1.5A Step-Up Current Regulator for Flash LEDs
Flash Mode LED Current
The flash sink current can be programmed up to a max-
imum flash current level of 1.5A.
The maximum flash current is set by the RSET resistor.
For the desired flash current in output, the resistor value
can be calculated using the following equation:
A flash event is initiated by asserting the FLEN pin. A
flash event is automatically terminated when FLEN is de-
asserted or if the safety timer terminates before the
FLEN pin is de-asserted. Any time that the FLINH pin is
asserted, the default movie-mode current level will
appear at FL. The default movie-mode current level will
be maintained on FL as long as the FLINH and FLEN pins
are asserted, and the safety timer continues to run.
AS2Cwire Control of Movie Mode
Operation and Flash Safety Timer
In the AAT1290, control of the movie mode operation
and flash timer is managed by the Advanced Simple
Serial Control (AS2Cwire) interface. AS2Cwire relies on
the number of rising edges of the EN/SET pin to address
and load the AAT1290’s registers. As shown in Table 1,
Address 0 controls the Movie Current level as a percent-
age of the maximum movie mode current level. Address
1 controls the safety timer duration as a percentage of
the maximum value set by an external timing capacitor.
Address 2 enables the LED channel during movie mode.
Finally, Address 3 sets the maximum possible current for
movie mode operation. The maximum movie mode cur-
rent is set as a fraction of the flash current with a peak
value of 1/2 and a default value of 1/7.3. The last col-
umn in Table 1 shows the default values for each of the
AS2Cwire Serial Interface
AS2Cwire latches data or address after the EN/SET pin
has been held high for longer than tLAT (500µs). Address
or data is differentiated by the number of EN/SET rising
edges. Since the data registers are 4 bits each, the dif-
ferentiating number of pulses is 24 or 16, so that Address
0 is signified by 17 rising edges, Address 1 by 18 rising
edges and Address 2 by 19 rising edges and Address 3
by 20 rising edges. Data is applied to any number of ris-
ing edges between 1 and 16, inclusive. A typical write
protocol is a burst of EN/SET rising edges, signifying a
particular address, followed by a pause with EN/SET
held high for the prescribed tLAT timeout period, a burst
of rising edges signifying data, and a tLAT timeout for the
data registers. Once an address is set, then multiple
writes to the corresponding data register are allowed.
Address 0 is the default address on the first rising edge
after the AAT1290 has been disabled.
Movie Mode Current
Flash Safety Timer
Movie Mode Output Configuration
Flash/Movie Mode Current Ratio
Table 1: AS2Cwire Serial Interface Addressing.
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