ISL6402 INTERSIL [Intersil Corporation], ISL6402 Datasheet - Page 13

• Manufacturer Part Number: ISL6402
• Description: 300kHz Dual, 180 Degree Out-of-Phase, Step-Down PWM and Single Linear Controller
• Manufacturer: INTERSIL [Intersil Corporation]

Because of the nature of this current sensing technique, and
to accommodate a wide range of r
value of the overcurrent threshold should represent an
overload current about 150% to 180% of the maximum
operating current. If more accurate current protection is
desired place a current sense resistor in series with the
lower MOSFET source.
Over-Temperature Protection
The IC incorporates an over-temperature protection circuit
that shuts the IC down when a die temperature of 150°C is
reached. Normal operation resumes when the die
temperatures drops below 130°C through the initiation of a
full soft-start cycle.
Implementing Synchronization
The SYNC pin may be used to synchronize two or more
controllers. When the SYNC pins of two controllers are
connected together, one controller becomes the master and
the other controller synchronizes to the master. A pull-down
FIGURE 17. OVERCURRENT CONTINUOUS HICCUP MODE
FIGURE 16. OVERCURRENT TRIP WAVEFORMS
WAVEFORMS
13
V
I
OUT2
SS2 2V/DIV
OUT2
DS(ON)
2V/DIV
2V/DIV
PHASE2 10V/DIV
V
I
L
OUT2
2V/DIV
variations, the
2V/DIV
ISL6402
resistor is required and must be sized to provide a low
enough time constant to pass the SYNC pulse. Connect this
pin to VCC_5V if not used. Figure 18 shows the SYNC pin
waveform operating at 16 times the switching frequency.
Feedback Loop Compensation
To reduce the number of external components and to
simplify the process of determining compensation
components, both PWM controllers have internally
compensated error amplifiers. To make internal
compensation possible several design measures were
taken.
First, the ramp signal applied to the PWM comparator is
proportional to the input voltage provided via the VIN pin.
This keeps the modulator gain constant with variation in the
input voltage. Second, the load current proportional signal is
derived from the voltage drop across the lower MOSFET
during the PWM time interval and is subtracted from the
amplified error signal on the comparator input. This creates
an internal current control loop. The resistor connected to
the ISEN pin sets the gain in the current feedback loop. The
following expression estimates the required value of the
current sense resistor depending on the maximum operating
load current and the value of the MOSFET’s r
Choosing R
sample and hold circuitry will ensure accurate overcurrent
detection.
R
CS
≥
(
-------------------------------------------- -
I
MAX
CS
32µA
) R
(
FIGURE 18. SYNC WAVEFORM
to provide 32µA of current to the current
DSon )
)
DS(ON)
November 8, 2004
.
FN9123.3