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
I
Switch-mode buck controller that drives strings of LEDs up to 600 V power-efficiently
I
Controller with power-efficient boundary conduction mode of operation:
N
No reverse recovery losses in freewheel diode
N
Zero current switching for turn-on of switch
N
Zero voltage or valley switching for turn-on of switch
N
Minimal required inductance value and size
I
Direct Pulse Width Modulation (PWM) dimming available
I
Fast transient response through cycle-by-cycle current control, thereby:
N
Preventing over or undershoots in the LED current
N
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
I
Single loosely controlled input voltage required for all LED strings in RGB backlights
I
No binning on LED forward voltage required
I
Protections:
N
Undervoltage lockout
N
Leading edge blanking
N
Overcurrent
N
Overtemperature
I
Low cost LED driver solution:
N
No Schottky diode required because of zero-current switching
N
No dim switch and high-side driver required for PWM dimming
N
Smaller inductor possible compared to fixed-frequency continuous conduction
mode controllers
3. Applications
I
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
4. Ordering information
Table 1.
Ordering information
Package
Name
UBA3070T
SO8
Description
plastic small outline package; 8 leads; body width 3.9 mm
Version
SOT96-1
Type number
5. Block diagram
V
CC
1
SUPPLY
MANAGEMENT
VALLEY
8
DRAIN
clamp
Internal UVLO Start
supply
2
GND
LOGIC
OSCILLATOR
100
mV
Iprot(mask)
4
MASK
Iprot(PWM)
MASK
PROTECTION
3
PWM
LOGIC
DRIVER
Istartup(soft)
6
GATE
POWER-ON
RESET
LEB
S
Q
Blank
UVLO
OVER-
TEMPERATURE
PROTECTION
R
Q
soft
start
S2
0.5 V
5
S
Q
−
0.5 V
RSENSE
V
CC
< 4.5 V
R
Q
Short
winding
0.88 V
014aaa257
Fig 1.
Block diagram of single channel 8-pin LED backlight controller IC
UBA3070_2
© NXP B.V. 2008. All rights reserved.
Product data sheet
Rev. 02 — 2 December 2008
2 of 13
NXP Semiconductors
UBA3070
LED backlight driver IC
Vin
12 V
V
CC
GND
PWM
PWM
MASK
1
2
8
7
DRAIN
HVS
GATE
RSENSE
UBA3070
3
4
6
5
014aaa092
Fig 2.
Basic application diagram
6. Pinning information
6.1 Pinning
V
CC
GND
PWM
MASK
1
2
8
7
DRAIN
HVS
GATE
RSENSE
UBA3070
3
4
014aaa094
6
5
Fig 3. Pin configuration SO8
6.2 Pin description
Table 2.
Pin description
Pin
SO8
V
CC
GND
PWM
MASK
SENSE
1
2
3
4
5
supply voltage
ground
PWM input voltage
masking input voltage
resistor programmable current sense input
Description
Symbol
UBA3070_2
© NXP B.V. 2008. All rights reserved.
Product data sheet
Rev. 02 — 2 December 2008
3 of 13
NXP Semiconductors
UBA3070
LED backlight driver IC
Pin description
…continued
Pin
SO8
6
7
8
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
CC
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
CC
pin passes
the V
CC(startup)
level. The moment the voltage on pin V
CC
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
© 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
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
V
SENSE
= I
ch
×
R
ss
(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
ss
and C
ss
.
V
sense
(
max
)
–
(
I
ch
×
R
ss
)
I
DM
=
-------------------------------------------------------------
R
sense
τ
=
R
ss
×
C
ss
UBA3070_2
© NXP B.V. 2008. All rights reserved.
Product data sheet
Rev. 02 — 2 December 2008
5 of 13
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