SGM3735 Datasheet, PDF (10/13 Pages) SG Micro Corp – 38V Step-Up LED Driver

SGM3735
APPLICATION INFORMATION
Current Setting at EN/SET Pin
Current control can be as simple as a bi-level signal at
the EN/SET pin, resulting in LEDs ON at 100% I_MAX or
LED OFF state. However, more sophisticated control
techniques can be achieved by pulsing the EN/SET pin.
Active logic low or high is required since there is no
internal pull-up or pull-down at the EN/SET pin. An
example for programming the output current is shown in
Figure 2.
There are two ways to adjust the channels’ ON/OFF state
or current level. The first way is by simply adding the
number of pulses according to Table 2. For example, we
will use R_SET = 10Ω to program 20mA I_MAX. In this
example, the user can add 12 more pulses when
changing from 14/32 (8.75mA when I_MAX = 20mA) to 2/32
(1.25mA when I_MAX = 20mA). However, increasing the
current level can be accomplished by two ways, allowing
for more flexible programming.
38V Step-Up LED Driver
Since the data in Table 1 automatically circles around
after 32 pulses, adding 32 - 8 = 24 pulses changes from
6/32 (DATA 27) to 14/32 (DATA 19). The second way is
to reset the IC by pulling EN/SET pin low for 3ms
(guaranteed shutdown), and then inputting the desired
number of pulses.
Example: going from 6/32 (DATA 27) to 14/32 (DATA 19)
Option 1: send in 24 pulses (19+32-27 = 24);
Option 2: pull low for 3ms and then send in 19 pulses.
Layout Considerations
PCB layout is very important for high frequency switching
regulators in order to keep the loop stable and minimize
noise. The input capacitor should be very close to the IC
to get the best decoupling. The path of the inductor and
output capacitor should be kept as short as possible to
minimize noise and ringing. Please see the SGM3735
evaluation document for detailed PCB layout guidelines.
t_HIGH > 0.4µs _{0.4µs < tLOW < 750µs}
t_OFF > 3ms
EN/SET
t_S = 800µs (TYP)
100%31/32 _30/32
I_LED
4/32 _{3/32 2/32}
1/32
OFF
OFF
Figure 2. Output Current Programming via EN/SET Pin
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SG Micro Corp
www.sg-micro.com