LM3533 Datasheet, PDF (17/53 Pages) Texas Instruments – Complete Lighting Power Solution for Smartphone Handsets

LM3533
Integrated Charge Pump
The LM3533 features an integrated (2x/1x) charge pump capable of supplying up to 150mA. The fixed 1MHz switching frequency
allows for use of tiny 1µF ceramic flying capacitors (CP) and output capacitor (CPOUT). The charge pump can supply the power
for the low-voltage LEDs connected to LVLED1-LVLED5 and can operate in 4 different modes: disabled, automatic gain, 1X gain,
or 2X gain (see Figure 4 ).
FIGURE 4. Integrated Charge Pump
30135703
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 section). 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 will continue to try to sink current.
AUTOMATIC GAIN
In Automatic Gain Mode the charge pump gain transition is actively selected to maintain LED current regulation in the CPOUT-
connected, low-voltage current sinks. At higher input voltages the charge pump will operate in Pass Mode (1x gain) allowing the
voltage at CPOUT to track the input voltage. As VIN drops, the voltage on the low-voltage current sink(s) will drop also. Once any
of the active, CPOUT-connected, low-voltage current sink input voltages reach typically 100mV, the charge pump will automatically
switch to a gain of 2x thus preventing dropout (see 2X GAIN). Once the charge pump switches over to 2X gain it will remain in 2X
gain, even if the current sink input voltage goes above the switch over threshold.
AUTOMATIC GAIN (FLYING CAPACITOR DETECTION)
In Automatic Gain Mode the LM3533 will start up and automatically detect if there is a flying capacitor (CP) connected between C
+ and C−. If there is, Automatic Gain Mode will operate normally. If the detection circuitry detects that there is no flying capacitor
connected, the LM3533 will automatically switch to 1X Gain mode.
1X GAIN
In 1X Gain Mode the charge pump will pass VIN directly through to CPOUT. There is a resistive drop between IN and CPOUT in
this mode (1.1Ω) which should be accounted for when determining the headroom requirement for the low-voltage current sinks. In
forced 1X Gain Mode the charge pump will not switch; thus, the flying capacitor (CP) and output capacitor (CPOUT) can be omitted
from the circuit.
2X GAIN
In 2X Gain Mode the internal charge pump will double VIN and post-regulate CPOUT to typically 4.4V. This allows for biasing LEDs
whose forward voltages are greater than the input supply (VIN).
LOW-VOLTAGE CURRENT SINKS (LVLED1–LVLED5)
Current sinks LVLED1 to LVLED5 each provide the current for a single LED. These low-voltage sinks are configurable with different
blinking patterns via the 4 internal pattern generators. Each low-voltage current sink has 8-bit brightness control and 5-bit full-scale
current programmability. Additionally, each low-voltage current sink can have its current set through a dedicated brightness register,
the PWM input, the ambient light sensor interface, or a combination of these. Configuration of the low-voltage current sinks is done
through the low-voltage Control Banks (C, D, E, or F). Any low-voltage current sink can be mapped to any of the low-voltage control
banks.
Copyright © 1999-2012, Texas Instruments Incorporated
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