DS3882E+C Datasheet DS3882E+C, DS3882E+ | P28-P30

DS3882

Applications Information

Addressing Multiple DS3882s

On a Common I

C Bus

Each DS3882 responds to one of four possible slave

addresses based on the state of the address input pins

(A0 and A1). For information about device addressing,

see the

C Communication

section.

Setting the RMS Lamp Current

Resistor R7 and R8 in the

Typical Operating Circuit

set

the lamp current. R7 and R8 = 140Ω corresponds to a

5mA

RMS

lamp current as long as the current waveform

is approximately sinusoidal. The formula to determine

the resistor value for a given sinusoidal lamp current is:

Component Selection

External component selection has a large impact on the

overall system performance and cost. The two most

important external components are the transformers

and n-channel MOSFETs.

The transformer should be able to operate in the 40kHz

to 80kHz frequency range of the DS3882, and the turns

ratio should be selected so the MOSFET drivers run at

28% to 35% duty cycle during steady state operation.

The transformer must be able to withstand the high

open-circuit voltage that is used to strike the lamp.

Additionally, its primary/secondary resistance and induc-

tance characteristics must be considered because they

contribute significantly to determining the efficiency and

transient response of the system. Table 10 shows a

transformer specification that has been used for a 12V

inverter supply, 438mm x 2.2mm lamp design.

The n-channel MOSFET must have a threshold voltage

that is low enough to work with logic-level signals, a low

on-resistance to maximize efficiency and limit the n-

channel MOSFET’s power dissipation, and a break-

down voltage high enough to handle the transient. The

breakdown voltage should be a minimum of 3x the invert-

er voltage supply. Additionally, the total gate charge must

be less than Q

, which is specified in the

Recommended

Operating Conditions

table. These specifications are eas-

ily met by many of the dual n-channel MOSFETs now

available in 8-pin SO packages.

Table 11 lists suggested values for the external resistors

and capacitors used in the

Typical Operating Circuit

LAMP RMS

()

Dual-Channel Automotive CCFL Controller

28 ____________________________________________________________________

XXXXXXXX

101 0 A

COMMUNICATIONS KEY

WRITE A SINGLE BYTE

8-BITS ADDRESS OR DATA

WHITE BOXES INDICATE THE MASTER IS

CONTROLLING SDA

NOTES

2) THE FIRST BYTE SENT AFTER A START CONDITION IS

ALWAYS THE SLAVE ADDRESS FOLLOWED BY THE

READ/WRITE BIT.

SHADED BOXES INDICATE THE SLAVE IS

CONTROLLING SDA

START ACK

NOT

ACK

DATA

MEMORY ADDRESS

101 0 A

READ A SINGLE BYTE

ASR

DATA

MEMORY ADDRESS

STOP

REPEATED

START

1) ALL BYTES ARE SENT MOST SIGNIFICANT BIT FIRST.

Figure 11. I

C Communications Examples

DS3882

Dual-Channel Automotive CCFL Controller

____________________________________________________________________ 29

Table 10. Transformer Specifications (as Used in the

Typical Operating Circuit

)

PARAMETER CONDITIONS MIN TYP MAX UNITS

Turns Ratio (Secondary/Primary) (Notes 1, 2, 3) 40

Frequency 40 80 kHz

Output Power 6W

Output Current 58mA

Primary DCR Center tap to one end 200 mΩ

Secondary DCR 500 Ω

Primary Leakage 12 µH

Secondary Leakage 185 mH

Primary Inductance 70 µH

Secondary Inductance 500 mH

100ms minimum 2000

Secondary Output Voltage

Continuous 1000

RMS

Note 1: Primary should be Bifilar wound with center tap connection.

Note 2: Turns ratio is defined as secondary winding divided by the sum of both primary windings.

Note 3: 40:1 is the nominal turns ratio for driving a 438mm x 2.2mm lamp with a 12V supply. Refer to Application Note 3375 for more

information.

Table 11. Resistor and Capacitor Selection Guide

DESIGNATOR QTY VALUE

TOLERANCE

(%) AT +25°C

TEMPERATURE

COEFFICIENT

NOTES

R5, R6 1 10kΩ 1——

R3, R4 1

12.5kΩ to

105kΩ

1 — See the Setting the SVM Threshold Voltage section.

