參數(shù)資料
型號(hào)： AAT3131
廠商： Advanced Analogic Technologies, Inc.
英文描述： High Efficiency 1X/1.5X Fractional Charge Pump for White LED Applications
中文描述： 高效率電荷泵分?jǐn)?shù)電荷泵白光LED應(yīng)用
文件頁(yè)數(shù)： 12/14頁(yè)
文件大?。?/td> 329K
代理商： AAT3131
AAT3131
High Efficiency 1X/1.5X Fractional
Charge Pump for White LED Applications
12
3131.2004.08.1.1
Equivalent Series Resistance (ESR)
ESR is an important characteristic to consider when
selecting a capacitor. ESR is a resistance internal
to a capacitor, which is caused by the leads, inter-
nal connections, size or area, material composition
and ambient temperature. Capacitor ESR is typi-
cally measured in milliohms for ceramic capacitors
and can range to more than several ohms for tanta-
lum or aluminum electrolytic capacitors.
Ceramic Capacitor Materials
Ceramic capacitors less than 0.1μF are typically
made from NPO or COG materials. NPO and COG
materials typically have tight tolerance and are sta-
ble over temperature. Large capacitor values are
typically composed of X7R, X5R, Z5U or Y5V
dielectric materials. Large ceramic capacitors, typ-
ically greater than 2.2 F are often available in low
cost Y5V and Z5U dielectrics, but capacitors
greater than 1μF are typically not required for
AAT3131 applications.
Capacitor area is another contributor to ESR.
Capacitors that are physically large will have a lower
ESR when compared to an equivalent material
smaller capacitor. These larger devices can improve
circuit transient response when compared to an
equal value capacitor in a smaller package size.
Thermal Protection
The AAT3131 has a thermal protection circuit that
will shut down the internal LDO and charge pump if
the die temperature rises above the thermal limit as
is the case during a short circuit of the OUT pin.
Driving Multiple LED's, White LED
display module back lights and
individual LED's connected in parallel
The AAT3131 D1 to D4 outputs are true constant
current sources capable of driving up to 20mA (D1
- D3) or 30mA (D4) each over the operation input
voltage range. Since these outputs are true con-
stant current sources, they may be connected in
parallel to drive a single power output. Any combi-
nation of outputs (D1 to D4) may be connected in
parallel. The maximum total output current is a sum
of how many current sources are parallel connect-
ed. This feature is particularly useful to power pre-
manufactured display modules which are pre-wired
with white LED backlights connected in a parallel
circuit configuration. Any combination of outputs
may be connected in parallel to drive groups of
LED's. The AAT3131 internal current source refer-
ence circuit bases feedback from current sensed
on the D1 and D4 outputs. For best operation, the
only requirement for this type of application is the
outputs D1 and D5 should always be connected to
the load circuit.
The AAT3131 may be used to drive multiple LED's
having differing forward voltages. Using feedback
techniques, the current in D1 to D3 output currents
sources are referenced to the current in the LED
connected to D1. Current source output D4 is its
own reference. If all LED's are of similar type, the
diodes will be matched in current, maintaining uni-
form LED brightness despite variations in manu-
facturer, production, etc.
If however, the diodes are dramatically different in
type comprising a mix of high-VF type and low-VF-
type LED's, the AAT3131 has the capability to opti-
mally drive up to four LED's of one-type and up to
two LED's of another type simultaneously. Such a
feature can be useful for driving different color
LED's; driving both display backlight and photo-
flash LED's; or for driving main-LCD and sub-LCD
display LED backlights from a single Charge Pump
IC. For example, when driving independent RGB
LED's, the green and blue type LED's typically
require a high VF to operate (e.g. 3.7V) while the
red LED needs a low forward voltage (e.g. 2V). By
connecting the green and blue diodes to outputs
D1 to D3 and the red diodes to D4, good control
and uniformity in brightness is maintained despite
the 2V difference in the diode forward voltages.
The AAT3131 determines if the 1.5X charge pump
circuit is needed based on the voltage on D1 and
D4, which ever one is higher. If adequate voltage is
available to drive the higher voltage LED (of output
D1 or D4) without the charge pump running, the IC
automatically switches into load switch (1X) mode
to maximize efficiency.
Similarly, if a 4V photo-flash LED-array is connect-
ed to outputs D1 through D3 (with the outputs
shorted together) and two 3.3V sub-LCD-display
backlight LED's are connected to output D4, then
the AAT3131 can optimally drive each set of LED's
at the programmed current level (see application
schematics).
相關(guān)PDF資料
PDF描述
AAT3131ITP-T1 High Efficiency 1X/1.5X Fractional Charge Pump for White LED Applications
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相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
AAT3131_08 制造商:ANALOGICTECH 制造商全稱(chēng):Advanced Analogic Technologies 功能描述:High Efficiency 1X/1.5X Fractional Charge Pump for White LED Applications
AAT3131ITP-T1 制造商:ANALOGICTECH 制造商全稱(chēng):Advanced Analogic Technologies 功能描述:High Efficiency 1X/1.5X Fractional Charge Pump for White LED Applications
AAT3132 制造商:ANALOGICTECH 制造商全稱(chēng):Advanced Analogic Technologies 功能描述:High Efficiency 1.5X Fractional Charge Pump for White LED Applications
AAT3132A 制造商:ANALOGICTECH 制造商全稱(chēng):Advanced Analogic Technologies 功能描述:High Efficiency 1.5X Fractional Charge Pump for White LED Applications
AAT3132AITP-1-T1 制造商:ANALOGICTECH 制造商全稱(chēng):Advanced Analogic Technologies 功能描述:High Efficiency 1.5X Fractional Charge Pump for White LED Applications
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