ISL6558 Intersil Corporation, ISL6558 Datasheet - Page 10

• Manufacturer Part Number: ISL6558
• Description: Multi-Purpose Precision Multi-Phase PWM Controller With Optional Active Voltage Positioning
• Manufacturer: Intersil Corporation

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
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
Figure 5 provides a graph of oscillator frequency vs R
maximum recommended channel frequency is 1.5MHz.
R
FIGURE 4. FOUR ACTIVE CHANNEL PWM DRIVE SIGNALS
T
0V
0V
0V
0V
=
1,000
500
200
100
10
50
20
10
5
2
1
10
FIGURE 5. OSCILLATOR FREQUENCY vs R
10.9 1.1
CHANNEL OSCILLATOR FREQUENCY, F
PWM1, 5V/DIV
T
–
, connected between the FS/EN pin and
20
log
F
SW
PWM2, 5V/DIV
50
100
1ms/DIV
10
200
PWM3, 5V/DIV
500 1,000 2,000
SW
PWM4, 5V/DIV
.
SW
, [kHz]
T
(EQ. 5)
T
. The
ISL6558
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 ±
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
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
FIGURE 6. INTERNAL OVERCURRENT DETECTION
0V
0V
0A
ISEN
ISL6558
FIGURE 7. OVERCURRENT OPERATION
SHORT APPLIED
resistor scales the voltage sampled across the
OC
CIRCUITRY
V
PGOOD (5V/DIV)
n = ACTIVE CHANNELS
OUT
+
-
(1V/DIV)
I
I
TOTAL
TRIP
82.5µA
10ms/DIV
+
SHORT REMOVED
I
∑
n
OUT
+
+
(5A/DIV)
1
+
% over
ISEN1
ISEN2
ISEN3
ISEN4
TOTAL
.