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ISL6551ABZ Datasheet(PDF) 11 Page - Intersil Corporation |
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ISL6551ABZ Datasheet(HTML) 11 Page - Intersil Corporation |
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11 / 26 page  11 FN9066.4 July 8, 2005 - Note that the capacitance of a scope probe (~12pF for single ended) would induce a smaller frequency at the CT pin. It can be easily seen at a higher frequency. An accurate operating frequency can be measured at the outputs of the bridge/synchronous drivers. - The dead time is the delay to turn on the upper FET (UPPER1/UPPER2) after its corresponding lower FET (LOWER1/LOWER2) is turned off when the bridge is operating at maximum duty cycle in normal conditions, or is responding to load transients or input line dipping conditions. This helps to prevent shoot through between the upper FET and the lower FET that are located at the same side of the bridge. The dead time can be estimated using Equation 2: where M=11.4(VDD=12V), 11.1(VDD=14V), and 12(VDD=10V), and RD is in k Ω. This relationship is shown in Figure 3. • Error Amplifier (EAI, EANI, EAO) - This amplifier compares the feedback signal received at the EAI pin to a reference signal set at the EANI pin and provides an error signal (EAO) to the PWM Logic. The feedback loop compensation can be programmed via these pins. - Both EANI and EAO are clamped by the voltage (Vclamp) set at the CSS pin, as shown in Figure 4. Note that the diodes in the functional block diagram represent the clamp function of the CSS in a simplified way. • Soft-Start (CSS) - The voltage on an external capacitor charged by an internal current source ISS is fed into a control pin on the error amplifier. This causes the Error Amplifier to: 1) limit the EAO to the soft-start voltage level; and 2) over- ride the reference signal at the EANI with the soft-start voltage, when the EANI voltage is higher than the soft- start voltage. Thus, both the output voltage and current of the power supply can be controlled by the soft-start. - The clamping voltage determines the cycle-by-cycle peak current limiting of the power supply. It should be set above the EANI and EAO voltages and can be programmed by an external resistor as shown in Figure 4 using Equation 3. FIGURE 2. CT vs FREQUENCY 3,000 2,500 2,000 1,500 1,000 500 0 0 °C 60 °C 10 100 10,000 CT (pF) 1,000 RECOMMENDED RANGE 120 °C DT MRD × k Ω -------------------- = (EQ. 2) (ns) FIGURE 3. RD vs DEAD TIME (VDD = 12V) 2 1.6 1.2 0.8 0.4 0 0 20 40 60 80 100 120 140 160 RD (k Ω) Vclamp Rcss Iss • = (EQ. 3) (V) CSS VDD Iss SHUTDOWN 400mV + - SSL (TO BLANKING CIRCUIT) ERROR AMP EAO EAI (–) EANI (+) FIGURE 4. SIMPLIFIED CLAMP/SOFT-START RCSS (See Fig. 9) ISL6551 |
Similar Part No. - ISL6551ABZ |
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Similar Description - ISL6551ABZ |
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