LP5520 datasheet(18/46 Pages) TI1

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LP5520

SNVS440B – MAY 2007 – REVISED MARCH 2016

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If register value is lower than 5, then value of 5 is used internally. If register value is higher than 20, then value of

20 is used internally.

7.3.3.2 Adaptive Output Voltage Control

When automatic boost voltage control is selected using the <vout_auto> bit in the Control (06H) register, the

user-defined boost output voltage is ignored. The boost output voltage is adjusted for sufficient operating

headroom by monitoring all enabled LED driver outputs. The boosted voltage is adjusted so that the lowest driver

voltage is from 0.85 V to 1.35 V when the LED output currents are below 30 mA and from 1 V to 1.5V when any

LED current is above 30 mA. The output voltage range is from 5 V to 20 V in adaptive mode.

The adaptive voltage control helps saving energy by always setting the boost voltage to minimum sufficient

value. It eliminates the need for extra voltage margins due to LED forward voltage variation or temperature

variation. With very small brightness settings, when the PWM pulses in LED outputs are very narrow, the

adaptive voltage setting gives higher than necessary boost voltage. This does not harm the overall efficiency,

because this happens only at low power levels.

After reset the adaptive control is on by default. In stand-alone mode the adaptive output voltage is always used.

7.4 Device Functional Modes

The LP5520 has three different operating modes: manual mode, automatic mode, and stand-alone mode.

Automatic mode has two sub modes: normal mode and sequential mode. In manual and automatic modes the

device is controlled through the serial interface. In stand-alone mode only BRC input must be controlled, and all

registers have the default values. The modes are controlled according Table 8.

Table 8. Device Operating Modes Control

<RGB_auto>

(RBG control bit 3)

<seq_mode[0:1]>

(RBG control bits 6 and 7)

DEVICE OPERATING MODE

Manual mode

Automatic mode, normal operation (overlapping)

01, 10, or 11

Automatic mode, sequential operation with 2, 3, or 4 pulses per sequence

7.4.1 Manual Mode

In the manual mode the automatic LED intensity adjustment is not in use. The internal PWM control is disabled,

and the LEDs are driven with DC current. The user can set the LED currents through the serial port using three

current control registers, current_control_R/G/B, and use the external PWM control inputs to adjust LED

intensities if needed. There is an independent PWM control pin for each output. If PWM control is not used, the

PWMR, PWMG, and PWMR inputs must be tied to the VDDIO. All the functions implemented with the internal

PWM control are unavailable in manual mode (logarithmic brightness control from PWM Control register,

temperature compensation, fading, sequential mode).

7.4.2 Automatic Mode

In the automatic mode the LED intensities are controlled with the 12-bit PWM values obtained from the EEPROM

memory according to the temperature information. PWM values are stored at 16°C intervals for the

–40°C to +120°C temperature range, and the PWM values for the intermediate temperatures are linearly

interpolated.

When creating white light from a RGB LED, the intention is to program PWM values, which keep the individual

LED intensities constant in all temperatures. For possible other applications, other kind of PWM behavior can be

programmed. The variable parameter can be other than temperature if the sensor is changed to, for example, a

light sensor.

12-bit ADC is used for the measurements. The ADC has two inputs: S1_IN and S2_IN. The temperature

measurement result from the S1_IN input is converted to EEPROM address using the sensor calibration data

from EEPROM. This EEPROM address is then used to get the PWM values for each output. The second input

S2_IN can be used for example for ambient light measurement. The ADC data from selected input can be read

through the serial interface. Control bit <comp_sel> can be used to select which input is used for compensation.

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