R9 1

20kΩ to

40kΩ

1 ≤153ppm/°C

2% or less total tolerance. See the Lamp Frequency

Configuration section to determine value.

R10 1

18kΩ to

45kΩ

1 ≤153ppm/°C

2% or less total tolerance. See the Lamp Frequency

Configuration section to determine value.

R1 1 4.7kΩ 5 Any grade —

R2 1 4.7kΩ 5 Any grade —

R11 1 4.7kΩ 5 Any grade —

R7, R8 1/Chan 140Ω 1 — See the Setting the RMS Lamp Current section.

C6, C8 1/Chan 100nF 10 X7R

C ap aci tor val ue w i l l al so affect LC M b i as vol tag e d ur i ng

p ow er - up . A l ar g er cap aci tor m ay cause a l ong er ti m e

for V

D C B

to r each i ts nor m al op er ati ng l evel .

C2 1/Chan 10pF 5 ±1000ppm/°C 2kV to 4kV breakdown voltage required.

C3 1/Chan 27nF 5 X7R

C ap aci tor val ue w i l l al so affect LC M b i as vol tag e d ur i ng

p ow er - up . A l ar g er cap aci tor m ay cause a l ong er ti m e

for V

D C B

to r each i ts nor m al op er ati ng l evel .

C1 1/Chan 33µF 20 Any grade —

C7 2/DS3882 0.1µF 10 X7R Place close to V

and GND on DS3882.

DS3882

Dual-Channel Automotive CCFL Controller

30 ____________________________________________________________________

INVERTER SUPPLY

VOLTAGE (V

INV

)

(8V TO 16V)

GA1

LAMP CURRENT MONITOR

CCFL LAMP

GB1

OVD1

BRIGHT

SVMH

LAMP BRIGHTNESS

TRANSFORMER

DUAL POWER

MOSFET

DEVICE

SUPPLY VOLTAGE

(5V ±5%)

OVERVOLTAGE DETECTION

LCM1

GND

LAMP FREQUENCY

INPUT/OUTPUT

LSYNC

SCL

SDA

CONFIGURATION

AND CONTROL PORT

FAULT

PSYNC

DPWM SIGNAL

INPUT/OUTPUT

LOSC

POSC

LCO

PDN

LAMP ON/OFF

LAMP CURRENT

OVERDRIVE ENABLE

SVML

HARDWARE

CONTROL

STEP LAMP

FREQUENCY

STEP

GND_S

R10

R11

GA2

LAMP CURRENT MONITOR

CCFL LAMP

GB2

OVD2

TRANSFORMER

DUAL POWER

MOSFET

OVERVOLTAGE DETECTION

LCM2

DS3882

Typical Operating Circuit

Power-Supply Decoupling

To achieve best results, it is highly recommended that

a decoupling capacitor is used on the IC power-supply

pin. Typical values of decoupling capacitors are

0.01µF or 0.1µF. Use a high-quality, ceramic, surface-

mount capacitor, and mount it as close as possible to

the V

and GND pins of the IC to minimize lead

inductance.

Chip Information

SUBSTRATE CONNECTED TO GROUND

Package Information

For the latest package outline information and land patterns,

go to www.maxim-ic.com/packages

. Note that a “+”, “#”, or

“-” in the package code indicates RoHS status only. Package

drawings may show a different suffix character, but the drawing

pertains to the package regardless of RoHS status.

PACKAGE

TYPE

PACKAGE

CODE

OUTLINE

NO.

LAND

PATTERN NO.

28 TSSOP

(173 mils)

U28+2

21-0066 90-0171

P1-P3 P4-P6 P7-P9 P10-P12 P13-P15 P16-P18 P19-P21 P22-P24 P25-P27 P28-P30 P31-P31

DS3882E+C

Mfr. #:

Buy DS3882E+C

Manufacturer:

Maxim Integrated

Description:

Display Drivers & Controllers DualCh Automotive CCFL Controller

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DS3882E+C

DS3882E+C

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