AAT3157 Datasheet, PDF (9/11 Pages) Advanced Analogic Technologies – High Efficiency 1X/1.5X/2X Charge Pump For White LED Applications

AAT3157
High Efficiency 1X/1.5X/2X Charge Pump
For White LED Applications
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 (1MHz
data rate), the input sink current of the AAT3157 can
be changed successively to brighten or dim LEDs, in
smooth transitions (e.g., to fade-out) or in abrupt
steps, giving the user complete programmability and
real-time control of LED brightness.
S²Cwire Serial Interface
The current level magnitude is controlled by
AnalogicTech's Simple Serial Control (S²Cwire)
serial interface. The interface records rising edges
of the EN/SET pin and decodes them into 16 differ-
ent states. The 16 current level settings available
are indicated in Table 1.
Data
1
2
3
4
5
6
7
8
Output
(mA/Ch)
20.0
17.0
14.0
12.0
10.0
8.6
7.0
6.0
Data
9
10
11
12
13
14
15
16
Output
(mA/Ch)
5.0
4.2
3.4
2.8
1.0
0.5
0.1
0.05
Table 1: Current Level Settings.
The S²Cwire serial interface has flexible timing.
Data can be clocked-in at speeds greater than
1MHz, or much slower, such as 15kHz. After data
is submitted, EN/SET is held high to latch the data.
Once EN/SET has been held in the logic high state
for time T_LAT, the programmed current becomes
active and the internal data register is reset to zero.
For subsequent current level programming, the
number of rising edges corresponding to the
desired code must be entered on the EN/SET pin.
When EN/SET is held low for an amount of time
greater than T_OFF, the AAT3157 enters into shutdown
mode and draws less than 1µA from V_IN. The internal
data register is reset to zero during shutdown.
Auto-Disable Feature
The AAT3157 is equipped with an auto-disable fea-
ture for each LED channel. After the IC is enabled
and started up, a test current of 100µA (typical) is
forced through each sink channel. The channel will
be disabled if the voltage of that particular SINK pin
does not drop to certain threshold. This feature is
very convenient for disabling an unused channel or
during an LED fail-short event.
Thermal Protection
The AAT3157 has a thermal protection circuit that
will shut down the charge pump if the die tempera-
ture rises above the thermal limit, as would be the
case during a short circuit of the OUTCP pin.
S²Cwire Serial Interface Timing
EN/SET
Data Reg
T _HI
T_LO
T_LAT
1
2
n
n <= 16
1
T_OFF
n
0
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