ISL6441 datasheet(13/19 Pages) RENESAS

13 / 19 page

ISL6441

FN9197 Rev 3.00

Page 13 of 19

May 26, 2009

is detected for 2 consecutive clock cycles then the IC enters

a hiccup mode by turning off the gate drivers and entering

into soft-start. The IC will cycle 2x through soft-start before

trying to restart. The IC will continue to cycle through

soft-start until the overcurrent condition is removed.

Figure 17 shows this behavior.

Because of the nature of this current sensing technique, and

to accommodate a wide range of rDS(ON) variations, the

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

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 4x 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 rDS(ON).

Choosing RCS to provide 32µA of current to the current

sample and hold circuitry is recommended but can operate

down to 2µA up to 100µA.

VOUT2 2V/DIV

PHASE2 10V/DIV

IL 2V/DIV

FIGURE 16. OVERCURRENT TRIP WAVEFORMS

VOUT2 2V/DIV

SS2 2V/DIV

IOUT2 2V/DIV

FIGURE 17. OVERCURRENT CONTINUOUS HICCUP MODE

WAVEFORMS

FIGURE 18. SYNC WAVEFORM

SYNC 1V/DIV

RCS

IMAX

 r

DS ON



A

-----------------------------------------------



(EQ. 6)

ISL6441 Datasheet(PDF) 13 Page - Renesas Technology Corp

ISL6441 Datasheet(HTML) 13 Page - Renesas Technology Corp

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

Datasheet Download

Link URL