EEPROM

CONTROL

LOGIC

DYNAMIC REGISTERS

I

LM3549

SNVS640A – AUGUST 2010 – REVISED MAY 2013

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CONTROL REGISTERS

Figure 17 shows the structure of the control registers. Control registers consists of volatile dynamic registers and

non volatile EEPROM.

Figure 17. Register Structure

set the device parameters. All registers except FAULT and EEPROM CONTROL register can be stored to

EEPROM. EEPROM values are automatically read to dynamic registers during startup. This makes device use

registers can be written to adjust parameters on the fly. If registers need to be set back to default values this can

be done by first writing 04h to register 40h (EE init bit to “1”) followed by 01h to register 40h (EE read bit to “1”).

EEPROM PROGRAMMING

EEPROM values can be rewritten if device needs recalibration. This can be done for example if white point

changes due to aging effect of the LEDs. To store current register values to EEPROM user needs to first write

04h to register 40h (EE init bit to “1”) followed by 02h to register 40h (EE prog bit to “1”). LM3549 Internal charge

pump generates the high voltage required for programming the EEPROM. To be able to generate this high

voltage Vin needs to be set to 5V during EEPROM programming. EEPROM programming should be completed

within approximately 200 ms. Once EEPROM programming is completed LM3549 sets EE_ready bit to 1. After

this Vin voltage can be set back to normal operating level. EEPROM programming should always be done in

standby mode.

CURRENT SETTING

There are three 10 bit current settings for each driver. 10 bits are divided into two eight bit registers. First register

holds the eight least significant bits (LSB) and the second register holds the two most significant bits (MSB).

These settings are grouped into three banks. IR0, IG0 and IB0 form a bank0; IR1, IG1 and IB1 form a bank1 and

IR2, IG2 and IB2 form a bank2. For example IR0_MSB holds the two MSB for red on bank0 and IR0_LSB the

eight LSB for red on bank0. Bank is selected with BANK_SEL register (00 = bank0, 01 = bank1 and 10 or 11 =

bank2).

Current setting is linear up to 550mA output current (see figure LED Current vs Current Setting in Typical

step decreases slightly. For currents up to 550 mA current setting can be calculated using formula:

Fot currents between 550mA and 700mA current setting can be calculated using formula:

10

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