DS3994Z+W Maxim Integrated Products, DS3994Z+W Datasheet - Page 13

• Manufacturer Part Number: DS3994Z+W
• Description: Display Drivers 4-Ch Cold-Cathode Fl uorescent Controller
• Manufacturer: Maxim Integrated Products

Specifications of DS3994Z+W

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

The DS3994 also features a programmable lamp strike
frequency boost option. During the strike period, the
transformer secondary is essentially unloaded. The
lamp frequency be can be easily increased causing a
higher strike voltage. The SB0/1/2 bits in CR3 control
how the frequency is increased during lamp strike. A
setting of 000b results in no frequency increase, while
the maximum setting (111b) causes a 100% increase.
Once the DS3994 detects that the lamp has struck, the
lamp frequency is automatically reset to the nominal
run level.
The DS3994 can generate its own lamp frequency clock
internally (set LFSS = 0 in CR1), which can then be
sourced to other DS3994s if required, or the lamp clock
can be supplied from an external source (set LFSS = 1 in
CR1). When the lamp clock is internally generated, the
frequency (20kHz to 80kHz) is set by an external resistor
at the LOSC. In this case, the DS3994 can act as a lamp
frequency source because the lamp clock is output at
the LSYNC I/O pin for synchronizing any other DS3994s
configured as lamp frequency receivers.
The DS3994 acts as a lamp frequency receiver when
the lamp clock is supplied externally. In this case, a
20kHz to 80kHz clock must be supplied at the LSYNC
I/O. The external clock can originate from the LSYNC
I/O of a DS3994 configured as a lamp frequency
source or from some other source.
The LOFS bit in CR3 must be set to match the appropri-
ate lamp frequency range. If a 20kHz to 40kHz frequen-
cy is used, then LOFS must be set to 1; if a 40kHz to
80kHz frequency is used, then LOFS must be set to 0.
Lamp Frequency Configuration
Lamp Strike Frequency Boost
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Fluorescent Lamp Controller
4-Channel Cold-Cathode
The source and receiver options for the lamp frequency
clock and DPWM signal allow multiple DS3994s to be
synchronized in systems requiring more than four
lamps. The lamp and dimming clocks can either be
generated on board the DS3994 using external resis-
tors to set the frequency, or they can be sourced by the
host system to synchronize the DS3994 to other system
resources. Figure 6 shows various multiple DS3994
configurations that allow both lamp and/or DPWM syn-
chronization for all DS3994s in the system.
At the beginning of each lamp burst, the DS3994 pro-
vides a soft-start that slowly increases the MOSFET
gate-driver duty cycle (see Figure 7). 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.
Configuring Systems with
Multiple DS3994s
DPWM Soft-Start
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