Electronic Components Datasheet Search |
|
ISL6560 Datasheet(PDF) 10 Page - Intersil Corporation |
|
ISL6560 Datasheet(HTML) 10 Page - Intersil Corporation |
10 / 14 page 10 FN9011.3 To calculate the dissipation in the 5m Ω resistor, we used only half of the ripple current, 4A, to give a nominal dissipation of: Where IP is the peak current and D is the duty cycle. Two 10m Ω, 1W resistors in parallel were selected. RL Selection As discussed in the section under Droop Voltage and shown in Figure 1, resistor RL establishes the gain of the transconductance error amplifier. It is this resistor that sets the droop voltage or regulation. Like any feedback system, the higher the gain the better the regulation. The value of this resistor may be determined from the following equation: The ni term is the ratio of the VCOMP to the current comparator threshold voltage; see Figure 2. RL is made up of two resistors that form a voltage divider from the internal 3V reference supply. As described earlier in the Circuit Description section, the output voltage of the gm amplifier establishes the threshold voltage of the current comparator. At approximately 1V, the current comparator threshold voltage is near zero. With no current demands, the regulator output voltage would be the same as the programmed DAC voltage. However, an 8A ripple current was selected for this design. This results in the output of the gm amplifier moving upwards to supply the ripple current. The voltage at the COMP pin, VSET, will be: The voltage divider establishes the reference voltage for VCOMP that was set to 1.2V for this design, so the error amplifier must drive the COMP pin 50mV more positive to bring it to 1.25V from the 1.2V originally set. This additional 50mV output will result in an input voltage to the error amplifier of: 50mv / 19.1 = 2.62mV below the programmed DAC voltage of 1.8V. Neglected, is a negative term associated with the 60ns delay of the current comparator. This delay will cause the current ramp to be slightly greater than predicted by the equation. This means that the initial setting should be slightly reduced to account for the increase in current. Once the value for RL is set, only the values of the resistors that make up the voltage divider must be determined. Figure 8 shows the equations to determine the resistor network that makes up RL. CC and RC Selection Optimum transient response depends upon the selection of the compensation capacitor network placed across the output of the transconductance error amplifier. To a first order, the selection of the capacitor, CC, placed across the error amplifier may be determined by making the product of the regulator output resistance and output capacitors equal to the product of the RL and CC. This yields the equation for the compensation capacitor: A 1nF capacitor was selected from transient testing. To prevent excessive phase shift due to the compensation capacitor, it is usually necessary to place a resistor inseries with the capacitor to prevent excessive phase shift beyond the frequency of interest. This is pole cancellation and the resistor is approximately 0.5 x RL. Figure 9 shows this network and the equivalent circuit is approximately 0.5 x RL. Many variables have been used in the selection of the various gain and filter networks to this point. A broad range of component tolerances range from ±1% to ±20% have been used in the design. Therefore, it is important to evaluate the entire system with dynamic pulse load testing. This will verify optimum transient response and also indicate poor response in terms of excessive overshoot, ringing or oscillation if the compensation network is not optimum. I RMS Ip D Ip 1.8V 12V ------------ == Power 0.69W per channel or 1.38W for both channels = Power Ip 2 DR SENSE 3 = × × = ∴ 0.4 2 0.15 · 5m Ω × × R L ni R SENSE × gm R OUT 2 × × ----------------------------------------- 12.5 5m Ω × 2.2mS 1.63m Ω 2 × × -------------------------------------------------------- 8.7k Ω == = gmAmplifierGain gm RL × 2.2mS 8.7k 19.1 = × = = ∴ gm Amplifier Gain = 1V 8A 5m Ω 12.5 × × 2 --------------------------------------------- + = 1V 250mV + 1.25V == V SET 1V I RIPPLE R SENSE ni × × 2 ---------------------------------------------------------------- + = RU RB VREF = 3V To COMP pin, this voltage is VSET R U R B || R L = R U V REF V SET --------------- = R L × R B V SET V REF V SET – ------------------------------------ = R U × V SET 1V I RIPPLE R SENSE ni × × 2 ---------------------------------------------------------------- + = R U 3V 1.25V ---------------- = 8.7k × 20.9k = R B 1.25V 3V 1.25V – ----------------------------- = 20.9k × 14.9k = FIGURE 8. EQUATIONS TO DETERMINE RL DIVIDER C C R OUT C OUT × R L --------------------------------------- 1.63m Ω 9mF × 8.7k ----------------------------------------- 1.68nF == = RU RB VREF = 3V CC RC RC = 0.5 x RL RL CC RC AC Equivalent To COMP pin FIGURE 9. COMPENSATION CIRCUIT ISL6560 |
Similar Part No. - ISL6560 |
|
Similar Description - ISL6560 |
|
|
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 |