Electronic Components Datasheet Search |
|
ISL6268CAZ Datasheet(PDF) 7 Page - Intersil Corporation |
|
ISL6268CAZ Datasheet(HTML) 7 Page - Intersil Corporation |
7 / 14 page 7 FN6348.0 August 22, 2006 Theory of Operation Modulator The ISL6268 is a hybrid of fixed frequency PWM control, and variable frequency hysteretic control. Intersil’s R3 technology can simultaneously affect the PWM switching frequency and PWM duty cycle in response to input voltage and output load transients. The term “Ripple” in the name “Robust Ripple Regulator” refers to the converter output inductor ripple current, not the converter output ripple voltage. The R3 modulator synthesizes an AC signal VR, which is an ideal representation of the output inductor ripple current. The duty-cycle of VR is the result of charge and discharge current through a ripple capacitor CR. The current through CR is provided by a transconductance amplifier gm that measures the VIN and VO pin voltages. The positive slope of VR can be written as: The negative slope of VR can be written as: where gm is the gain of the transconductance amplifier. A window voltage VW is referenced with respect to the error amplifier output voltage VCOMP, creating an envelope into which the ripple voltage VR is compared. The amplitude of VW is set by a resistor connected across the FSET and GND pins. The VR, VCOMP, and VW signals feed into a window comparator in which VCOMP is the lower threshold voltage and VW is the higher threshold voltage. Figure 2 shows PWM pulses being generated as VR traverses the VW and VCOMP thresholds . The PWM switching frequency is proportional to the slew rates of the positive and negative slopes of VR; the PWM switching frequency is inversely proportional to the voltage between VW and VCOMP. Power-On Reset The ISL6268 is disabled until the voltage at the VCC pin has increased above the rising power-on reset (POR) VCCR threshold voltage. The controller will become once again disabled when the voltage at the VCC pin decreases below the falling POR VCCF threshold voltage. EN, Soft-Start, and PGOOD The ISL6268 uses a digital soft-start circuit to ramp the output voltage of the converter to the programmed regulation setpoint at a predictable slew rate. The slew rate of the soft-start sequence has been selected to limit the inrush current through the output capacitors as they charge to the desired regulation voltage. When the EN pin is pulled above the rising EN threshold voltage VENTHR the PGOOD Soft-Start Delay TSS begins and the output voltage begins to rise. The output voltage enters regulation in approximately 1.5ms and the PGOOD pin goes to high impedance once TSS has elapsed. The PGOOD pin indicates when the converter is capable of supplying regulated voltage. The PGOOD pin is an undefined impedance if VCC has not reached the rising POR threshold VCCR, or if VCC is below the falling POR threshold VCCF. The ISL6268 features a unique fault-identification capability that can drastically reduce trouble-shooting time and effort. The pull-down resistance of the PGOOD pin corresponds to the fault status of the controller. During soft-start or if an undervoltage fault occurs, the PGOOD pull-down resistance is 95 Ω, or 32Ω for an overcurrent fault, or 63 Ω for an overvoltage fault. V RPOS g m () V IN V OUT – () • = (EQ. 1) V RNEG g m VOUT ⋅ = (EQ. 2) Ripple Capacitor Voltage CR Error Amplifier Voltage VCOMP Window Voltage VW PWM FIGURE 2. MODULATOR WAVEFORMS DURING LOAD TRANSIENT EN VCC and PVCC VOUT PGOOD 1.5ms 2.75ms FIGURE 3. SOFT-START SEQUENCE ISL6268 |
Similar Part No. - ISL6268CAZ |
|
Similar Description - ISL6268CAZ |
|
|
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 |