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TPS61180RTERG4 Datasheet(PDF) 11 Page - Texas Instruments |
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TPS61180RTERG4 Datasheet(HTML) 11 Page - Texas Instruments |
11 / 26 page www.ti.com DETAILED DESCRIPTION SUPPLY VOLTAGE BOOST REGULATOR TPS61180/1/2 SLVS801A – DECEMBER 2007 – REVISED MARCH 2008 Recently, WLEDs have gained popularity as an alternative to CCFL for backlighting media size LCD displays. The advantages of WLEDs are power efficiency and low profile design. Due to the large number of WLEDs, they are often arranged in series and parallel, and powered by a boost regulator with multiple current sink regulators. Having more WLEDs in series reduces the number of parallel strings and therefore improves overall current matching. However, the efficiency of the boost regulator declines due to the need for high output voltage. Also, there have to be enough WLEDs in series to ensure the output voltage stays above the input voltage range. Otherwise, a buck-boost (for example, SEPIC) power converter has to be adopted which could be more expensive and complicated. The TPS61180/1/2 family of ICs have integrated all the key function blocks to power and control up to 60 WLEDs. The devices include a 40V/1.5A boost regulator, six 25mA current sink regulators and protection circuit for over-current, over-voltage and short circuit failures. The key advantages of the devices are small solution size, low output AC ripple during PWM dimming control, and the capability to isolate the input and output during fault conditions. The TPS61181/2 ICs have built-in LDO linear regulator to supply the IC analog and logic circuit. The LDO is powered up when the EN pin is high. The output of the LDO is connected to the Cin pin. A 0.1 µF bypass capacitor is required for LDO’s stable operation. Do not connect the Cin pin to the EN pin because this prevents the IC from starting up. In addition, avoid connecting the Cin pin to any other circuit as this could introduce noise into the IC supply voltage. The TPS61180 has no built-in LDO linear regulator, and therefore requires an external supply voltage in the range of 2.7V to 3.6V connected to the Cin pin. The benefit of using external supply is to reduce the power losses incurred by the LDO as it provides the IC supply current. This loss could become a significant percentage of total output power under light load condition. The Cin pin has 2.2V (typical) under-voltage lock out which turns off the IC when the Cin pin voltage is below this threshold. The voltage on the VBAT pin is the reference for the pull-up circuit of the Fault pin. In addition, it also serves as the input signal to the short circuit protection. For TPS61181/2 ICs, the VBAT connects to the input of the internal LDO, and powers the IC. There is an under-voltage lockout on the VBAT pin which disables the IC when its voltage reduces to 4.2V (Typical). The IC restarts when the VBAT pin voltage recovers by 300mV. The boost regulator is controlled by current mode PWM, and loop compensation is integrated inside the IC. The internal compensation ensures stable output over the full input and output voltage range. The TPS61180/1 switches at 1.0MHz, and the TPS61182 switches at 1.3MHz. The switching frequencies of the two devices, including their tolerance, due not over-lap. Therefore, in the unlikely event that one device creates electromagnetic inference to the system; the other device, switching at a different frequency, can provide an alternative solution. The output voltage of the boost regulator is automatically set by the IC to minimize the voltage drop across the IFB pins. The IC automatically regulates the lowest IFB pin to 400mV, and consistently adjusts the boost output voltage to account for any changes of the LED forward voltages. When the output voltage is too close to the input, the boost regulator may not be able to regulate the output due to the limitation of minimum duty cycle. In this case, increase the number of WLED in series or include series ballast resistors in order to provide enough headroom for the boost operation. The TPS61180/1/2 boost regulators cannot regulate their outputs to voltages below 15V. Copyright © 2007–2008, Texas Instruments Incorporated Submit Documentation Feedback 11 Product Folder Link(s): TPS61180/1/2 |
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