AAT3152
High Efficiency 1X/1.5X/2X Charge Pump
For White LED Applications
Constant Current Output Level Settings
The constant current sink levels for D1 to D4 are
set via the serial interface. No PWM (pulse width
modulation) or additional control circuitry is needed
to control LED brightness. This feature greatly
reduces the burden on a microcontroller or system
IC to manage LED or display brightness, allowing
the user to "set it and forget it." With its high-speed
serial interface (up to 1MHz data rate), the input
sink current of the AAT3152 can be changed suc-
cessively to brighten or dim LEDs, giving the users
real-time control of LED brightness. Because the
inputs D1 to D4 are true independent constant cur-
rent sinks, the voltage observed on any single
given input will be determined by the actual forward
voltage (V
F
) for the LED being driven.
AAT3152 Current Setting
Main Group
(D1-D3)
I
OUT
(mA)
20
14
10
7
20
14
10
7
0
0
0
0
0.05
0.5
1
2
Data
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Sub Group
(D4)
I
OUT
(mA)
20
14
10
7
0
0
0
0
20
14
10
7
0.05
0.5
1
2
S
2
Cwire Serial Interface
The current sink input magnitude on the AAT3152 is
controlled by AnalogicTech's S
2
Cwire serial digital
input. It relies on the number of rising edges of the
EN/SET pin to address and load the registers.
S
2
Cwire latches data or address after the EN/SET
pin has been held high for time T
LAT
. The interface
records rising edges of the EN/SET pin and
decodes them into 16 different states, as indicated
in the Current Setting table. There are four bright-
ness levels for main or sub-display group with the
possibility of individually turning ON or OFF each
group. To further optimize power efficiency, the
AAT3152 also offers four low-current levels for dim
LED operation (Data 13-16). During this low-current
mode, the internal supply current reduces to only
80µA typical.
The counter can be clocked at speeds up to 1MHz,
such that intermediate states are not visible. The
first rising edge of EN/SET enables the IC and ini-
tially sets the output LED current to 20mA. Once
the final clock cycle is input for the desired bright-
ness level, the EN/SET pin is held high to maintain
the device output current at the programmed level.
The device is disabled 500µs (T
OFF
) 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. The
current outputs remain constant as long as
EN/SET remains in a logic high state. The current
outputs are switched off after EN/SET has
remained in a low state for at least the T
OFF
timeout
period; then, the AAT3152 enters shutdown mode
and draws less than 1µA from V
IN
. Data are reset
to 0 during shutdown.
3152.2005.08.1.2
9
ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
