Datasheet

UBA2071_A_1 © NXP B.V. 2008. All rights reserved.
Product data sheet Rev. 01 — 23 June 2008 7 of 35
NXP Semiconductors
UBA2071; UBA2071A
Half bridge control IC for CCFL backlighting
8.1 Supply, Start-up and UnderVoltage LockOut (UVLO)
The UBA2071 is supplied via the VDD pin as shown in Figure 4. The supply voltage is
either made by the inverter itself, using a ∆V/∆t or is a auxiliary fixed supply voltage. A
start-up current source that can supply minimal I
startup(VDD)
is needed for start-up. This can
be a resistor to the half bridge supply voltage.
The IC starts up when the voltage at the VDD pin goes over V
startup(VDD)
and shuts down
when the voltage at the VDD pin drops below V
stop(VDD)
and the output GL is high
1
. The
hysteresis between the start and stop levels allows the IC to be supplied by the supply
buffer capacitor (C1 in Figure 4) until the auxiliary supply is settled. The auxiliary supply
must not exceed the maximum voltage allowed on the VDD pin and has to be above
V
stop(VDD)
.
The UBA2071A can directly be supplied by a fixed voltage source on the VDD pin. The
voltage supplied by this source has to be above the maximum value of V
startup(VDD)
but
below the maximum of V
VDD
. Typically it will be a 12 V ± 5 % source.
Fig 3. Basic half bridge inverter
LOAD
V
HV
0.5 V
HV
V
HB
GL
SH
GH
FS
VDD
PGND
UBA2071
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C
FS
Q
HS
Q
LS
C
block
Fig 4. Supply configuration (for UBA2071 only)
1. When both GH and GL are low, during the lamps-off period of PWM dimming (PWMD is high), the IC will shut down until the
PWMD is low and the GL is high again.
UBA2071
V
DD
start
up
current
AUXILARY
SUPPLY
C1
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