6

FN6395.0

November 22, 2006

Timing Diagram

Operation and Adaptive Shoot-Through Protection

Designed for high speed switching, the ISL6610, ISL6610A

MOSFET driver controls both high-side and low-side N-

Channel FETs from one externally provided PWM signal.

A rising transition on PWM initiates the turn-off of the lower

MOSFET (see Figure 1). After a short propagation delay

are provided in the Electrical Specifications. Adaptive shoot-

through circuitry monitors the LGATE voltage and turns on

LGATE voltage drops below ~1V. The upper gate drive then

A falling transition on PWM indicates the turn-off of the upper

MOSFET and the turn-on of the lower MOSFET. A short

monitors the UGATE-PHASE voltage and turns on the lower

MOSFET’s gate voltage drops below 1V. The lower gate then

prevent both the lower and upper MOSFETs from conducting

simultaneously (shoot-through), while adapting the dead

time to the gate charge characteristics of the MOSFETs

being used.

This driver is optimized for voltage regulators with large step

down ratio. The lower MOSFET is usually sized larger

compared to the upper MOSFET because the lower

MOSFET conducts for a longer time during a switching

period. The lower gate driver is therefore sized much larger

to meet this application requirement. The 0.4

Ω on-resistance

and 4A sink current capability enable the lower gate driver to

absorb the current injected into the lower gate through the

help prevent shoot through caused by the self turn-on of the

lower MOSFET due to high dV/dt of the switching node.

Tri-State PWM Input

A unique feature of the ISL6610, ISL6610A is the adaptable

tri-state PWM input. Once the PWM signal enters the

shutdown window, either MOSFET previously conducting is

turned off. If the PWM signal remains within the shutdown

window for longer than 80ns of the previously conducting

MOSFET, the output drivers are disabled and both MOSFET

gates are pulled and held low. The shutdown state is

removed when the PWM signal moves outside the shutdown

window. The PWM rising and falling thresholds outlined in

the Electrical Specifications determine when the lower and

upper gates are enabled. During normal operation in a

typical application, the PWM rise and fall times through the

shutdown window should not exceed either output’s turn-off

propagation delay plus the MOSFET gate discharge time to

~1V. Abnormally long PWM signal transition times through

the shutdown window will simply introduce additional dead

time between turn off and turn on of the synchronous

bridge’s MOSFETs. For optimal performance, no more than

100pF parasitic capacitive load should be present on the

PWM line of ISL6610, ISL6610A (assuming an Intersil PWM

controller is used).

Bootstrap Considerations

This driver features an internal bootstrap diode. Simply

adding an external capacitor across the BOOT and PHASE

pins completes the bootstrap circuit. The ISL6610A’s internal

bootstrap resistor is designed to reduce the overcharging of

PWM

UGATE

LGATE

1V

2.5V

1V

FIGURE 1. TIMING DIAGRAM

ISL6610, ISL6610A