LM3537_13 Datasheet, PDF (16/33 Pages) Texas Instruments – 8-Channel WLED Driver with Four Integrated LDOs

LM3537
SNVS634B – JUNE 2011 – REVISED MAY 2013
www.ti.com
LIGHT INTENSITY INCREASES
Z0 Z1 Z2
Z3
Z4
1000
t_2-3
HIGH-to-LOW gain
transition
750
t_1-2
500
t_0-1
250
t_3-4
t_3-2
0
Z0 Z1 Z2
LOW-to-HIGH gain
transition
LOW INTENSITY
Z3
LIGHT INTENSITY DECREASES
Z4
HIGH INTENSITY
The higher X-axis is for increasing light intensity, while the lower axis is for decreasing light intensity
There are some limits in Zone transitions when the autogain is enabled, for example a direct transition from the lowest
Zone0 to the highest Zone4 (and vice versa) is not possible, because the device must go through the gain change
process first.
Figure 4. ALS Zone Transitions with AutoGain
Countdown Timer
The ALS engine includes a pre-defined countdown timer function. This function is targeted to applications where
it's favorable to only increase through the zones; i.e., the LM3537 will stick to the highest zone reached, but won't
allow transitions to lower Zones until the countdown has completed. At the end of every countdown, the timer
sets the countdown timer flag (reg 40H), and after that, any Zone transition to a lower Zone re-loads the timer
and starts the next timer period. See Table 3 and Figure 5 for details.
TIMER[1]
0
0
1
1
Table 3. Countdown Timer
Pre-defined Countdown Timer Function
TIMER[0]
Timer Function
0
Countdown timer is disabled
1
10s countdown timer is enabled (stick to the highest zone for 10s).
0
Always stick to the highest zone the ALS reached.
1
Always stick to the highest zone the ALS reached.
16
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