Datasheet

UBA2071_A_1 © NXP B.V. 2008. All rights reserved.
Product data sheet Rev. 01 — 23 June 2008 6 of 35
NXP Semiconductors
UBA2071; UBA2071A
Half bridge control IC for CCFL backlighting
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.
NONFAULT 12 status signal
input/output
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.
PWMD 13 digital PWM dimming
input/output
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.
PWMA 14 analog PWM dimming
input
The duty cycle of the internally generated PWM signal is proportional to the
voltage on this pin.
EN 15 chip enable input 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.
VDD 16 supply input A buffer capacitor must be connected between this pin and power ground.
PGND 17 power ground return for the low-side driver.
GL 18 low-side driver output Gate connection of the low-side power switch.
n.c. 19 not connected HV spacer pin.
n.c. 20 not connected HV spacer pin.
n.c. 21 not connected HV spacer pin.
SH 22 high-side source
connection
Return for high side gate driver. Must be connected to the source of the
high-side half bridge power switch.
FS 23 floating supply A buffer capacitor must be connected between this pin and the SH pin. This
capacitor is charged when the low-side power switch is on and supplies the
high-side driver when the high-side power switch is on.
GH 24 high-side driver output Gate connection of the high-side half bridge power switch.
Table 3. Pin description
…continued
Symbol Pin Description Function