TPS61311 datasheet(29/57 Pages) TI

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TPS61310, TPS61311

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SLVS978C – MARCH 2010 – REVISED NOVEMBER 2012

The integrated current control loop automatically selects the minimum boost ratio to maintain regulation based on

the LED forward voltage and current requirements. The low-side current regulators drop the voltage difference

between the input voltage and the LEDs forward voltage (VF(LED) < VIN). When running in boost mode (VF(LED) >

VIN), the voltage present at the LED1-3 pins of the low-side current regulators is typically 400mV, leading to high

power conversion efficiency. Depending on the input voltage and the LEDs forward voltage characteristic the

converter efficiency is approximately 75% to 90%.

START-UP SEQUENCE

To avoid high inrush current during start-up, special care is taken to control the inrush current. When the device

enables, the internal startup cycle starts with the first step, the pre-charge phase.

During pre-charge, the rectifying switch is turned on until the output capacitor is either charged to a value close

to the input voltage or

≈ 3.3V, whichever occurs first. The rectifying switch is current-limited during that phase.

The current limit increases with decreasing input-to-output voltage difference. This circuit also limits the output

current under output short-circuit conditions.

After having pre-charged the output capacitor, the device starts switching, and increases its current limit in three

steps of typically 25mA, 250mA and full current limit (ILIM setting). The current-limit transition from the first to the

second step occurs after 1ms of operation. Full current limit operation is set once the output voltage has reached

its regulation limits. In this mode, the active balancing circuit is disabled.

NRESET INPUT: HARDWARE ENABLE / DISABLE

The TPS6131x family features a hardware reset pin (NRESET). This reset pin allows the device to be disabled

by an external controller without requiring an I2C write command. Under normal operation, the NRESET pin

should be held high to prevent an unwanted reset. When the NRESET is driven low, the I2C control interface and

all internal control registers are reset to the default states and the part enters shutdown mode.

SHUTDOWN

Writing 00 to MODE_CTRL[1:0] bits forces the device into shutdown. The shutdown state can only be entered

when the voltage regulation (ENVM = 0) and light modes are both turned off.

In the shutdown state:

•

The regulator stops switching.

•

The high-side PMOS disconnects the load from the input.

•

The LEDx pins are high impedance thus eliminating any DC conduction path.

•

The TPS6131x device actively discharges the output capacitor when it turns off.

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Product Folder Links: TPS61310 TPS61311

TPS61311 Datasheet(PDF) 29 Page - Texas Instruments