DS3988T+T&R Maxim Integrated Products, DS3988T+T&R Datasheet - Page 13

• Manufacturer Part Number: DS3988T+T&R
• Description: Display Drivers 8-Ch CCFL Controller All N-FET Drive, La
• Manufacturer: Maxim Integrated Products

Specifications of DS3988T+T&R

• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

At the beginning of each lamp burst, the DS3988 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
Figure 6. Digital PWM Dimming and Soft-Start
LAMP CURRENT
DPWM SIGNAL
SOFT-START PROFILE REGISTER
MOSFET GATE DRIVERS
SOFT-START
LAMP CURRENT
LAMP CYCLE
GAn/GBn
22.5Hz TO 440Hz
1
SSP1. 0-3
PROGRAMMABLE SOFT-START PROFILE WITH INCREASING MOSFET PULSE WIDTHS OVER
A 16 LAMP CYCLE PERIOD RESULTS IN A LINEAR RAMP IN LAMP CURRENT.
DPWM Soft-Start
2
____________________________________________________________________
3
SSP1. 4-7
4
Fluorescent Lamp Controller
SSP2. 0-3
5
6
8-Channel Cold-Cathode
7
SSP2. 4-7
adjusted to match the application. There are seven dif-
ferent driver duty cycles to select from to customize the
soft-start ramp (see Table 1). 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.
8
SOFT-START (EXPANDED)
SSP3. 0-3
9
10
11
SSP3. 4-7
12
SSP4. 0-3
13
14
SSP4. 4-7
15
16
13