AAT3151B_08 ANALOGICTECH [Advanced Analogic Technologies], AAT3151B_08 Datasheet - Page 10

• Manufacturer Part Number: AAT3151B_08
• Description: High Efficiency 1X/1.5X Charge Pump For White LED Applications
• Manufacturer: ANALOGICTECH [Advanced Analogic Technologies]

When the Max Current register is programmed to 1, 4,
or 5, changing the data for Address 1 will result in the
corresponding values found in the Constant Current
Programming Levels table. When the Max Current regis-
ter is programmed to 4, the part is programmed to oper-
ate in Low Current mode and the Data for Address 1 is
irrelevant. In Low Current mode, the Low Current regis-
ter takes precedence. See Table 4 for the available cur-
rent level settings.
Max Current and Low Current Registers
Use the Max Current and Low Current registers to pro-
gram constant current settings outside of the 20mA Max
scale. By default (without changing the Max Current reg-
ister), the AAT3151B operates in the 20mA Max scale (see
Constant Current Programming Levels). For example, to
change to the 30mA Max scale, address the Max Current
register with 20 rising edges and pause for T
the Max Current register with 2 rising edges and pause for
T
for the setting found in the 30mA Max column. Next, to
change to a different setting on the 30mA Max scale,
address the D1-D4 register with 17 rising edges. Program
the new constant current level with 1-16 rising edges. The
part will update to the new Data setting according to the
Constant Current Programming Levels table.
The AAT3151B has a distinct Low Current mode with
ultra-low quiescent current. For drive currents of 2mA or
less, the part operates with significantly reduced quies-
cent current. This is particularly useful for applications
requiring an “always on” condition, such as transmissive
displays. As an example, to change to Low Current
mode, address the Max Current register with 20 rising
edges and pause for T
ister with 4 rising edges and pause for T
10
ChargePump
LAT
Address
Table 2: Addresses for Setting Current Level.
. The part will next operate in the same Data row, but
1
4
5
EN/SET Edges
TM
17
20
21
LAT
. Program the Max Current reg-
High Efficiency 1X/1.5X Charge Pump For White LED Applications
Addressed Register
D1-D4 Current
Max Current
Low Current
LAT
. Address the
LAT
w w w . a n a l o g i c t e c h . c o m
. Program
Low Current register with 21 rising edges and pause for
T
edges. The part will update to the new Low Current
mode setting and operate with significantly reduced qui-
escent current.
Disabled Current Sinks
Current sink inputs that are not used should be disabled.
To disable and properly terminate unused current sink
inputs, they must be tied to V
Properly terminating unused current sink inputs is
important to prevent the charge pump modes from pre-
maturely activating. When properly terminated, only a
small sense current flows for each disabled channel. The
sense current for each disabled channel is 120μA.
The AAT3151B is also equipped with an “auto-disable”
feature to protect against an LED failure condition.
Thermal Protection
The AAT3151B has a thermal protection circuit that will
shut down the charge pump if the die temperature rises
above the thermal limit, as is the case during a short-
circuit of the VOUT pin.
LAT
. Program the Low Current register with 1-16 rising
Table 3: Max Current Register Settings—
Table 4: Low Current Register Settings—
Data
1
2
3
4
Data
1
2
3
4
PRODUCT DATASHEET
Address 4.
Address 5.
AAT3151B
Low Current Mode
OUT
20mA Max Scale
30mA Max Scale
15mA Max Scale
Max Current
.
D1-D4 (mA)
0.05
0.5
3151B.2008.02.1.1
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