PRODUCT DATASHEET
AAT3195
TM
ChargePump
4-Channel Charge-Pump LED Driver
EN/PWM Duty Cycle
D1-D3 Current (mA)
30
25
20
15
10
5
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
30
27
24
21
18
15
12
9
0
6
3
100
90
80
70
60
50
40
30
20
10
EN/PWM Input Pin Duty Cycle (%)
Table 2: AAT3195-3 LED Current Settings
Figure 3: AAT3195-3 Current Control Profile
20mV peak-to peak, typically ten times less than induc-
tor-based DC/DC boost converter white LED backlight
solutions. The AAT3195 soft-start feature prevents noise
transient effects associated with inrush currents during
start-up of the charge pump circuit.
Applications Information
LED Selection
The AAT3195 is specifically intended for driving white
LEDs. However, the device design will allow the AAT3195
to drive most types of LEDs with forward voltage speci-
fications ranging from 2.0V to 4.7V. LED applications
may include mixed arrangements for display backlight-
ing, infrared (IR) diodes, and any other load needing a
constant current source generated from a varying input
voltage. Since the D1 to D4 constant current sinks are
matched with negligible voltage dependence, the con-
stant current channels will be matched regardless of the
specific LED forward voltage (VF) levels.
Shutdown
Since the sink switches are the only power returns for all
loads, there is no leakage current when all of the sink
switches are disabled. To activate the shutdown mode,
hold the EN/SET input low for longer than tOFF (500μs).
In this state, the AAT3195 typically draws less than 1μA
from the input. Data and address registers are reset to
0 in shutdown.
The low dropout current sinks in the AAT3195 maximize
performance and make it capable of driving LEDs with
high forward voltages. Multiple channels can be com-
bined to obtain a higher LED drive current without
complication. Current sink inputs that are not used
should be disabled. To disable and properly terminate
unused current sink inputs, they must be tied to OUT.
If left unconnected or terminated to ground, the part
will be forced to operate in 2x charge pump mode.
Power Efficiency and Device Evaluation
The charge pump efficiency discussion in the following
sections accounts only for efficiency of the charge pump
section itself.
Since the AAT3195 outputs are pure constant current
sinks and typically drive individual loads, it is difficult to
measure the output voltage for a given output to derive
an overall output power measurement. For any given
application, white LED forward voltage levels can differ,
yet the output drive current will be maintained as a
constant.
Device Switching Noise Performance
The AAT3195 operates at a fixed frequency of approxi-
mately 1MHz to control noise and limit harmonics that
can interfere with the RF operation of cellular telephone
handsets or other communication devices. Back-injected
noise appearing on the input pin of the charge pump is
This makes quantifying output power a difficult task
when taken in the context of comparing to other white
LED driver circuit topologies. A better way to quantify
total device efficiency is to observe the total input power
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