Datasheet

UBA2071_A_1 © NXP B.V. 2008. All rights reserved.
Product data sheet Rev. 01 — 23 June 2008 10 of 35
NXP Semiconductors
UBA2071; UBA2071A
Half bridge control IC for CCFL backlighting
When the voltage on the EN pin goes over V
th(H)1(EN)
after the IC has been disabled (EN
pin below V
th(L)(EN)
) the IC will start up in DC blocking capacitor charging mode
3
. When
the voltage on the EN pin goes over V
th(H)1(EN)
after the IC has been off (EN pin below
V
th(L)(EN)
or V
DD
below V
stop(VDD)
) the IC will start up in DC blocking capacitor charging
mode. When the voltage on the EN pin goes over V
th(H)2(EN)
the IC will continue with the
initial ignition frequency sweep and normal operation mode. Figure 6, EN configuration,
shows three examples of how the enable input can be used:
1. Digital enable input with DC blocking capacitor charging. R1 and C1 define a fixed
DC blocking capacitor charging time.
Remark: The digital input signal high level has to be above the maximum value of
V
th(H)2(EN)
.
2. Sensing of HV supply and DC blocking capacitor voltages via the EN pin. The IC will
start in DC blocking capacitor charging mode if V
VDD
is above V
startup(VDD)
and V
HV
is
above . It will then go into initial ignition frequency
sweep and normal operation mode once V
Cblock
has been charged to
.
3. Sensing of HV supply and DC blocking capacitor voltages via the EN pin combined
with digital enable input.
In DC blocking capacitor charging mode the low-side power switch (Q
LS
in Figure 3) is
turned on for a period ((1/f
sw(max)
) − t
no
) and then the high-side power switch (Q
HS
in
Figure 3) is turned on for a period ((1/f
sw(max)
) − t
no
) followed by a period of (3/f
sw(min)
)
during which both power switches are off. This is repeated until the mode is left. When
leaving the DC blocking capacitor charging mode by raising the EN pin above V
th(H)2(EN)
,
the running cycle of the DC blocking capacitor charging mode will first be completed (see
Figure 7).
3. When the enable input is kept high during the time that the IC is off, because the supply voltage is too low, the IC might not start in
DC blocking capacitor charging mode.
Fig 6. EN configuration
014aaa253
UBA2071
EN
C1
R1
enable
(1)
UBA2071
EN
R
4
V
Cblock
V
Hv
(2)
R
3
R
2
C
block
UBA2071
EN
R
4
V
Cblock
V
Hv
(3)
R
3
R
2
C
block
R
5
disable
R2/R4()R2/R3()1++()V
th(H)1(EN)
×
R4/R2()R4/R3()1++()V
th(H)2(EN)
R4/R2 V
HV
×–×()