Texas Instruments TPS61181(82/81A)-259 Evaluation Board TPS61181(82/81A)EVM-259 TPS61181AEVM-259 TPS61181AEVM-259 Datenbogen
Produktcode
TPS61181AEVM-259
SLVSAN6A
–
FEBRUARY 2011
–
REVISED MARCH 2011
DETAILED DESCRIPTION
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 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 TPS61181A IC has integrated all the key function blocks to power and control up to 60 WLEDs. The devices
include a 40V/1.5A boost regulator, six 30mA 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.
include a 40V/1.5A boost regulator, six 30mA 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.
SUPPLY VOLTAGE
The TPS61181A has built-in LDO linear regulator to supply the IC analog and logic circuits. 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
up when the EN pin is high. The output of the LDO is connected to the Cin pin. A 0.1
μ
F 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.
supply voltage.
The V
BAT
connects to the input of the internal LDO, and powers the IC. The voltage on the V
BAT
pin is also the
reference for the pull-up circuit of the Fault pin. In addition, it serves as the input signal to the short circuit
protection. There is an under-voltage lockout on the V
protection. There is an under-voltage lockout on the V
BAT
pin which disables the IC when its voltage reduces to
4.2V (Typical). The IC restarts when the V
BAT
pin voltage recovers by 220mV.
BOOST REGULATOR
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 TPS61181A
switches at 1.0MHz which optimize boost converter efficiency and voltage ripple with a small form factor inductor
and output capacitor.
internal compensation ensures stable output over the full input and output voltage range. The TPS61181A
switches at 1.0MHz which optimize boost converter efficiency and voltage ripple with a small form factor inductor
and output capacitor.
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.
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.
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 TPS61181A boost regulator cannot regulate its output to voltages below 15V.
Copyright
©
2011, Texas Instruments Incorporated
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