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UBA3070: DescriptionLED backlight driver IC; File Size62KB，13 Pages; ManufacturerNXP; Websitehttps://www.nxp.com

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LED backlight driver IC

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UBA3070

LED backlight driver IC

Rev. 02 — 2 December 2008

Product data sheet

1. General description

The UBA3070 driver IC is the ﬁrst member of a ﬁrst generation of power-efﬁcient LED

backlight driver ICs.

Highly efﬁcient, ﬂexible and reliable LED drivers can easily be designed using the

UBA3070 control IC.

2. Features

Switch-mode buck controller that drives strings of LEDs up to 600 V power-efﬁciently

Controller with power-efﬁcient boundary conduction mode of operation:

No reverse recovery losses in freewheel diode

Zero current switching for turn-on of switch

Zero voltage or valley switching for turn-on of switch

Minimal required inductance value and size

Direct Pulse Width Modulation (PWM) dimming available

Fast transient response through cycle-by-cycle current control, thereby:

Preventing over or undershoots in the LED current

Enabling efﬁcient PWM dimming by quickly turning the converter on and off and

thereby removing the need for extra dim switches and high-side drivers

Single loosely controlled input voltage required for all LED strings in RGB backlights

No binning on LED forward voltage required

Protections:

Undervoltage lockout

Leading edge blanking

Overcurrent

Overtemperature

Low cost LED driver solution:

No Schottky diode required because of zero-current switching

No dim switch and high-side driver required for PWM dimming

Smaller inductor possible compared to ﬁxed-frequency continuous conduction

mode controllers

3. Applications

The UBA3070 is typically suited as a high voltage LED backlighting application in LCD

televisions and monitors (See

Figure 1)

NXP Semiconductors

UBA3070

LED backlight driver IC

Pin description

…continued

SO8

gate driver output

high voltage safety spacer: not connected

drain of external MOS switch: input for valley sensing

Description

Table 2.

Symbol

GATE

HVS

DRAIN

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

As long as V

is below the V

CC(startup)

level of typically 10 V, the supply current is below

600

µA.

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

pin passes

the V

CC(startup)

level. The moment the voltage on pin V

drops below the undervoltage

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.

UBA3070_2

Product data sheet

Rev. 02 — 2 December 2008

4 of 13

NXP Semiconductors

UBA3070

LED backlight driver IC

If the PWM pin is open circuit or not connected, a fault condition is assumed and the

converter will stop switching. Operation will recommence as soon as the fault condition is

removed.

7.3 Masking and valley switching

The mask pin ensures that turn-on of the converter is at a valley during ringing and not at

a peak during freewheeling of the inductor. If the voltage level at the mask pin is typically

above 100 mV, then turn-on of the switching FET is prevented. If the voltage level is below

this 100 mV, then turn-on prevention of the FET is released and at the moment of valley

detection the FET will actually turn on. The signal for the mask pin can be easily derived

from the signal at the switch node as shown in the application diagram. The current

ﬂowing into the mask pin should be lower than the typical stop current of 60

µA.

If pin MASK is open circuit or not connected, a fault condition is assumed and the

converter will stop operating immediately. Operation will recommence as soon as the fault

condition is removed.

7.4 Conversion frequency

The maximum conversion frequency is limited to minimally 145 kHz by an internal

oscillator. Consequently the inductance value should be chosen such that with the given

supply voltage, LED voltage and component spread the conversion frequency is always

smaller than this. There is no limitation for the minimum conversion frequency.

7.5 Minimum on-time

The minimum on-time of the switch mode converter is determined by the leading edge

blanking time of typically 370 ns. The leading edge blanking time is required to prevent

inadvertent switch off after turn on of the FET due to coupling to the sense node.

7.6 Overcurrent protection

Since the converter behaves as a current source it is principally self-protected from

overcurrent. An extra level of protection is added by means of a second trip level at

typically 0.88 V at the sense node to protect against short-circuits in external components

like diodes, inductors, capacitors or LEDs. Upon detection of this abnormal situation the

converter will stop switching.

7.7 Soft start-up (pin SENSE)

To have slow start-up the inductor peak current is slowly increased by the soft start-up

function. This can be achieved by inserting a resistor and a capacitor between the

SENSE-pin (pin 5) and sense resistor R

sense

. An internal current source charges the

capacitor to

SENSE

= I

(about 0.5 V maximum).

The start level and the time constant of the increasing primary current level can be

adjusted externally by changing the values of R

and C

sense

(

max

)

–

(

)

-------------------------------------------------------------

sense

UBA3070_2

Product data sheet

Rev. 02 — 2 December 2008

5 of 13

UBA3070 Related Products

	UBA3070	UBA3070T
Description	LED backlight driver IC	LED backlight driver IC

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