13/28

XDL603/XDL604

Series

■

OPERATIONAL EXPLANATION (Continued)

< Normal Operation >

The standard voltage Vref and FB pin voltage are compared using an error amplifier and then the control signal to which phase

compensation has been added to the error amplifier output is input to the PWM comparator. The PWM comparator compares the

above control signal and lamp wave to control the duty width during PWM control. Continuously conducting these controls

stabilizes the output voltage.

In addition, the current detecting circuit monitors the driver FET current for each switching and modulates the error amplifier

output signal into a multiple feedback signal (current feedback circuit). This achieves stable feedback control even when low ESR

capacitors, such as ceramic capacitors, are used to stabilize the output voltage.

XDL603 Series

loads the on time is short and the circuit operates in discontinuous mode, and as the output current increases, the on time becomes

longer and the circuit operates in continuous mode.

XDL604 Series

loads the on time is short and the circuit operates in discontinuous mode, and as the output current increases, the on time becomes

longer and the circuit operates in continuous mode.

< 100% Duty Cycle Mode >

When the dropout voltage is low or there is a transient response, the circuit might change to the 100% Duty cycle mode where

the High side driver FET is continuously on.

The 100% Duty cycle mode operation makes it possible to maintain the output current even when the dropout voltage is low

such as when the input voltage declines due to cranking, etc.

0mA

Coil

Current

Lx

0V

0mA

Coil

Current

Lx

0V

0mA

Coil

Current

Lx

0V

0mA

Coil

Current

Lx

0V