Datasheet
DS3882
Dual-Channel Automotive CCFL Controller
14 ____________________________________________________________________
Configuring Systems
with Multiple DS3882s
The source and receiver options for the lamp frequency
clock and DPWM signal allow multiple DS3882s to be
synchronized in systems requiring more than two
lamps. The lamp and dimming clocks can either be
generated on board the DS3882 using external resis-
tors to set the frequency, or they can be sourced by the
host system to synchronize the DS3882 to other system
resources. Figure 5 shows various multiple DS3882
configurations that allow both lamp and/or DPWM syn-
chronization for all DS3882s in the system.
DPWM Soft-Start
At the beginning of each lamp burst, the DS3882 pro-
vides a soft-start that slowly increases the MOSFET
gate-driver duty cycle (see Figure 6). This minimizes
the possibility of audible transformer noise that could
result from current surges in the transformer primary.
The soft-start length is fixed at 16 lamp cycles, but the
soft-start ramp profile is programmable through the four
soft-start profile registers (SSP1/2/3/4) and can be
adjusted to match the application. There are seven dif-
ferent driver duty cycles to select from to customize the
soft-start ramp (see Tables 5a and 5b). The available
duty cycles range from 0% to 19% in ~3% increments.
In addition, the MOSFET duty cycle from the last lamp
cycle of the previous burst can be used as part of the
soft-start ramp by using the most recent value duty cycle
code. Each programmed MOSFET gate duty cycle
repeats twice to make up the 16 soft-start lamp cycles.
1615141312111098765432
SSP1. 0-3
LAMP CURRENT
SOFT-START PROFILE REGISTER
SOFT-START
SOFT-START (EXPANDED)
22.5Hz TO 440Hz
DPWM SIGNAL
LAMP CURRENT
LAMP CYCLE
GAn/GBn
MOSFET GATE DRIVERS
PROGRAMMABLE SOFT-START PROFILE WITH INCREASING MOSFET PULSE WIDTHS OVER
A 16 LAMP CYCLE PERIOD RESULTS IN A LINEAR RAMP IN LAMP CURRENT.
SSP1. 4-7
SSP2. 0-3
SSP2. 4-7
SSP3. 0-3
SSP3. 4-7
SSP4. 0-3
SSP4. 4-7
1
Figure 6. Digital PWM Dimming and Soft-Start