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參數(shù)資料
| 型號： | AAT3114AISN-20-T1 |
| 廠商： | Advanced Analog Technology,lnc. |
| 英文描述： | High Efficiency 1.5X Fractional Charge Pumps For White LED Applications |
| 中文描述： | 高效率1.5倍分?jǐn)?shù)電荷泵為白光LED應(yīng)用 |
| 文件頁數(shù)： | 10/15頁 |
| 文件大?。?/td> | 331K |
| 代理商： | AAT3114AISN-20-T1 |
AAT3113, AAT3114/14A
High Efficiency 1.5X Fractional Charge
Pumps For White LED Applications
10
3113.2006.07.1.9
EN/SET Serial Interface
The current source output magnitude is controlled
by the EN/SET pin using AnalogicTech’s Simple
Serial Control (S
2
Cwire) interface. The interface
records rising edges of the EN/SET pin and
decodes them into 32 individual current level set-
tings each 1dB apart. Code 32 is full scale, and
Code 1 is full scale attenuated by 31dB. The mod-
ulo 32 interface wraps states back to state 1 after
the 32nd clock, so 1dB of attenuation is achieved by
clocking the EN/SET pin 31 times (see graph titled,
“I
DIODE
Response -9dB to -10dB”). The counter can
be clocked at speeds up to 1MHz, so intermediate
states are not visible. The first rising edge of
EN/SET enables the IC and initially sets the output
LED current to -31dB, the lowest setting equal to
525μA. Once the final clock cycle is input for the
desired brightness level, the EN/SET pin is held
high to maintain the device output current at the
programmed level. The device is disabled 500μs
after the EN/SET pin transitions to a logic low state.
The EN/SET timing is designed to accommodate a
wide range of data rates. After the first rising edge
of EN/SET, the charge pump is enabled and reach-
es full capacity after the soft-start time (T
SS
).
During the soft-start time, multiple clock pulses
may be entered on the EN/SET pin to set the final
output current level with a single burst of clocks.
Alternatively, the EN/SET clock pulses may be
entered one at a time to gradually increase the
LED brightness over any desired time period. A
constant current is sourced as long as EN/SET
remains in a logic high state. The current source
outputs are switched off after EN/SET has
remained in a low state for at least the t
OFF
timeout
period (see Figure 1).
LED Selection
AAT3113 and AAT3114/14A devices are designed
to drive white LEDs with forward voltages to 4.2V.
Since the D1:D6 output current sources are
matched with negligible voltage dependence, the
LED brightness will be matched regardless of their
forward voltage matching.
Charge Pump Efficiency
The AAT3113 and AAT3114/14A devices are frac-
tional charge pumps. The efficiency (
η
) can be sim-
ply defined as a linear voltage regulator with an
effective output voltage that is equal to one and one
half times the input voltage. Efficiency (
η
) for an
ideal 1.5X charge pump can typically be expressed
as the output power divided by the input power:
In addition, with an ideal 1.5X charge pump, the
output current may be expressed as 2/3 of the
input current. The expression to define the ideal
efficiency (
η
) can be rewritten as:
-or-
For a charge pump with an output of 5 volts and a
nominal input of 3.5 volts, the theoretical efficiency
is 95%. Due to internal switching losses and IC
quiescent current consumption, the actual efficien-
cy can be measured at 93%. These figures are in
close agreement for output load conditions from
1mA to 100mA. Efficiency will decrease as load
η
(%) = 100
V
OUT
1.5V
IN
η
= P
OUT
= V
OUT
· I
OUT
= V
OUT
P
IN
V
IN
· 1.5I
OUT
1.5V
IN
η
= P
OUT
P
IN
Figure 1: EN/SET Timing Diagram.
EN/SET
Code
1
2
3
OFF
OFF
t
HI
t
LO
t
OFF
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| AAT3114ISN | 制造商:ANALOGICTECH 制造商全稱:Advanced Analogic Technologies 功能描述:High Efficiency 1.5X Fractional Charge Pumps For White LED Applications |
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