UBA3070_2

© NXP B.V. 2008. All rights reserved.

Product data sheet

Rev. 02 — 2 December 2008

4 of 13

NXP Semiconductors

UBA3070

LED backlight driver IC

7.

Functional description

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.

7.1 Supply management and undervoltage lockout

600

µA. The IC will activate the converter as soon as the voltage on the V

lockout voltage of typically 8.7 V the IC stops switching.

7.2 Current control and PWM

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

6

gate driver output

HVS

7

high voltage safety spacer: not connected

DRAIN

8

drain of external MOS switch: input for valley sensing

Table 2.

Symbol

Pin

Description

SO8