AAT3164 Datasheet, PDF (11/14 Pages) Advanced Analogic Technologies – High Efficiency 1X/1.5X/2X Charge Pump for Six-Channel White LED Applications

AAT3164
High Efficiency 1X/1.5X/2X Charge Pump for
Six-Channel White LED Applications
Additionally, a digital-to-analog converter can be
used with the RSET pin to control the brightness
level. The result is like the equation above, where
V_IO is replaced with V_DAC:
I_LED(LO)
=
870
⎛ 0.6
⎝R₁ // R₂
-
V_DAC⎞
R₂ ⎠
For cases where PWM dimming is preferred, the
PWM signal can be applied directly to the RSET resis-
tor, as shown in Figure 4. In order for the LED current
to go to zero, the voltage level of the PWM signal
must exceed the RSET pin voltage level of 0.6V.
PWM
R1
AAT 3164
RSET
Figure 4: RSET Configuration for PWM
Dimming Control.
Device Power Efficiency
The AAT3164 power conversion efficiency
depends on the charge pump mode. By definition,
device efficiency is expressed as the output power
delivered to the LEDs divided by the total input
power consumed.
η
=
P_OUT
P_IN
When the input voltage is sufficiently greater than
the LED forward voltages, the device optimizes
efficiency by operating in 1X mode. In 1X mode,
the device is working as a bypass switch and pass-
ing the input supply directly to the output. By sim-
plifying the conditions such that the LEDs have uni-
form V_F, the power conversion efficiency can be
approximated by:
η=
V_F · I_LED
V_IN · I_IN
≈
V_F
V_IN
3164.2006.07.1.0
Due to the very low 1X mode quiescent current, the
input current nearly equals the total output current
delivered to the LEDs. Further, the low resistance
bypass switch introduces negligible voltage drop
from input to output.
The AAT3164 further maintains optimized perform-
ance and efficiency by detecting when the input
voltage is not sufficient to sustain LED drive cur-
rent. The device automatically switches to 1.5X
mode when the input voltage drops too low in rela-
tion to the LED forward voltages.
In 1.5X mode, the output voltage can be boosted to
3/2 the input voltage. The 3/2 conversion ratio
introduces a corresponding 1/2 increase in input
current. For ideal conversion, the 1.5X mode effi-
ciency is given by:
η=
V_F · I_LED
V_IN · 1.5I_IN
≈
V_F
1.5 · V_IN
Similarly, when the input falls further, such that
1.5X mode can no longer sustain LED drive cur-
rent, the device will automatically switch to 2X
mode. In 2X mode, the output voltage can be
boosted to twice the input voltage. The doubling
conversion ratio introduces a corresponding dou-
bling of the input current. For ideal conversion, the
2X mode efficiency is given by:
η=
V_F · I_LED
V_IN · 2I_IN
≈
V_F
2 · V_IN
Additional Applications
The current sinks of the AAT3164 can be combined
to drive higher current levels through a single LED.
As an example, each LED of a three-die arrange-
ment can be driven at 80mA each, or 240mA total
(see Figure 5).
Other applications that require constant current
can also be accommodated by combining constant
current channels to achieve the necessary current
levels.
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