LM3533 datasheet(14/63 Pages) TI1

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SDA

VIN

CPOUT

LVLED

LVLEDX

C+

C-

1X, 2X

Charge Pump

SCL

Mode Control bits

4.4V Typ

LM3533

SNOSC68C – APRIL 2012 – REVISED SEPTEMBER 2015

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Device Functional Modes (continued)

7.4.1.1 High-Voltage Current Sinks (HVLED1 And HVLED2)

HVLED1 and HVLED2 control the current in the high-voltage LED strings. Each current sink has 5-bit full-scale

current programmability and 8-bit brightness control. Either current sink can have its current set through a

dedicated brightness register or be controlled via the ambient light sensor interface. Configuration of the high-

voltage current sinks is done through the Control A/B Brightness Configuration Register (see Table 8).

7.4.1.2 High-Voltage Current String Biasing

Each high-voltage current string can be powered from the LM3533’s boost output (COUT) or from an external

source. The Anode Connect Register bits [1:0] determine where the high-voltage current string anodes are

connected. When set to 1 (default) the high-voltage current sink inputs are included in the boost feedback loop.

This allows the boost converter to adjust its output voltage in order to maintain at least 400 mV at the current

sink input.

When powered from alternate sources, bits [1:0] must be set to 0 . This removes the particular current sink from

the boost feedback loop. In these configurations the application must ensure that the headroom voltage across

the high-voltage current sink is high enough to prevent the current sink from going into dropout (see the Typical

Characteristics for data on the high-voltage LED current vs headroom voltage).

Setting the Anode Connect Register bits also determines how the shorted high-voltage LED String Fault flag is

triggered (see Fault Flags/Protection Features).

7.4.1.3 Boost Switching-Frequency Select

The LM3533’s boost converter can have a 1-MHz or 500-kHz switching frequency. For a 500-kHz switching

frequency the inductor must be between 10 µH and 22 µH. For the 1MHz switching frequency the inductor can

be between 4.7 µH and 22 µH. The boost frequency is programmed through bit [1] of the OVP/Boost

Frequency/PWM Polarity Select register.

7.4.2 Integrated Charge Pump

The LM3533 features an integrated (2×/1×) charge pump capable of supplying up to 150 mA. The fixed 1-MHz

switching frequency allows for use of tiny 1-µF ceramic flying capacitors (CP) and output capacitor (CPOUT).

The charge pump can supply the power for the low-voltage LEDs connected to LVLED1 to LVLED5 and can

operate in 4 different modes: disabled, automatic gain, 1× gain, or 2× gain (see Figure 23).

Figure 23. Integrated Charge Pump

7.4.2.1 Charge Pump Disabled

With the charge pump disabled, the path from IN to CPOUT is high impedance. Additionally, with the charge

pump disabled, the low-voltage current sinks can still be active, thus allowing the low-voltage LEDs to be biased

from external sources (see Low-Voltage LED Biasing). Disabling the charge pump also has no influence on the

state of the low-voltage current sinks. For instance, if a low-voltage current string is set to have its anode

connected to CPOUT, and the charge pump is disabled, the current sink continues to try to sink current.

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