AME9001AETH AME, AME9001AETH Datasheet - Page 20

• Manufacturer Part Number: AME9001AETH
• Description: CCFL Inverters & Accessories Backlight Controller
• Manufacturer: AME

Specifications of AME9001AETH

• Function: Backlight Controller
• Input Voltage: 24 V
• Output Voltage: 5.35 V
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

AME9001
Application Component Description
tube drive. Figure 16 shows a similar application circuit
that is optimized for 4 tube operation. Similar compo-
nent designations are used on similar components both
in figure 2 and figure 16 as well as throughout this appli-
cation note.
20
Figure 2 shows one typical application circuit for single
R1 - Weak pull up for the chip enable (CE) pin. The
voltage at CE will normally rise to 5 volts for a 12V
supply. Pull down on the CE node to disable the chip
and put it into a zero Idd mode. If the user wishes to
drive node CE with 3.3 or 5.5 volt logic then R1 is not
necessary
C1 - This capacitor acts to de-bounce the CE pin and
to slow the turn on time when using R1 to pull up CE.
This can be useful when the battery power is discon-
nected from the circuit in order to turn the circuit off,
when the battery is reconnected the chip does not
immediately turn on which allows the battery voltage
to stabilize before switching starts. If the user is ac-
tively driving the CE pin then the C1 capacitor may not
be necessary.
R3 - This resistor connected to the RDELTA pin deter-
mines how much the oscillator frequency will change
with battery voltage. The relation, which is found ear-
lier in the text, is:
C2 - This 1uF capacitor bypasses and stabilizes the
internal reference
C3 - This capacitor determines the length of the blank-
ing interval at the beginning of every dimming cycle
and when the chip is first powered on. At the end of
every dimming cycle this capacitor is discharged to
VSS then allowed to charge up at a rate controlled by
its internal current source and C3. When the voltage
on C3 (pin SSC) crosses 3 volts the blanking interval
is over and all fault checks are enabled. The charging
current into C3 (out of pin SSC) is normally 150uA but
for the very first cycle after the chip is enabled the
current is only 1uA. So the blanking interval for the
first cycle is:
Delta frequency (Hz) = 3.44e8 * (Vbatt-1.25) / R3
T(seconds) =( C3) * (3volts) / (1e-6amps)
AME, Inc.
And for subsequent dimming cycles the blanking in-
terval is:
C31 - This capacitor is used to prevent chatter on the
FAULTB pin during start up
R2 - R2 sets the frequency of the oscillator that drives
the FETs. The relation between R2 and frequency,
that was found previously in the text, is:
Note: that this is the frequency of the NMOS(Q3) gate drive.
The PMOS(Q2) gate drive is exactly twice this value.
C30 - This capacitor filters signals feeding the OVP
pin. By increasing C30 the user makes the circuit
less sensitive to fast overvoltage conditions.
R4 - This resistors pulls the base of Q1 up to Vbatt.
Coupled with Q1 and C7 it is part of the 5V regulator
that supplies the working power to the AME9001.
When the PNP pin is turned off the base of Q1 is
pulled high through R4, turning off Q1 and allowing the
voltage at the VDD node (VSUPPLY) to decay towards
zero.
Q1 - This common PNP transistor (2n3906 is ad-
equate) forms part of the 5V linear regulator which
supplies power to most of the AME9001.
R6 - This resistor, together with adjustable resistor
R20, form a resistor divider that divides the regulated
5V down to some lower voltage. That lower voltage is
used to drive the BRIGHT pin which, in turn, deter-
mines the duty cycle of the the dimming cycles and
therefore the brightness of the lamps. If the user is
driving the BRIGHT pin with his/her own voltage source
then R6 and R20 are not necessary.
C6 - This capacitor bypasses the BRIGHT pin. A noisy
BRIGHT pin can cause unwanted flicker.
T(seconds) = (C3) * (3volts) / (150e-6amps)
Frequency (Hz) = 2.8e9/R2
R2 = 56K yields approximately 50khz
CCFL Backlight Controller