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ISL6558IRZ-T Datasheet(PDF) 10 Page - Intersil Corporation |
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ISL6558IRZ-T Datasheet(HTML) 10 Page - Intersil Corporation |
10 / 16 page 10 FN9027.12 June 21, 2005 The PWM drive signals are switched out of phase. The PWM drive signal phase relationship is 360° divided by the number of active channels. Figure shows the PWM drive signals for a four channel converter running at 125kHz. Each PWM drive signal is 90° out of phase with the other. Frequency Setting A resistor, RT, connected between the FS/EN pin and ground sets the frequency of the internal oscillator. Tying the FS/EN pin to ground disables the oscillator, thus shutting down the converter. The resistor can be calculated given the desired channel switching frequency, FSW. Figure 5 provides a graph of oscillator frequency vs RT. The maximum recommended channel frequency is 1.5MHz. Reference Voltage An internal 0.8V reference is used for both PWM duty cycle determination as well as output voltage protection. The reference is trimmed such that the system, including amplifier offset voltages, is accurate to ± 1% over temperature range. Fault Protection The ISL6558 protects the load device from damaging stress levels. The overcurrent trip point is integral in preventing output shorts of varying degrees from causing current spikes which would damage a load device. The output voltage detection features insure a safe window of operation for the load device. Overcurrent The RISEN resistor scales the voltage sampled across the lower MOSFET and provides current feedback proportional to the output current of each active channel. The ISEN currents from all the active channels are averaged together to form a scaled version of the total output current, ITOTAL. 0V PWM1, 5V/DIV FIGURE 4. FOUR ACTIVE CHANNEL PWM DRIVE SIGNALS 1ms/DIV 0V PWM3, 5V/DIV PWM4, 5V/DIV 0V 0V PWM2, 5V/DIV R T 10 10.9 1.1 F SW log – = (EQ. 5) 50 100 10 20 200 500 1,000 2,000 1 2 5 10 20 50 100 200 500 1,000 CHANNEL OSCILLATOR FREQUENCY, FSW, [kHz] FIGURE 5. OSCILLATOR FREQUENCY vs RT OC + - ITOTAL + ISEN1 ITRIP 82.5 µA FIGURE 6. INTERNAL OVERCURRENT DETECTION CIRCUITRY ∑ n n = ACTIVE CHANNELS ISEN4 ISL6558 ISEN3 ISEN2 + + + 0V 0A 0V FIGURE 7. OVERCURRENT OPERATION 10ms/DIV IOUT (5A/DIV) VOUT (1V/DIV) SHORT APPLIED SHORT REMOVED PGOOD (5V/DIV) ISL6558 |
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