LP5521 datasheet(13/51 Pages) TI2

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Charge

Pump

Current

Source

Saturation

Monitor

Digital

Filter

Mode

Control

Command

Look-ahead

Program

Memory

Comparator

VOUT

VOFS

R/G/B

Control

Registers

PWM

MODE

LP5521

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SNVS441I – JANUARY 2007 – REVISED NOVEMBER 2016

Product Folder Links: LP5521

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7.3.1.3 LED Forward Voltage Monitoring

When charge pump automatic mode selection is enabled, voltages over LED drivers are monitored. If drivers do

not have enough headroom, charge pump gain is set to 1.5×. Driver saturation monitor does not have a fixed

voltage limit, since saturation voltage is a function of temperature and current. Charge pump gain is set to 1×,

when battery voltage is high enough to supply all LEDs.

In automatic gain change mode, charge pump is switched to bypass mode (1×), when LEDs are inactive for over

50 ms.

Charge pump gain control utilizes digital filtering to prevent supply voltage disturbances from triggering gain

changes. If the R driver current source is connected to a battery (address 08H, bit R_TO_BATT = 1), voltage

monitoring is disabled in R output, but still functional in B and G outputs.

LED forward voltage monitoring and gain control block diagram is shown in Figure 15.

Figure 15. Voltage Monitoring Block Diagram for One Output

7.3.2 LED Driver Operational Description

The LP5521 LED drivers are constant current sources with 8-bit PWM control. Output current can be

programmed with I2C register up to 25.5 mA. Current setting resolution is 100 μA (8-bit control).

R driver has two modes: current source can be connected to the battery (VDD) or to the charge pump output. If a

current source is connected to the battery, automatic charge pump gain control is not used for this output. This

approach provides better efficiency when LED with low VF is connected to R driver, and battery voltage is high

enough to drive this LED in all conditions. R driver mode can be selected with I2C register bit. When address

08H, bit R_TO_BATT = 1, R current source is connected to battery. When it is 0 (default), R current source is

connected to charge pump same way as in G and B drivers. G and B drivers are always connected to charge

pump output.

Some LED configuration examples are given in Table 2. When LEDs with low VF are used, charge pump can be

operating in bypass mode (1×). This eliminates the need of having double drivers for all outputs; one connected

to battery and another connected to charge pump output. When LP5521 is driving a RGB LED, R channel can be

configured to use battery power. This configuration increases power efficiency by minimizing the voltage drop

across the LED driver.

Table 2. LED Configuration Examples

CONFIGURATION

R OUTPUT TO BATT

R OUTPUT TO CP

CP MODE

RGB LED with low VF red

Auto (1× or 1.5×)

3 × low VF LED

1×

3 × white LED

Auto (1× or 1.5×)

1 × low VF LED (R output)

Disabled

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