ISL6721 datasheet(18/21 Pages) INTERSIL

18 / 21 page

FN9110.4

April 13, 2007

Regulation Performance

Waveforms

Typical waveforms can be found in Figures 10 through 12.

Figure 10 shows the steady state operation of the sawtooth

oscillator waveform at RTCT (Trace 2), the SYNC output

pulse (Trace 1), and the GATE output to the converter FET

(Trace 3). Figure 11 shows the converter behavior while

operating in an overcurrent fault condition. Trace 1 is the

soft-start voltage, which increases from 0V to 4.5V, at which

point the OC fault function is enabled. The OC condition is

detected and the soft-start capacitor is discharged to the

4.375V OC fault threshold at which point the IC enters the

fault shutdown mode. Trace 2 shows the behavior of the

timing capacitor voltage during a shutdown fault. Most of the

functions of the IC are de-powered during a fault, and the

oscillator is among those functions. During a fault, the IC is

turned off until the restart delay has timed out. After the

delay, power is restored and the IC resumes normal

operation. Trace 3 is the GATE output during the soft-start

cycle and OC fault.

Figure 12 shows the switching FET waveforms during

steady state operation. Trace 1 is drain - source voltage and

Trace 2 is gate - source voltage.

TABLE 1. OUTPUT LOAD REGULATION, VIN = 48V

IOUT (A), 3.3V IOUT (A), 1.8V VOUT (V), 3.3V VOUT (V), 1.8V

0.030

3.351

1.825

0.39

0.030

3.281

1.956

0.88

0.030

3.251

1.988

1.38

0.030

3.223

2.014

1.87

0.030

3.204

2.029

2.39

0.030

3.185

2.057

2.89

0030

3.168

2.084

3.37

0.030

3.153

2.103

0.52

3.471

1.497

0.39

0.52

3.283

1.800

0.88

0.52

3.254

1.836

1.38

0.52

3.233

1.848

1.87

0.52

3.218

1.855

2.39

0.52

3.203

1.859

2.89

0.52

3.191

1.862

1.05

3.619

1.347

0.39

1.05

3.290

1.730

0.88

1.05

3.254

1.785

1.38

1.05

3.235

1.805

1.87

1.05

3.220

1.814

2.39

1.05

3.207

1.820

1.55

3.699

1.265

0.39

1.55

3.306

1.682

0.88

1.55

3.260

1.750

1.38

1.55

3.239

1.776

1.87

1.55

3.224

1.789

2.07

3.762

1.201

0.39

2.07

3.329

1.645

0.88

2.07

3.270

1.722

1.38

2.07

3.245

1.752

2.62

3.819

1.142

0.39

2.62

3.355

1.612

0.88

2.62

3.282

1.697

3.14

3.869

1.091

.39

3.14

3.383

1.581

FIGURE 10. TYPICAL WAVEFORMS

NOTE:

Trace 1: SYNC Output

Trace 2: RTCT Sawtooth

Trace 3: GATE Output

FIGURE 11. SOFT-START WITH OVERCURRENT FAULT

NOTE:

Trace 1: SS

Trace 2: RTCT Sawtooth

Trace 3: GATE Output

ISL6721

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