DATA SHEET
AAT2822/2823/2824/2825
TFT-LCD DC/DC Converter with WLED Driver and VCOM Buffer
Application Information
Start
Main Step-Up Converter
Output Capacitor
The high output ripple inherent in the boost converter
necessitates low impedance output filtering. Multi-layer
ceramic (MLC) capacitors provide small size and ade-
quate capacitance, low parasitic equivalent series resis-
tance (ESR) and equivalent series inductance (ESL), and
are well suited for use with the primary step-up con-
verter. MLCs of type X7R or X5R are recommended to
ensure good capacitance stability over the full operating
temperature range.
EN High
No
Yes
MAIN BOOST
No
The output capacitor is sized to maintain the output load
without significant voltage droop during the power
switch ON interval, when the output diode is not con-
ducting. And because the VGH, VGL also have their input
power from the main step-up converter output, the out-
put capacitor may also decrease the inrush current dur-
ing VGH and VGL start up. A ceramic output capacitor
with a minimum value of 22µF is recommended. For
inrush current sensitive applications, two 22µF are rec-
ommended. Typically, 25V rated ceramic capacitors are
required for the 24V boost output. Ceramic capacitors
sized as small as 0805 are available which meet these
requirements. MLCs exhibit significant capacitance
reduction with applied voltage. Output ripple measure-
ments should confirm that output voltage droop is
acceptable.
VFB > FB Fault Trip
Level and Persist
Yes
NEGATIVE CP
No
VFBN >FBN Fault Trip
Level and Persist
Yes
POSITIVE CP
Input Capacitor
No
VFBP >FBP Fault Trip
Level and Persist
The boost converter input current flows during both ON
and OFF switching intervals. The input ripple current is
less than the output ripple and, as a result, less input
Yes
Shut-Down Main Boos,t
capacitance is required. However, the AAT2822 input
OPAMP
Negative CP, and
voltage is shared among other channels; a ceramic input
capacitor from 4.7µF to 10µF is recommended. Minimum
6.3V rated ceramic capacitors are required at the input.
Ceramic capacitors sized as small as 0603 are available
which meet these requirements.
Positive CP
Start-Up Sequence
Complete
No
EN Low
Large capacitance tantalum or solid-electrolytic capaci-
tors may be necessary to meet stringent output ripple
and transient load requirements. These can replace (or
be used in parallel with) ceramic capacitors. Both tanta-
lum and OSCON-type capacitors are suitable due to their
low ESR and excellent temperature stability (although
they exhibit much higher ESR than MLCs). Aluminum-
electrolytic types are less suitable due to their high ESR
Figure 2: Startup Sequence for AAT282X-11.
1. For AAT282x the startup sequence is positive charge pump followed by the nega-
tive charge pump.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
13
202081B
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