UBA3070T NXP [NXP Semiconductors], UBA3070T Datasheet - Page 4

• Manufacturer Part Number: UBA3070T
• Description: LED backlight driver IC
• Manufacturer: NXP [NXP Semiconductors]

NXP Semiconductors
7. Functional description
UBA3070_2
Product data sheet
7.1 Supply management and undervoltage lockout
7.2 Current control and PWM
Table 2.
The UBA3070 is a monolithic driver IC for controlling the current through LED strings and
is especially suitable as driver stage for LED Backlighting applications like LCD
televisions.
The driver stage enables optimal performance for series connected LED strings in 0D, 1D
and 2D segmented backlight units (BLUs). Since the UBA3070 drives an external power
device, it can be used for all kinds of BLU designs ranging from high-power to low-power
LEDs, and high-voltage to low-voltage LED strings. Consequently it provides a driver
solution for all LCD screen sizes and types of LEDs. By combining the UBA3070 with the
appropriate power devices, the amount of drivers can be minimized by optimizing the
amount of LEDs put in series.
Each driver stage consists of a buck converter operating in boundary conduction mode of
which the peak level can be chosen by means of the external sense resistor. Since the
peak and zero levels are fixed by design, the converter behaves as a current source. This
gives an average current through the LEDs that is half the peak value of that through the
inductor. The ripple current through the LEDs can be chosen by means of the external
capacitor in parallel to the LEDs.
As long as V
600 A. The IC will activate the converter as soon as the voltage on the V
the V
lockout voltage of typically 8.7 V the IC stops switching.
If the PWM input is high (> 2 V) the converter is disabled, it will not switch and the LED
current is zero. If the PWM input pin is low (< 0.5 V) the converter is enabled and
operation is as follows. The external FET is turned on and current in the inductor will build
up. During this charging phase of the inductor the current is sensed across an external
sense resistor. The internal driver turns off the external FET upon detection of a voltage
level of typically 0.52 V at the SENSE pin. The inductor will freewheel its current through
the external diode and will discharge. After discharge the switch node will ring. Upon
detection of a valley or zero voltage on the switch node the internal driver will turn on the
external FET. Consequently turn-on of the FET is at zero current and at minimal voltage
resulting in minimal power losses and EMI. The conversion cycle will repeat as described
above, until the PWM input signal is driven high to disable the converter and steer the LED
current to zero.
GATE
HVS
DRAIN
Symbol
CC(startup)
Pin description
CC
level. The moment the voltage on pin V
is below the V
6
7
8
SO8
Pin
Rev. 02 — 2 December 2008
…continued
gate driver output
high voltage safety spacer: not connected
drain of external MOS switch: input for valley sensing
CC(startup)
level of typically 10 V, the supply current is below
Description
CC
drops below the undervoltage
LED backlight driver IC
UBA3070
© NXP B.V. 2008. All rights reserved.
CC
pin passes
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