ISL6558 Datasheet, PDF (10/16 Pages) Intersil Corporation – Multi-Purpose Precision Multi-Phase PWM Controller With Optional Active Voltage Positioning

ISL6558
PWM1, 5V/DIV
0V
PWM2, 5V/DIV
0V
PWM3, 5V/DIV
0V
PWM4, 5V/DIV
0V
1ms/DIV
FIGURE 4. FOUR ACTIVE CHANNEL PWM DRIVE SIGNALS
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, R_T, 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, F_SW.
R_T
=
10.9
10
–
1.1
log
FSW
(EQ. 5)
Figure 5 provides a graph of oscillator frequency vs R_T. The
maximum recommended channel frequency is 1.5MHz.
1,000
500
200
100
50
20
10
5
2
1
10 20
50 100 200 500 1,000 2,000
CHANNEL OSCILLATOR FREQUENCY, F_SW, [kHz]
FIGURE 5. OSCILLATOR FREQUENCY vs R_T
10
ISL6558
ISEN1
+
OC
-
I_TOTAL
I_TRIP
+
+ ^ISEN2
∑
n
+ _ISEN3
+
82.5µA
ISEN4
n = ACTIVE CHANNELS
FIGURE 6. INTERNAL OVERCURRENT DETECTION
CIRCUITRY
V_OUT (1V/DIV)
0V
SHORT APPLIED
I_OUT (5A/DIV)
0A
PGOOD (5V/DIV)
SHORT REMOVED
0V
10ms/DIV
FIGURE 7. OVERCURRENT OPERATION
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 R_ISEN 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, I_TOTAL.
FN9027.12
June 21, 2005