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UBA2071 Schematic ( PDF Datasheet ) - NXP Semiconductors

Teilenummer UBA2071
Beschreibung Half bridge control IC
Hersteller NXP Semiconductors
Logo NXP Semiconductors Logo 




Gesamt 35 Seiten
UBA2071 Datasheet, Funktion
UBA2071; UBA2071A
Half bridge control IC for CCFL backlighting
Rev. 01 — 23 June 2008
Product data sheet
1. General description
2. Features
The UBA2071 and UBA2071A are high voltage ICs intended to drive Cold Cathode
Fluorescent Lamps (CCFLs) or External Electrode Fluorescent Lamps (EEFLs) for
backlighting applications. They can drive a half bridge circuit made up of two NMOSFETs
with a supply voltage of up to 550 V, so the inverter can be supplied directly from a 400 V
PFC bus.
The UBA2071 and UBA2071A contain a controller, a level shifter, a bootstrap diode and
drivers for the external half bridge power switches. It also contains a low frequency PWM
generator, which can be used to control the brightness level of the lamps, using an analog
brightness/dimming control voltage. PWM dimming can also be realized, using a digital
PWM input signal. PWM dimming can be synchronized with other ICs. The lamp current is
controlled by means of a true zero voltage switching resonant control principle, ensuring
lowest possible switch losses in the half bridge power structure.
The UBA2071 is designed to be supplied by a V/t supply from the half bridge circuit that
it drives. The IC itself needs little current and if the IC is off, a clamp protects the supply
voltage from getting too high.
The UBA2071A is designed to be supplied by a fixed 12 V supply. It has a lower supply
start voltage and no supply clamp.
http://www.DataSheet4U.net/
I Suitable for operating in a very wide inverter supply voltage range (up to 550 V DC).
I Integrated level shifter.
I Integrated bootstrap diode.
I Lamp current control by means of a true zero voltage switching resonant control
principle.
I Sample & Hold circuit, maintaining current control value during PWM lamp-off
situation.
I Separately definable time constants for current control loop and PWM dimming
attack/decay setting.
I Overvoltage control.
I Overcurrent protection.
I Ignition failure detection.
I Hard switching control.
I Arcing detection.
I Open/short pin protections on feedback pins.
I Integrated, programmable fault timer.
datasheet pdf - http://www.DataSheet4U.net/






UBA2071 Datasheet, Funktion
NXP Semiconductors
UBA2071; UBA2071A
Half bridge control IC for CCFL backlighting
Table 3. Pin description …continued
Symbol Pin Description
NONFAULT 12 status signal
input/output
PWMD
13 digital PWM dimming
input/output
PWMA
EN
14 analog PWM dimming
input
15 chip enable input
VDD
PGND
GL
n.c.
n.c.
n.c.
SH
FS
16 supply input
17 power ground
18 low-side driver output
19 not connected
20 not connected
21 not connected
22 high-side source
connection
23 floating supply
GH 24 high-side driver output
Function
The IC signals a fault condition to external circuits by pulling this pin low. Also
external circuits can signal a fault condition to the IC by pulling this pin low.
Digital output of internally generated PWM signal if a capacitor is connected
to the CPWM pin.
Digital input of PWM signal if the CPWM pin is connected to signal ground.
Remark: The signal on the PWMD pin is active low, so low voltage on the
PWMD pin means lamps are on.
The duty cycle of the internally generated PWM signal is proportional to the
voltage on this pin.
A low voltage on this pin will reset and shut down the IC. This pin is also used
to select between DC blocking capacitor charging mode and normal
operation.
A buffer capacitor must be connected between this pin and power ground.
return for the low-side driver.
Gate connection of the low-side power switch.
HV spacer pin.
HV spacer pin.
HV spacer pin.
Return for high side gate driver. Must be connected to the source of the
high-side half bridge power switch.
A buffer capacitor must be connected between this pin and the SH pin. This
capacitor is charged whenhttp://www.DataSheet4U.net/ the low-side power switch is on and supplies the
high-side driver when the high-side power switch is on.
Gate connection of the high-side half bridge power switch.
8. Functional description
The UBA2071 and UBA2071A are designed to drive a half bridge inverter (as shown in
Figure 3) with a resonant load. The load consists typically of a transformer with CCFLs or
EEFLs.
The IC has an AC lamp current sense input (IFB). It regulates the average absolute value
of the lamp current by varying its switching frequency. The load is presumed to be
inductive: higher frequency results in lower lamp current.
The UBA2071 and UBA2071A include a PWM dimming function. The ICs switch the
lamps on and off with a frequency lower than the lamp current frequency but higher than
what the human eye can see. The light output of the lamps can be set by setting the ratio
of the on-time and off-time.
These ICs have several forms of protection and the next chapters will describe each
function in more detail.
UBA2071_A_1
Product data sheet
Rev. 01 — 23 June 2008
© NXP B.V. 2008. All rights reserved.
6 of 35
datasheet pdf - http://www.DataSheet4U.net/

6 Page









UBA2071 pdf, datenblatt
NXP Semiconductors
UBA2071; UBA2071A
Half bridge control IC for CCFL backlighting
Vlamp
(V)
Vign
Vburn
(1)
(2)
fsw(min) freg fign
fsw(max)
f (kHz)
014aaa103
(1) Indicates lamp-OFF.
(2) Indicates lamp-ON.
Fig 8. Initial ignition of cold cathode fluorescent lamp via frequency sweep and load
resonance
Advantage of the sweep rather than a fixed ignition frequency is that sensitivity for spread
in resonance frequency is much lower.
Once the lamps are ignited the frequency sweep-down continues, gradually increasing the
lamp current (the resonance circuit shouldhttp://www.DataSheet4U.net/ now still be inductive, so current increases as
frequency drops) until the current regulation level is reached (at fsw = freg). The frequency
will not reach fsw(min) if the lamp current comes into regulation. Once it has been detected
that the lamps are on (if the average absolute voltage at the current feedback input (pin
IFB) is above Vth(lod)(IFB)) PWM dimming is enabled. See Figure 9.
The initial ignition frequency sweep and the PWM generator are not synchronized. Once
the regulation frequency is reached, PWM dimming can start anywhere in its cycle. A
small internal PWM dimming enable delay time, td(en)PWM, allows the lamps to settle
before PWM dimming starts.
At the start of the lamps-off period of the PWM dimming, the switching frequency is swept
up to fsw(max). This reduces the lamp voltage so the lamps go out. If fsw(max) is reached,
both GL and GH are made low, so both half bridge powers will be non-conducting. This is
indicated by the dotted part of the switching frequency (fsw) line in Figure 9.
UBA2071_A_1
Product data sheet
Rev. 01 — 23 June 2008
© NXP B.V. 2008. All rights reserved.
12 of 35
datasheet pdf - http://www.DataSheet4U.net/

12 Page





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