Datasheet
DS3881
Single-Channel Automotive CCFL Controller
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EMI Suppression Functionality
The DS3881 contains two electromagnetic interference
suppression features: spread-spectrum modulation and
lamp oscillator frequency stepping. The first is the abili-
ty to spread the spectrum of the lamp frequency. By
setting either SS0 and/or SS1 in EMIC register, the con-
troller can be configured to dither the lamp frequency
by ±1.5%, ±3%, or ±6%. By setting a non-zero value in
SS0/1, spread-spectrum modulation is enabled and
oscillator frequency stepping is disabled. In spread-
spectrum modulation mode the dither modulation rate
is also selectable by setting FS0/1/2, and has either a
triangular (SSM = 0) or a pseudorandom profile (SSM =
1). Users have the flexibility to choosing the best modu-
lation rate (through FS0/1/2) for the application.
The second EMI suppression scheme is the ability to
move the lamp frequency up or down by 1%, 2%, 3%,
or 4%. In this scheme, the actual radiated EMI is not
reduced but it is moved out of a sensitive frequency
region. STEPE bit and/or STEP pin is used to enable
lamp frequency stepping (SS0/1 must be 0). Once
enabled, the FS0/1/2 value controls the lamp oscillator
frequency shift. For example, if the lamp frequency cre-
ates EMI disturbing an audio radio station, it can be
moved up or down slightly to slide the spurious interfer-
er out of band.
Lamp Current Overdrive Functionality
Another feature the DS3881 offers is the ability to over-
drive the lamps to allow them to heat up quickly in cold
environments. After setting the LCO0/1/2 bits in the
LCOC register and enabling the LCOE bit or LCO pin,
the DS3881 overdrives the nominal current settings in
12.5% steps from 112.5% up to 200%. The DS3881
accomplishes this by automatically shifting the lamp
regulation threshold, V
LRT
, upward to allow more cur-
rent to flow in the lamps (Figure 2). This multilevel
adjustment makes it possible to slowly decrease the
current overdrive (through I
2
C) after the lamps have
warmed up, so the end user does not see any change
in brightness when the overdrive is no longer needed.
The DS3881 also features an optional timer capable of
automatically turning off the current overdrive. This
timer is adjustable from approximately 1.5 minutes to
21 minutes (if a 50kHz lamp frequency is used).
Detailed Register Descriptions
The DS3881’s register map is shown in Table 1.
Detailed register and bit descriptions follow in the sub-
sequent tables.
Table 1. Register Map
BYTE
ADDRESS
BYTE
NAME
FACTORY
DEFAULT
BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0
E0h SR1 00h SVMH_RT SVML_RT LOC_L1 LOUT_L1 OV_L1 STO_L1 FAULT_L1 FAULT_RT1
E1h RSVD 00h RSVD RSVD RSVD RSVD RSVD RSVD RSVD RSVD
E2h BPWM 00h RSVD PWM6 PWM5 PWM4 PWM3 PWM2 PWM1 PWM0
E3h BLC 1Fh SEEB RSVD CH1D LC4 LC3 LC2 LC1 LC0
F0h SSP1 21h LST1
MDC code for soft-start lamp
cycles 3, 4
LST0 M D C cod e for soft- star t l am p cycl es 1, 2
F1h SSP2 43h MDC code for soft-start lamp cycles 7, 8 MDC code for soft-start lamp cycles 5, 6
F2h SSP3 65h MDC code for soft-start lamp cycles 11, 12 MDC code for soft-start lamp cycles 9, 10
F3h SSP4 77h MDC code for soft-start lamp cycles 15, 16 MDC code for soft-start lamp cycles 13, 14
F4h CR1 00h DPD RSVD ARD RGSO DPSS LFSS POSCS LOCE
F5h CR2 08h PDNE RSVD RSVD LSR1 LSR0 POSCR1 POSCR0 UMWP
F6h EMIC 00h FS2 FS1 FS0 STEPE RSVD SSM SS1 SS0
F7h LCOC 00h TO3 TO2 TO1 TO0 LCOE LCO2 LCO1 LCO0
F8h–FFh USER 00h EE EE EE EE EE EE EE EE
Note 1: E0h–E3h are SRAM locations, and F0h–FFh are SRAM-shadowed EEPROM.
Note 2: Altering the DS3881 configuration during active CCFL operation can cause serious adverse effects.