ds3881et-r-c Maxim Integrated Products, Inc., ds3881et-r-c Datasheet - Page 17

• Manufacturer Part Number: ds3881et-r-c
• Description: Ds3881 Single-channel, Automotive Ccfl Controller
• Manufacturer: Maxim Integrated Products, Inc.

Table 1. Register Map
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.
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.
ADDRESS
F8h–FFh
BYTE
E0h
E1h
E2h
E3h
F0h
F1h
F2h
F3h
F4h
F5h
F6h
F7h
Single-Channel Automotive CCFL Controller
BPWM
NAME
LCOC
BYTE
RSVD
USER
EMIC
SSP1
SSP2
SSP3
SSP4
SR1
BLC
CR1
CR2
EMI Suppression Functionality
FACTORY
DEFAULT
00h
00h
00h
1Fh
21h
43h
65h
77h
00h
08h
00h
00h
00h
SVMH_RT SVML_RT LOC_L1
MDC code for soft-start lamp cycles 7, 8
MDC code for soft-start lamp cycles 11, 12
MDC code for soft-start lamp cycles 15, 16
PDNE
RSVD
RSVD
BIT 7
SEEB
LST1
DPD
TO3
FS2
EE
____________________________________________________________________
MDC code for soft-start lamp
cycles 3, 4
PWM6
RSVD
RSVD
RSVD
RSVD
BIT 6
TO2
FS1
EE
PWM5
RSVD
CH1D
RSVD
BIT 5
ARD
TO1
FS0
EE
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
rent to flow in the lamps (Figure 2). This multilevel
adjustment makes it possible to slowly decrease the
current overdrive (through I
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).
The DS3881’s register map is shown in Table 1.
Detailed register and bit descriptions follow in the sub-
sequent tables.
LOUT_L1
STEPE
PWM4
RGSO
RSVD
BIT 4
LSR1
TO0
LC4
EE
Lamp Current Overdrive Functionality
MDC code for soft-start lamp cycles 5, 6
MDC code for soft-start lamp cycles 9, 10
MDC code for soft-start lamp cycles 13, 14
OV_L1
PWM3
LCOE
RSVD
DPSS
RSVD
BIT 3
LSR0
LST0
LC3
EE
Detailed Register Descriptions
M D C cod e for soft- star t l am p cycl es 1, 2
POSCR1
STO_L1
PWM2
LRT
RSVD
LCO2
BIT 2
LFSS
SSM
LC2
EE
, upward to allow more cur-
2
C) after the lamps have
FAULT_L1
POSCR0
POSCS
PWM1
RSVD
LCO1
BIT 1
LC1
SS1
EE
FAULT_RT1
UMWP
PWM0
RSVD
LOCE
LCO0
BIT 0
LC0
SS0
EE
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