has the effect of increasing the duty cycle from zero to the regulation pulse width during the soft- start period. When the soft-start voltage exceeds the error voltage, soft-start is completed. Soft-start occurs during start-up and after recovery from a fault condition. The soft- start charging period may be calculated as follows: where t is the charging period in ms and C is the value of the soft-start capacitor in µF. The soft-start duration experienced by the power supply will be less than or equal to this value, depending on when the feedback loop takes control. The soft-start voltage is clamped to 4.50V with an overall tolerance of 2%. It is suitable for use as a “soft-started” reference provided the current draw is kept well below the 70 µA charging current. The outputs may be inhibited by using the SS pin as a disable input. Pulling SS below 0.25V forces all outputs low. An open collector/drain configuration may be used to couple the disable signal to the SS pin. Gate Drive The ISL6742 outputs are capable of sourcing and sinking 10mA (at rated VOH, VOL) and are intended to be used in conjunction with integrated FET drivers or discrete bipolar totem pole drivers. The typical on resistance of the outputs is 50 Ω. Overcurrent Operation Two overcurrent protection mechanisms are available to the power supply designer. The first method is cycle-by-cycle peak overcurrent protection which provides fast response. The second method is a slower, averaging method which produces constant or “brick-wall” current limit behavior. If voltage-mode control is used, the average overcurrent protection also maintains flux balance in the transformer by maintaining duty cycle symmetry between half-cycles. The current sense signal applied to the CS pin connects to the peak current comparator and a sample and hold averaging circuit. After a 70ns leading edge blanking (LEB) delay, the current sense signal is actively sampled during the on time, the average current for the cycle is determined, and the result is amplified by 4x and output on the IOUT pin. If an RC filter is placed on the CS input, its time constant should not exceed ~50ns or significant error may be introduced on IOUT. Figure 5 shows the relationship between the CS signal and IOUT under steady state conditions. IOUT is 4x the average of CS. Figure 6 shows the dynamic behavior of the current averaging circuitry when CS is modulated by an external sine wave. Notice IOUT is updated by the sample and hold circuitry at the termination of the active output pulse. D TC TSW ------------ = (EQ. 4) DT 1 D – = (EQ. 5) t 64.3 C ⋅ = mS (EQ. 6) FIGURE 5. CS INPUT vs IOUT CHANNEL 1 (YELLOW): OUTA CHANNEL 3 (BLUE): CS CHANNEL 2 (RED): OUTB CHANNEL 4 (GREEN): IOUT FIGURE 6. DYNAMIC BEHAVIOR OF CS vs IOUT CHANNEL 1 (YELLOW): OUTA CHANNEL 3 (BLUE): CS CHANNEL 2 (RED): OUTB CHANNEL 4 (GREEN): IOUT ISL6742 |
Similar Part No. - ISL6742AAZA |
|
Similar Description - ISL6742AAZA |
|
|
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 |